On Mon, Nov 27, 2006 at 08:29:49AM -0600, Larry Menzel wrote:
> 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.
....
> Just my $.02. OK boys...let 'er rip. What are others doing with this
> little dilemma?
A popular device with SWL's is a pair of silicon switching diodes, 1N914
or equivalent back to back across the antenna terminals. The diodes start
to conduct at about .25 volts, so usually two in series are used.
An easy way to do it is to take a small aluminum box, mount SO-239's at
each end and run a wire directly from the center of one to the other.
Drill a hole in the box and attach a solder lug with a bolt, nut and
lockwasher. Connect the diodes to the wire and the lug.
Another option is an NE-2 type neon bulb, but the crossover voltage
may be too high.
Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM
IL Voice: (07)-7424-1667 Fax ONLY: 972-2-648-1443 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/
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