Sure, a UHF isolator will not protect the transmitter from
VHF transmitter junk. But isn't the flip side that out of
band VHF junk is less likely to produce UHF transmitter
intermod than in band transmitter junk?
Not necessarily. If it were the other way around (UHF coming back down the
The other ways to correct the problem, other than using a different
transmitter that is not bothered by reactive loads as much,
is to use a Z
match or try different length cables that make the
transmitter happier.
But if the transmitter is bothered by the bad Z at frequencies outside of
Doesn't the isolator typically installed at the transmitter output spin off
any anything reflected from the duplexer (or the feedline) into it's load?
In a message dated 7/1/2007 5:33:33 P.M. Pacific Daylight Time,
[EMAIL PROTECTED] writes:
But at some off frequency that is not 50+j0
_
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED]
Sent: Sunday, July 01, 2007 8:30 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Cable formula
Doesn't the isolator typically installed at the transmitter output spin off
any
@yahoogroups.com
Subject: Re: [Repeater-Builder] Cable formula
That would be the typical installation, unless you install the isolator
at the output of the duplexer with the #1 (input) toward the TX
cavities, #3 (load) toward the receive cavities, and #2 port (output)
toward the antenna, used in place
).
73
Gary K4FMX
-Original Message-
From: Repeater-Builder@yahoogroups.com [mailto:Repeater-
[EMAIL PROTECTED] On Behalf Of Steve S. Bosshard (NU5D)
Sent: Sunday, July 01, 2007 9:35 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Cable formula
That (isolator
I remember asking Lloyd at Wacom about using an isolator in the output -
seems like he told me that it allowed more flexibility in cable lengths
on the output - might make sense because the Q package had frequencies
from 458 to 468 with the apcor carry in units. Ancient history -
nightmares when
Doesn't the isolator typically installed at the transmitter
output spin off any anything reflected from the duplexer (or
the feedline) into it's load?
The generic answer is yes, but the qualified answer is that isolators,
like everything else, have a finite bandwidth, so if the energy is
If your duplexer presents 50+j0 at its input at the operating
frequency and
you are using 50 ohm cable to connect it to the transmitter then the
transmitter is always going to see 50+j0 at the operating frequency no
matter what the cable length is. But at some off frequency
that is not
Hi Steve,
I don't recall ever seeing that done. What was the purpose of using an
isolator there?
Steve will probably reply too, but I'll give you the quick answer. UHF
Micor mobiles all came stock with an isolator in the antenna network, just
like their big brother base/repeater stations.
You can't convert to a perfect 50 ohms using cable lengths
if the load isn't already 50 ohms. I've said before, and I'm
saying it again. If your duplexer 50 ohms load, you can pull
all of the 50 ohm cables you want out of your bag and you'll
never get it back to 50 ohms at the PA.
Boy,
of that
radio??
73
Gary K4FMX
-Original Message-
From: Repeater-Builder@yahoogroups.com [mailto:Repeater-
[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Sunday, July 01, 2007 10:47 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Cable formula
Hi Steve,
I
-Original Message-
From: Repeater-Builder@yahoogroups.com [mailto:Repeater-
[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Sunday, July 01, 2007 10:51 PM
To: 'Jeff DePolo'; Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Cable formula
You can't convert
Sure, a UHF isolator will not protect the transmitter from VHF transmitter
junk. But isn't the flip side that out of band VHF junk is less likely to
produce UHF transmitter intermod than in band transmitter junk? And also, while
a
VHF band pass cavity might do its job resisting unwanted
impedance adjustable
line- general radio USA no striped paint here im afraid!
Ian Ashford
G8PWE
- Original Message -
From: [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Saturday, June 30, 2007 3:50 AM
Subject: Re: [Repeater-Builder] Cable formula
A good
However, the load impedance of most PAs
will vary
significantly with the drive level,
I think you meant source impedance.
and the input impedance
of a duplexer
cavity is always reactive
Not necessarily. You can tune a duplexer very close to 50+j0 at the pass
frequency. It's at
I don't think the cable cares whether the source and load
impedances are 50 ohms
resistive. I think the cable is indifferent to whether the
load and source values are
resistive or whether they present a complex impedance
involving +/- J. as long as the
composite value looks like 50
OK so you have a reel of cable and two connectors to make up
the jumper between transmitter and duplexer.
