Antenna Switchboxes?

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erikn1

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G'day

Thought I'd ask if anyone has home-brewed an antenna switch-box - because, it seems that mine has issues and I will try and explain these as best I can.

First of all, I have a 2m mobile and a 70cm mobile radio connected to the switching unit, and each radio has its own antenna socket, which in turn is connected to a toggle switch and then on to the main antenna which is on the roof.

Without the antenna switchbox connected, the SWR meter calibrates and gives accurate power readings. However, with the switchbox connected, the relevant antenna socket turned 'on' by the toggle switch, I've noticed a significant loss of power output being registered on the SWR meter.
Connecting the radio back directly to the antenna restores correct power output and a correct reading on the SWR meter, so at this point I'm suspecting the antenna switchbox is to blame - although I've checked the insides and there is not a solder joint out of place, cold or loose, all wires are correctly connected.

Wondering what could be wrong, if anything, and grateful for any help.

Cheers

erikn
 

Thunderknight

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You said toggle switch? Is this just an off the shelf toggle switch meant for AC or DC power? You probably aren't maintaining 50 ohms
 

jackj

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Erikn,
You don't mention anything about reflected power with and without the switch in the antenna circuit. Most commercial radios have a protection circuit that monitors the amount of reflected power and adjusts the output power accordingly. If the box is causing high reflected power then your radio is most likely reducing it's output power so that it can stay within the power dissipation limits of the final amplifier. Another thought is your pig tails, are you sure that they are good?
 

jim202

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As a suggestion, you will be much better off obtaining a switch made for antenna switching. They are designed to match the coax cable being used and provide the normal 50 Ohm match that the radio is looking for. They even come with coax connectors already on the switch. All you need is a jumper piece of coax cable with the required connectors to mate with the radio and antenna switch.
 

k9rzz

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Your leads need to be SHORT. As short as possible. I think you can get away with home brewing antenna switching pretty easily on 160m through 20m, but 2m and up you've got to be careful with construction.

I always picked up one of these bad boys for 6 through 432. Pretty cheap used.

Son of a gun, I just grabbed a photo from Google search, and it turned out to be MINE! This is actually one of my switches that I sold some time back.

 

rescue161

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Why not just use a 2m/70cm diplexer and forget the switch. It would be automatic then. Run the coax from each radio to the respective VHF/UHF ports and then connect the antenna to it.
 

W3DMV

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All the B&W switches I have owned were rated for 0-30 Mhz. They contain a rotary switch
and do a great job on HF, but would be unsuitable for VHF/UHF. If you really need a switch,
a coaxial relay would do but the diplexer is the way to go.
Good luck
 
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