Satellite TV Multiswitch Issue

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KenLowe
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Satellite TV Multiswitch Issue

Post by KenLowe »

Any Satellite TV experts here?

I've got Satellite TV distribution in my house. I'm using a Triax TMP 5x24 Multiswitch, which has 4 Satellite inputs (Vertical H/L and Horizontal H/L) and one Terrestrial input. The satellite inputs are fed from a Quad (or Quatro, I can't quite remember) LNB, and the terrestrial input is fed from an external mux, which combines separate UHF, FM & DAB aerials. On the output side of the Multiswitch two cables are run to each room where there is a Quad demux wall plate, that splits out SAT1, TV and Radio via one cable, and SAT2 on the other cable

This all used to work fine, but I've recently noticed that my TVs are not receiving the terrestrial channels. Satellite channels are fine, and I'm not sure about the radio signals, because I've not really tested those. There are terrestrial gain adjustments on the Multiswitch but adjusting those pots doesn't improve things (it actually makes it worse). I've tried feeding the UHF only signal into the Multiswitch, but that didn't make any difference.

However, if I bypass the Multiswitch and feed the combined UHF / DAB / FM signal (or UHF only) to one of the cables that feed the wall plates, then the TV will successfully tune into all the terrestrial channels.

From this, I concluded that the terrestrial input on the Multiswitch must be faulty, so thought I'd have a look inside. Unfortunately there are two PCBs back to back with each other that are soldered to a surrounding metal frame making it very difficult to see what's on the underside of each PCB, so I just put it back together again.
Side one
Side one
Side two
Side two
Next up, I decided to buy an identical replacement off eBay. The unit was second hand, having been 'removed from a working broadcast site'. However, it is behaving in exactly the same way.

Any thoughts on where I should go from here?

TIA.
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1024MAK
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Re: Satellite TV Multiswitch Issue

Post by 1024MAK »

The important thing to remember here is that often the problem is not simply signal level, but rather signal to noise ratio.

What does the combining of the UHF TV/DAB/VHF FM signals? An amplifier?
Is there any sign of any dampness or corrosion in the connectors or the cables leading in from the aerials?

The other possibility is that the Multiswitch (I always thought that was stupid name for what is actually a multiplexer) you bought has the same fault.

It was easier to tell with good old analogue TV, but can your digital TV tell you which channel groups it is getting or not getting? Sometimes problems occur and only affect one range of frequencies. Or are all available channel groups affected?

Mark
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KenLowe
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Re: Satellite TV Multiswitch Issue

Post by KenLowe »

1024MAK wrote:
Thu Jun 10, 2021 11:40 pm
What does the combining of the UHF TV/DAB/VHF FM signals? An amplifier?
I'm using an old Global loftbox to do this; so yes, an amplifier.
1024MAK wrote:
Thu Jun 10, 2021 11:40 pm
The other possibility is that the Multiswitch (I always thought that was stupid name for what is actually a multiplexer) you bought has the same fault.
It's entirely possible, if it's an age related issue (like leaky capacitors). I guess the switch part in the name is to acknowledge that the satellite feed coming down each drop is switched to one of the four inputs from the LNB, depending on the switching voltage and frequency from the satellite box.
1024MAK wrote:
Thu Jun 10, 2021 11:40 pm
It was easier to tell with good old analogue TV, but can your digital TV tell you which channel groups it is getting or not getting? Sometimes problems occur and only affect one range of frequencies. Or are all available channel groups affected?
Yes, the TV can tell me which frequencies are working and which ones aren't. It seems to be the lower frequency channels that are worse affected. I'll post up a couple of photos later; one with the multiswitch in line, and one with it bypassed.

This all came to light when I tried to add a HDMI to Digital TV modulator into the UHF feed. This was to allow me to distribute Sky TV throughout the house. The modulator is currently set to channel 36, but is configurable. I'll remove the TV aerial and try this device on its own through the multiswitch at various frequencies to see if I still loose signal strength / quality.

Thank you for the pointers.
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KenLowe
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Re: Satellite TV Multiswitch Issue

Post by KenLowe »

KenLowe wrote:
Fri Jun 11, 2021 8:38 am
This all came to light when I tried to add a HDMI to Digital TV modulator into the UHF feed. This was to allow me to distribute Sky TV throughout the house. The modulator is currently set to channel 36, but is configurable. I'll remove the TV aerial and try this device on its own through the multiswitch at various frequencies to see if I still loose signal strength / quality.
With just the Triax HDMI to DTV modulator connected to the Mulitswitch the TV is tuning into that device without any problem, and reports 100% signal strength & 100% signal quality. I've tried the modulator at various channels (21, 22, 23, 24 & 36) and the TV picks it up at each of these frequencies just fine. So, this does indeed look like an aerial / cabling issue. Time to get onto the roof!

Edit 1: Right, cable looked ok, but the aerial looks a bit suspect. There's a PCB that sits on top of these pads, and it's quite corroded as well. I'm not entirely sure how the PCB made contact with these pads, though. There doesn't seem to be anything that holds the two together, other than the plastic clips...
Aerial connection
Aerial connection
PCB
PCB
Anyway, time for a new aerial.

Edit 2:New Labgear 'Tri-Boom Mast Digital' aerial from Screwfix installed, and that's it all working again. Signal strength and quality is now back up to 100% even when routed via the Multiswitch. It's quite a nice quality aerial, so hopefully this one will last! I've now also got a spare multiswitch :roll:
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