The duplexer is tuned using 50 ohm test gear and the
transmitter has been optimised into a 50 ohm load.
Unfortunatley the output impedance of the transmitter is not
50 ohms and
Do you recall if the leakage you observed was on channel or whether it was
broadband noise?
In a message dated 6/30/2007 3:53:42 A.M. Pacific Daylight Time,
[EMAIL PROTECTED] writes:
The cable leakage stopped when the z matcher was removed and the cable
length was altered for
I don't think I ever suggested otherwise. I never said that using a half
wave cable would improve
anything. What I did say was that a half wave cable would repeat the
prevailing condition neither
making it better or worse and I further said that using any variation from a
half wave cable
Jeff
You make some excellent points. Thanks!
Bruce K7IJ
** See what's free at http://www.aol.com.
I don't think I ever suggested otherwise. I never said that
using a half wave cable would improve
anything. What I did say was that a half wave cable would
repeat the prevailing condition neither
making it better or worse and I further said that using any
variation from a half wave cable
Can't argue with your analysis. My only point is that if you are intent on
dealing with a
TX to duplexer mismatch, a half wave cable replicates what ever mismatch
exists. A
random length cable can mask the real world condition by making the apparent
mismatch
better or worse than it really
6:22 PM
Subject: RE: [Repeater-Builder] Cable formula
Do you have any thoughts on why or how a well designed Z
match could produce cable
radiation?
For the feedline to radiate, there would have to be currents flowing on
the
shield. It would seem to me the only way to get that to happen
It looks like I am able to post here again. Don't know what happened.
This subject was examined a little about a month ago. You can search for my
comments back then but I will state again similar to what I said then.
Some transmitters do not like to see any reactive load on them. They will
cut
Does anyone know the formula for the cable length between a repeater
and the duplexer?
Thanks
Don VE7EDA
Sent: Friday, June 29, 2007 8:25 AM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Cable formula
Does anyone know the formula for the cable length between a repeater
and the duplexer?
Thanks
Don VE7EDA
The length from the repeater to the duplexer isno critical (or SHOULD
not be when properly tuned). Therefore, there is no 'formula' other than
you want it as short as possible yet allowing enough flex/extra that it
won't get stressed.
Joe M.
Don Morehouse wrote:
Does anyone know the formula
Sheesh. isno should have been is not.
Joe M.
mch wrote:
The length from the repeater to the duplexer isno critical (or SHOULD
not be when properly tuned). Therefore, there is no 'formula' other than
you want it as short as possible yet allowing enough flex/extra that it
won't get stressed.
Why would the presence or absence of +/- J affect the determination of
whether or not the feedline is functioning as an impedance transformer? When
the source and load impedances are different, even though purely resistive,
won't the connecting cable still act as a line transformer?
Roger, Roger, Roger.Steve NU5D
mch wrote:
*The length from the repeater to the duplexer is not critical (or SHOULD
not be when properly tuned). Therefore, there is no 'formula' other than
you want it as short as possible yet allowing enough flex/extra that it
won't get stressed.*
I'll third that...even though duplexers are typically reactive, if it's
right, length of the cables should not be an issue.
If it is, I would look at either the duplexer or the antenna/feedline.
As always, put a dummy load after the duplexer and see if all is well.
If it is, it's an antenna
OK so you have a reel of cable and two connectors to make up the jumper between
transmitter and duplexer.
The duplexer is tuned using 50 ohm test gear and the transmitter has been
optimised into a 50 ohm load.
Unfortunatley the output impedance of the transmitter is not 50 ohms and a
length
I saw that line stretcher guy, Ian. He was next to the striped tower
paint salesman. 73, Steve NU5D
PS - I have used an isolator in place of the TEE on the output of a
duplexer. Not very practical there, though, and it sure knocks down the
receive if you put it in series with the antenna, else
A good quality Z-Matcher has isolation caps on the trimmer ports so I don't
think the matcher itself is producing any RF radiation. I don't understand
your description of the z Matcher as introducing any
mismatch. The mismatch is already there as a result of some disparity
between the
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