VHF/UHF TV Distribution

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VHF/UHF TV Distribution

Postby Chris » Thu Jan 09, 2014 12:47 pm

One job I've been putting off for a while is sorting out my vintage UHF/VHF TV distribution.

To replace my rather modern distribution amp a Comtel CX-8, I've recently purchased a couple of vintage items. (see below)

  • Labgear E5165 Distribution amp
  • Altai Splitter amp.

I can now hopefully address in part, some of the signal issues I've had with my previous lash up. Before hand the TV distribution room could run many 405 sets but when I added 625 UHF only two UHF sets before the signal degraded.

The plan is in the workshop to feed the Aurora & Testcard Generator ( 405) into the Labgears VHF input. The Imogen ( 625 testcard and teletext generator), DVD and Philips PM5515T into the UHF. This will provide the workshop and bench with 5 outlets. The sixth output which is a 16.5 meter run, will feed the TV display room, at that end the Altai splitter will provide 8 outlets instead of my crappy little cheapo Y-Spitters

Well that's the theory

dist-1.jpg

dist-2.jpg

labint-1.jpg

labint-2.jpg

dist-3.jpg

altint-1.jpg

altint-2.jpg

plan.jpg
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Re: VHF/UHF TV Distribution

Postby Michael Watterson » Thu Jan 09, 2014 1:17 pm

Terry is the guy to advise. Absolute Guru on this.

Really you need the spec for a miniature Cable TV system and not the usual aerial + 4 to 8 TVs.

I'd have those only as collector items and use modern F-connector based Cable TV quality amps. The domestic retail models are very hit and miss for VHF or more than 5 channels, though I have a modern non-cable TV amp with F-connectors, VHF & UHF and Sky-Eye (or other) pass through.

I have a 77 channel rated Cable Amp with plug in filter for VHF so that VHF is either passive upstream (for Cable Broadband) or amplified downstream. It has only one output as it's designed to drive either a trunk cable (there is equalisation filter) or a passive splitter.

The more channels there are you need more power for same signal level so it doesn't cross modulate.
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Re: VHF/UHF TV Distribution

Postby Chris » Thu Jan 09, 2014 1:27 pm

Michael Watterson wrote:Terry is the guy to advise. Absolute Guru on this.



Absolutely and you're pretty much up there as well Mike. However whenever both of you speak about the subject within seconds I glaze over and all I hear/read, is the Charlie Brown teacher. If you've ever seen the cartoon you will know the "Mwarrr!..... Mwarrr!..... Mwarrr!" effect :bba

Not either of your faults, just my inability to make sense of anything either of you say.
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Re: VHF/UHF TV Distribution

Postby Michael Watterson » Thu Jan 09, 2014 2:23 pm

Say the amp can do 10mW of RF without overloading.

Then with 8 way ferrite "hybrid" core splitter you have about 1mW per outlet. But a pure resistive splitter might give only 0.2mW per outlet = 200uW.

If you have 10 channels, then simplistically each channel can only be 1/10th of the power, so the Altai resistive splitter then is only giving 20uW per channel.

Then subtract loss in the cables. If using PF100, it's not much at 50MHz, but a lot at 500MHz. The loss is a fixed amount per meter depending on frequency.

Typically for 1mm core decent 75 Ohm cable
860MHz 18dB /100m
1000MHz 20.3dB / 100M
2150MHz 31.6dB / 100M

Terry did a table or spreadsheet.

So also the cables need higher drive levels at UHF than VHF.

For Power (voltage is 6dB per half rather than 3dB as Power is Voltage Squared)
3dB is 1/2
6db = 1/4
12db = 1/8
18 = 1/16th
21 = 1/32th

RG6 is meaningless today as there are many various grades. CT100 is historic. Some "RG6" is only Aluminium and others are same as PF100.

The issue with different grades of 75 Ohm cable the same size (1mm inner core is RG6 or PF100) is mainly
Corrosion (all copper is best)
Screen: Metallised plastic screen and open braid, vs Aluminum, vs copper foil and copper braid with no gaps.
Core: Solid copper, vs copper plated steel and larger cables can be Aluminium or pipes. Some "professional" cables and smaller ones can be silver plated copper or steel.
UV resistance
Water proof or not
Crush proofness (semi airspaced or foam. Old type foam sucks in water (bad), newer foams are hydrophobic (good)).
Minimum bend allowed
Type of outer coating.

