[TowerTalk] station to station interference

[Jim Brown]

On Wed,9/28/2016 5:54 AM, Ed Sawyer wrote:
> I would advocate "going clean" on the worst offender scenario and have pure
> coax going from the amp to the antenna.

Yes. I had more crosstalk between stations than I thought I should, and 
SWR was higher at different points in the station than made sense.  I 
bought  a big spool of BuryFlex and 100 or so 83-1SP connectors and 
replaced every piece of coax inside my shack, starting with my entry 
panel. I also replaced a Daiwa power meter with N8LP's LP100A, and got 
rid of sampling points to look at harmonics on a spectrum analyzer. And 
I replaced a Six Pak with 4O3A's 6x2 (and a year ago,with his new 8x2).

I'm using several Top Ten relay boxes (some 6x2s to switch stub matching 
networks for my 80 and 40 dipoles, and some 2x1s to trade several 
antennas between the two radios). Taking apart one of the 2x1s, I 
learned that they fail to provide a return path for RF current on the 
circuit board -- the only return path is the chassis -- so SWR is a mess 
at 10M and 6M, and while I didn't measure it, that sort of thing also 
can increase crosstalk. I rebuilt those boxes to add a return path 
paralleling the center conductor path, and the SWR through the box 
dropped by more than half.  The failure to provide a return path is all 
too common in HF antenna switching systems and antennas. It's present in 
the big Ten Tec tuners (229, 238), and in several expensive high power 
antenna tuners I inspected in booths at Dayton a few years ago. When I 
pointed it out to the engineer who designed them, he didn't understand 
the problem. This can also be critical in filters. 5B4AGN has done an 
excellent job with his design of the TXBPF filter sets for which he's 
arranged several group purchases.

Ten Tec did it right in the power amps that I own (Titan 425 and Herc 
II) -- there's coax from both input and output to the vacuum relay.

> By the way, I don't need stubs - I have found out.  Just Bandpass filters
> and antenna separation.  1.5kW on all bands and SO2R.

You must have a LOT of separation. Where I think most of us run into 
trouble is between 80, 40, and 20 CW, because the harmonics end up where 
we're likely to want to operate on the higher band.

73, Jim K9YC