Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[Jim Brown]

On Sat,3/26/2016 3:49 AM, Mark van Wijk, PA5MW wrote:
Our fixed setups usually had  harmonic coax stub filters per 
individual antenna. 


You may find my applications note on optimizing the location of harmonic 
stubs useful. It's on my website. k9yc.com/publish.htm Using the 
technique I've described, stubs can be 20-30 dB more effective than if 
randomly placed along the line.


73, Jim K9YC
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Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[Mark van Wijk, PA5MW]

Thanks Jim,

Our learning point so far:

Our fixed setups usually had  harmonic coax stub filters per individual 
antenna.
Antenna interaction was carefully measured with help of a spectrum analyzer 
(worst case ever found = -17dB)

The RX inputs often had individual BPF's (home made or Dunestar)
The TX lines always had 6-band 200W BPF's

Often the TX antenna was never used for RX and switched to GND  to avoid 
noise coupling to RX antennas.

As such the TRX internal RX/TX cros-talk was never noticed.
In some other cases this event was perhaps overseen?
For me this is a new challenge.


Our typical field-day setups only have the TX  6-band BPF's
None of the other measurements/precautions have been taken as the building 
of the FD-style setup already takes a lot of time and the QTH offers limited 
access as it is being used for commercial workshops where participants fear 
electronics and antennas.



One ham recently switched to 4O3A hardware and noticed similar positive 
performance results.

Sheet metal boxes perform better than aluminium?


About coax and plugs/sockets; we are already for years busy replacing old 
stuff by Amphenol or Kabel Kusch hardware.


For my Wellbrook Loop antenna I used a home made 3-pole 160m BPF with a DC 
bypass for the head-amp. That was effective for the Topband contest.



Measurements using  calibrated generator ( Marconi 2955) and now the new 
Elecraft XG3 (very handy in the field), together with a analyzer , or even a 
good SDR like the Microtelecom Perseus (lowest phase noise ) is very helpful 
making steps forward at home.
A VNWA sure can be helpful too. At least it is more portable than our L 
HP analyzer.


In the field the challenges are different and take a lot of debugging time.




Thanks for all the tips

73 Mark, PA5MW




-Original Message- 
From: Jim Brown

Sent: Thursday, March 24, 2016 6:11 PM
To: topband@contesting.com
Subject: Re: Topband: Post contest season: TX antenna vs RX antenna 
cros-stalk. What do you do?


On Wed,3/23/2016 11:38 PM, Mark van Wijk, PA5MW wrote:
The problem is that while listening to your receiving antennas, there is 
also some signal from the transmit antenna getting through thanks to the 
internal cross-talk of your rig's TX/RX relay.


There are many heads to this snake, but also many fixes. This post is
about crosstalk, NOT interaction. First, there is coupling between the
antennas themselves. Cross-band interference between transmit antennas
can be greatly reduced by the use of bandpass filters, but these filters
don't help with RX antennas not within the filter loop.

Second, there is coupling due to leakage capacitance between relays,
poor layout of relay boxes, and currents within our stations. My station
uses a 6x2 relay box to distribute monoband antennas between rigs for
SO2R, but some have a lot more crosstalk than others. Last spring, I
replaced an Array Solutions Six-Pak with a 4O3A box. I measured both
boxes for isolation using the DG8SAQ VNWA -- the 4O3A unit had more than
20 dB better isolation than the SixPak.

But even with that improvement in hardware, I still found isolation
insufficient, so I bought a spool of BuryFlex and a box of Amphenol
83-1SP (solder-type coax connectors) and replaced every piece of coax in
my station and made sure that all were wrench-tight. (I didn't count,
but I'd guess about 25 cables). That provided another 10 dB or so (not
measured, but looking at P3 traces while operating).

Another issue I still need to address is bandpass filters on RX
antennas. I often use my Beverages up to 30M. My K3 can handle the
signal strength without damage, but while contesting, I hear very strong
harmonics there.

