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[TowerTalk] what is the experience with F12 dual-band ants and N radios?

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Subject: [TowerTalk] what is the experience with F12 dual-band ants and N radios?
From: (Guy Olinger, K2AV)
Date: Tue, 21 Dec 1999 22:27:23 -0500
We used Dunestars at N4AF for the CQWW CW. They were between the exciters and
the amps, never subjected to the 1.5 kW levels.

Some antenna/band combos were on different towers, some combos in use were on
the same tower. I felt the results were outstanding. We had zero crossband
interference except +/- 1 kHz on a direct harmonic (a 50 over 9 signal). If we
had added maybe a half dozen stubs here and there, even those would have gone to

The problem that began this thread was the exceptional closeness of antenna's on
the same boom. Clearly the filters are overmatched here and help from stubs is
required, besides possible cross-modulation if two transmitters were running at
the same time. Particularly since other antenna combos may not require stubs
beyond the filters, the stubs I mentioned deal with the same boom combination,
without requiring switching the entire station to a stub-based operation.

A stub system is not without expense beyond the RG213. You still have to have a
switching system to make sure a given stub is out when it's band is being
transmitted on. How many switches and relays? Not at all to argue with what you
can do with stubs, or with your figures on how much isolation can be gained.

After that contest, I'm really in favor of Dunestars with targeted stubs where
overloads still occur. This would **certainly** include any situation with two
separately useable antenna's on the same boom.

- - . . .   . . . - -     .   . . .     - - .   . - . .

73, Guy
Apex, NC, USA

----- Original Message -----
From: George Cutsogeorge <>
To: <>
Sent: Tuesday, December 21, 1999 7:59 PM
Subject: Re: [TowerTalk] what is the experience with F12 dual-band ants and N

> I might worry about toasting the bandpass filter.

RG-213 costs $0.33 per foot these days.  The bandpass filters out
there for amateur use give a max of 45 to 50 dB isolation and not
even that much between adjacent bands,  You cannot transmit at
the KW level through them.  Cost is about $40 per band.  This
buys a lot of coax.  There is NO burn out problem with RG213 used
for stubs.  A pair of stubs will give 55 to 65 dB isolation.
Three stubs cascaded will give 80 to 100 dB.  Four stubs cascaded
will give over 110 dB, the limit of my measuring equipment.


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