Re: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[no6b]

At 10/24/2007 19:46, you wrote:

>145.25 can be a real pain. We have a repeater on that frequency. It is CATV
>channel E. We always have leaks from the cable rendering the repeater
>useless in some areas until a call is made to the CATV plant. They go out
>and tighten the screws on an amplifier (left loose by the last tech working
>on it), replace a damaged section of hardline or tighten up some connectors
>that worked loose due to temperature variations. It is a never ending battle.

You'd think the CATV ingress problem would be worse, given that 145.25 is 
an output.  My guess is that the CATV companies know that, & stick the 
local "must carry" sellavision channels that nobody watches there.

;)

Bob NO6B

RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jeff DePolo]

> Again, the circulator will produce intermod when external strong
> signals enter the antenna port when used as a switch for the duplexer
> and there is transmitter power also going through it. 50 Watts or
> 47dBm to -116dBm receiver sensitivity is 163dBm dynamic range. The
> device is not linear enough to prevent detectable IM when strong
> signals are received that are of the correct frequencies to cause IM
> to a receiver.

Which was why I was reluctant to go along with the idea of feeding a
receiver off the third port, or even worse, passing multiple high-level
signals through a common circulator.

Have you ever quantified IMD in a run-of-the-mill VHF/UHF ferrite circulator
before Harold?  When I get some time, I plan on trying to do that.  I figure
I'll use a high-quality pass/reject duplexer with > 100 dB of isolation as a
two-transmitter combiner, and feed the output to a circulator with the
remaining two ports terminated properly, and measure the third-order
products at both terminated ports.  I'll also be curious to see at what rate
the IM products increase as you start to approach (or even exceed) the
isolator's power-handling rating.

--- Jeff

Re: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Glenn Little WB4UIV]

145.25 can be a real pain. We have a repeater on that frequency. It is CATV 
channel E. We always have leaks from the cable rendering the repeater 
useless in some areas until a call is made to the CATV plant. They go out 
and tighten the screws on an amplifier (left loose by the last tech working 
on it), replace a damaged section of hardline or tighten up some connectors 
that worked loose due to temperature variations. It is a never ending battle.

The major CATV plants here have offset from 145.25 as they have to do for 
the FAA when using some of the channels in the aviation band. That helps 
until the leakage gets real bad. The minor players, the apartment complexes 
and motels just do not care and will not offset. There is always leakage 
from CATV.

73
Glenn
WB4UIV



At 09:17 AM 10/24/07, you wrote:

> >> OK - Here are my requirements for the transmit chain. minimal
> >> physical space and minimal insertion loss :-) (ok - too
> >> bloody obvious) Tuning simplicity is also a factor. I'm
> >> combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25
>
> >> Can you list out some of the other options that I might be
> >> able to squeeze onto my trailer ??
>
>You're trying to do all this in a trailer?
>Forget it, put up separate antennas for each radio and live with the
>desense.
>Not unless you feel like spending 10's of thousands of $.
>
>Went back and looked again, the 145.25 is to be a REPEATER??? Dude, hang
>it up. Put the repeater on UHF and be done with it. Anything else is
>ASKING for trouble. And put the other two on separate antennas and live
>with it. You'll spend thousands of dollars and hundreds of hours making
>this work and *KEEPING* it working!
>
> > I've run into some hitches getting a UHF backyard pair, or I would move the
> > repeater to UHF in a heartbeat -- already have the duplexer for that, and
> > that would leave me with a pretty standard BP/BP duplexer setup to separate
> > the simplex radios, and would additionally get me back on a single antenna.
>
>Hogwash. 2M is FAR tougher to get a pair on then UHF. Unless you live in
>one of the areas that UHF is getting taken out by mil radar, I guarantee
>there is a pair available on UHF somewhere. In the *REALLY* strange
>event there isn't, I GUARANTEE there is no pairs on 2M either.
>
>Find something like, oh, say, 444.0125 for instance, something where
>there isn't a nearby repeater on either side, keep the deviation down to
>+/-4KHz max, and you'll be fine.
>--
>Jim Barbour
>WD8CHL
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
>

Re: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jim]

Ron Wright wrote:

> Also if packet on VHF and repeater on UHF a simple crossband coupler
> and dual-band antenna will simplify things.
> 
> 73, ron, n9ee/r

Yes-greatly!

-- 
Jim Barbour
WD8CHL

RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

Yes - I made that suggestion. I'm no RF engineer, but it seemed like an
interesting idea. A circulator configured as an isolator (dummy load on the
3rd port) would be counterproductive, my idea was to hook the 3rd port to
the receive chain, adding the reverse port to port isolation of the
circulator to the existing isolation of the duplexer, and incidentally
splitting a single antenna into separate TX and RX paths. I've got a VHF
circulator here, and plan to load it up on my friend's network analyzer
tonight and see just how far out in left field this idea is :-)

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Ken Arck
Sent: Wednesday, October 24, 2007 12:04 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise
budget

 

At 09:51 AM 10/24/2007, you wrote:

>OK, I have to comment,
>
>An isolator/circulator should not be used in a duplexer at the 
>antenna connector when there are other strong signals floating 
>around the air that can get into the isolator.

<---Uh...a couple of things here:

1) Did I miss something here? Did someone suggest connecting a 
circulator to the antenna port of a duplexer?

2) The whole point of a circulator is to act as a "one-way" path for 
RF. Placing it in the antenna path is a bit counterproductive, no?

3) I disagree with your comments about "strong signals that can 'get 
into' the circulator. Again, that's the whole point, isn't it?

Ken

--
President and CTO - Arcom Communications
Makers of repeater controllers and accessories.
http://www.arcomcon <http://www.arcomcontrollers.com/> trollers.com/
Authorized Dealers for Kenwood and Telewave and
we offer complete repeater packages!
AH6LE/R - IRLP Node 3000
http://www.irlp. <http://www.irlp.net> net
"We don't just make 'em. We use 'em!"

 

Re: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[DCFluX]

Replace the duplexers antenna tee with a circulator. Tune the
circulator as follows: Port A to B to pass TX frequency, port B to C
to pass RX frequency. Port A to Port C isolation should be in the 20dB
range or better and it still protects the transmitter and helps with
mixing. RF from the antenna will still go into the receiver side of
the duplexer but hey, it was going to do that anyway.

This makes a 4 cavity set of 5" cans perform like a 6 cavity set on VHF.

>
> <---Uh...a couple of things here:
>
> 1) Did I miss something here? Did someone suggest connecting a
> circulator to the antenna port of a duplexer?
>
> 2) The whole point of a circulator is to act as a "one-way" path for
> RF. Placing it in the antenna path is a bit counterproductive, no?
>
> 3) I disagree with your comments about "strong signals that can 'get
> into' the circulator. Again, that's the whole point, isn't it?
>
> Ken
>

RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Ken Arck]

At 09:51 AM 10/24/2007, you wrote:

>OK, I have to comment,
>
>An isolator/circulator should not be used in a duplexer at the 
>antenna connector when there are other strong signals floating 
>around the air that can get into the isolator.

<---Uh...a couple of things here:

1) Did I miss something here? Did someone suggest connecting a 
circulator to the antenna port of a duplexer?

2) The whole point of a circulator is to act as a "one-way" path for 
RF. Placing it in the antenna path is a bit counterproductive, no?

3) I disagree with your comments about "strong signals that can 'get 
into' the circulator. Again, that's the whole point, isn't it?