In one of the early chapters of his classic book, "Managing Interstation
Interference," W2VJN advises us to begin by measuring the coupling
between our antennas so that we understand the levels of crosstalk that
can be present. It's easy to do that with a vector network analyzer like
the DG8SAQ VNWA. [Note that antenna analyzers are NOT network analyzers
-- they are single-port devices. The difference is that a VNA is a
2-port device, so it can measure BOTH impedance and the gain (or loss)
between input and output ports.] We can, of course, make these
measurements with gear as simple as an amplitude-calibrated RF generator
and a calibrated voltmeter (anything from a scope to a spectrum analyzer).

The VNWA 3e is a real bargain. It's full spec to 500 MHz, reduced spec
to 1.3 GHz, and self-powers from the USB connection to your computer. I
paid about $750 shipped to my home in W6 about 3 years ago for a unit
with calibration kit.

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

73, Jim K9YC
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Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[Jim Brown]

On Wed,3/23/2016 11:38 PM, Mark van Wijk, PA5MW wrote:
The problem is that while listening to your receiving antennas, there 
is also some signal from the transmit antenna getting through thanks 
to the internal cross-talk of your rig's TX/RX relay. 


There are many heads to this snake, but also many fixes. This post is 
about crosstalk, NOT interaction. First, there is coupling between the 
antennas themselves. Cross-band interference between transmit antennas 
can be greatly reduced by the use of bandpass filters, but these filters 
don't help with RX antennas not within the filter loop.


Second, there is coupling due to leakage capacitance between relays, 
poor layout of relay boxes, and currents within our stations. My station 
uses a 6x2 relay box to distribute monoband antennas between rigs for 
SO2R, but some have a lot more crosstalk than others. Last spring, I 
replaced an Array Solutions Six-Pak with a 4O3A box. I measured both 
boxes for isolation using the DG8SAQ VNWA -- the 4O3A unit had more than 
20 dB better isolation than the SixPak.


But even with that improvement in hardware, I still found isolation 
insufficient, so I bought a spool of BuryFlex and a box of Amphenol 
83-1SP (solder-type coax connectors) and replaced every piece of coax in 
my station and made sure that all were wrench-tight. (I didn't count, 
but I'd guess about 25 cables). That provided another 10 dB or so (not 
measured, but looking at P3 traces while operating).


Another issue I still need to address is bandpass filters on RX 
antennas. I often use my Beverages up to 30M. My K3 can handle the 
signal strength without damage, but while contesting, I hear very strong 
harmonics there.


In one of the early chapters of his classic book, "Managing Interstation 
Interference," W2VJN advises us to begin by measuring the coupling 
between our antennas so that we understand the levels of crosstalk that 
can be present. It's easy to do that with a vector network analyzer like 
the DG8SAQ VNWA. [Note that antenna analyzers are NOT network analyzers 
-- they are single-port devices. The difference is that a VNA is a 
2-port device, so it can measure BOTH impedance and the gain (or loss) 
between input and output ports.] We can, of course, make these 
measurements with gear as simple as an amplitude-calibrated RF generator 
and a calibrated voltmeter (anything from a scope to a spectrum analyzer).


The VNWA 3e is a real bargain. It's full spec to 500 MHz, reduced spec 
to 1.3 GHz, and self-powers from the USB connection to your computer. I 
paid about $750 shipped to my home in W6 about 3 years ago for a unit 
with calibration kit.


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

73, Jim K9YC
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[JC]

>>I was wondering what people do besides the obvious 'kill the TX antenna
input during RX mode' ?<<

There are several reasons why it is necessary to detune the TX antenna
during RX, however disconnecting the center of the TX coax during RX on 160m
is a MUST. 

If you don't understand the problem you never implement the solution. Some
broadcast signal can reach -10 dbm or even 0 dbm. Most radios have very poor
isolation and pin 1 problem on both the RX input and TX input.

