G4NSJ – Coax switch antenna switches amateur radio


Coax switchCoax switches are very useful but, be careful! If you use the cheaper types, then losses at VHF and particularly UHF can be high. The switch shown on the left is used to switch my 10 metre antenna to either my Kenwood TD-570D or my Anytone AT5555. At 28MHz, losses are negligible. I have an 80 foot run of RG8X introducing some loss but, overall, the set up isn’t too bad. If you do have a lengthy run of coax then, even at 28MHz, it’s best to use decent cable. The loss at 28MHZ for 100 foot of RG8X will be around 1.58dB. That’s not too bad considering the length of coax. However, the loss at 433MHz for 100 foot of RG8X will be in the region of 8.07dB. That is not good!

It’s important to note that, when switched to one position, the other position is left floating. It’s preferable to use a better quality switch which grounds the unused sockets.

I also use a similar switch for the lower HF bands to switch the coax from the ATU to different transceivers. The loss for 2 feet of RG8X is virtually zero. There’s some information and a video about making a switch box to select aerials for receive only here. Short wave listeners might find the info useful.

For VHF frequencies, I use a rather better quality switch, shown on the right. The highest frequency I use it on is 70MHz. It has N-type sockets so it’s probably good for Coax switch VHF144MHz but I’m not sure about higher frequencies. I bought it second-hand so I don’t know the spec. To be honest, I wouldn’t use any form of coax switching at UHF frequencies. No matter how long or short the run to your UHF antenna, use RG213 or better. There’s no point in having an expensive antenna high up on the chimney if it’s fed with cheap RG58 coax. The loss will be dreadful!

The switch arrangement looks awful but, as the Icom 7300 only has one aerial socket for HF, 6 metres and 4 metres, it makes things awkward. My 4 metre aerial comes in and is switched between the Icom and my Anytone 4 metre rig. The Icom is switched between the 4 metre position and 6m or HF. Why they couldn’t fit three aerial socket on the 7300 is a mystery.




I also have to use a triplexer for my tri-band antenna. One cable into the shack from the antenna into the triplexer with three outputs. One output to the 6m position on the antenna switch. The 2 metre output to a 2 metre rig and the 70cms output to a 70cms rig. All rather messy, to be honest. There’s more info on the triplexer here.

CB aerial switch



The last photo is of a very cheap CB antenna switch. It uses rocker switches which are not really suitable for RF. Apart from loss, there must be a miss-match with these switches.  Having said that, it’s probably fine for switching an aerial to different receivers for short wave listening.

I hasten to add that I didn’t buy this switch box, it was given to me. I’ll be removing the five S0239 socket at some stage as they will be useful. The rest of the unit will go in the bin!

If you want a decent coax switch, use a relay like the one pictured here. It has N-type connectors and is suitable for UHF frequencies. I’m not sure where I got it from but I’ve owned is for years. One day, I’ll put it to good use.Coax antenna relay