Ken

--
President and CTO - Arcom Communications
Makers of repeater controllers and accessories.
http://www.arcomcontrollers.com/
Authorized Dealers for Kenwood and Telewave and
we offer complete repeater packages!
AH6LE/R - IRLP Node 3000
http://www.irlp.net
"We don't just make 'em. We use 'em!"

RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Harold Farrenkopf]

OK, I have to comment,

An isolator/circulator should not be used in a duplexer at the antenna
connector when there are other strong signals floating around the air
that can get into the isolator.  The strong transmit signal will mix
with off air signals in the circulator BECAUSE IT IS NOT LINEAR ENOUGH!

There is an intermod combination with your frequencies! 145.25TX with
145.05TX will produce a 5th order IM at 144.65RX.  Look at the
spacings for multiples, 200KHz to 400KHz and 600KHz.

If there wasn't an IM potential, you need 2 antennas separated by 40
to 50dB (30' vertically) and 16 7" Q (FQ20107*2) style cavities
(quoting Sinclair parts due to my knowledge of them). The
145.25/144.65 on one antenna and 145.05 and 144.39 on the other.  Each
antenna would start off as a Q202 Sinclair duplexer and 2 more Q
cavities added to each equipment leg to reject the other antenna's
nearest frequency, namely, 145.25TX leg needs 2 Q cans rejecting
145.05, 144.65RX leg rejecting 144.39 only (cause 145.05 is rejected
enough with the Q202 response to 145.25 frequency and antenna
separation), 145.05 TX/RX leg needs 2 Q cans rejecting 145.25 (same
arguement for 144.65 as above) and 144.39TX/RX rejecting 144.65 with 2
Q cans.  All Q cans set to 0.6dB insertion loss by themselves and
rejections for 200, 260, 600 and 690KHz are 24, 27, 38 and 39dB
respectively.

Approximate insertion loss is 3.2dB per leg.

Can't help you with the size problemphysics unless you want to use
Reslok style and have about 80% higher insertion loss.

BTW, Circulators have non-linear parts in them as well as nickel
plating and ferromagnetic material.

Harold, VA3HF

--- In Repeater-Builder@yahoogroups.com, "John Barrett" <[EMAIL PROTECTED]>
wrote:
>
> I'm basing those isolation figures on a calculator I found online
that asked
> for the gain of the antennas and the separation (horizontal or vertical)
> 
>  
> 
> Re splitting the simplex: a circulator with the radio hooked to the
input,
> the transmit chain on the standard output, and the receive chain
feeding the
> load port is what I was thinking - a relay would do the job just as
well,
> but would require changes to the PC based Packet Engine software to
support
> flipping the relay before and after transmitting. I don't think that's a
> built in feature, and source code is not available.
> 
>  
> 
> Re 4/5 ports: I have 3 transmit frequencies. 144.39, 145.05, and
145.25, and
> 3 receive frequencies. 144.39, 144.65, and 145.05 - if I keep
transmit and
> receive on separate chains, I only need a 4 port splitter/combiner
on each
> chain. if I go full out with all BP cavities, combined transmit/receive
> chain for the simplex rigs, and no circulators/isolators, I need a 5
port.
> If I understand the products correctly, a standard star coupler is just
> resistance on each port to balance the impedance presented, and
there is no
> port to port isolation. I feel I would be better off with a Wilkinson at
> that point because it would give me some additional port to port
isolation,
> and If I'm reading it right, for about the same insertion loss.
> 
>  
> 
> I have approximately 18"x18"x60" without moving cans to the cargo bay.
> perhaps a little less - I'll have to measure - say enough for 9 5-6"
cans,
> or as many as 18 of the smaller cans that I have - the cans I have
are a mix
> from 5" to 8", with the idea that the larger cans would be used where I
> needed sharper skirts, on the close spaced frequencies. The key here
is the
> height of the cans. if they are short enough (less than 30" total
including
> tuning rod), I can do 2 banks, facing different sides of the trailer..
> doubling the number of cans I can pack in. Only one of the cans I
have so
> far exceeds that spec, and only by a little.. once its tuned it may
be less
> than the 30" max, or I can trade it off with a shorter can on the
other side
> to make up the difference.
> 
>  
> 
> I would prefer to keep all the cans on one side if possible, but it is
> looking more and more like it will not be, so I'm willing to give up
some
> space in the power electronics bay to make space for more cans.
> 
>  
> 
>   _  
> 
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
> Sent: Tuesday, October 23, 2007 6:43 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and
reciever
> noise budget
> 
>  
> 
> > If I do two antennas, the best I can do is about 30db 
> > isolation (30ft separation, 6db multi-bay folded dipole 
> > antenna on bottom, 9db 2m/440 base station antenna on top), 
> 
> If you can get 30 feet of separation, you'll get

Re: Re: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Ron Wright]

Jim,

I agree with you.  Going to UHF for the repeater greatly simplifies things and 
UHF pairs are often much easier to find.  

Also, one reason 145.25 might be open is it is the cable channel video carrier 
freq.  Tune in many areas and you get a constant usually pretty strong signal.  
Tone is usually required by the repeater and users, but still a distant user 
might have problems hearing the repeater due to the cable signal.

Here where I live we have 2 cable networks.  Verizon is totally fiber and 
Bright House is fiber into the neighbor to a box about every 10th house and 
analog and digital cable on coax to the home.  145.25 is loud and clear.  When 
Bright House goes full fiber, which will be a long ways off, then 145.25 will 
be free for at least in my area.

Also if packet on VHF and repeater on UHF a simple crossband coupler and 
dual-band antenna will simplify things.

73, ron, n9ee/r



>From: Jim <[EMAIL PROTECTED]>
>Date: 2007/10/24 Wed AM 09:17:56 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: Re: [Repeater-Builder] Re: duplexer isolation and reciever noise 
>budget

>  
>
>>> OK - Here are my requirements for the transmit chain. minimal 
>>> physical space and minimal insertion loss :-) (ok - too 
>>> bloody obvious) Tuning simplicity is also a factor. I'm 
>>> combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25
>
>>> Can you list out some of the other options that I might be 
>>> able to squeeze onto my trailer ??
>
>You're trying to do all this in a trailer?
>Forget it, put up separate antennas for each radio and live with the 
>desense.
>Not unless you feel like spending 10's of thousands of $.
>
>Went back and looked again, the 145.25 is to be a REPEATER??? Dude, hang 
>it up. Put the repeater on UHF and be done with it. Anything else is 
>ASKING for trouble. And put the other two on separate antennas and live 
>with it. You'll spend thousands of dollars and hundreds of hours making 
>this work and *KEEPING* it working!
>
>> I've run into some hitches getting a UHF backyard pair, or I would move the
>> repeater to UHF in a heartbeat -- already have the duplexer for that, and
>> that would leave me with a pretty standard BP/BP duplexer setup to separate
>> the simplex radios, and would additionally get me back on a single antenna.
>
>Hogwash. 2M is FAR tougher to get a pair on then UHF. Unless you live in 
>one of the areas that UHF is getting taken out by mil radar, I guarantee 
>there is a pair available on UHF somewhere. In the *REALLY* strange 
>event there isn't, I GUARANTEE there is no pairs on 2M either.
>
>Find something like, oh, say, 444.0125 for instance, something where 
>there isn't a nearby repeater on either side, keep the deviation down to 
>+/-4KHz max, and you'll be fine.
>-- 
>Jim Barbour
>WD8CHL
>
>


Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

Re: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jim]

>> OK - Here are my requirements for the transmit chain. minimal 
>> physical space and minimal insertion loss :-) (ok - too 
>> bloody obvious) Tuning simplicity is also a factor. I'm 
>> combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25

>> Can you list out some of the other options that I might be 
>> able to squeeze onto my trailer ??

