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FM aerial cables - guidance needed

1000RPM

pfm Member
I need advice on cable runs from a rooftop FM aerial...

The installer plans to use a UVF/VHF diplexer, using the same down cable for both TV and FM. Does this make a difference?

The current down cable is the standard brown 75 ohm coax. If I replace with say, Belden shielded 75 ohm coax, would that be a worthwhile improvement?

I can either run the cable to one room, or split the signal to two rooms. Does this make a difference to signal quality?

Aerial won't be too fancy - a three or four element antiference is the limit because of chimney/windage factors.
 
I presume you are watching digital TV channels ? In which case don't use the old cable, it should be replaced with new shielded cable. Are you having a specific FM antenna?
 
The installer plans to use a UVF/VHF diplexer, using the same down cable for both TV and FM. Does this make a difference? In theory no, not with proper filtering at each end, but I'd run two separate cables if I could.

The current down cable is the standard brown 75 ohm coax. If I replace with say, Belden shielded 75 ohm coax, would that be a worthwhile improvement? YES! The brown stuff is absolutely terrible. No copper, very little shielding, probably has water ingress by now and plenty of loss. No need to go Belden, the standard CT100 type stuff used en mass for satellite work will do nicely here.

I can either run the cable to one room, or split the signal to two rooms. Does this make a difference to signal quality? If you use a passive splitter you halve the signal to each leg. It depends on your signal strength. If you're line of sight to the nearest transmitter you'll probably be OK, if not then a distribution amp would help.
 
You have a good taste in tuners then. They need around 1mV of decent signal. Where are you located and which transmitter are you pointing at?
 
Don't need to run 2 cables the Multiplexor carrying UHF and VHF will be fine. Deffo replace the cable they have a limited life.
 
I use WF100 cable, CAI certified, its good for FM, terrestrial TV and Satellite.

I would keep TV and FM radio separate.
 
Avoid sharing with TV, each diplexer still adds a dB or so loss.

A Wilkinson passive splitter can give 3dB loss, its the cheaper resistive ones that are 6dB

Use satellite cable, very low loss at VHF and no intermodulation problems from a poor cable with a head amplifier
 
I'm in east surrey, so FM comes from Wrotham.

Thanks for all the advice chaps, much appreciated
 
Yes, Wrotham has enough signal strength. I remember a NAP250 that was just along the way on top of hill that really didn't like that much RF up its speaker cables.
 
My Sony ST-S361 has a relay on the input that can switch in a pad attenuator for these extra strong signal locations - not a problem that I have ever had
 
one more question, which might be silly, but...

Say I split the cable and effectively half the signal strength, I listen in only one room at a time, so if I unplugged the aerial in the other room, would it still continue to draw signal or would 100% of signal revert to the live connection?
 
If you are using a resistive splitter you will lose 6dB on each leg. If you disconnect one leg you will get a slightly higher signal and also a mismatch which for short cable runs you probably won`t notice.

If you leave a length of unterminated cable hanging off the splitter that`s not good though.
 


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