In order to open the center pin at the antenna feed point you need  a fast
vacuum relay to avoid hot switch. For an inverted L it will improve all RX
antennas removing re-radiation noise from the TX antenna.

Open the circuit between the transverter and the amplifier is a good idea.
You need a fast relay but it can be small.

Filters must be strong enough to hold at least 200w  with low insertion
loss.

The test to know if you have this problem is simple, disconnect the RX
antenna and use a 50ohms, shielded load to terminate the RX input. Tune on
the AM band and if you hear strong BC signals coming from you TX antenna
during RX with the RX port terminated with 50 ohms you have some homework to
do.

No carriers at all indicate that you have shield, grounding and choking in
good shape, if you hear strong AM signals means that you have isolation and
common node noise problems. If the BC signal can come in all QRN and other
noise sources also can come in and raise the noise floor of the receiver.

My station is quiet, I cannot detect any trace or light carrier doing the
test above. 

Regards
JC 
N4IS


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Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[Filipe Lopes]

I am using 2xTS590 and never had any issues either.

73s Filipe
CT1ILT CR6K

Sent from my Huawei Mate 8
Em 24/03/2016 12:05 p.m., "Terry Posey"  escreveu:

> Hi Mark -
>
> I have not experienced K3 TX/RX antenna isolation problems with my station
> configuration.  I expect that if there is an isolation problem with your
> rig's TX and external RX antenna routing/switching, that problem would be
> nearly impossible to quantify using your station's TX and RX antennas.  The
> rig's TX/RX isolation would need to be measured on the bench, using good
> laboratory grade equipment.
>
> Perhaps, Elecraft can provide a list of expected isolation values that were
> measured for each of the TX and external RX antenna routing/switching
> configurations possible with the K3 and K3S.  Those measurements would
> surely have been done during the rigs' design performance verification
> tests.
>
> GL
>
> 73,
> Terry K4RX
>
> ++
> Hi Bill,
>
> I think this is not what I meant here; I also do use BPF's and the Front
> End
> Savers.
>
> The problem is that while listening to your receiving antennas, there is
> also some signal from the transmit antenna getting through thanks to the
> internal cross-talk of your rig's TX/RX relay.
>
> I was wondering what people do besides the obvious 'kill the TX antenna
> input during RX mode' ?
>
> 73 Mark, PA5MW
>
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
>
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Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[Terry Posey]

Hi Mark -

I have not experienced K3 TX/RX antenna isolation problems with my station
configuration.  I expect that if there is an isolation problem with your
rig's TX and external RX antenna routing/switching, that problem would be
nearly impossible to quantify using your station's TX and RX antennas.  The
rig's TX/RX isolation would need to be measured on the bench, using good
laboratory grade equipment.

Perhaps, Elecraft can provide a list of expected isolation values that were
measured for each of the TX and external RX antenna routing/switching
configurations possible with the K3 and K3S.  Those measurements would
surely have been done during the rigs' design performance verification
tests.  

GL

73,
Terry K4RX

++
Hi Bill,

I think this is not what I meant here; I also do use BPF's and the Front End
Savers.

The problem is that while listening to your receiving antennas, there is
also some signal from the transmit antenna getting through thanks to the
internal cross-talk of your rig's TX/RX relay.

I was wondering what people do besides the obvious 'kill the TX antenna
input during RX mode' ?

73 Mark, PA5MW 

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[Mark van Wijk, PA5MW]

Hi Bill,

I think this is not what I meant here; I also do use BPF's and the Front End 
Savers.


The problem is that while listening to your receiving antennas, there is 
also some signal from the transmit antenna getting through thanks to the 
internal cross-talk of your rig's TX/RX relay.


I was wondering what people do besides the obvious 'kill the TX antenna 
input during RX mode' ?


73 Mark, PA5MW



-Original Message- 
From: william radice

Sent: Tuesday, March 22, 2016 2:05 PM
To: topband@contesting.com
Subject: Re: Topband: Post contest season: TX antenna vs RX antenna 
cros-stalk. What do you do?


