Posted by
gm3sek on
Jan 07, 2011; 9:37am
URL: http://elecraft.85.s1.nabble.com/Transmitting-while-listening-in-diversity-mode-tp5897822p5898618.html
Tony Estep wrote:
>Nobody commented on my question last night, but I'd still like to hear from
>your collective wisdom, so here's a repeat: I set up my sub-rx to listen on
>transmit antenna B while the main is listening and transmitting on A, and to
>listen on A while main is listening and transmitting on B. This allows for
>diversity reception.
>
>"...here's my question: My two antennas are located so each is in the
>other's null, but they are not far apart, maybe 50 feet at most. When I
>transmit, I don't hear any carrier-operated relays or see any adverse
>reactions, but I'm still not sure that it's okay. The manual sez "well
>isolated," but what I'm looking for is some objective way to test or
>measure. Can anyone tell me how I can establish for sure that I can, or
>cannot, transmit on A when the sub is connected to B, and vice versa? "
>
>Any info (especially first-hand knowledge) would be much appreciated.
Connect a simple diode milliwattmeter to the feed from the RX antenna.
All it needs is a 47 ohm resistor, a 1N914/4148 diode, a .01uF ceramic
cap and your DVM. (This is truly a "Construction 101" project - can
anyone supply a suitable web reference, please?)
Gently ramp up the power to the TX antenna, and see how much power is
coming back on the RX input. Repeat with every combination of bands and
antennas.
Also read "Managing Interstation Interference" by George Cutsogeorge
W2VJN:
<
http://www.inrad.net/product.php?productid=248&cat=148&page=1>
The first chapter is available as a free download and contains key
information about power levels for receiver front-end damage. The K3 can
protect itself... but as you say, you should make sure it doesn't have
to.
For diversity I am using an active antenna based on a small horizontal
dipole, which works very well in combination with the low-band
verticals. Checking with the milliwattmeter and gradually ramping up to
full TX power, both the active antenna and the K3 are well enough
protected by the cross-polarization. But the 20-10m beam is horizontal
and also much closer, so additional protection is needed on those bands.
--
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek______________________________________________________________
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