You're trying to do all this in a trailer?
Forget it, put up separate antennas for each radio and live with the 
desense.
Not unless you feel like spending 10's of thousands of $.

Went back and looked again, the 145.25 is to be a REPEATER??? Dude, hang 
it up. Put the repeater on UHF and be done with it. Anything else is 
ASKING for trouble. And put the other two on separate antennas and live 
with it. You'll spend thousands of dollars and hundreds of hours making 
this work and *KEEPING* it working!

> I've run into some hitches getting a UHF backyard pair, or I would move the
> repeater to UHF in a heartbeat -- already have the duplexer for that, and
> that would leave me with a pretty standard BP/BP duplexer setup to separate
> the simplex radios, and would additionally get me back on a single antenna.

Hogwash. 2M is FAR tougher to get a pair on then UHF. Unless you live in 
one of the areas that UHF is getting taken out by mil radar, I guarantee 
there is a pair available on UHF somewhere. In the *REALLY* strange 
event there isn't, I GUARANTEE there is no pairs on 2M either.

Find something like, oh, say, 444.0125 for instance, something where 
there isn't a nearby repeater on either side, keep the deviation down to 
+/-4KHz max, and you'll be fine.
-- 
Jim Barbour
WD8CHL

Re: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Nate Duehr]

On Oct 24, 2007, at 12:37 AM, John Barrett wrote:
> Re splitting the simplex: a circulator with the radio hooked to the  
> input, the transmit chain on the standard output, and the receive  
> chain feeding the load port is what I was thinking – a relay would  
> do the job just as well, but would require changes to the PC based  
> Packet Engine software to support flipping the relay before and  
> after transmitting. I don’t think that’s a built in feature, and  
> source code is not available.
Whoa whoa whoa, wait... one of your goals snuck into the last two e- 
mails... you're using the isolator to split TX/RX on a rig that has a  
single RF connector???

So you're just trying to figure out how to "split" a radio that  
doesn't have a separate TX/RX and uses a single RF connector...?

Did I misinterpret what you're trying to do there?  If all you're  
looking to do is split TX/RX in the "simplex" radios, that's a lot  
easier than you think -- no isolator required.



That can be done a number of ways...

1. Coaxial RF-rated relay... triggered by PTT logic signal, perhaps  
with a "sequencer" made out of discreet logic or if you're into  
writing some trivial ASM or BASIC code, a microcontroller -- which  
receives the PTT signal and then keys the relay first, then keys the  
rig slightly afterward.  (All depending on timing/speed of the rig to  
respond to the PTT signal and start transmitting RF.)  Your packet  
engine must be providing a PTT somewhere, right?

2. Use (relatively cheap but VERY good quality) older commercial  
radios were TX/RX chains inside are already separate and isolated to  
some extent from one-another.  (GE MASTR II, Motorola Micor, etc.)

3. Surgery on the rig -- something inside is switching between the TX  
and RX chain... find the right point and lift traces (or whatever)  
and add coax and a connector to bring out the appropriate "side"  
while leaving the other connector intact.  (This is similar to #2,  
but "harder" in more modern rigs, and you'll need to study the  
schematic to see how that rig is doing its T/R switching.  Not always  
for the electronics beginner.)

Heck, I'd go find a couple of MASTR II mobiles, buy crystals, tune  
'em up, and go.  Not only would you get the benefit of the separated  
T/R sections inside, but the front-end filtering on the M-II is heavy- 
duty, and would help your other design problems... not much gets  
through those helical-coil filters on the front-end of that  
receiver.  (Arguably, that's also a trade-off, the M-II isn't as  
sensitive as a modern barn-door-wide front-end rig.)


--
Nate Duehr, WY0X
[EMAIL PROTECTED]







 
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RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

I'm basing those isolation figures on a calculator I found online that asked
for the gain of the antennas and the separation (horizontal or vertical)

 

Re splitting the simplex: a circulator with the radio hooked to the input,
the transmit chain on the standard output, and the receive chain feeding the
load port is what I was thinking - a relay would do the job just as well,
but would require changes to the PC based Packet Engine software to support
flipping the relay before and after transmitting. I don't think that's a
built in feature, and source code is not available.

 

Re 4/5 ports: I have 3 transmit frequencies. 144.39, 145.05, and 145.25, and
3 receive frequencies. 144.39, 144.65, and 145.05 - if I keep transmit and
receive on separate chains, I only need a 4 port splitter/combiner on each
chain. if I go full out with all BP cavities, combined transmit/receive
chain for the simplex rigs, and no circulators/isolators, I need a 5 port.
If I understand the products correctly, a standard star coupler is just
resistance on each port to balance the impedance presented, and there is no
port to port isolation. I feel I would be better off with a Wilkinson at
that point because it would give me some additional port to port isolation,
and If I'm reading it right, for about the same insertion loss.

 

I have approximately 18"x18"x60" without moving cans to the cargo bay.
perhaps a little less - I'll have to measure - say enough for 9 5-6" cans,
or as many as 18 of the smaller cans that I have - the cans I have are a mix
from 5" to 8", with the idea that the larger cans would be used where I
needed sharper skirts, on the close spaced frequencies. The key here is the
height of the cans. if they are short enough (less than 30" total including
tuning rod), I can do 2 banks, facing different sides of the trailer..
doubling the number of cans I can pack in. Only one of the cans I have so
far exceeds that spec, and only by a little.. once its tuned it may be less
than the 30" max, or I can trade it off with a shorter can on the other side
to make up the difference.

 

I would prefer to keep all the cans on one side if possible, but it is
looking more and more like it will not be, so I'm willing to give up some
space in the power electronics bay to make space for more cans.

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Tuesday, October 23, 2007 6:43 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

 

> If I do two antennas, the best I can do is about 30db 
> isolation (30ft separation, 6db multi-bay folded dipole 
> antenna on bottom, 9db 2m/440 base station antenna on top), 

If you can get 30 feet of separation, you'll get more than 30 dB of
isolation. More like 50 dB on VHF, 60 dB or more on UHF as a guess. 

> Going to split the simplex radios with a circulator on each.. 

Maybe I'm missing something. I was talking about splitting the transmitter
and receiver apart so you could combine the transmitters separate from the
receivers if you were going to use hybrids as the primary means of
combining.

> I've done some checking around for "stars".. haven't found 
> any - I'm combining three transmitters - so 4 ports ?? 

You have four frequencies (144.39, 144.65, 145.05, 145.25), plus an antenna.
Five ports.

> got 
> some vendors or links I can look at 

Try Delta Electronics, Pasternak, maybe Kings. A 4-port "cross" is easy to
find. It's easy to build stars with more ports in a small die-cast box (the

ideal-sized box would make all of the center pins of the connectors
coincident).

> If I can use the star 
> to eliminate hybrid couplers, that would be great :-) that 
> would leave me with a 2 stage isolator and one or more cans 
> per transmitter.

Split antennas is, by far, the best way to go. Your biggest problem is the
145.05 Tx/Rx versus 145.250 Tx. I'd be inclined to start doing the analysis
assuming 145.05 is on its own antenna, with the remaining frequencies
three-wayed on another antenna using conventional cavity-ferrite combining.

