Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Scott McGrath]

Because Velocity Factor determines the time it takes a EM wave to traverse the 
cable it ALSO shortens the wavelength by the same amount relative to free space 
this is why coaxial cables can be used as delay lines and why when cutting 
resonant sections of coaxial cable the Velocity Factor must be known

Content by Scott
Typos by Siri

> On Aug 11, 2016, at 2:56 PM, Bob Stewart <b...@evoria.net> wrote:
> 
> Why is velocity factor an issue?  Aren't we only interested in the electrical 
> time from one end of the coax to the other?
> Bob
>  -
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
> 
>  From: Didier Juges <shali...@gmail.com>
> To: Bob Albert <bob91...@yahoo.com>; Discussion of precise time and frequency 
> measurement <time-nuts@febo.com> 
> Sent: Thursday, August 11, 2016 1:20 PM
> Subject: Re: [time-nuts] Safely getting the electrical length of a connected 
> antenna feedline
> 
> I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, was 
> handy) and a digital storage scope and a couple of resistors to make a 
> reflectometer based on this experiment:
> 
> www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching
> 
> You can very clearly see a 50 ohm/75 ohm mismatch.
> 
> The biggest variable will be the velocity factor.
> 
> Didier KO4BB
> 
> 
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Didier Juges]

Good point! It is only an issue when you try to calibrate/correlate to the 
physical length.
Didier

On August 11, 2016 1:56:09 PM CDT, Bob Stewart <b...@evoria.net> wrote:
>Why is velocity factor an issue?  Aren't we only interested in the
>electrical time from one end of the coax to the other?
>Bob
> -
>AE6RV.com
>
>GFS GPSDO list:
>groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>
>  From: Didier Juges <shali...@gmail.com>
>To: Bob Albert <bob91...@yahoo.com>; Discussion of precise time and
>frequency measurement <time-nuts@febo.com> 
> Sent: Thursday, August 11, 2016 1:20 PM
>Subject: Re: [time-nuts] Safely getting the electrical length of a
>connected antenna feedline
>   
>I used the PPS from a Thunderbolt (fast rise lime, low rep frequency,
>was handy) and a digital storage scope and a couple of resistors to
>make a reflectometer based on this experiment:
>
>www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching
>
>You can very clearly see a 50 ohm/75 ohm mismatch.
>
>The biggest variable will be the velocity factor.
>
>Didier KO4BB
>
>  
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-- 
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Re: [time-nuts] Safely getting the electrical length of a connected, antenna feedline

[Joe Leikhim]

"The biggest variable will be the velocity factor."

If you determine the length electrically, you will already have the 
electricallength. If you need the physical length, then multiply electrical 
length times the inverse of the velocity factor.


--
Joe Leikhim


Leikhim and Associates

Communications Consultants

Oviedo, Florida

jleik...@leikhim.com

407-982-0446

WWW.LEIKHIM.COM

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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Stewart]

Why is velocity factor an issue?  Aren't we only interested in the electrical 
time from one end of the coax to the other?
Bob
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Didier Juges <shali...@gmail.com>
 To: Bob Albert <bob91...@yahoo.com>; Discussion of precise time and frequency 
measurement <time-nuts@febo.com> 
 Sent: Thursday, August 11, 2016 1:20 PM
 Subject: Re: [time-nuts] Safely getting the electrical length of a connected 
antenna feedline
   
I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, was 
handy) and a digital storage scope and a couple of resistors to make a 
reflectometer based on this experiment:

www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching

You can very clearly see a 50 ohm/75 ohm mismatch.

The biggest variable will be the velocity factor.

Didier KO4BB

  
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Didier Juges]

I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, was 
handy) and a digital storage scope and a couple of resistors to make a 
reflectometer based on this experiment:

www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching

You can very clearly see a 50 ohm/75 ohm mismatch.

The biggest variable will be the velocity factor.

Didier KO4BB


On August 8, 2016 2:18:02 PM CDT, Bob Albert via time-nuts  
wrote:
>I host a group called something like HF Antennas.  There I posted a
>link to an article on how to measure coaxial cable.  The easiest way is
>with a spectrum analyzer and a tracking generator.
>You connect the generator to the analyzer through a Tee that goes to
>the unknown coax.  You will see a group of peaks and nulls over the
>spectrum.  The spacing is a half wave of the cable.  The match needs to
>not be good to see the nulls best, and you will need to know the
>propagation constant of the cable.  Chances are, the match won't be
>good over the entire range so you are okay with that.  Propagation
>constant of most coaxial cable runs around 66%.
>You can also use a TDR setup but you'll have to make one, with a pulser
>and a 'scope.  I downloaded a circuit for a pulser that uses one IC.  I
>have the parts but haven't built it yet, as I am stalled by the problem
>of connecting to a 14 pin SMD part.  The IC uses one part as an
>oscillator and the other 5 in parallel to drive 50 Ohms.  Again, you
>use a Tee and measure the time for a reflection, bearing in mind that
>the trip is two ways over the same cable and the time shown will be
>double the time for the calculation.
>Bob
> 
>
>On Monday, August 8, 2016 12:00 PM, Bob Stewart  wrote:
> 
>
>Earlier this year, with some help, I pulled the dish off of an old
>DishTV antenna on the roof and put a 5V bullet antenna on the mast.  I
>also pulled a new cable through by attaching it to the old one.  The
>problem is that I was not able to measure the new cable.  So, the
>question is, without going back on the roof in this heat, how can I
>measure the electrical length of the line I pulled?  
>
>I was thinking of using my 8640B signal generator and sending some RF
>back up the line to get a quarter wavelength at the null.  But that
>assumes a lot, including that the other end is open at 3MHz, or
>whatever the frequency works out to be, as well as that the high
>voltage on the antenna end won't be high enough to blow the LNA.
>
>So, how much RF I can safely send up the line?  I've got an 8558B
>spectrum analyzer, but it's not on the bench, and it would be easier to
>use my scope, which sadly is a 70s vintage Tek 455.  Do I put this all
>together with a lead from the generator to a tee at the measuring
>device and tune for a null?  My experience at getting precise
>measurements on anything longer than a few inches is effectively none,
>but I'd guess that I want less than 0.5V at the LNA during this test. 
>Oh, and I do have an 8444A tracking generator that can output -10 dbm
>as well as a 10 db attenuator within easy access.  That could get a
>quick spot on the null point.
>
>Most importantly, of course is the question of whether this will even
>work.  
>
>Bob -
>AE6RV -
>AE6RV.com
>
>GFS GPSDO list:
>groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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>
>  
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Tim Shoppa]