Screening is as much about stopping signal leaking out of coax as about leaking in. Both are problems!

Belling Lee connectors are mostly rubbish. Not really 75 Ohm, may leak etc or give bad centre connection. F Connectors fitted with tool, 75 Ohm BNC, 75 Ohm N (both trickier to get than 50 Ohm version unless you know where to look). I'd guess MUSA is better than Belling Lee which was invented for MW & SW radios, not TV!

On longer than a patch cord an impedance mis-match (connector, source or load not 75 Ohms) creates a ghost.

One trick is to have more signal than needed and a 6dB attenuator (F type) at each TV socket and then F to Belling plug (off the shelf). Then even if TV is madly NOT 75 Ohms the cable sees much more like 75 ohms and Ghosts are dramatically attenuated (as EACH reflection is attenuated 12dB). This also reduces LO re-radiation up the cable and makes system "cleaner".
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Re: VHF/UHF TV Distribution

Postby marc » Thu Jan 09, 2014 5:19 pm

Hi Chris,

I don't know if you remember the conversation we had a few months ago when we visited you, I was trying to describe a Splitter/amp that I remembered from my childhood but didn't know the make or model. Well you've only gone and got it...It's the Labgear one !
At least I know what it is now and can look for one :aad

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Re: VHF/UHF TV Distribution

Postby Terrykc » Fri Jan 10, 2014 8:14 pm

Michael Watterson wrote:Terry is the guy to advise. Absolute Guru on this ...

:ccg

Oh wow! I suppose I'll have to try to live up to my reputation, then ... :ccg

Michael Watterson wrote:Really you need the spec for a miniature Cable TV system and not the usual aerial + 4 to 8 TVs ...

If I saw either of those two amplifiers at Dulwich, other than as display items, I'd probably walk straight out of the door and never return!

However, this is an entirely different set-up and, although it is (or, hopefully, eventually will be) a miniature Cable TV system, it is only reasonable to expect a more relaxed attitude to choice of equipment - particularly bearing in mind that both availability and cost will be important factors here - and Chris may just have found the right bit of kit for the job, albeit by accident!

Chris has three channels, exactly the same as Dulwich, and it shouldn't be too difficult to set up a reasonably well balanced system with well controlled noise and distortion performance.

Being completely completely isolated from the outside world from an RF point of view, there should be no TETRA or other Base/Mobile interference, CB, Amateur, etc signals - just a nice clear spectrum with just three carriers - OK, six, if you include sound!

I don't think Chris is intent on setting up a 50 channel CATV service any time soon ...!

I've only just seen Chris' original post so I've just one initial observation - is that set in the Display Room really that deaf ...?

I think this might be better ...

OTT_Rev-1.jpg
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What's in the boxes? - VHF/UHF TV Distribution

Postby Terrykc » Sat Jan 11, 2014 3:08 am

No disrespect to OTT's pretty pictures but I prefer a proper schematic ...

Prior to the introduction of integrated circuits into TVs, a schematic would usually show every single component, so that you could see exactly what it was and work out its function.

There was the odd exception - a box simply marked 'VHF Tuner', for example. No problem: you knew exactly what it did - or was supposed to do - and how it was connected into the rest of the circuit.

At least there was no problem unless you needed to probe the inner workings of this mysterious box - but there was usually a nice clear schematic a few pages further on in the Service Manual ...

We need to know exactly what is going on inside a couple of boxes in Chris' diagram but there ain't no manual (and, in truth, there probably never ever was one published!)

So, we need to make a few intelligent guesses and, I must admit, I nearly made a serious error in my initial assessment of one of them!

The boxes in question are the Labgear and Altai ones and it is the Labgear one that nearly tripped me up, until I recalled the identical unit that was mounted under my bench 50 years ago ...

I had assumed that it comprised a UHF/VHF diplex filter followed by an amplifier and splitter like this:
Labgear_Guess.PNG
Labgear_Guess.PNG (5.24 KiB) Viewed 423 times

However, mea culpa, I forgot to read the clues that are so clearly evident in Chris' picture: the first says UHF Distribution Amplifier and the second says Insert VHF.

Clang! This box doesn't amplify the VHF signal - Labgear produced a separate unit for that - and what is really inside the box looks like this:
Labgear_Amp.PNG

From memory, these units only had a small overall gain at UHF, so I've assumed 3dB.

