Multicore co-ax cable use

Hi, has anyone any experience of using multicore co-ax from rig/s to multiple antennas? I currently have a co-ax running to a number of antennas but want to move the shack to another part of the house where the only access for cable is through a small conduit. Currently the conduit has 1x 75ohm Satellite running through it. I can remove this or use it. But if I use it I can only attach one antenna and dealing with the mismatch is simple. But I'd like to run at least three co-ax cables, preferably 50 Ohm. Seeing as the house is concrete I don't really have an option to make the pipe larger. I have seen some 75ohm multi co-ax used for TV/Video etc. that might suit as it is available with 2/3/5/cores each with it's own shield. I would love to hear any experiences or thoughts on this idea. Again while I'd prefer 50ohm, I can work with 75ohm and in fact on the half wave dipole this may be a better match. The rest of the antennas would just need a small match. Thx.

Hi Kate,

The only time I've seen multi-cored coaxial cable in use is with studio audio equipment and as you mention CCTV/video signals. I would have thought that the losses could be quite high for RF as you only have to take a look at the losses associated with thin coax such as RG174 compared to typical thicker cabling.

That said many utilise RG174/316 and the like for portable operations so I suppose if the run is small enough the losses will obviously be less.

It might be worth looking at a remote switching solution if you can fit a thin control cable along with a length of coax in the pipe you have available. At least that way you can use some decent coax with less losses. There are also coaxial relay switching units that apply a control voltage up the same coax with voltage isolation at the rig/antenna ends but you'll be limited in the number of connections you can have.

Remote switching can be an expensive solution but there are some DIY projects out there if you can challenge your own build.

I hope that helps.

(Also nice to see someone that understands impedance matching and I've often utilised 75 ohm coax myself sometimes with better matching capabilities than would be achievable otherwise. )

73,
Victor

Thanks for the reply Victor. I'm always up for giving something new a try as I thank that is what the hobby is about. No point learning about all the aspects of radio transmission and never pushing the boundaries. My plan is to have two HF rigs, one Ham connected to an inverted V long wire covering 10-40m but specifically turned for 20m and a half wave horizontal dipole covering 10/11/12/6m (My current setup) and one CB (Legal) connected to a vertical (yet to be made my me). In an ideal world, in time I'd like to add to this, a 2mtr external (that I also made). I have the 450D manually switching between the V and the dipole at present. The CB will be the CRT 3900 I'm saving for. EDIT: I have now looked at the idea of remote switching and I think that's a good probable solution. The box is quite simple to make and I'm guessing could even power it using DC over one of the existing co-ax cables as the DC source doesn't need to be in the same room as the radios. I could then operate the control box via wifi or ethernet switching from the room I want to use. I've seem cheap wifi controllers. This looks like a winter project. :-)

No worries there Kate and I like your way of thinking, both with pushing your boundaries for the radio interest and the ideas for remote switching.  

I wish you well with it all.

73,
Victor

Hi Kate. The only multicore coax I have seen is twinax used to connect terminals and printers on old IBM AS/400 systems. I have never tried putting any RF down a length, though it has entered my mind more than once when I seen some now and again at work. The cable and connectors are very well made, a decent shield on the cable, but I have no idea what impedance the cable would be. Certainly the cable was not designed for RF, or at least not RF frequencies we might play with.

For adding a 2m antenna later, I'd go with a diplexer outside splitting to the HF and VHF antennas, simples. You'd need a coax switch inside to switch between HF and VHF radios. That would be an easy way for one piece of coax to feed those two antennas. But splitting to two HF antennas covering same or similar bands probably will need coax switch of some sort.

I've 'built' (no real building involved lol) cheap HF coax switches recently using electrical appliance relay switches with 12V relay coils that can be picked up very cheaply. I've powered them with a thin length of twin wire. I hadn't thought about powering over coax, I'll have to look into that. Photo of the relay type in this thread:
charlietangodxgroup.forumotion.com/t6738-cheap-remote-antenna-switch

Do let us know which option you go for any how you get on.