You left out the obvious time-nut solution: Calibrate and characterize an
ensemble of HP5071A's to correct absolute time at NIST. Transport the
ensemble (correcting, if necessary, for general relativisitic effects) to
your house. Set the cable delay in your GPS receiver to zero. The delta
between your receiver PPS and the HP5071A Ensemble is the time delay in
your cable and GPS Antenna - AFTER you account for the time delta between
USNO and NIST time (available at
http://www.nist.gov/pml/div688/grp50/nistusno.cfm )

Tim N3QE

On Mon, Aug 8, 2016 at 2:18 PM, Bob Stewart  wrote:

> Earlier this year, with some help, I pulled the dish off of an old DishTV
> antenna on the roof and put a 5V bullet antenna on the mast.  I also pulled
> a new cable through by attaching it to the old one.  The problem is that I
> was not able to measure the new cable.  So, the question is, without going
> back on the roof in this heat, how can I measure the electrical length of
> the line I pulled?
>
> I was thinking of using my 8640B signal generator and sending some RF back
> up the line to get a quarter wavelength at the null.  But that assumes a
> lot, including that the other end is open at 3MHz, or whatever the
> frequency works out to be, as well as that the high voltage on the antenna
> end won't be high enough to blow the LNA.
>
> So, how much RF I can safely send up the line?  I've got an 8558B spectrum
> analyzer, but it's not on the bench, and it would be easier to use my
> scope, which sadly is a 70s vintage Tek 455.  Do I put this all together
> with a lead from the generator to a tee at the measuring device and tune
> for a null?  My experience at getting precise measurements on anything
> longer than a few inches is effectively none, but I'd guess that I want
> less than 0.5V at the LNA during this test.  Oh, and I do have an 8444A
> tracking generator that can output -10 dbm as well as a 10 db attenuator
> within easy access.  That could get a quick spot on the null point.
>
> Most importantly, of course is the question of whether this will even
> work.
>
> Bob - AE6RV --
> ---
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
> ___
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>
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Albert via time-nuts]

Thanks David.  I have ordered some from ebay, very cheap.
5pcs SO/SOP/SOIC/SSOP/TSSOP/MSOP14 to DIP 14 Adapter PCB Board Converter MA

|   |
|   |  |   |   |   |   |   |
| 5pcs SO/SOP/SOIC/SSOP/TSSOP/MSOP14 to DIP 14 Ad...US $1.32 New other (see 
details) in Business & Industrial, Electrical & Test Equipment, Electronic 
Components |
|  |
| View on www.ebay.com | Preview by Yahoo |
|  |
|   |

 

On Wednesday, August 10, 2016 11:01 AM, David  wrote:
 

 These are a little larger than what I was thinking of but were
mentioned the other day in funwithtu...@yahoogroups.com and are
probable more suitable for most projects anyway:

http://qrpme.com/?p=product=MEP

On Tue, 9 Aug 2016 16:10:38 + (UTC), you wrote:

>Yes, a board with the required footprint would be the way to go.  Where does 
>one find that?
> 
>
>    On Tuesday, August 9, 2016 12:00 AM, David  wrote:
> 
>
> Richard mentioned the SMD to leaded adapters which work well.
>
>Another way which is more suitable for Manhattan or dead bug type
>construction is to glue or solder down just tiny printed circuit board
>which has the SMD footprint and then solder directly to the leads or
>extensions to the pads.  This does not increase the lead length any
>more than necessary and places the ground plane in close proximity for
>best RF performance.  If you are desperate, you can cut an SMD
>footprint out of an existing unused donor board.
>
>On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote:
>
>>Your comments on layout made me think again of how to implement these 
>>projects.  How do you use a 14 pin SMD IC?  I could try to connect it with 
>>flying leads but I'd like something better.  Is there some kind of socket for 
>>these devices?  Or a generic board to receive such things?
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[David]

These are a little larger than what I was thinking of but were
mentioned the other day in funwithtu...@yahoogroups.com and are
probable more suitable for most projects anyway:

http://qrpme.com/?p=product=MEP

On Tue, 9 Aug 2016 16:10:38 + (UTC), you wrote:

>Yes, a board with the required footprint would be the way to go.  Where does 
>one find that?
> 
>
>On Tuesday, August 9, 2016 12:00 AM, David  wrote:
> 
>
> Richard mentioned the SMD to leaded adapters which work well.
>
>Another way which is more suitable for Manhattan or dead bug type
>construction is to glue or solder down just tiny printed circuit board
>which has the SMD footprint and then solder directly to the leads or
>extensions to the pads.  This does not increase the lead length any
>more than necessary and places the ground plane in close proximity for
>best RF performance.  If you are desperate, you can cut an SMD
>footprint out of an existing unused donor board.
>
>On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote:
>
>>Your comments on layout made me think again of how to implement these 
>>projects.  How do you use a 14 pin SMD IC?  I could try to connect it with 
>>flying leads but I'd like something better.  Is there some kind of socket for 
>>these devices?  Or a generic board to receive such things?
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Brooke Clarke]

Hi:

Another option is so Google for a "Breakout board" for the IC you're looking to work with.  People like Spark Fun, Seed 
studio,  make these.

It's a board that holds the chip and the needed accessory parts, but needs 
something else like an Arduino.