> I don't have t-pass cavities, but since I'm still acquiring 
> cavities, I can get them if warranted. I've got 4 regular 
> band pass cans right now, 2 more on ebay I'm trying to get, 
> and a 6 can helical BR/BR duplexer that I can use for a 
> really deep notch if I need it somewhere (or will become part 
> of the receiver filters if I decide to stack BR filters for 
> receive, as per my previous post)

A helical pass/reject duplexer isn't going to help with the close spacings
involved. You might get lucky and be able to it to get some filtering
between the extremes (144.39 vs 145.25), but otherwise, the notches aren't
going to be sharp enough to avoid degrading the frequencies in between.
Have you swept it to really see what its performance is like (both
transmission and reflection)?

How much room do you have?

--- Jeff

 

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jeff DePolo]

> If I do two antennas, the best I can do is about 30db 
> isolation (30ft separation, 6db multi-bay folded dipole 
> antenna on bottom, 9db 2m/440 base station antenna on top), 

If you can get 30 feet of separation, you'll get more than 30 dB of
isolation.  More like 50 dB on VHF, 60 dB or more on UHF as a guess.  

> Going to split the simplex radios with a circulator on each.. 

Maybe I'm missing something.  I was talking about splitting the transmitter
and receiver apart so you could combine the transmitters separate from the
receivers if you were going to use hybrids as the primary means of
combining.

> I've done some checking around for "stars".. haven't found 
> any - I'm combining three transmitters - so 4 ports ?? 

You have four frequencies (144.39, 144.65, 145.05, 145.25), plus an antenna.
Five ports.

> got 
> some vendors or links I can look at 

Try Delta Electronics, Pasternak, maybe Kings.  A 4-port "cross" is easy to
find.  It's easy to build stars with more ports in a small die-cast box (the

ideal-sized box would make all of the center pins of the connectors
coincident).

> If I can use the star 
> to eliminate hybrid couplers, that would be great :-) that 
> would leave me with a 2 stage isolator and one or more cans 
> per transmitter.

Split antennas is, by far, the best way to go.  Your biggest problem is the
145.05 Tx/Rx versus 145.250 Tx.  I'd be inclined to start doing the analysis
assuming 145.05 is on its own antenna, with the remaining frequencies
three-wayed on another antenna using conventional cavity-ferrite combining.

> I don't have t-pass cavities, but since I'm still acquiring 
> cavities, I can get them if warranted. I've got 4 regular 
> band pass cans right now, 2 more on ebay I'm trying to get, 
> and a 6 can helical BR/BR duplexer that I can use for a 
> really deep notch if I need it somewhere (or will become part 
> of the receiver filters if I decide to stack BR filters for 
> receive, as per my previous post)

A helical pass/reject duplexer isn't going to help with the close spacings
involved.  You might get lucky and be able to it to get some filtering
between the extremes (144.39 vs 145.25), but otherwise, the notches aren't
going to be sharp enough to avoid degrading the frequencies in between.
Have you swept it to really see what its performance is like (both
transmission and reflection)?

How much room do you have?

--- Jeff

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

If I do two antennas, the best I can do is about 30db isolation (30ft
separation, 6db multi-bay folded dipole antenna on bottom, 9db 2m/440 base
station antenna on top), or I can get close to the same isolation with a
circulator and one antenna.. so I don't see a difference there and one
antenna really simplifies things. (plus gets more gain and height compared
to the dipole array mounted low on the tower).. there is another issue, a
2nd antenna is at best a month away before I can slip it into the budget - I
have the base antenna available now.

 

Going to split the simplex radios with a circulator on each.. anything that
leaks through from transmit to receive will be 30db down and have to get
through the receive splitter and receive filters on the other receivers
before it can be a problem. Also, non-mechanical so removes a potential
point of failure !!

 

I've done some checking around for "stars".. haven't found any - I'm
combining three transmitters - so 4 ports ?? got some vendors or links I can
look at ?? If I can use the star to eliminate hybrid couplers, that would be
great :-) that would leave me with a 2 stage isolator and one or more cans
per transmitter.

 

I don't have t-pass cavities, but since I'm still acquiring cavities, I can
get them if warranted. I've got 4 regular band pass cans right now, 2 more
on ebay I'm trying to get, and a 6 can helical BR/BR duplexer that I can use
for a really deep notch if I need it somewhere (or will become part of the
receiver filters if I decide to stack BR filters for receive, as per my
previous post)

 

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Tuesday, October 23, 2007 4:37 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

 

> OK - Here are my requirements for the transmit chain. minimal 
> physical space and minimal insertion loss :-) (ok - too 
> bloody obvious) Tuning simplicity is also a factor. I'm 
> combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25

Before we get to what hardware to use, we still need to quantify how much
isolation you really need between each transmitter and receiver. I'll throw
out real rough numbers but they really need to be determined ahead of time:

144.39 Tx noise supression at 145.05 (660 kHz) - 80 dB
144.39 Tx noise supression at 144.65 (260 kHz) - 105 dB
145.05 Tx noise supression at 144.39 (660 kHz) - 80 dB
145.05 Tx noise supression at 144.65 (400 kHz) - 95 dB
145.25 Tx noise supression at 144.39 (860 kHz) - 70 dB
145.25 Tx noise supression at 145.05 (200 kHz) - 110 dB
145.25 Tx noise supression at 144.65 (600 kHz) - 85 dB

144.39 carrier supression at 145.05 Rx (660 kHz) - 80 dB
144.39 carrier supression at 144.65 Rx (260 kHz) - 85 dB
145.05 carrier supression at 144.39 Rx (660 kHz) - 80 dB
145.05 carrier supression at 144.65 Rx (400 kHz) - 80 dB
145.25 carrier supression at 144.39 Rx (860 kHz) - 80 dB
145.25 carrier supression at 145.05 Rx (200 kHz) - 85 dB
145.25 carrier supression at 144.65 Rx (600 kHz) - 80 dB

144.39 Tx to/from 145.05 Tx - 60 dB
144.39 Tx to/from 145.25 Tx - 60 dB
145.05 Tx to/from 145.25 Tx - 60 dB

>From lowest to highest, it looks like this:

144.39 Tx/Rx --260 khz-- 144.65 Rx --400 kHz-- 145.05 Tx/Rx ---200 kHz--
145.25 Tx

Question 1: Are you locked in to a single antenna, or are two antennas a
possibility?

Question 2: If two antennas are a possibility, how much isolation can you
reasonably expect to get between them?

Question 3: Did you decide how you're going to "split" the simplex
transmitters and receivers (digis)?

> Right now by best bet for minimal space is the hybrid coupler 
> approach, but I pay in insertion loss. 

As a real rough estimate, you'd be looking at 10 dB or more insertion loss
for two of the transmitters and 7 dB or more for the third once you factor
in filter losses. If you're willing to take a 7 dB hit on one transmitter
alone, you'd be better off putting up two half-height antennas (3 dB gain
reduction) which will buy you 20-30 dB of isolation right there, and you'd
be almost guaranteed to come out better in ERP and sensitivity even
including the 3 dB antenna gain hit.

> loss is the T-Pass, but the T-Pass is starting to cut heavily 
> into my available space --- I'm already looking at 6-9 cans 
> on the receive side and would prefer something with NO cans 
> on the transmit side.

No cans on the transmit site - forget it. You've got 100 dB+ of noise
supression to make up somehow.

> Despite the space issues I'm still considering the T-Pass 
> because of the improved spurious signal suppression. Getting 
> the cans is another issue - could I use a regular band pass 
> can with a coax T rather than an actual T-Pass can ??

