Diplexer, masthead amp, and power unit confusion!

driveshark

Hi lads,

I just have a few questions to try improve my weak freeview signal from Brougher Mountain. We've never got a great signal, very grainy to say the least from analoge and the culprit is a mountain directly behind our house. The neighbours get perfect signal about 100-150mtrs away from the mountain.

I want to add a masthead amp & power unit, but the aerial as it stands is on top of a steel pole, on top of an unused electricity pole so there is a fair distance between it and the house where the power unit will be located. Does this distance matter or can I go ahead? I'll be putting the power unit in the attic.

I'm also using a diplexer so I can join the two signals from irish & english aerials. Is the following possible, power unit line to the masthead amp, and then connecting the combined line from the diplexer into the masthead amp. I'm not sure if the power will pass through the diplexer to the aerial?

And finally, I have a Wolsey 4 way amp in the attic to split & boost the signal from the aerial to 3 tvs, since this is already powered I'm guessing I can't put the output line coming from the power unit into it? I think I'll just have to use a power passing splitter?

Any feedback would be appeciated!

Thanks,

Peter Rhea

What length of cable are we talking from psu to amplifier? Certainly in this piece on mastheads, the writer reckons the ones he sells are good for cable runs of 150 metres or more.

The diplexer should have at least 1 power-passing leg, some have 2 & some are switchable; it should be labeled. There should have been at least 1 amplifier for the combined signal to cope with the long cable & if you want to get the most from a weak signal, there should be 2 seperate amps between aerials & diplexer. It's strange that such a setup doesn't already have a masthead amp, did you install it yourself?

As for the distribution amp, it will depend on what input signal level it can accept & the input level will depend on the rating of the masthead amp(s) & the cable length between it & the attic.

driveshark

Thanks for the detailed reply. My current setup is as follows, two aerials (irish from Cairn Hill, english from Brougher Mountain) diplexed with Triax UHF Diplexer TFC 3537, which is switchable to the best of my knowledge, then RG6 about 35 metres into the attic from the pole. Its then fed into a powered splitter Wolsey 4 Way TV Amplifier that allows a 12V DC UHF line in, and then connected to TV Aerial & Satellite Combiner from each output as I'm planning on adding a dish in a few months.

When you say two amps, where exactly do you mean placing them?

Peter Rhea

How good is the signal from Cairn Hill with this setup?

A 35 metre run of 'RG6' cable would typically lose between 5 & 8 dB of signal. Depending on the relative signal strengths from each transmitter, you can amplify the weaker one, both combined or both seperately. The 12v, 50 mA line power from the distribution amp should be fine for all but the highest gain mastheads (used singly).

The use of seperate amps for each aerial would be to amplify the signal at its strongest, before the small (about 1 dB) insertion loss of the diplexer & to allow differing levels of amplification for each. There are masthead amps available with 2 UHF inputs but those I've found, examples here are high gain & require their own psus. These would probably have enough gain to enable a passive splitter to be used in place of the distribution amp but they're probably unnecessary in your case.

driveshark

The Cairn Hill signal is great, we're close enough to the transmitter plus a clear line of sight, its just the Brougher transmitter we have the problem with.

I'd like to amplify the Brougher aerial, I'm thinking a high gain masthead (27db?) to pull in as strong a signal as possible. I don't think anything lower would suffice to be honest.

I'm guessing that putting the powered line from the masthead through the diplexer will have a negative effect on the strong Cairn Hill signal?

Thanks again for the info,

Peter Rhea

The amplifier doesn't 'pull in' anything, it only increases the strength of the signal picked up by the aerial & ensures that minimum signal levels are maintained further down the line.
A decent aerial should be your 1st line of attack in a poor signal situation & an amp. placed at the masthead can get to work before any significant cable losses occur.

If the Cairn Hill signal is satisfactory, I would use no more than 16 dB of amplification, with the amp. placed between the Brougher aerial & the diplexer & powered by the distribution amp's line power. The Brougher signal should then hopefully arrive at the dist. amp. with healthy but not overwhelming strength.