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

 Original Message 

On Tue, Aug 9, 2016 at 9:10 AM, Bob Albert via time-nuts
 wrote:

Yes, a board with the required footprint would be the way to go.  Where does 
one find that?


You can have small PCBs made for $3 each.
There are places here in the US that will do PCBs for $3/square inch
with a one square inch minimum.   basicpcb.com sone of these.

It is not hard to design a basic "carrier board" that has just one
chip's footprint and maybe a decoupling capacitor and a 0.1" header
connector.   Many times the chip's data sheet will have an example PCB
layout you can borrow that will fit in a one square inch board.




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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Chris Albertson]

On Tue, Aug 9, 2016 at 9:10 AM, Bob Albert via time-nuts
 wrote:
>
> Yes, a board with the required footprint would be the way to go.  Where does 
> one find that?


You can have small PCBs made for $3 each.
There are places here in the US that will do PCBs for $3/square inch
with a one square inch minimum.   basicpcb.com sone of these.

It is not hard to design a basic "carrier board" that has just one
chip's footprint and maybe a decoupling capacitor and a 0.1" header
connector.   Many times the chip's data sheet will have an example PCB
layout you can borrow that will fit in a one square inch board.


-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Albert via time-nuts]

Yes, a board with the required footprint would be the way to go.  Where does 
one find that?
 

On Tuesday, August 9, 2016 12:00 AM, David  wrote:
 

 Richard mentioned the SMD to leaded adapters which work well.

Another way which is more suitable for Manhattan or dead bug type
construction is to glue or solder down just tiny printed circuit board
which has the SMD footprint and then solder directly to the leads or
extensions to the pads.  This does not increase the lead length any
more than necessary and places the ground plane in close proximity for
best RF performance.  If you are desperate, you can cut an SMD
footprint out of an existing unused donor board.

On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote:

>Your comments on layout made me think again of how to implement these 
>projects.  How do you use a 14 pin SMD IC?  I could try to connect it with 
>flying leads but I'd like something better.  Is there some kind of socket for 
>these devices?  Or a generic board to receive such things?
>
>Bob
>
>On Monday, August 8, 2016 8:02 PM, David  wrote:
>
> I actually tested various 74120 dual 4-input NAND drivers which
>produce the sync output on my B function generator to find ones
>which would provide the fastest and cleanest pulse.  AS (advanced
>schottky) and FAST (fast advanced schottky TTL) were the best for me.
>Modern inexpensive discrete logic however can do a much better these
>days.
>
>One interesting thing I learned is that the dual 4-input NAND pinout
>overlaps the quad 2-input NAND pinout so in a properly designed layout
>where only 2 gates are used, either part can be used.
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[David J Taylor]

From: Dr. David Kirkby (Kirkby Microwave Ltd)

I thought i might be possible to do this with a VNA, and a test antenna
located a known distance apart. So I asked in the Keysight forum on 8th Feb
2015
[]
Dave
___

Folks,

Yes, I've used the DG8SAQ Vector Network Analyser to measure cable lengths 
and impedance very easily.  The procedure is documented on page 458 et.seq. 
of this help file:


 http://sdr-kits.net/DG8SAQ/VNWA/VNWA_HELP.pdf

The VNWA proven one of the most useful pieces of kit I've bought, and 
support is superb.


 http://sdr-kits.net/VNWA3_Description.html

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Chuck Harris]

If you have *the* active antenna, it is pretty easy to
make a little quadrapole circularly polarized antenna out
of a couple of pieces of 141 semi-riged coax, and to transmit
signal into the active GPS antenna, and measure the signal
coming out of the active GPS antenna.

If you don't have the actual antenna being used, you could
get close by using another of the same type and manufacture.

I tested all of my GPS antennas that way for gain, as a way
to be sure that they were functioning properly, but there is
no reason that you couldn't use a VNA to test them for phase
delay, group delay, whatever you desire.

You could even modulate your sweep generator with a pulse,
detect the pulse with a diode, and measure the delay with
your oscilloscope.

-Chuck Harris

Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> On 8 Aug 2016 21:23, "Bob Camp"  wrote:
>>
>> Hi
>>
>> An even more significant question:
>>
>> Is it worth doing?
> 
>> Your antenna and module could easily have delays
>> in the 40 ns range. It has no impact on a “frequency” GPSDO. It is one of
> a number of static offsets in a time transfer system.
>>
>> Even the NIST level outfits seem to have issues coming up with a purely
> mathematical answer to “what is the offset”.
> 
> I thought i might be possible to do this with a VNA, and a test antenna
> located a known distance apart. So I asked in the Keysight forum on 8th Feb
> 2015
> 
> https://community.keysight.com/thread/23082
> 
> There's a replay by Dr_Joel, who is a VNA guru. Dr. Joel Dunsmore,
> suggesting the use of the group delay function. In one sentence he wrote
> 
> "What is the level of delay accuracy you are looking to achieve.  With this
> method, 1 nsec is reasonable, but if you need 100 psec or 10 psec, then we
> will have to be much more careful."
> 
> The thread never got a complete solution, but it might help if other look
> at that, and perhaps start another thread on a similar topic, as that one
> is very old. However, if you don't have a VNA, I would not bother asking,
> as you are not going to get a response (no pun intended), to a non-VNA
> question on a VNA forum.
> 
> But IF it was possible to determine the delay through the antenna/filter
> within a ns, it would make measurements of coax length useful, whereas as
> Bob said, it is pointless unless you know the characteristics of the active
> antenna.
> 
> I don't know if there would be a way of generating a pulse and feeding that
> into two antenna
> 
> 1) Active one.
> 
> 2) Passive one at the same distance, and same length of cable.
> 
> The pulse should arrive at the same time if the two antennas had equal
> delay. But the signal from the active one will arrive later due to the
> delay. That might be possible to see on a scope.
> 
> I think assuming that the delay in the active antenna can't be measured is
> maybe an assumption that is untrue. You could perhaps do better if you
> built your own antenna, and characterized the SAW filter separately.
> 
> Dave
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Clint Jay]

I doubt it's worth mentioning that a random SMD footprint cut from a larger
board and some of the currently available eBay SMD adapter boards may have
plated through holes which could short if used to prototype on copper clad
board so it's worth paying a little attention to insulating the
'underside'  of the boards.

