Amplified signal distribution help

[19Seventy7]

Hi All

I've been looking into finding a way to get a signal to all of my sets without having to move them around too much, and having them work in situ, having around 20 sets means of course I'll need to split the signal which creates a dilemma of loss of strength and interference.

I'm feeding several signals in through one cable via my daisy chained RF modulators which can have long runs of cable between the two. I have low loss cable with thicker cores and better shielding which works quite well.

The main problem is my main RF mod which outputs all combined signals is in the opposite corner of the room to where most of my sets are, and that can't change due to a couple of reasons, such as plugs and external TV aerial feed.

My question is what do people use to amplify and distribute their signals? I'm looking for as clear a picture I can get on as many sets as possible. 4 of my sets are 405 line only but the rest are 625 which is what I'd like to distribute. Not all sets are working at the moment so I think I could get away with having say around 10 outputs for now.

I bought a SLX8 distribution amplifier but this is giving me a much grainier picture than if I were to short the two cores of the F connectors, bypassing the amplifier so was just wondering what others use to improve picture quality amongst their distributions.

Thanks
'77

[simpsons]

Hi '77

I too use a distribution amplifier but is 4 way, using "cable TV" splitters, not Y, to give me 8 outputs. What I did find when daisy chaining modulators was that unlike a video recorder the modulators simply connected the output and input aerial sockets together with a great loss in signal, as you would expect. To overcome this rather than daisy chain for the 405 VHF signal through the UHF modulator, I use the VHF input on the distribution amp.

I am using an amplified AV switch to feed the combination of UHF and Aurora modulators.

One last note, beware of having the UHF modulator tuned to the same channel as the local digital mux. It led me a merry dance.

Hope this helps

Chris

[19Seventy7]

Hi

Thats actually quite surprising to me as I don't find any signal loss when daisy chaining the RF mods together on a TV which doesn't use the amplifier and actually uses a Y splitter (which feeds that TV and then the signal to the amplifier) that's worked well for my old set up (which was a mess and had too few outputs) so I don't think the modulators and/or the Y splitter is faulty, but I may look into getting a cable TV splitter and using F connectors as the coax always falls out! I've given them all a bit of a squeeze to make fit tighter but that doesnt cure everything!

Do you have a link to your distribution amplifier at all?

Thanks
'77

[simpsons]

Hi '77

If the input to the distribution amplifier is noise free and it should be if fed by the modulator, then the amplified signal will also be noise free unless something is wrong.

A Philex SlxRF modulator is used to feed my set up and the same "branded" distribution amplifier.

I also use a distribution amplifier for my home and have had no problem with noise added to the analogue signal "back in the day."

I can only suggest that you make up a known good coax lead and use it to trace FORWARD the signal, if necessary using an attenuator, to locate the source of the noise.

F connectors are good but the RF out from the modulator and distribution amp should be well above the threshold for a noise free picture.

To put the issue in perspective, a chimney to set would easily be 10 metres of "bog standard" coax and joe public didn't have to use a amplifier unless outside the service area.


Chris

[Vintage Engr]

I also currently use an SLX8, although I will be changing this to a more professional Vision V51-204 MATV unit. I will use that in conjunction with various tapped attenuators.
I'm not having a problem with the SLX8, I'm replacing it because I need more outputs over a large area. The problem you are experiencing could possibly be exacerbated by the modulators. You've not stated what they are, but if they are the common double-sideband type, then with a few channels operating you may find that the intermodulation products are de-sensitizing the receiver front ends, making the picture appear grainy.
It would be useful to measure the signal strength of the various channels.

As I'm already calling in to see you next week, I'll see if I can find room to bring my signal strength meter, which might help sort out the problem.

David.

[Hybrid tellies]

In my small workshop the main aerial goes to the Philips Freeview box which is then fed to my VCR via scart the RF output then feeds my Antiference 6 way distribution amp which then feed around the workshop including my Aurura 625/405 convertor.
It works a treat.

When I switched from my loft aerial to the main rooftop aerial I had to reduce the signal input level into my Philips Freeview box by turning the level down on the main aerial distribution amp I fitted in the loft but that is the only issue I have had.

[19Seventy7]

Hi all, thanks for your replies

The signal is relatively noise free, its very minor, noticeable if up close but very much watchable, through the amplifier its unwatchable. I always thought the job of an amplifier was to clean the signal and remove any noise. I do wonder as it was sold on amazon at a lower price as a damaged item, describing it as damaged packaging but the box was fine…

The cable used is good, as I say if I short the two cores of the input and output together the picture is near perfect, the amplifier brings in noise, and lots of it! Even using the “full” output made no difference.