The dc power passing through the diplexer won't affect the unpowered leg.

driveshark

I'll that setup a try. I just want to make sure I'm getting this right, I run the coax from the Brougher aerial to the masthead, then to the diplexer and the combined feed to the distributed amp in the attic. Am I correct in saying that the power leaves the distribution amp in only the outputs? If this is the case will the signal coming back down the line from the diplexer not just hit a "dead end" coming back into an output?

Peter Rhea

driveshark wrote: »

a powered splitter Wolsey 4 Way TV Amplifier that allows a 12V DC UHF line in

I understood this to mean that you have one of the Wolsey distribution amplifiers, either a 334034 or 334035 at page 2 here, that provide a 12V, 50mA power supply for a masthead amplifier from the UHF input, or is it exactly like the one in the link i.e. supplies 9V DC for 'magic eyes' through the outputs?

This whole setup is just a rough outline on my part, as I don't know the actual signal levels involved.
From your description, there's a good chance that using a medium gain amp on the Brougher signal while allowing Cairn Hill to be attenuated by the long cable will result in both being reasonably leveled by the time they get to the attic.

Vince Cable

driveshark wrote: »

I'd like to amplify the Brougher aerial, I'm thinking a high gain masthead (27db?) to pull in as strong a signal as possible. I don't think anything lower would suffice to be honest.

As mentioned already, it's the aerial does the 'pulling in' but if you want the option of turning up the juice, you can use a variable gain amp. as mentioned in the ATV link above. You have to be aware of the possibility of causing overload further downstream, though.

Vince Cable

Peter Rhea wrote: »

The use of seperate amps for each aerial would be to amplify the signal at its strongest, before the small (about 1 dB) insertion loss of the diplexer & to allow differing levels of amplification for each.

Would have thought the interference picked up by old unscreened diplexers would be more of a problem than the insertion loss; you'd definitely want your amp in before that.
Otherwise, a passive device shouldn't degrade signal quality so I wouldn't worry much about using 1 amplifier after the signal has been combined in a decent screened combiner, unless as you say, different amplification levels are required.

Peter Rhea

Vince Cable wrote: »

you can use a variable gain amp. as mentioned in the ATV link above.

Variable gain amp not a bad idea, but I have to admit to 2nd thoughts about giving detailed advice on these threads where no proper signal level measurements are available.
It's all just guesswork & may not be of any value to the OP unless it confuses them so much they get an installer in. I should know better tbh . . .

Vince Cable

Peter Rhea wrote: »

. . . these threads where no proper signal level measurements are available.

That would be all of them, then.

It's true though, even knowing someone's receiver is operating just on the threshold of reception isn't much help, as they seem to vary quite a bit in sensitivity. Proper levels (voltage) are what's needed for specifying amps, splitters etc.

driveshark

I'm going to have to try get a accurate signal level measurements to get this right, is there any other option than actually using a tv to check the signal? I'd like to find out the actual signal loss betweem the aerial itself and the tv and work from there.

We used to be able to get mux 1, 2, A, B, C & D, but recently this dropped to only recieving 1 & D. I thought this could of been caused by the aerial being only able to pick up the stronger 16QAM over the 64QAM, but this doesn't explain the B & C being lost also as they are 16QAM to the best of my knowledge. Could this be a filtering problem? The diplexer filters the brougher input from 47-590 MHz, so I don't see it as being a problem and the amp input range is from 47-862MHz. If the 1 & D are being subjected to the same noise & signal loss in the cable run, shouldn't B & C be the same? I've also noticed that mux D is holds picture and sound quality a lot better than mux 1, could there be a interference problem?

It seems that the best option at the minute is to locate the masthead amp between the brougher aerial and the diplexer, but its just difficult to test anything at the minute as the aerial is at such a height. Would a 16dB masthead be adequate with my amp? Also I'm just a little confused with the distibution amp, am I right in saying that the input on it also acts as a 12v power line, the same as a dedicated psu would?

Peter Rhea

driveshark wrote: »

I'm going to have to try get a accurate signal level measurements to get this right, is there any other option than actually using a tv to check the signal?