On 9 Aug 2016 08:00, "David"  wrote:

> Richard mentioned the SMD to leaded adapters which work well.
>
> Another way which is more suitable for Manhattan or dead bug type
> construction is to glue or solder down just tiny printed circuit board
> which has the SMD footprint and then solder directly to the leads or
> extensions to the pads.  This does not increase the lead length any
> more than necessary and places the ground plane in close proximity for
> best RF performance.  If you are desperate, you can cut an SMD
> footprint out of an existing unused donor board.
>
> On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote:
>
> >Your comments on layout made me think again of how to implement these
> projects.  How do you use a 14 pin SMD IC?  I could try to connect it with
> flying leads but I'd like something better.  Is there some kind of socket
> for these devices?  Or a generic board to receive such things?
> >
> >Bob
> >
> >On Monday, August 8, 2016 8:02 PM, David  wrote:
> >
> > I actually tested various 74120 dual 4-input NAND drivers which
> >produce the sync output on my B function generator to find ones
> >which would provide the fastest and cleanest pulse.  AS (advanced
> >schottky) and FAST (fast advanced schottky TTL) were the best for me.
> >Modern inexpensive discrete logic however can do a much better these
> >days.
> >
> >One interesting thing I learned is that the dual 4-input NAND pinout
> >overlaps the quad 2-input NAND pinout so in a properly designed layout
> >where only 2 gates are used, either part can be used.
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[David]

Richard mentioned the SMD to leaded adapters which work well.

Another way which is more suitable for Manhattan or dead bug type
construction is to glue or solder down just tiny printed circuit board
which has the SMD footprint and then solder directly to the leads or
extensions to the pads.  This does not increase the lead length any
more than necessary and places the ground plane in close proximity for
best RF performance.  If you are desperate, you can cut an SMD
footprint out of an existing unused donor board.

On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote:

>Your comments on layout made me think again of how to implement these 
>projects.  How do you use a 14 pin SMD IC?  I could try to connect it with 
>flying leads but I'd like something better.  Is there some kind of socket for 
>these devices?  Or a generic board to receive such things?
>
>Bob
>
>On Monday, August 8, 2016 8:02 PM, David  wrote:
>
> I actually tested various 74120 dual 4-input NAND drivers which
>produce the sync output on my B function generator to find ones
>which would provide the fastest and cleanest pulse.  AS (advanced
>schottky) and FAST (fast advanced schottky TTL) were the best for me.
>Modern inexpensive discrete logic however can do a much better these
>days.
>
>One interesting thing I learned is that the dual 4-input NAND pinout
>overlaps the quad 2-input NAND pinout so in a properly designed layout
>where only 2 gates are used, either part can be used.
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Albert via time-nuts]

Thanks for the tip!  I found a few at around a buck apiece.  Now to do due 
diligence to see if they will fit my parts.
Bob
 

On Monday, August 8, 2016 9:06 PM, Richard W. Solomon <w1...@earthlink.net> 
wrote:
 

 There are a few adapters over on that "auction" site.
Do a search on 14 pin smd to 14 pin dip.

73, Dick, W1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Albert via 
time-nuts
Sent: Monday, August 08, 2016 8:37 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Safely getting the electrical length of a connected 
antenna feedline

Your comments on layout made me think again of how to implement these projects. 
 How do you use a 14 pin SMD IC?  I could try to connect it with flying leads 
but I'd like something better.  Is there some kind of socket for these devices? 
 Or a generic board to receive such things?
Bob
 

    On Monday, August 8, 2016 8:02 PM, David <davidwh...@gmail.com> wrote:
 

 I actually tested various 74120 dual 4-input NAND drivers which produce the 
sync output on my B function generator to find ones which would provide the 
fastest and cleanest pulse.  AS (advanced
schottky) and FAST (fast advanced schottky TTL) were the best for me.
Modern inexpensive discrete logic however can do a much better these days.

One interesting thing I learned is that the dual 4-input NAND pinout overlaps 
the quad 2-input NAND pinout so in a properly designed layout where only 2 
gates are used, either part can be used.

On Mon, 08 Aug 2016 16:31:44 -0400, you wrote:

>If you have a function generator with a sync output, you can use that 
>pulse into a T connector with your scope to do a TDR measurement of the 
>cable. If you have a scrap of the new cable, you can use that to calibrate the 
>setup.
>
>Regards,
>Tom
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Hal Murray]

You could get a low cost GPS unit and compare the PPS from it to the PPS from 
your setup with the long cable.

Modern GPS receivers are sensitive enough to work with a poor antenna 
(indoors) and don't cost much.



-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Scott Stobbe]

Gate drivers are pretty zippy when you leave out the capacitive load of a
power fet's gate. They are also available in 8 pin dip.

On Monday, 8 August 2016, Bob Albert via time-nuts 
wrote:

> Your comments on layout made me think again of how to implement these
> projects.  How do you use a 14 pin SMD IC?  I could try to connect it with
> flying leads but I'd like something better.  Is there some kind of socket
> for these devices?  Or a generic board to receive such things?
> Bob
>
>
> On Monday, August 8, 2016 8:02 PM, David  > wrote:
>
>
>  I actually tested various 74120 dual 4-input NAND drivers which
> produce the sync output on my B function generator to find ones
> which would provide the fastest and cleanest pulse.  AS (advanced
> schottky) and FAST (fast advanced schottky TTL) were the best for me.
> Modern inexpensive discrete logic however can do a much better these
> days.
>
> One interesting thing I learned is that the dual 4-input NAND pinout
> overlaps the quad 2-input NAND pinout so in a properly designed layout
> where only 2 gates are used, either part can be used.
>
> On Mon, 08 Aug 2016 16:31:44 -0400, you wrote:
>
> >If you have a function generator with a sync output, you can use that
> pulse
> >into a T connector with your scope to do a TDR measurement of the cable.
> If
> >you have a scrap of the new cable, you can use that to calibrate the
> setup.
> >
> >Regards,
> >Tom
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>
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Richard W. Solomon]

There are a few adapters over on that "auction" site.
Do a search on 14 pin smd to 14 pin dip.

