[TowerTalk] Field Day
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
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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