If you yield to temptation and buy the Elecraft 1KW or 1.5 KW (almost here according to a well placed representative last night) amp, or if you use any amp, be VERY careful about switching as you describe. Of course most QRPers would not dream of defecting to the dark side, but a few do from time to time. The switches mentioned in this thread do not have any or tight specs on port to port isolation. Commercial switches such as the Transco's are speced at 50-60 db port isolation. I learned this after frying a transceiver front end with a consumer grade switch which did ground the unused terminal. A contesting buddy educated me about the need for a high isolation positive contact crossover or transfer switch.
Another thing I have learned over the years is that most ground systems are RF "hot" to a certain extent in many very well built ham installations. For instance, W8JI, RF designer par excellence for DXEngineering and previously for many companies, tells me that despite his extensive ground system --with a ring surrounding his building ( his system is intended to protect the electronics from lightning attacking his 300' and smaller tower farm), his ground system is RF "hot." Maybe I should say RF "warm." What I mean is that if he (or I) look with a spectrum analyzer ( or listen with a receiver) at the RF "noise" that comes off a connection to the station ground, you find that the station ground may make a pretty decent RX antenna. The signals may be many dB down from what's coming off your wire or yagi, but they are there in areas with less than perfect earth. If your ground system shows signals 30-40dB down and you are QRO you may have a problem. I also found out about this the hard way. Just for fun, try connecting a short wire from the cover screw on an AC receptacle to a receiver input terminal. You might be surprised as to the signal pickup--including various power system noise sources. So if you are going to use rig switching, especially if using an amp, you do want to make sure that the switch shorts the unused transceiver input. There is a neat way to check whether you are going to experience a dangerous amount of RF pickup. If you can find a Radio Shack that still has and can find hobbyist parts, look for their "grain of wheat" miniature incandescent bulbs. They have some that are rated at 6v/25ma etc, but you want the one rated at 1.5V/25ma. Solder it to a coax connector and screw it into an unoccupied port on your switch. Crank up your tx/amp to the max power you are going to use and key the TX. Watch the bulb. If you see nothing from the lamp, you are ok. If you see a dull glow, be worried about just how consistent your switch is (I have an Alpha Delta--which I use now only for beverage switching) which shows variable performance, the reason for which is apparent if you open it up and look at the guts). If you see a bright glow or pop the bulb don't even think about using the switch. I have squirreled away the info somewhere, but one of the Beverage gurus has calculated that the typical modern rig is probably borderline with about 15ma being driven into the RX, either through a connection to a RX antenna like a beverage, or power flowing into the transceiver antenna connection when the transceiver is in the receive mode. By the way, that bulb in series with a RX antenna with back-to-back signal diodes across the RX antenna jack, makes a pretty decent protector/indicator when used in low-band dxing. I combined this with ON4UNs front end protection box and have found it very useful. Bob W2WG -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, March 01, 2006 10:17 AM To: [EMAIL PROTECTED] Cc: elecraft@mailman.qth.net Subject: Re: [Elecraft] Coax Switch between two rigs The Daiwa CS201 DOES ground the unused terminal. Check it out. K3YT _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