73, Dick, W1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Albert via 
time-nuts
Sent: Monday, August 08, 2016 8:37 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Safely getting the electrical length of a connected 
antenna feedline

Your comments on layout made me think again of how to implement these projects. 
 How do you use a 14 pin SMD IC?  I could try to connect it with flying leads 
but I'd like something better.  Is there some kind of socket for these devices? 
 Or a generic board to receive such things?
Bob
 

On Monday, August 8, 2016 8:02 PM, David <davidwh...@gmail.com> wrote:
 

 I actually tested various 74120 dual 4-input NAND drivers which produce the 
sync output on my B function generator to find ones which would provide the 
fastest and cleanest pulse.  AS (advanced
schottky) and FAST (fast advanced schottky TTL) were the best for me.
Modern inexpensive discrete logic however can do a much better these days.

One interesting thing I learned is that the dual 4-input NAND pinout overlaps 
the quad 2-input NAND pinout so in a properly designed layout where only 2 
gates are used, either part can be used.

On Mon, 08 Aug 2016 16:31:44 -0400, you wrote:

>If you have a function generator with a sync output, you can use that 
>pulse into a T connector with your scope to do a TDR measurement of the 
>cable. If you have a scrap of the new cable, you can use that to calibrate the 
>setup.
>
>Regards,
>Tom
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Albert via time-nuts]

Your comments on layout made me think again of how to implement these projects. 
 How do you use a 14 pin SMD IC?  I could try to connect it with flying leads 
but I'd like something better.  Is there some kind of socket for these devices? 
 Or a generic board to receive such things?
Bob
 

On Monday, August 8, 2016 8:02 PM, David  wrote:
 

 I actually tested various 74120 dual 4-input NAND drivers which
produce the sync output on my B function generator to find ones
which would provide the fastest and cleanest pulse.  AS (advanced
schottky) and FAST (fast advanced schottky TTL) were the best for me.
Modern inexpensive discrete logic however can do a much better these
days.

One interesting thing I learned is that the dual 4-input NAND pinout
overlaps the quad 2-input NAND pinout so in a properly designed layout
where only 2 gates are used, either part can be used.

On Mon, 08 Aug 2016 16:31:44 -0400, you wrote:

>If you have a function generator with a sync output, you can use that pulse 
>into a T connector with your scope to do a TDR measurement of the cable. If 
>you have a scrap of the new cable, you can use that to calibrate the setup.
>
>Regards,
>Tom
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[David]

I actually tested various 74120 dual 4-input NAND drivers which
produce the sync output on my B function generator to find ones
which would provide the fastest and cleanest pulse.  AS (advanced
schottky) and FAST (fast advanced schottky TTL) were the best for me.
Modern inexpensive discrete logic however can do a much better these
days.

One interesting thing I learned is that the dual 4-input NAND pinout
overlaps the quad 2-input NAND pinout so in a properly designed layout
where only 2 gates are used, either part can be used.

On Mon, 08 Aug 2016 16:31:44 -0400, you wrote:

>If you have a function generator with a sync output, you can use that pulse 
>into a T connector with your scope to do a TDR measurement of the cable. If 
>you have a scrap of the new cable, you can use that to calibrate the setup.
>
>Regards,
>Tom
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Albert via time-nuts]

First, the nulls are sharper than the peaks.  What you do is measure the 
frequency of adjacent nulls and calculate what frequency makes both of those a 
half wave or multiple thereof.  Then you know the number of half waves to the 
mismatch.  It's the distance from the tee to the remote end.
It takes a little thought, or you can read the article which presents some 
formulas to make for less confusion.  I guess.  The article focuses on shorted 
or open lines but you can get readings from nearly any line, as long as it's 
not a flat line.  Of course, the closer you are to a good match, the harder it 
is to make the  measurement, which is why I suggest finding a frequency range 
far from the design of the termination equipment.
Your TDR should work also.
Bob
 

On Monday, August 8, 2016 1:23 PM, Bob Albert via time-nuts 
 wrote:
 

 I host a group called something like HF Antennas.  There I posted a link to an 
article on how to measure coaxial cable.  The easiest way is with a spectrum 
analyzer and a tracking generator.
You connect the generator to the analyzer through a Tee that goes to the 
unknown coax.  You will see a group of peaks and nulls over the spectrum.  The 
spacing is a half wave of the cable.  The match needs to not be good to see the 
nulls best, and you will need to know the propagation constant of the cable.  
Chances are, the match won't be good over the entire range so you are okay with 
that.  Propagation constant of most coaxial cable runs around 66%.
You can also use a TDR setup but you'll have to make one, with a pulser and a 
'scope.  I downloaded a circuit for a pulser that uses one IC.  I have the 
parts but haven't built it yet, as I am stalled by the problem of connecting to 
a 14 pin SMD part.  The IC uses one part as an oscillator and the other 5 in 
parallel to drive 50 Ohms.  Again, you use a Tee and measure the time for a 
reflection, bearing in mind that the trip is two ways over the same cable and 
the time shown will be double the time for the calculation.
Bob
 

    On Monday, August 8, 2016 12:00 PM, Bob Stewart  wrote:
 

 Earlier this year, with some help, I pulled the dish off of an old DishTV 
antenna on the roof and put a 5V bullet antenna on the mast.  I also pulled a 
new cable through by attaching it to the old one.  The problem is that I was 
not able to measure the new cable.  So, the question is, without going back on 
the roof in this heat, how can I measure the electrical length of the line I 
pulled?  

