[TowerTalk] Field Day
cw_de_n5op at sbcglobal.net
Tue Jul 4 16:26:39 EDT 2017
I'll bear witness to the "good connectors, properly installed" aspect of
Jim's post. At this year's field day, the GOTA station was running a 43
ft vertical with an SGC 237 remote tuner about 200 ft away from the
end-to-end dipoles was getting trash no matter what bands were being
used. Then, it quit altogether. A brief inspection showed perhaps the
worst coax connector installation I'd ever seen. On RG-8 sized cable,
every bit of any solder joint I saw was cold as ice. If we wiggled it
around, trash appeared everywhere, all bands, when we transmitted. My
guess is that the same crummy piece of coax had been to every club FD
for years. We concluded that this was clearly a case of local
rectification RFI. It was at the end of field day, so we simply closed
up the GOTA shop. But, I raised the issue with the next FD captain and
gave him a decent write-up on all of what we saw and what needs
attention. Sometimes, it's the things that shouldn't need looking
after... For example, the 10 kW generator at the site donated for our
use FD by the local campus police department was set to 50 Hz for some
inexplicable reason. Anyone with a linear power supply was complaining
that their regulation was very poor. The air conditioner wasn't acting
happy, either. Everything magically got better when we switched to 60 Hz.
On 7/4/2017 11:53 AM, Jim Brown wrote:
> 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
>> 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
>> 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
> TowerTalk mailing list
> TowerTalk at contesting.com
Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)
/"In theory there is no difference between theory and practice. But, in
practice, there is." //– Attributed to many people; it’s so true that it
doesn’t matter who said it./
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