Dear Jim and Mike,
Thanks very much for the prompt replies.
Jim, I think the chokes are either from your latest work using big 31
rings or from the design by GM3SEK using multiple big beads and with I
believe at least two such chokes in series. That is for each of the
feeds to the antennas. The chokes are placed just slightly before the
Array solution balun, again one at each feed point. I will review your
other document as well, I can see it references issues similar to that
which I have observed first hand. Yes the harmonic DOES have a growl to it!
The cable is predominantly 1/2" heliax of various manufacturer, based on
what is available in country but all used in pro installations so
generally decent stuff. There is some RG214 and some may have a foil. I
do know that some of the stubs and their associated coupling cables I
prepared are made with an RG214 that has 2 braids plus a foil and a
dielectric that has 0.8v.f.
If foil and braid coax is used what is the issue?
Is there a PIM risk between the braid and the foil?
I am familiar with PIM having seen it first hand at VHF though it was
always true intermod, being two incident signals creating a third order
product. Though in those cases we never considered or cared about
harmonics, for other reasons, I can agree that the non linear device
should indeed produce all possible products including harmonics of a
single source.
Regards es tnx
Martin, HS0ZED
On 21/11/2019 12:40, Mike - W5JR wrote:
If any of the “RG214” is in fact a shield over foil braid, replace it with real
RG214. As Jim mentions, passive intermod (PIM) usually rears its ugly head after installation
of all the cool stuff. You will want to confirm that all of the components, radios,
amplifiers, filters, feedlines, towers, guy systems, are *bonded* together to further reduce
the possibility of PIM.
PIM will be the biggest hurdle in making any multi transmitter situation play nice. Often the PIM
generator is external to your feedline or antenna. It’s the “killjoy” of many a
Field Day setup over here.
tnx
Mike / W5JR
Alpharetta GA
On 21/11/2019 11:52, Jim Brown wrote:
Hi Martin,
here's an "overview" talk that I've done at Visalia last spring and
for a couple of clubs, including NCCC, this fall.
http://k9yc.com/Multi-Station.pdf
Among other things, check out the chokes in my newest Cookbook, which
are significantly better and more repeatable designs than what I was
able to do 10 years earlier.
Also, consider passive intermod.
73, Jim K9YC
On 11/20/2019 8:22 PM, Martin Sole wrote:
Hi,
This is about a two radio inter-station interference problem. A bit
different perhaps but still RFI of a sort
Looking for some input to help me understand a bit better what is
happening and maybe correct some errors in my thinking.
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