I was thinking of using my 8640B signal generator and sending some RF back up 
the line to get a quarter wavelength at the null.  But that assumes a lot, 
including that the other end is open at 3MHz, or whatever the frequency works 
out to be, as well as that the high voltage on the antenna end won't be high 
enough to blow the LNA.

So, how much RF I can safely send up the line?  I've got an 8558B spectrum 
analyzer, but it's not on the bench, and it would be easier to use my scope, 
which sadly is a 70s vintage Tek 455.  Do I put this all together with a lead 
from the generator to a tee at the measuring device and tune for a null?  My 
experience at getting precise measurements on anything longer than a few inches 
is effectively none, but I'd guess that I want less than 0.5V at the LNA during 
this test.  Oh, and I do have an 8444A tracking generator that can output -10 
dbm as well as a 10 db attenuator within easy access.  That could get a quick 
spot on the null point.

Most importantly, of course is the question of whether this will even work.  

Bob - AE6RV -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Tom Miller]

If you have a function generator with a sync output, you can use that pulse 
into a T connector with your scope to do a TDR measurement of the cable. If 
you have a scrap of the new cable, you can use that to calibrate the setup.


Regards,
Tom

- Original Message - 
From: "Bob Stewart" <b...@evoria.net>
To: "Discussion of Precise Time and Frequency Measurement" 
<time-nuts@febo.com>

Sent: Monday, August 08, 2016 2:18 PM
Subject: [time-nuts] Safely getting the electrical length of a connected 
antenna feedline



Earlier this year, with some help, I pulled the dish off of an old DishTV 
antenna on the roof and put a 5V bullet antenna on the mast. I also pulled 
a new cable through by attaching it to the old one. The problem is that I 
was not able to measure the new cable. So, the question is, without going 
back on the roof in this heat, how can I measure the electrical length of 
the line I pulled?


I was thinking of using my 8640B signal generator and sending some RF back 
up the line to get a quarter wavelength at the null. But that assumes a 
lot, including that the other end is open at 3MHz, or whatever the 
frequency works out to be, as well as that the high voltage on the antenna 
end won't be high enough to blow the LNA.


So, how much RF I can safely send up the line? I've got an 8558B spectrum 
analyzer, but it's not on the bench, and it would be easier to use my 
scope, which sadly is a 70s vintage Tek 455. Do I put this all together 
with a lead from the generator to a tee at the measuring device and tune 
for a null? My experience at getting precise measurements on anything 
longer than a few inches is effectively none, but I'd guess that I want 
less than 0.5V at the LNA during this test. Oh, and I do have an 8444A 
tracking generator that can output -10 dbm as well as a 10 db attenuator 
within easy access. That could get a quick spot on the null point.


Most importantly, of course is the question of whether this will even 
work.


Bob - 
AE6RV -

AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Stewart]

Hi Bob,
Correct me if I'm wrong, but for timing purposes, I think that what I want is 
the electrical length in nanoseconds, not the physical length.  I hadn't 
considered the fact that the distance between peaks would give me a halfwave.  
But, that's a halfwave of what, exactly?  Is it the distance from the far end 
to the tee, or to the generator or to the measurement device (SA/scope/meter)?  
And since nanoseconds are important, is it actually to some point within the 
measuring device?  Or, since it's only nanoseconds, maybe the last few inches 
inside the scope aren't that important?  It's starting to sound like what I 
really want to do the final measurement with is my old Voltohmyst with the RF 
probe at the tee if I really want to be accurate.  That would be using the 8640 
and tuning for either null or peak, whichever is sharper.

As far as a TDR is concerned, I think that the 1PPS output from my GPSDO should 
be sufficient.  In this case, I think I'd send the 1PPS to a tee at the start 
input on my 5370 and lock start and stop together with the phase switches 
opposite for start and stop.  For this test, I could actually control the 
length of time the 1PPS is high so that it doesn't spoil the measurement.  But, 
once again, will I see any sort of spike on the other end with a 3.3V 1PPS 
pulse?

Bob
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Bob Albert <bob91...@yahoo.com>
 To: Bob Stewart <b...@evoria.net>; Discussion of Precise Time and Frequency 
Measurement <time-nuts@febo.com>; Discussion of precise time and frequency 
measurement <time-nuts@febo.com> 
 Sent: Monday, August 8, 2016 2:18 PM
 Subject: Re: [time-nuts] Safely getting the electrical length of a connected 
antenna feedline
   
I host a group called something like HF Antennas.  There I posted a link to an 
article on how to measure coaxial cable.  The easiest way is with a spectrum 
analyzer and a tracking generator.
You connect the generator to the analyzer through a Tee that goes to the 
unknown coax.  You will see a group of peaks and nulls over the spectrum.  The 
spacing is a half wave of the cable.  The match needs to not be good to see the 
nulls best, and you will need to know the propagation constant of the cable.  
Chances are, the match won't be good over the entire range so you are okay with 
that.  Propagation constant of most coaxial cable runs around 66%.
You can also use a TDR setup but you'll have to make one, with a pulser and a 
'scope.  I downloaded a circuit for a pulser that uses one IC.  I have the 
parts but haven't built it yet, as I am stalled by the problem of connecting to 
a 14 pin SMD part.  The IC uses one part as an oscillator and the other 5 in 
parallel to drive 50 Ohms.  Again, you use a Tee and measure the time for a 
reflection, bearing in mind that the trip is two ways over the same cable and 
the time shown will be double the time for the calculation.
Bob
 

On Monday, August 8, 2016 12:00 PM, Bob Stewart <b...@evoria.net> wrote:
 

 Earlier this year, with some help, I pulled the dish off of an old DishTV 
antenna on the roof and put a 5V bullet antenna on the mast.  I also pulled a 
new cable through by attaching it to the old one.  The problem is that I was 
not able to measure the new cable.  So, the question is, without going back on 
the roof in this heat, how can I measure the electrical length of the line I 
pulled?  