You could do a five-port

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jeff DePolo]

> OK - Here are my requirements for the transmit chain. minimal 
> physical space and minimal insertion loss :-) (ok - too 
> bloody obvious) Tuning simplicity is also a factor. I'm 
> combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25

Before we get to what hardware to use, we still need to quantify how much
isolation you really need between each transmitter and receiver.  I'll throw
out real rough numbers but they really need to be determined ahead of time:

144.39 Tx noise supression at 145.05 (660 kHz) - 80 dB
144.39 Tx noise supression at 144.65 (260 kHz) - 105 dB
145.05 Tx noise supression at 144.39 (660 kHz) - 80 dB
145.05 Tx noise supression at 144.65 (400 kHz) - 95 dB
145.25 Tx noise supression at 144.39 (860 kHz) - 70 dB
145.25 Tx noise supression at 145.05 (200 kHz) - 110 dB
145.25 Tx noise supression at 144.65 (600 kHz) - 85 dB

144.39 carrier supression at 145.05 Rx (660 kHz) - 80 dB
144.39 carrier supression at 144.65 Rx (260 kHz) - 85 dB
145.05 carrier supression at 144.39 Rx (660 kHz) - 80 dB
145.05 carrier supression at 144.65 Rx (400 kHz) - 80 dB
145.25 carrier supression at 144.39 Rx (860 kHz) - 80 dB
145.25 carrier supression at 145.05 Rx (200 kHz) - 85 dB
145.25 carrier supression at 144.65 Rx (600 kHz) - 80 dB

144.39 Tx to/from 145.05 Tx - 60 dB
144.39 Tx to/from 145.25 Tx - 60 dB
145.05 Tx to/from 145.25 Tx - 60 dB

>From lowest to highest, it looks like this:

144.39 Tx/Rx --260 khz-- 144.65 Rx --400 kHz-- 145.05 Tx/Rx ---200 kHz--
145.25 Tx

Question 1: Are you locked in to a single antenna, or are two antennas a
possibility?

Question 2: If two antennas are a possibility, how much isolation can you
reasonably expect to get between them?

Question 3: Did you decide how you're going to "split" the simplex
transmitters and receivers (digis)?

> Right now by best bet for minimal space is the hybrid coupler 
> approach, but I pay in insertion loss. 

As a real rough estimate, you'd be looking at 10 dB or more insertion loss
for two of the transmitters and 7 dB or more for the third once you factor
in filter losses.  If you're willing to take a 7 dB hit on one transmitter
alone, you'd be better off putting up two half-height antennas (3 dB gain
reduction) which will buy you 20-30 dB of isolation right there, and you'd
be almost guaranteed to come out better in ERP and sensitivity even
including the 3 dB antenna gain hit.

> loss is the T-Pass, but the T-Pass is starting to cut heavily 
> into my available space --- I'm already looking at 6-9 cans 
> on the receive side and would prefer something with NO cans 
> on the transmit side.

No cans on the transmit site - forget it.  You've got 100 dB+ of noise
supression to make up somehow.

> Despite the space issues I'm still considering the T-Pass 
> because of the improved spurious signal suppression. Getting 
> the cans is another issue - could I use a regular band pass 
> can with a coax T rather than an actual T-Pass can ??

You could do a five-port star.  If you don't already have cavities with
T-pass style loops in them, there's no reason to try to build using that
design.

> Can you list out some of the other options that I might be 
> able to squeeze onto my trailer ??

What are the space limitations?

--- Jeff

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

OK - Here are my requirements for the transmit chain. minimal physical space
and minimal insertion loss :-) (ok - too bloody obvious) Tuning simplicity
is also a factor. I'm combining 3 transmitters at 144.39, 145.05 +/- 0.04
and 145.25

 

Right now by best bet for minimal space is the hybrid coupler approach, but
I pay in insertion loss. best for insertion loss is the T-Pass, but the
T-Pass is starting to cut heavily into my available space --- I'm already
looking at 6-9 cans on the receive side and would prefer something with NO
cans on the transmit side. 

 

Despite the space issues I'm still considering the T-Pass because of the
improved spurious signal suppression. Getting the cans is another issue -
could I use a regular band pass can with a coax T rather than an actual
T-Pass can ??

 

Can you list out some of the other options that I might be able to squeeze
onto my trailer ??

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Monday, October 22, 2007 9:41 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

> Commercial installations usually use either a harmonic filter 
> and 3db hybrid coupler, or a special type of band pass cavity 
> to couple the output from the isolator to the feed line. 
> (This info from an RX TX application note on transmitter combiners)

Well, that's just two out of a myriad of ways of combining, duplexing,
multicoupling, etc. Hybrid-ferrite and TX-RX's T-pass are by no means the
only two ways of combining transmitters.

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

Keith: A very good point - and multiplied since there will be 3 receivers
involved :-) Perhaps a good reason to stick with 3 cans per receiver,
instead of 2, since that will give me the same protection any standard
duplexer would, and even more isolation when things are working right, at
the cost of a little more insertion loss. Depending on the insertion loss of
the cavities in the receive chain - I'm looking at 6 to 9db of loss between
the splitter and the cavity filters.

 

It makes putting a preamp before the receive splitter an interesting
possibility, to make up some of the losses further down the chain, at the
cost of intermod in the preamp, which might be covered with a single band
pass filter right before the preamp (1mhz wide, centered on my receive
window). though that wont stop intermod with my own transmit signals. Still,
if the antenna were to go bad, its more likely the preamp would smoke before
enough got through to smoke the radios :-)

 

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Keith McQueen
Sent: Tuesday, October 23, 2007 12:11 AM
To: Repeater-Builder@yahoogroups.com
Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

 

The danger I see with this is when your antenna goes bad (and they all do
eventually), your receiver will be hit with the full reflected power of the
PA almost certainly turning it into a smoldering doorstop.

 

 

Keith McQueen

801-224-9460

[EMAIL PROTECTED]

 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of John Barrett
Sent: Monday, October 22, 2007 7:47 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

An isolator wont cause intermod, but it may cause harmonics. Commercial
installations usually use either a harmonic filter and 3db hybrid coupler,
or a special type of band pass cavity to couple the output from the isolator
to the feed line. (This info from an RX TX application note on transmitter
combiners)

I'm proposing a novel application of the circulator (an isolator without the
dummy load on one port).. Instead of the dummy load, the 3rd port feeds the
receiver chain. the transmit chain will still use more or less conventional
combining techniques to merge the signals from the 3 transmitters. the
output from the transmitter combiner goes to the input of an additional
circulator, the circulator output goes to the antenna as you would normally
expect for an isolator, and the "load" port goes to the receive chain
instead of a dummy load.  Since the path from the transmit chain port to the
receive chain port is "reversed" compared to the normal signal flow in a
circulator, it will incur 20-30db of loss, depending on the circulator
specs. So long as the antenna is well matched, there will be minimum
reflected power fed back into the receive chain. My "window" for all the
transmitters and receivers is less than 1mhz, so matching the antenna
shouldn't be a huge problem.



  _  


From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright
Sent: Monday, October 22, 2007 8:19 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

I am not sure why an isolator would cause intermod. Usually there are not
active or non-linear components in them and they are often used to prevent
intermod by preventing outside signals from coming in thru the feedline into
the transmitter.

In the past commerical sites would often require an isolator for this reason
with strong transmitters close by. In better repeater equipment an isolator
was built in.