Vintage Engr: the RF mods I’m using are a Technomate TM-RF and a “Mercury” RF modulator. I’d imagine they’re internally the same. I believe one is on UHF23 and the other UHF26 should that make any difference.

I would definitely be interested in measuring signal strength as I’d like to get everything performing as well as possible, and of course the signal strength makes all the difference!

Hybrid Tellies: Thanks for the info about the antiference. I’ll look into that brand if needed. It’s definitely confused me. Writing this has given me a thought too, to look internally in case theres something amiss internally.

Thanks all
‘77

[kan_turk]

Hi - just been reading through this thread and a number of possible issues come to mind
1. Without the appropriate equipment a solution may be elusive and very much a matter of trial and error - of course you can strike it lucky
2. An amplifier can not clean up anything or eliminate noise - quite the contrary it will ‘amplify’ any noise as well as other unwanted signals - it does not discriminate - it is, therefore, essential to start off with a noise-free signal - ‘relatively’ noise-free does not sound like a good starting point
3. I would be concerned with how ‘clean’ or otherwise the outputs of the modulators are as well as the daisy chaining arrangements which, if unfiltered, can contribute to the ‘mess’ - double sideband modulators are notoriously variable in their performance both in terms of output level and cleanliness of output - some adjustment of output level to balance level between modulators as well as establishing as high an undistorted level as possible before amplification should be the objective

Sorry if this sounds pessimistic but achieving reproducible performance without the appropriate equipment can be a frustrating exercise

I would suggest the following approach (if you have a reliable signal level meter so much the better):
1. Disconnect the 2nd modulator and feed output of 1st modulator to TV (no amplifier in circuit) - adjust output level for maximum undistorted signal as observed on TV - there should be absolutely no noise visible
2. Disconnect 1st modulator, connect 2nd modulator and repeat ‘1’ above
3. Reconnect ‘daisy chain’ ie both modulators connected (still no amplifier in circuit) if successful jump to ‘5’ below
4. If unsuccessful ie noise on signals try changing operating channel of modulator to a higher frequency while avoiding local digital mux frequencies
5. Reconnect amplifier and evaluate performance

Sorry if this sounds tedious - you may be lucky and find a ‘sweet spot’ without having to go through every step but I have tried to address the ‘worst case’ scenario

If you had access to a spectrum analyser all the above could be achieved very quickly but if you had you wouldn’t need to be ‘on here’ in the first place

Best of luck with this and please let us know how you get on or if you need a more focussed ‘steer’ on any particular aspect

Rgds
John

[simpsons]

Hi '77

"The signal is relatively noise free, its very minor, noticeable if up close but very much watchable."

Blimey, didn't know 405 Alive are now transmitting material. Which channel are they using!!

OK, OK, being stupid but '77 what are you feeding the modulators with? Digital sourced material, such as a DVD player, are noise free or are you using a Freeview box located some distance away?

On the question of channel spacing, for the Philix model I use, users are instructed to have a 3 channel spacing eg 39,41 and so on between similar double sideband modulators.

Chris

[simpsons]

'77

Did you solve your "noise" problem?

Chris

[19Seventy7]

Hi,

Sorry I seemed to have missed the last to replies somehow. Not sure how, but my apologies.

I’ve not yet fixed it as I’ve decided to do it once and for all and never have to worry about it again. And as it’s being carried all around my room going to-and-fro it’s certainly not the best system. I’ve been redoing my room in general so have waited for it to be finished so I can then work around what I have in place, and hopefully it will improve the layout of sources and RF mods etc so the run of cables should be much shorter than they are now. That’s part of my plan anyway.

My current sources are a Freeview box, xbox 360 and a VCR. However I want to add more at some point but not sure exactly what sources just yet as I’d like constant period viewing with continuity and test cards thrown in. I’m thinking maybe raspberry pi for that. The Freeview box and 360 are connected to RF mods via SCART and composite AV respectively, the VCR is through RF.

I was originally using a double-sideband modulator but have swapped it out for a single sideband, so both rf mods are now single sidebands but of course i’ve seen no difference yet.

Hopefully my room will be done soon and so the signals can be sorted out. I think I know my mistakes and will certainly use the tips and pointers given to me in the final set up.

I’ll let you all know how it goes when done. Hopefully it shouldn’t be too long now.

Thanks again for all of your help
‘77