I was thinking of using my 8640B signal generator and sending some RF back up 
the line to get a quarter wavelength at the null.  But that assumes a lot, 
including that the other end is open at 3MHz, or whatever the frequency works 
out to be, as well as that the high voltage on the antenna end won't be high 
enough to blow the LNA.

So, how much RF I can safely send up the line?  I've got an 8558B spectrum 
analyzer, but it's not on the bench, and it would be easier to use my scope, 
which sadly is a 70s vintage Tek 455.  Do I put this all together with a lead 
from the generator to a tee at the measuring device and tune for a null?  My 
experience at getting precise measurements on anything longer than a few inches 
is effectively none, but I'd guess that I want less than 0.5V at the LNA during 
this test.  Oh, and I do have an 8444A tracking generator that can output -10 
dbm as well as a 10 db attenuator within easy access.  That could get a quick 
spot on the null point.

Most importantly, of course is the question of whether this will even work.  

Bob - AE6RV -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Stewart]

Hi Bob,
I believe I know the delay for the antenna and Ublox specifies the delay in the 
receiver.  I can't guess within 20ft of the physical length of the antenna.  
But, this is time-nuts, so yeah I want to be able to work this out.  And 
besides...

I figured out how to output an accurate 1PPS with my unit.  So, it's no longer 
just a frequency standard.  Briefly: I take advantage of the fact that the 
sawtooth on the Ublox units is less 22ns wide (about +/- 10.5ns according to my 
data).  I send the 1PPS from the receiver through a 30ns delay line to trigger 
a d-flop in a 7474, which arms the other d-flop in the 7474.  The 30ns delay 
ensures that the 1PPS output of the Ublox, including the sawtooth, is always 
within the dead time between the pulses from the OCXO.  So, the next 10MHz 
pulse triggers the other d-flop which goes through a 125 gate to the 1PPS 
output.  1/16th of a second later (a convenient time for me), the PIC resets 
the two d-flops and so it goes.  So, yeah, that's 100ns late, but the Ublox has 
a userDelay field, which I set to 100ns.  That moves the PPS back to the proper 
time.  Yes, there is a delay of the 10MHz through the d-flop and the gate, but 
that's knowable.  And there's about a 5ns difference bet
 ween the 1PPS output and the 10MHz output.  So, given that the delays are all 
knowable, I think it's usable as a timing unit now; given the limitations of a 
GPSDO for that purpose.  

Any discussion about this method of getting a 1PPS should probably be in a new 
thread.  I'd be happy to link to a schematic if wanted.

Bob
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Bob Camp <kb...@n1k.org>
 To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency 
measurement <time-nuts@febo.com> 
 Sent: Monday, August 8, 2016 3:14 PM
 Subject: Re: [time-nuts] Safely getting the electrical length of a connected 
antenna feedline
   
Hi

An even more significant question:

Is it worth doing? 

More or less:

Do you know the delay numbers for your antenna?

Do you know the delay numbers for your GPS module? 

How close can you *guess* the length of the cable?

Knowing absolutely nothing at all about your setup, I’ll guess the cable is 50 
feet long. Maybe I’m off by 20 or 30 feet. 
Call that +/-40 to 60 ns. I’d hope you can guess closer than that. Your antenna 
and module could easily have delays 
in the 40 ns range. It has no impact on a “frequency” GPSDO. It is one of a 
number of static offsets in a time transfer system. 

Even the NIST level outfits seem to have issues coming up with a purely 
mathematical answer to “what is the offset”.  
The standard answer is to bring in a calibrated receiver and see how it all 
measures out. 

None of that is to say you should *not* work out the line length. It’s just to 
say that there is only so much value to the 
measurement. 

Bob

> On Aug 8, 2016, at 2:18 PM, Bob Stewart <b...@evoria.net> wrote:
> 
> Earlier this year, with some help, I pulled the dish off of an old DishTV 
> antenna on the roof and put a 5V bullet antenna on the mast.  I also pulled a 
> new cable through by attaching it to the old one.  The problem is that I was 
> not able to measure the new cable.  So, the question is, without going back 
> on the roof in this heat, how can I measure the electrical length of the line 
> I pulled?  
> 
> I was thinking of using my 8640B signal generator and sending some RF back up 
> the line to get a quarter wavelength at the null.  But that assumes a lot, 
> including that the other end is open at 3MHz, or whatever the frequency works 
> out to be, as well as that the high voltage on the antenna end won't be high 
> enough to blow the LNA.
> 
> So, how much RF I can safely send up the line?  I've got an 8558B spectrum 
> analyzer, but it's not on the bench, and it would be easier to use my scope, 
> which sadly is a 70s vintage Tek 455.  Do I put this all together with a lead 
> from the generator to a tee at the measuring device and tune for a null?  My 
> experience at getting precise measurements on anything longer than a few 
> inches is effectively none, but I'd guess that I want less than 0.5V at the 
> LNA during this test.  Oh, and I do have an 8444A tracking generator that can 
> output -10 dbm as well as a 10 db attenuator within easy access.  That could 
> get a quick spot on the null point.
> 
> Most importantly, of course is the question of whether this will even work.  
> 
> Bob - AE6RV -
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Camp]

Hi

An even more significant question:

Is it worth doing? 

More or less:

Do you know the delay numbers for your antenna?

Do you know the delay numbers for your GPS module? 

How close can you *guess* the length of the cable?

Knowing absolutely nothing at all about your setup, I’ll guess the cable is 50 
feet long. Maybe I’m off by 20 or 30 feet. 
Call that +/-40 to 60 ns. I’d hope you can guess closer than that. Your antenna 
and module could easily have delays 
in the 40 ns range. It has no impact on a “frequency” GPSDO. It is one of a 
number of static offsets in a time transfer system. 

Even the NIST level outfits seem to have issues coming up with a purely 
mathematical answer to “what is the offset”.  
The standard answer is to bring in a calibrated receiver and see how it all 
measures out. 