73, ron, n9ee/r

>From: Jeff DePolo <[EMAIL PROTECTED] <mailto:jd0%40broadsci.com> com>
>Date: 2007/10/22 Mon PM 07:27:09 CDT
>To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com>
yahoogroups.com
>Subject: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

> 
>> This isn't guessing - its called RESEARCH
>
>When I said guessing, I was talking about quantifying the performance of
>your radios rather than guessing how much isolation you need. In other
>words, make measurements to actually determine how much noise supression
and
>carrier attenuation you need using the actual frequencies involved. Once
>you know how much isolation you truly need, then you can work backwards
from
>there to determine the filtering requirements.
>
>I still think using an isolator is going to cause you new problems with
>respect to IM into your receivers unless you have adequate filtering
between
>the isolator and antenna, which I believe you have no way of acheiving if
>I'm understanding your layout right (i.e. isolator is connected directly to
>the antenn

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Keith McQueen]

The danger I see with this is when your antenna goes bad (and they all do
eventually), your receiver will be hit with the full reflected power of the
PA almost certainly turning it into a smoldering doorstop.
 
 
Keith McQueen
801-224-9460
[EMAIL PROTECTED]
 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of John Barrett
Sent: Monday, October 22, 2007 7:47 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget






An isolator wont cause intermod, but it may cause harmonics. Commercial
installations usually use either a harmonic filter and 3db hybrid coupler,
or a special type of band pass cavity to couple the output from the isolator
to the feed line. (This info from an RX TX application note on transmitter
combiners)



I'm proposing a novel application of the circulator (an isolator without the
dummy load on one port).. Instead of the dummy load, the 3rd port feeds the
receiver chain. the transmit chain will still use more or less conventional
combining techniques to merge the signals from the 3 transmitters. the
output from the transmitter combiner goes to the input of an additional
circulator, the circulator output goes to the antenna as you would normally
expect for an isolator, and the "load" port goes to the receive chain
instead of a dummy load.  Since the path from the transmit chain port to the
receive chain port is "reversed" compared to the normal signal flow in a
circulator, it will incur 20-30db of loss, depending on the circulator
specs. So long as the antenna is well matched, there will be minimum
reflected power fed back into the receive chain. My "window" for all the
transmitters and receivers is less than 1mhz, so matching the antenna
shouldn't be a huge problem.




  _  


From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright
Sent: Monday, October 22, 2007 8:19 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget



I am not sure why an isolator would cause intermod. Usually there are not
active or non-linear components in them and they are often used to prevent
intermod by preventing outside signals from coming in thru the feedline into
the transmitter.

In the past commerical sites would often require an isolator for this reason
with strong transmitters close by. In better repeater equipment an isolator
was built in.

73, ron, n9ee/r

>From: Jeff DePolo <[EMAIL PROTECTED] <mailto:jd0%40broadsci.com> com>
>Date: 2007/10/22 Mon PM 07:27:09 CDT
>To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com>
yahoogroups.com
>Subject: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

> 
>> This isn't guessing - its called RESEARCH
>
>When I said guessing, I was talking about quantifying the performance of
>your radios rather than guessing how much isolation you need. In other
>words, make measurements to actually determine how much noise supression
and
>carrier attenuation you need using the actual frequencies involved. Once
>you know how much isolation you truly need, then you can work backwards
from
>there to determine the filtering requirements.
>
>I still think using an isolator is going to cause you new problems with
>respect to IM into your receivers unless you have adequate filtering
between
>the isolator and antenna, which I believe you have no way of acheiving if
>I'm understanding your layout right (i.e. isolator is connected directly to
>the antenna with nothing in between save for a harmonic filter).
>
> --- Jeff
>
> 

Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.





 

Re: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Nate Duehr]

On Oct 22, 2007, at 7:19 PM, Ron Wright wrote:

> I am not sure why an isolator would cause intermod.

The fact that they create harmonics unless filtering is done  
"downstream" of the output port going toward the antenna, means that  
the opportunities for external mixing are increased greatly by  
however many harmonics are strong enough out at the antenna and  
whatever is in its near-field.

> In the past commerical sites would often require an isolator for  
> this reason with strong transmitters close by.  In better repeater  
> equipment an isolator was built in.

Most commercial sites require the isolator to keep the mixing/IM from  
happening in ANY PA's on the site, since mixing in an active junction  
is likely to be amplifed and much worse than passive IM external to  
the systems.

The addition of an isolator raises the opportunity to externally mix  
if it's not filtered, however.  Or perhaps mix in the ONE site  
tenant's transmitter that doesn't have an isolator.

Best practice with isolators includes adding bandpass filtering  
beyond them to alleviate those harmonics... or shall we call them,  
"external mixing opportunities".

It's all trade-offs... isolators do a specific job well (keeping  
unwanted RF out of active junctions in PA's), but add a new (far  
weaker/less likely) problem via the harmonics generated.

When you add in the other "side-benefits" of an isolator (PA  
protection against mis-matched/missing antenna with the correct load  
attached to the load port), they're adding more value than the  
harmonic problem creates... but the harmonics still need to be dealt  
with, in many site-specific scenarios.

--
Nate Duehr
[EMAIL PROTECTED]

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Mike Morris WA6ILQ]

At 07:41 PM 10/22/07, you wrote:

> > I'm proposing a novel application of the circulator (an
> > isolator without the dummy load on one port)..
>
>Yes, I know what you're trying to do, and it's nothing new.  UHF Micor
>mobiles have an isolator in the antenna network that routes received RF
>through the isolator to the receiver when the transmitter is not keyed.  I
>forget how the full-duplex Micor med radios were set up; I believe the
>antenna network in those radios was different, maybe somebody else
>remembers.

(rest deleted)

The original med radio manual is on the Micor page at repeater-builder as
a PDF:

 >Emergency Medical Systems Duplex / Repeater UHF Mobile Radio manual
 >supplement PDF file courtesy of K9ROD
 > 
 >This is the no-longer-available manual supplement for the full-duplex
 >dual-receiver repeating ambulance radio model Q2033 and Q1853.   Note
 >that you need the regular UHF mobile manual 68-81015E70 to go along with it.
 >Note this is a 16.6 MB file

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jeff DePolo]

> An isolator wont cause intermod, but it may cause harmonics. 

How so?  What phenomenon occurs in a ferrite circulator that creates
harmonics but won't generate IMD?

> Commercial installations usually use either a harmonic filter 
> and 3db hybrid coupler, or a special type of band pass cavity 
> to couple the output from the isolator to the feed line. 
> (This info from an RX TX application note on transmitter combiners)

Well, that's just two out of a myriad of ways of combining, duplexing,
multicoupling, etc.  Hybrid-ferrite and TX-RX's T-pass are by no means the
only two ways of combining transmitters.

> I'm proposing a novel application of the circulator (an 
> isolator without the dummy load on one port).. 

Yes, I know what you're trying to do, and it's nothing new.  UHF Micor
mobiles have an isolator in the antenna network that routes received RF
through the isolator to the receiver when the transmitter is not keyed.  I
forget how the full-duplex Micor med radios were set up; I believe the
antenna network in those radios was different, maybe somebody else
remembers.  Circulators are used in the manner you're contemplating in
duplex microwave systems all the time, but with the addition of filters in
both paths.

