Good morning, Tim,
I have been using receive only, Beverage style antennas for some years now.
You are correct in surmising that there is significant voltage on the
receive antenna while transmitting. At the contest station near me, W0AIH,
who uses high power and significant receive antennas, that has been measured
as high as 20+VOLTS and more coming into the receive antenna jack.
It would obviously follow that some kind of protection should be applied to
receive antenna input. A few years ago, a couple guys came out with a very
inexpensive reed relay box they called the Front End Saver. It also
controlled the amplifier keying relay, so that the receive antenna is
grounded prior to keying the linear. Great little box, unfortunately, one
of the guys passed away, the engineer of the duo, and the project was shut
down. It would seem like a great little business if someone with a
technical bent would pick it up. I know that Jim Smith at Burghardt's
Amateur Center has a device that he sells to install in Icom 756Pro radios,
so you may want to talk with him and see if it's adaptable to TT rigs.
So, what to do. According to Paul, W0AIH, the solution is really very
simple. He inserts a lamp holder, like from a boatanchor radio dial light,
and puts a #47 bulb in line with the receive antenna line. Simply take a
piece of coax, cut it and solder the braid and center conductor to the lamp
holder tabs, and VIOLA, a cheap and totally reliable fuse in the receive
line. Paul insists that using a WIDE spaced lamp element, as with the #47
bulb, is very important, and NOT to use a "grain of wheat" style light bulb
which has the two poles of the filament holder too close to provide enough
protection from arcing across. Although I submit that if one is only running
100 watts or less, that that would be sufficient. But running 1500 watts is
a whole 'nother kettle of RF. HI.
I have implemented the same thing here in my SO2R setup, and one of my
receive antenna for 160 runs right under my inverted vee. I have had zero
problems with my receive antenna causing interference or carrying too much
near field voltage. (I do see the lamp element glow at times-HI) It has
worked with every radio duo that I have used todate, Yaesu, Icom and Ten
Tec. It is especially important to have your receive antenna lines
protected if running two radios or more, as they'll be receiving while other
radios are transmitting...obviously a common problem in multi-multi
operations. If you have 200 acres to sprawl antennae around, it may not be
too much of a problem, but where most of us live, on city lots or small
acreages, care MUST be taken to protect those precious receivers.
Simple and maybe a bit inelegant but it works.
Just my $.02. OK boys...let 'er rip. What are others doing with this
little dilemma?
Larry, N0XB
----- Original Message -----
From: <k3hx@juno.com>
To: <tentec@contesting.com>
Sent: Monday, November 27, 2006 2:03 AM
Subject: [TenTec] RX input Orion 1
In the upcoming 160M contest, I plan to TX on ANT 1.
My RX antenna is about 1/4 wave away (that is as far as I can get it
away from the TX anenna)and will likely couple a
considerable amount of energy from the TX antenna. No amp, barefoot.
I have the original Orion.
Does the radio short out or open the RX antenna input during TX?
73
Tim Colbert K3HX
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