The following is a summary of the answers received regarding my question about building an antenna switch for 2 radio contesting. Sorry it took so long but I was ill for some weeks and afterwards had some other things to work out before, but here it is, finally. MANY THANKS TO W3CF, K6LL, K5YF, K8JP, K1VR, DL7AV, K8DD, WX0B, WA7BNM for the following comments and to K6LA who sent me his article he wrote on that topic. +++++++++++++++ my original question was: I want to build an antenna switchbox with which I can select from 10 antenna inputs and connect each of the 2 transceivers with one antenna at a time. I want to be able to connect each TRX to each ANT. All the unused ANT inputs will be on ground potential. The switchbox will only be used for 160m-10m I thought of the following concept: each antenna input leads to the first relay which switches the antenna either to ground or to the input of the second relay which selects between TX1 and TX2. Each transceiver input leads to 10 relay outputs. My questions are: 1., power rating of the relays: my thoughts are: - no hot switching of the relays - max. SWR of antennas connected: 3:1 - max CW output 2000W (Have only 800W PA but want to have a security reserve this results in the following conclusions: (are they correct??) maximum and minimum feeding impedance of the antenna cables Zmin = Z * s = 50 Ohm * 3 = 150 Ohm Zmax = Z / s = 50 Ohm / 3 = 16 Ohm resulting in: maximum voltage and current: P = Umax^2/Zmax --> Umax = sqrt(P * Zmax) = sqrt(2000 * 150) = 550V P = Imax^2/Zmin --> Imax = sqrt(P/Zmin) = sqrt(2000/16) = 11A I found a relais in the electronic mailorder catalogue which is for PCB mounting, rated at Imax = 15A, maximum switching voltage 380V/250v= (I THINK THIS REGARDS HOT SWITCHING - am I wrong??), maximum power rating 3500VA. Does this sound like the thing I need??? Any other hints for a good relay? 2., I want to install the 20 relays on a PCB with short, wide connections on this PCB and switch only the inner conductor of each coax. I am concerned about the following things: a) how bad does this box affect the SWR? b) how bad will be the losses?? c) how good will be the isolation between the different antennas and transceivers? After all I want to be able to listen on one transceiver (and antenna) while transmitting on the other transceiver (and antenna)... d) which steps can be taken to improve a) - c) ?? e.g. big grounded sections on the PCB, etc...? 3., which kind of cabinet would you use? plastik is bad because no shielding? metal cabinet will affect SWR? lighter cabinet preffered, so can take box on expeditions... should I use aluminium or is steel sheet a better choice? 4.,I would use SO239 (PL) connectors, as far as I know you really do not need N-style connectors on HF < 30MHz. Any objections? AND THESE ARE THE ANSWERS: +++++++++++++ All these questions are answered by N3RD, Dave Hawes and his company TOP TEN DEVICES....Automatic band switching the whole nine yards. I believe the Web page is www.qth.com/topten or Dave's EMAIL address is n3rd@ix.netcom.com +++++++++++++ Unless you have two widely separated towers, you will also need bandpass filters between the amps and the transceivers. Try www.qth.com and look at DUNESTAR and TOP TEN DEVICES. They may give you some good ideas. +++++++++++++ What I use is two boxes. The first box selects any of my nine antenna inputs via DPDT 12 VDC open frame relays I bought for $2.00 at a hamfest. The antennas are fed to each common contact on one side or the other of the relay. The normally closed side feed the output to the second box. The normally open contact is hooked to a common buss that feeds to the 1st Xcvr. The second box has inputs for each of the antennas and is the same as the first box, but the normally closed contacts are grounded and the normally open contacts are hooked to a buss for the 2nd Xcvr. I am working on a new interface that will alert me when the antenna is used by one or the other Xcvr. That is not finished yet. You could build this all in one box. I use DPDT to get extra isolation for the contacts from the armature and it gives me a built-in spare contact. I used aluminum boxes and mounted the relays with RTV (rubber like glue) to a plastic plate glued to the inside of the box (more voltage isolation). I have RF chokes in all the relay key lines and by-pass them at the connector. I run 1500 Watts with no problem. I have not used this a lot with the second radio yet, so I can advise how the isolation is between radios. I do know that since I started with the grounding of all unused antennas, I have greatly reduced my RFI in the shack! I used UHF connector, also. The relays you described sound like mine, except mine were for socket plug in and I removed their plastic cases and sockets, then hard wired them with #12 ga. copper wire. The SWR appeared to not change. I did not check insertion loss, nor was it noticable to prompt me to check it. Personally, I like the hardwire in case something happens, I can easily fix it. DPDT = Double Pole, Double Throw or two commons that switch between their respective NO & NC, Normally Open & Normally Closed contacts. The RF Chokes were the old 2.5 mHy 50 or 100 mA. variaty. The relays only draw about 15 mA. I, also, put one in between their coils common ground and the ground return for additional isolation. The bypass capacitors were either .01uF or .001 uF. ++++++++++++++++ Take a look at the 1995 ARRL Periodicals CD-ROM available from the ARRL. It not only covers QST, but it also has 6 issues of the National Contest Journal. In one of those NCJ issues there is an article, complete with pictures and schematics, of a switching arangement for a switching setup for two stations with multiple available antennas. It is an excellent article and looks like it will answer all your questions. As I remember, it is a remote relay box outside the shack area and a switch box in the shack to switch antennas between the two stations. And it looked like it had excellent shielding between the radios. ++++++++++++++++ 1) use HF relais only. They should be good for "dry" switching. If not, you may face receiving problems. Dry switching means the contacts of the relays will show good conductivity at small currents, not only at high currents. This is achieved with contacts that have a gold/silver surface. One good relay is the Matsushita S2 (capable of 3KW) 2) do not use PCB mounted relays. The capacities will be too high (even using strip lines) and the PCB might catch fire. use direct wiring for each relay. 2a) SWR will be worse but only at a very low degree. The load capacitance will be up to 30pF for 10 relays (Xc = 200Ohms at 30MHz) 2b) Isolation of the rigs: Use this switchbox with a bandpass filter only. Otherwise RX switching diodes are in danger 3) use an Aluminium housing 4) SO239 (PL) is ok for the connections ++++++++++++ I designed and built a remote antenna switch that was designed to properly phase and match stacked tribanders with separate feeds for 20, 15 and 10m (equivalent of feeding stacked monobanders on these bands) and three other antennas (40m, 80m and an extra). Previously I had used DX Engineering remote antenna switch boxes with good luck. So when I designed mine, I used the same relays and printed circuit board trace widths. The RF portion of the traces are about 0.25 inch (6 mm) wide in most cases on single sided PC board. After building I tested the unit using an MFJ SWR meter and could detect no impedance degradation from 3 to 30 MHz (I realize there are more sophisticated methods, but the MFJ is all I had). The unit has been operation almost two years with no failures. Although I run low power in contests, the unit has never exhibited any problem when running 1500W while DXing. ++++++++++++ microstrip line: A trace width of 115Mils above a ground plane on G10 standard width circuit board will be 50 ohm characteristic impeadance. +++++++++++++ Thanks for all the input, guys. I am running out of time now because of all that illness and other problems, so I will probably just use 4 coax switches hooked together. I will need to modify 2 of the switches so they do not short the transceivers they are not connected to at present. But I do not have time to build the switchbox. If you have any further suggestions (especially about cheap, but good relays (the Matsushita S2 is about 10 US$ each)), keep them coming... Good luck with your projects and SEE YOU IN THE CONTESTS! 73 Con DF4SA Cornelius Paul CP2235@aol.com