None of that is to say you should *not* work out the line length. It’s just to 
say that there is only so much value to the 
measurement. 

Bob

> On Aug 8, 2016, at 2:18 PM, Bob Stewart  wrote:
> 
> Earlier this year, with some help, I pulled the dish off of an old DishTV 
> antenna on the roof and put a 5V bullet antenna on the mast.  I also pulled a 
> new cable through by attaching it to the old one.  The problem is that I was 
> not able to measure the new cable.  So, the question is, without going back 
> on the roof in this heat, how can I measure the electrical length of the line 
> I pulled?  
> 
> I was thinking of using my 8640B signal generator and sending some RF back up 
> the line to get a quarter wavelength at the null.  But that assumes a lot, 
> including that the other end is open at 3MHz, or whatever the frequency works 
> out to be, as well as that the high voltage on the antenna end won't be high 
> enough to blow the LNA.
> 
> So, how much RF I can safely send up the line?  I've got an 8558B spectrum 
> analyzer, but it's not on the bench, and it would be easier to use my scope, 
> which sadly is a 70s vintage Tek 455.  Do I put this all together with a lead 
> from the generator to a tee at the measuring device and tune for a null?  My 
> experience at getting precise measurements on anything longer than a few 
> inches is effectively none, but I'd guess that I want less than 0.5V at the 
> LNA during this test.  Oh, and I do have an 8444A tracking generator that can 
> output -10 dbm as well as a 10 db attenuator within easy access.  That could 
> get a quick spot on the null point.
> 
> Most importantly, of course is the question of whether this will even work.  
> 
> Bob - AE6RV -
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Albert via time-nuts]

I host a group called something like HF Antennas.  There I posted a link to an 
article on how to measure coaxial cable.  The easiest way is with a spectrum 
analyzer and a tracking generator.
You connect the generator to the analyzer through a Tee that goes to the 
unknown coax.  You will see a group of peaks and nulls over the spectrum.  The 
spacing is a half wave of the cable.  The match needs to not be good to see the 
nulls best, and you will need to know the propagation constant of the cable.  
Chances are, the match won't be good over the entire range so you are okay with 
that.  Propagation constant of most coaxial cable runs around 66%.
You can also use a TDR setup but you'll have to make one, with a pulser and a 
'scope.  I downloaded a circuit for a pulser that uses one IC.  I have the 
parts but haven't built it yet, as I am stalled by the problem of connecting to 
a 14 pin SMD part.  The IC uses one part as an oscillator and the other 5 in 
parallel to drive 50 Ohms.  Again, you use a Tee and measure the time for a 
reflection, bearing in mind that the trip is two ways over the same cable and 
the time shown will be double the time for the calculation.
Bob
 

On Monday, August 8, 2016 12:00 PM, Bob Stewart  wrote:
 

 Earlier this year, with some help, I pulled the dish off of an old DishTV 
antenna on the roof and put a 5V bullet antenna on the mast.  I also pulled a 
new cable through by attaching it to the old one.  The problem is that I was 
not able to measure the new cable.  So, the question is, without going back on 
the roof in this heat, how can I measure the electrical length of the line I 
pulled?  

I was thinking of using my 8640B signal generator and sending some RF back up 
the line to get a quarter wavelength at the null.  But that assumes a lot, 
including that the other end is open at 3MHz, or whatever the frequency works 
out to be, as well as that the high voltage on the antenna end won't be high 
enough to blow the LNA.

So, how much RF I can safely send up the line?  I've got an 8558B spectrum 
analyzer, but it's not on the bench, and it would be easier to use my scope, 
which sadly is a 70s vintage Tek 455.  Do I put this all together with a lead 
from the generator to a tee at the measuring device and tune for a null?  My 
experience at getting precise measurements on anything longer than a few inches 
is effectively none, but I'd guess that I want less than 0.5V at the LNA during 
this test.  Oh, and I do have an 8444A tracking generator that can output -10 
dbm as well as a 10 db attenuator within easy access.  That could get a quick 
spot on the null point.

Most importantly, of course is the question of whether this will even work.  

Bob - AE6RV -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline

[Hal Murray]

b...@evoria.net said:
> Earlier this year, with some help, I pulled the dish off of an old DishTV
> antenna on the roof and put a 5V bullet antenna on the mast.  I also pulled
> a new cable through by attaching it to the old one.  The problem is that I
> was not able to measure the new cable.  So, the question is, without going
> back on the roof in this heat, how can I measure the electrical length of
> the line I pulled?   

Can you measure the old cable?


-- 
These are my opinions.  I hate spam.



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[time-nuts] Safely getting the electrical length of a connected antenna feedline

[Bob Stewart]

Earlier this year, with some help, I pulled the dish off of an old DishTV 
antenna on the roof and put a 5V bullet antenna on the mast.  I also pulled a 
new cable through by attaching it to the old one.  The problem is that I was 
not able to measure the new cable.  So, the question is, without going back on 
the roof in this heat, how can I measure the electrical length of the line I 
pulled?  

I was thinking of using my 8640B signal generator and sending some RF back up 
the line to get a quarter wavelength at the null.  But that assumes a lot, 
including that the other end is open at 3MHz, or whatever the frequency works 
out to be, as well as that the high voltage on the antenna end won't be high 
enough to blow the LNA.

So, how much RF I can safely send up the line?  I've got an 8558B spectrum 
analyzer, but it's not on the bench, and it would be easier to use my scope, 
which sadly is a 70s vintage Tek 455.  Do I put this all together with a lead 
from the generator to a tee at the measuring device and tune for a null?  My 
experience at getting precise measurements on anything longer than a few inches 
is effectively none, but I'd guess that I want less than 0.5V at the LNA during 
this test.  Oh, and I do have an 8444A tracking generator that can output -10 
dbm as well as a 10 db attenuator within easy access.  That could get a quick 
spot on the null point.

Most importantly, of course is the question of whether this will even work.  

Bob - AE6RV -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
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