 Serious multi-op contest stations face this issue all the time.
Most use individual band filters and they almost completely eliminate
the issue.
At our station we used the Dunestar filters for operating positions on
different bands. As for 160 I personally use the KD9SV "front end saver"
and it does the job completely.
BILL K4OWR

On 3/22/2016 5:44 AM, Mark van Wijk wrote:
Now that we are  'sort of in post contest season mode' and sharing some 
good

ideas, there is another question:

During recent Field-day setups I noticed severe cross-talk issues between 
TX

antennas and the separate RX antenna circuits.
For sure any TX/R relay circuitry offers roughly 50-65 dB dampening. So, 
during
a contest with >S9+30 signals received on the large TX antennas (Deltaloop 
for
40m and 80m) these would still show up S1 - S4 on the FD station's K3 RX 
input.
At home I normally de-tune my backyard TX antenna(switch to GND during RX) 
to

avoid noise pickup at the RX antennas, so I never noticed this.


Question 1: how do you manage the TX-RX cross-talk at your setup?

- switch TX antenna to GND during RX
- switch-in en external attenuator, so the cross-talk is below noise 
level, but

you are still able to use the TX antenna during RX
- any other solution?


Question 2: is there any other basic circuitry or setup in a basic contest
station which offer possible similar negative side effects?



73, Mark PA5MW
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Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[william radice]

 Serious multi-op contest stations face this issue all the time. 
Most use individual band filters and they almost completely eliminate 
the issue.
At our station we used the Dunestar filters for operating positions on 
different bands. As for 160 I personally use the KD9SV "front end saver" 
and it does the job completely.
BILL K4OWR

On 3/22/2016 5:44 AM, Mark van Wijk wrote:
> Now that we are  'sort of in post contest season mode' and sharing some good
> ideas, there is another question:
>
> During recent Field-day setups I noticed severe cross-talk issues between TX
> antennas and the separate RX antenna circuits.
> For sure any TX/R relay circuitry offers roughly 50-65 dB dampening. So, 
> during
> a contest with >S9+30 signals received on the large TX antennas (Deltaloop for
> 40m and 80m) these would still show up S1 - S4 on the FD station's K3 RX 
> input.
> At home I normally de-tune my backyard TX antenna(switch to GND during RX) to
> avoid noise pickup at the RX antennas, so I never noticed this.
>
>
> Question 1: how do you manage the TX-RX cross-talk at your setup?
>
> - switch TX antenna to GND during RX
> - switch-in en external attenuator, so the cross-talk is below noise level, 
> but
> you are still able to use the TX antenna during RX
> - any other solution?
>
>
> Question 2: is there any other basic circuitry or setup in a basic contest
> station which offer possible similar negative side effects?
>
>
>
> 73, Mark PA5MW
> _
> Topband Reflector Archives - http://www.contesting.com/_topband

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Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?

[Mark van Wijk]

Now that we are  'sort of in post contest season mode' and sharing some good
ideas, there is another question:

During recent Field-day setups I noticed severe cross-talk issues between TX
antennas and the separate RX antenna circuits.
For sure any TX/R relay circuitry offers roughly 50-65 dB dampening. So, during
a contest with >S9+30 signals received on the large TX antennas (Deltaloop for
40m and 80m) these would still show up S1 - S4 on the FD station's K3 RX input. 
At home I normally de-tune my backyard TX antenna(switch to GND during RX) to
avoid noise pickup at the RX antennas, so I never noticed this.


Question 1: how do you manage the TX-RX cross-talk at your setup?

- switch TX antenna to GND during RX
- switch-in en external attenuator, so the cross-talk is below noise level, but
you are still able to use the TX antenna during RX
- any other solution?


Question 2: is there any other basic circuitry or setup in a basic contest
station which offer possible similar negative side effects?



73, Mark PA5MW
_
Topband Reflector Archives - http://www.contesting.com/_topband