A professional meter at the aerial would be ideal, showing signal levels as well as digital parameters such as BER (Bit Error Rate).

Would a 16dB masthead be adequate with my amp?

It would certainly compensate for the cable & diplexer losses & then some, but there's no guarantee that it wouldn't raise the analogue signal level too much for the distribution amp to handle. The dist. amp. may have a built-in level control (attenuator) but this would also attenuate the unamplified Cairn Hill signal, which may be undesirable.

Also I'm just a little confused with the distibution amp, am I right in saying that the input on it also acts as a 12v power line, the same as a dedicated psu would?

Post the model no. & I'll tell you.

driveshark

I'm guessing a signal level meter cost would be in the hundreds so that probably won't be an option But if I can get my hands on one, I know an Eircom tech maybe they'll have something that will do that trick.

The model number is 334035, and the input has 12V DC/50mA automatic line power?

Peter Rhea

driveshark wrote: »

The model number is 334035, and the input has 12V DC/50mA automatic line power?

That should power most mastheads. As mentioned above, a variable one is a good idea. There's 1 single output model in the Wolsey catalogue linked to above but a 100mA psu may be required (turns out it works with 50mA but it doesn't matter now).

The proMHD11V 7-22dB amp. mentioned here definitely works with 12V 50mA. It's also the one sold by ATV (link in my 1st post) & their owner puts a lot of thought into the gear he stocks.

driveshark

Actually sorry, I made a mistake with the model number of the distribution amp, its 334060

Peter Rhea

That amp. only seems to have 9V power for magic eyes so a seperate psu will be required for the pre-amp.

What part of the country are you in? If some of your problems are due to co-channel interference from another transmitter, an amplifier won't help with that.

driveshark

Ok, this will probably be the psu I go for. I live in Cavan, I don't think there's any interference from other transmitters though. Cairn Hill is from ch 41-51 and Brougher is from 21-28, plus the fact that we used to get all the muxes decent enough and irish stations are perfect leads me to believe that there isn't any interference? Correct me if I'm wrong!

I seem to be picking up RTE1 on 183 & 215 MHz, and RTE2 on 199 & 207MHz. This is a very weak signal in comparison to Cairn Hills 623MHz RTE1 and 647MHz RTE2, not sure which transmitter this is.

Peter Rhea

Shouldn't be a problem with CCI in Cavan, the problem transmitters as regards Brougher Freeview would be Divis (low powered Freeview on 23, 26, 29, 33 & 34), Hollywell Hill (analogue on 23, 26, 29, 33, Saorview on 30) & Castlebar (analogue on 23, 29 & 33).

As to why reception has deteriorated, assuming nothing in the setup has been changed, it could be due to environmental factors such as trees in the signal path growing, or new buildings being erected, or it could be weather damage to the aerial/cable/connections.

Those faint analogue channels you are receiving are VHF transmissions from Truskmore & either Kippure or Maghera.

driveshark

Got the psu & masthead installed today, picture quality is a lot better on analog, not perfect but certainly watchable. All the muxes are visible now without problem and I'm getting a "Good" digital signal quality on the tv. Cheers for all the info Peter, helped alot!

Peter Rhea

Glad to here it, which amplifier did you go with?

driveshark

I went with the 16db Proception unit, I figured the signal was being picked up about 40-45 dBμV at the aerial (around the cliff edge I guess because it was breaking up quite a bit) so taking into account all the noise introduced along the way it should now reach the tv at about 60 - 65 dBμV. Although the analog English channels are a little grainy, it shouldn't make much of a difference when we put in proper recievers to pick up only the digital and satellite.

Vince Cable

The 'cliff edge' is actually down around 30dBuV at the receiver, 45dB gives a useful margin & is the recommended useful working minimum.

You need to get the best possible signal to noise ratio & that is set at the aerial, you can only worsen it afterwards. A very low level signal that needs excessive amplification just to maintain minimum working levels, will also start out with poor S/N & the amplifier will keep this ratio as well as adding its own noise (after the aerial, there's always a price to be paid for gain).
By the time this is viewed on the tv (analogue program), the signal may have quite a high level but still be very noisy.