> the 
> transmit chain will still use more or less conventional 
> combining techniques to merge the signals from the 3 
> transmitters. the output from the transmitter combiner goes 
> to the input of an additional circulator, the circulator 
> output goes to the antenna as you would normally expect for 
> an isolator, and the "load" port goes to the receive chain 
> instead of a dummy load

In your example, you will have three transmitter carriers going through a
common isolator.  That's where I think you may have spectral problems show
up due to IM amidst the high-level carriers. 

> Since the path from the transmit 
> chain port to the receive chain port is "reversed" compared 
> to the normal signal flow in a circulator, it will incur 
> 20-30db of loss, depending on the circulator specs. 

It's not only a function of the circulator's inherent directivity spec; the
usable isolation is likely going to be dominated by the mismatch at the
antenna port as I said before.  Even if you match well when you install it,
feedline phase change with temperature, feedpoint Z varying with weather
conditions, and all of the other uncertainties and uncontrollables in the
antenna system are only going to degrade the match (and therefore isolation)
over time.

--- Jeff

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jeff DePolo]

> I am not sure why an isolator would cause intermod. Usually 
> there are not active or non-linear components in them 

An isolator IS a non-linear device.

> and 
> they are often used to prevent intermod by preventing outside 
> signals from coming in thru the feedline into the transmitter.

As a nonlinear device, they will naturally generate harmonics on their own,
and likewise act as mixers (however lossy), which is why filtering after an
isolator is necessary.

> In the past commerical sites would often require an isolator 
> for this reason with strong transmitters close by. In better 
> repeater equipment an isolator was built in.

Yes.  The isolator "isolates" the transmitter from the antenna by diverting
incoming (from the antenna) RF into the reject load rather than letting it
get back into the transmitter as a way of preventing IM from occuring.  But
in some instances, that's more of an "added bonus" than the real reason the
isolator was built in to some stations - to protect the PA from anomalies
that would cause high VSWR that could damage the PA or lead to instability
issues.

My concern, in the instant case, is that when the isolator is carrying
high-level RF from the transmitter will mix with other signals coming back
down from the antenna.  I might try a two-tone IM text on an isolator to get
a handle on what might be expected.

--- Jeff

RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

An isolator wont cause intermod, but it may cause harmonics. Commercial
installations usually use either a harmonic filter and 3db hybrid coupler,
or a special type of band pass cavity to couple the output from the isolator
to the feed line. (This info from an RX TX application note on transmitter
combiners)

 

I'm proposing a novel application of the circulator (an isolator without the
dummy load on one port).. Instead of the dummy load, the 3rd port feeds the
receiver chain. the transmit chain will still use more or less conventional
combining techniques to merge the signals from the 3 transmitters. the
output from the transmitter combiner goes to the input of an additional
circulator, the circulator output goes to the antenna as you would normally
expect for an isolator, and the "load" port goes to the receive chain
instead of a dummy load.  Since the path from the transmit chain port to the
receive chain port is "reversed" compared to the normal signal flow in a
circulator, it will incur 20-30db of loss, depending on the circulator
specs. So long as the antenna is well matched, there will be minimum
reflected power fed back into the receive chain. My "window" for all the
transmitters and receivers is less than 1mhz, so matching the antenna
shouldn't be a huge problem.

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright
Sent: Monday, October 22, 2007 8:19 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

 

I am not sure why an isolator would cause intermod. Usually there are not
active or non-linear components in them and they are often used to prevent
intermod by preventing outside signals from coming in thru the feedline into
the transmitter.

In the past commerical sites would often require an isolator for this reason
with strong transmitters close by. In better repeater equipment an isolator
was built in.

73, ron, n9ee/r

>From: Jeff DePolo <[EMAIL PROTECTED] <mailto:jd0%40broadsci.com> com>
>Date: 2007/10/22 Mon PM 07:27:09 CDT
>To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com>
yahoogroups.com
>Subject: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

> 
>> This isn't guessing - its called RESEARCH
>
>When I said guessing, I was talking about quantifying the performance of
>your radios rather than guessing how much isolation you need. In other
>words, make measurements to actually determine how much noise supression
and
>carrier attenuation you need using the actual frequencies involved. Once
>you know how much isolation you truly need, then you can work backwards
from
>there to determine the filtering requirements.
>
>I still think using an isolator is going to cause you new problems with
>respect to IM into your receivers unless you have adequate filtering
between
>the isolator and antenna, which I believe you have no way of acheiving if
>I'm understanding your layout right (i.e. isolator is connected directly to
>the antenna with nothing in between save for a harmonic filter).
>
> --- Jeff
>
> 

Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

 

Re: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Ron Wright]

I am not sure why an isolator would cause intermod.  Usually there are not 
active or non-linear components in them and they are often used to prevent 
intermod by preventing outside signals from coming in thru the feedline into 
the transmitter.

In the past commerical sites would often require an isolator for this reason 
with strong transmitters close by.  In better repeater equipment an isolator 
was built in.

73, ron, n9ee/r



>From: Jeff DePolo <[EMAIL PROTECTED]>
>Date: 2007/10/22 Mon PM 07:27:09 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise 
>budget

>  
>> This isn't guessing - its called RESEARCH
>
>When I said guessing, I was talking about quantifying the performance of
>your radios rather than guessing how much isolation you need.  In other
>words, make measurements to actually determine how much noise supression and
>carrier attenuation you need using the actual frequencies involved.  Once
>you know how much isolation you truly need, then you can work backwards from
>there to determine the filtering requirements.
>
>I still think using an isolator is going to cause you new problems with
>respect to IM into your receivers unless you have adequate filtering between
>the isolator and antenna, which I believe you have no way of acheiving if
>I'm understanding your layout right (i.e. isolator is connected directly to
>the antenna with nothing in between save for a harmonic filter).
>
>   --- Jeff
>
>


Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jeff DePolo]

> This isn't guessing - its called RESEARCH

When I said guessing, I was talking about quantifying the performance of
your radios rather than guessing how much isolation you need.  In other
words, make measurements to actually determine how much noise supression and
carrier attenuation you need using the actual frequencies involved.  Once
you know how much isolation you truly need, then you can work backwards from
there to determine the filtering requirements.

I still think using an isolator is going to cause you new problems with
respect to IM into your receivers unless you have adequate filtering between
the isolator and antenna, which I believe you have no way of acheiving if
I'm understanding your layout right (i.e. isolator is connected directly to
the antenna with nothing in between save for a harmonic filter).

--- Jeff

RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

I got your post before, and since then I have acquired a 2m circulator, and
a 50 ohm dummy load for an antenna. My network analyzer says that it does
exhibit the 30db isolation that I'm looking for.. I can insure that the
isolator sees that load with a 2m antenna tuner which I already have, or a
custom built loading circuit if needed - the frequency range that needs to
be covered is very narrow - less than 1mhz wide.. so I should be able to get
a good match across the entire range.

 

You say "makeshift" but it gets me about the same isolation that splitting
the rx and tx antennas does for the space I have available to split the
antenna, or the same amount of isolation as a single cavity (which would be
multiplied by 3 for my 3 receivers).. so I'm just as well off and the
circulator is as cheap if not cheaper than the 2nd antenna, and definitely
cheaper than 3 cavities in terms of both cost and space. it also gets my RX
and TX at the same height and the same gain. definite benefits. And even if
I don't achieve full 30db isolation, I can make up the difference elsewhere
in the system - trading off cavity bandwidth and insertion loss to get the
additional isolation needed

 

To date I have acquired the repeater controller, 4 cavity filters, 1 2m
circulator, and 2 of the 4 radios I'll be needing.. still a bit more to go
before I can do a full systems check - at least one more circulator and one
more radio before I can setup a minimal test system (1 simplex radio + the
repeater). I've got 2 more cavities on the way that should get me all I need
for the receiver filters.

