Re: [Elecraft] Coax Switch between two rigs (long)
G'day,
| 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).
The Yaesu FT-101 had a lamp in series with the RX side of the TX/RX change
over relay. When I was in the Antarctic ('74 - '76) and running traffic
on the main station (1.5kW) it was not unusual to see the lamp flashing
along with the CW or SSB if I left the antenna on the '101. Never hurt
it.
Regards,
Mike VP8NO
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RE: [Elecraft] Coax Switch between two rigs (long)
Lee - K0WA I concur with these comments from Robert Carroll regarding commercial/military types of switches. You need to be very careful if you use any of the typical amateur type of coax switches. I have 3 stations connected to the same antenna switching network. The three position switch I use came from a swapmeet, and is an Amphenol Model 3N60M10-1 which I tested with a signal generator to determine adequate isolation before installing it. All 3 transceivers can be turned on at the same time on the same frequency, and the selected transceiver can transmit 100 watts which will produce input signals on the other two radios of approximately S9 to 10dB over S9. There are 500 watt amplifiers on two of the setups, but I do not turn on the idle radios when using the amplifiers (although I probably could). One of these transceivers is sometimes my K2. I Also have Icom, Yaesu, and Kenwood in the arrangement. At my barn workshop, I use a pair of Transco p/n CON6AB which are 6 position selector coax switches. Again, these were purchased at a swapmeet and tested before being placed into service. These are used to interconnect antennas and radios between two work benches. The radios are Icom, kenwood, and Collins - but can be whatever I am working on at the time. The collins runs over 500 watts. All these coax switches were made for commercial/military applications, and they all utilize N type connectors. Bird also makes some nice switches for this type of application. Bottom line is that you can do what you are considering, but just select your switches carefully, and test their port-to-port isolation before you interconnect the equipment. Other types of switches might be useable, but take lots of care with your testing before interconnecting the equipment. You can rule some of them out just by listening to a strong station with your antennas connected, and then switch to an open port. Do you still hear the station very weakly? If so, that is a clue to be careful. For example, many of my B&W coax switches, Heath antenna tuner with switchable inputs, and MFJ antenna tuner with switchable inputs do not have good isolation for this type of application. Don't misunderstand what I am saying Lee. I use a wide variety of coax switches in my station, but, when it comes to interconnecting radios with a switch, I only use high quality tested switches. In regard to the switches that ground the unused ports, these are also a part of my antenna switching arrangement, but I use them in other parts of my antenna switching system to ground out the incoming antenna feedlines as well as grounding the coax going to the radios. Lots of ways to "skin a cat". (Then you can get into spark plugs on 450 ohm balanced line, etc., etc) Have fun Lee. 73, Bill, K5GCW -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of ROBERT CARROLL Sent: Wednesday, March 01, 2006 11:21 AM To: elecraft@mailman.qth.net Subject: RE: [Elecraft] Coax Switch between two rigs (long) 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 t
RE: [Elecraft] Coax Switch between two rigs (long)
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
