[TowerTalk] Field Day

Jim Brown jim at audiosystemsgroup.com
Tue Jul 4 12:53:11 EDT 2017

On 7/4/2017 3:48 AM, Ed Sawyer wrote:
> I have done quite a bit of "in band" low power 2 radio work.  At 100 W, 2 A4
> tribanders, tip to tip, 225ft separation  should have still audible sounds
> on the cross band portion CW vs SSB - maybe 2 - 3 S units.

SHOULD is the wrong word. MAY is the better one. And when they DO have 
this problem, what is needed is better radios and/or feedline chokes, 
not attenuation.  See k9yc.com/RFI-Ham.pdf for band-by-band guidelines 
on the chokes.  The feedline also can make a big difference. We use 
nothing but high quality coax with Amphenol 83-1SP connectors, carefully 
installed, and Amphenol (or MIL-spec surplus) adapters.  "High quality 
coax" means that it has a very good copper braid shield. And all 
connectors are wrench-tight.  We also use nothing but that big, high 
quality coax WITHIN our stations -- rig to to bandpass filters, filters 
to amp, amp to tuner, (or stubs), and for any switching. A poor shield 
connection, or coax with mediocre shielding, anywhere in the system is a 
BIG window through which noise and crosstalk can enter a system.

With K3s, KPA500s and C3SS on each station, we run on the CW and SSB 
same band for CQP with that sort of spacing and no QRM between them.  At 
home, I've done the same with K3, Ten Tec Titan (legal limit tubes), a 
3-el SteppIR on one rig and a 3-el monobander on 20M, antennas 
parallel/colinear about 200 ft apart within 60 kHz on CW and each not 
hearing the other!  And I did NOT need attenuation on the K3s, and I did 
have the pre-amp on, needed at my often quiet QTH to hear the weakest 
signals on 20M and above.

> However 10 -
> 15dB of attenuation on the receivers should kill it if it becomes
> bothersome.  If you are not seeing that, consider grounding the systems
> together and trying other radios (making sure the SSB radio is not over
> driving).

Grounding is NOT a solution for RFI or crosstalk.  Good engineering 
practice with respect to antenna balance, choice of feedline, and chokes 
on feedlines IS part of the solution.

> On 40 - 160, try running a long - directional beverage, separated and to the
> side of the antenna if you have the room.  At 100W, and with the improved
> S/N ratio, you should do really well.  Potentially both stations could use
> the same beverage for receive.

As others have suggested, dedicated RX antennas can also be a good 
solution, BUT -- they also require very good coax with good connectors 
properly installed and effective feedline chokes both at the feedpoint 
and at the station(s).

73, Jim K9YC

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