I've written about simple diode RF detectors at http://www.cliftonlaboratories.com/diodes_for_rf_probes.htm
These are not 50 ohm terminated, so it would be a matter of adding a 51 ohm resistor (nearest 5% value) across the RF port). Jack K8ZOA On 1/7/2011 4:37 AM, Ian White GM3SEK wrote: > 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. > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