 

So, until I have a few more parts, it would help to have some sides of how
receiver specs will impact the required isolation needed.

 

This isn't guessing - its called RESEARCH

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Monday, October 22, 2007 3:11 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever
noise budget

 

> Transmit and receive paths will be separate with 30db of 
> isolation (either split antennas, or a 30db isolation 
> circulator just before the feed to the antenna)

I posted a followup to one of your previous messages regarding using
isolators as a makeshift way of getting more Tx to Rx isolation, using the
reject port to feed to a receiver, and the problems therein. For some
reason, that post never showed up.

Anyway, the 30 dB of theoretical isolation that you refer to is never going
to be realized in your application. The isolator's spec of 30 dB that
you're quoting is from antenna to transmitter, assuming an ideally-matched
reject load. You're using the isolator differently; that spec doesn't
apply. In your configuration, the Tx to "Rx" (reject port) isolation is
only as good as the return loss of the antenna; consider that a 1.5:1 VSWR
is only 14 dB return loss. Maybe you'll do a little better than that, but
you'll probably never get the full 30 dB.

And there are a whole slew of other issues related to IM and harmonic
generation within the isolator.

> That brings the transmit power down to +17dbm (55mw) before 
> any other splitting and filtering to get to the 3 receivers

What about noise supression? At close T/R spacings, the noise supression
requirement is likely going to be higher than the carrier supression
required.

> Am I blowing smoke ?? Is there a way to figure from the usual 
> receiver specs just how much signal can be handled before 
> de-sense occurs ??

A typical 50 watt solid state 2m repeater typically needs 80 dB or more of
noise supression at 600 kHz split, and about 80 dB of carrier supression
(both figures plus or minus maybe 10 dB depending on the radios used). If
your Tx is closer than 600 kHz to your Rx, you're going to need
proportionally more noise supression; 100 dB at 400 kHz spacing would
probably be a good guess. Carrier attenuation likely won't need to increase
substantially until you get appreciably close to the Rx frequency, like
maybe within 200 kHz as a rough ballpark guess (it will likely vary quite a
bit depending on the quality of IF filtering in the radio).

Instead of guessing at all of these numbers, why not quantify them if you
already have the equipment you're planning on using.

--- Jeff

 

RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[Jeff DePolo]

> Transmit and receive paths will be separate with 30db of 
> isolation (either split antennas, or a 30db isolation 
> circulator just before the feed to the antenna)

I posted a followup to one of your previous messages regarding using
isolators as a makeshift way of getting more Tx to Rx isolation, using the
reject port to feed to a receiver, and the problems therein.  For some
reason, that post never showed up.

Anyway, the 30 dB of theoretical isolation that you refer to is never going
to be realized in your application.  The isolator's spec of 30 dB that
you're quoting is from antenna to transmitter, assuming an ideally-matched
reject load.  You're using the isolator differently; that spec doesn't
apply.  In your configuration, the Tx to "Rx" (reject port) isolation is
only as good as the return loss of the antenna; consider that a 1.5:1 VSWR
is only 14 dB return loss.  Maybe you'll do a little better than that, but
you'll probably never get the full 30 dB.

And there are a whole slew of other issues related to IM and harmonic
generation within the isolator.

> That brings the transmit power down to +17dbm (55mw) before 
> any other splitting and filtering to get to the 3 receivers

What about noise supression?  At close T/R spacings, the noise supression
requirement is likely going to be higher than the carrier supression
required.

> Am I blowing smoke ?? Is there a way to figure from the usual 
> receiver specs just how much signal can be handled before 
> de-sense occurs ??

A typical 50 watt solid state 2m repeater typically needs 80 dB or more of
noise supression at 600 kHz split, and about 80 dB of carrier supression
(both figures plus or minus maybe 10 dB depending on the radios used).  If
your Tx is closer than 600 kHz to your Rx, you're going to need
proportionally more noise supression; 100 dB at 400 kHz spacing would
probably be a good guess.  Carrier attenuation likely won't need to increase
substantially until you get appreciably close to the Rx frequency, like
maybe within 200 kHz as a rough ballpark guess (it will likely vary quite a
bit depending on the quality of IF filtering in the radio).

Instead of guessing at all of these numbers, why not quantify them if you
already have the equipment you're planning on using.

--- Jeff

RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

Time to reopen this subject just a little !!

 

I'm currently looking at Icom V-8000 radios for the simplex and repeater
radios (0.15uV sensitivity (-123dbm) and 75db spurious/image rejection)

 

The most any transmitter in the system will ever be running is 50 watts
(+47dbm)

 

Transmit and receive paths will be separate with 30db of isolation (either
split antennas, or a 30db isolation circulator just before the feed to the
antenna)

 

That brings the transmit power down to +17dbm (55mw) before any other
splitting and filtering to get to the 3 receivers

 

I need to understand the sensitivity and rejection numbers on the radios a
bit better. I would think that sensitivity + rejection would indicate the
strongest nearby signal that the receiver front end can handle without
de-sense .. which would mean (if I'm not totally blowing smoke) that the
V8000 could handle a nearby signal at -50dbm. leaving me 67db of isolation
that I need to account for in the splitter/filter system connected to the
receivers.

 

Am I blowing smoke ?? Is there a way to figure from the usual receiver specs
just how much signal can be handled before de-sense occurs ??

RE: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

[John Barrett]

I don't have a coordinated pair at this time, and someone on my local
repeater mentioned something about
uncoordinated/unprotected/test/"community" pairs in 144 and 440 bands.. so
if you know what they are, that's probably where this repeater will live
until I get coordinated (if I get coordinated - NE Texas is pretty packed
up).. So until I get more information, I guess I should be focusing on
isolating the 2 digital rigs.

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of skipp025
Sent: Friday, October 05, 2007 4:51 PM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Re: duplexer isolation and reciever noise budget

 

Before I give you an answer I'd want to know where the repeater 
is going to be placed. Operation in the 146 and higher portion of 
the band is going to be a heck of a lot easier than a repeater 
in the 145 segment. 

both aprs and winlink radios on the same antenna are going to require 
some serious and unique protection methods. 

To talk about the cavity size question/issue... you'll notice the 
cavity Q is much higher for "most" larger diameter cavities. So pretty 
much anything you are going to want to hunt down is going to be 
the larger high Q cavities on the order of 8 inch min typical. 

s. 

> "John B" <[EMAIL PROTECTED]> wrote:
> I'm attempting to design a system that will have a VHF repeater (freqs
> not yet determined) sharing an antenna with 2 packet radios (APRS on
> 144.39 and Winlink on 145.05, either of which may be active as a
> digipeater at any time).
> 
> I'm currently considering a bandpass-only "quadplexor" to isolate the
> radios from each other.. each radio running through a bandpass filter
> tuned to its frequency only (that includes the transmitter and
> receiver for the repeater), on the theory that it is a lot easier to
> pass one frequency than it is to reject 3 others.
> 
> Assuming that none of the transmitters run more than 50w, how many DB
> down do I need to be outside of the passband to minimize desense for
> any of the 3 receivers ??
> 
> Any other suggestions on how I might handle this hookup would be
> greatly appreciated. I'm nearing completion my trailer-mounted 40ft
> crank up tower, and I'm having some problems budgeting space for a
> filtering system with 12 bandpass cavities without cutting into
> general cargo space.
>