An 8-way splitter has a loss of 11dB so, for an output of 3dBmV, requires an input of 14dBmV. Allowing a loss of 1dB for the filter means that the amplifier must have a gain of 15dB for an input of 0dBmV (1mV).

However, to produce the same output at VHF, the VHF input must be +15dBmV!

Now for the Altai box. This seems, from the markings on the front panel, to be a serious bit of kit!

This is how I think it looks inside:
Altai.PNG

For the same 0dBmV input as used for the Labgear unit, an amplifier with a gain of 22dB is required. This then passes to an 8dB directional coupler, the main output of which provides the 21dBmV output.

The 8dB leg feeds an 8-way splitter which has an additional loss of 11dB to provide the overall gain of 3dB to each outlet.

The term Directional Coupler may be unfamiliar - it is sometimes referred to as a 1-outlet tap - and has a main output and an auxiliary port which typically has losses of 8, 12, 16 or 20dB.

'Directional' means that there is a very high degree of isolation between the outputs which helps prevent problems on one of them affecting the other port.

It might assist your understanding if you consider this common symbol for a directional coupler:
M_DC.PNG
M_DC.PNG (8.91 KiB) Viewed 423 times

Assume you are approaching this sign and 70mph with the intention of continuing to the Display Area. In an ideal world you should be able to accomplish this with little change, if any, to your speed.

A visit to the Workshop should also be easy, although you will have lose some of your speed in the progress, depending on how acute the curves on the off-slip are, etc,

Now turn the sign upside down and try taking the turn to the workshop at 70mph ...
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Re: VHF/UHF TV Distribution

Postby Michael Watterson » Sat Jan 11, 2014 9:35 am

I thought the Altai was resistive splitter thus much more than 11db loss from amp to outputs?
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Re: VHF/UHF TV Distribution

Postby Chris » Sat Jan 11, 2014 10:21 am

I don't really know what you mean by resistive splitter other than I assume you mean the signal path is split with the use of resistors in the circuit. The altai has many other components, caps, 3 x transistors, coils, ferrite, and what looks like a diode.
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Re: VHF/UHF TV Distribution

Postby Terrykc » Sat Jan 11, 2014 12:08 pm

Michael Watterson wrote:I thought the Altai was resistive splitter thus much more than 11db loss from amp to outputs?

It may well be - but my intention was to analyse what is inside the box from the point of view of how it appears from the outside. What is important is to know is what it does - not necessarily how it does it!

Also, being particularly mindful of this ...

oldticktock wrote:... whenever both of you speak about the subject within seconds I glaze over ... just my inability to make sense of anything either of you say.

... I could see no point in adding an extra layer of complication ...

oldticktock wrote:I don't really know what you mean by resistive splitter other than I assume you mean the signal path is split with the use of resistors in the circuit ...

Precisely, Chris, nothing more, nothing less!

The point behind Michael's comment is that resistive splitters have higher losses than the inductive type (and very poor isolation between outputs).

A resistive splitter is a very cheap and simple device. Taking a 2-way splitter as an example, it consists of just 3 resistors which may be connected in either of the configurations shown (common ground omitted for clarity).

The superior inductive type is, of course, rather more complex ...

2-way Splitter.PNG
2-way Splitter.PNG (5.08 KiB) Viewed 386 times

(Both inductors are usually wound on one two-hole ferrite core.)

Perhaps this will help illustrate the difference between the two types ...

2-way Splitter Comparison.PNG
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Re: VHF/UHF TV Distribution

Postby Michael Watterson » Sat Jan 11, 2014 12:09 pm

A ferrite bead / ring / binocular core based splitter loses only 0.5db to 1db, the power is split. It can only split in 2, hence a cascade of 3 to get an 8 way splitter. If perfect no power is lost. Another name is a "hybrid".

Spitter 3db 2 outlets --> 2 x 3 db splitters 4 out --> 4 x 3dB splitters 8 out
so total level change is 3 + 3 +3 = 9, but we add about 0.65 dB loss per stage, so level on each output is -11dB compared to input. Total wasted power is less than 2dB. It's bidirectional so will work as a combiner.

A resistive splitter can be in theory more easily flat on wider frequency range, but is actually a potential divider. For 8 way the 8 inputs are in parallel and combine to be 75 ohms when loaded with 75 Ohms. The two resistors are chosen so the output socket is 75 Ohms when all the inputs are paralleled and driven from a 75 Ohm source. So it needs more power to drive it. Loss as combiner is much higher.

The input to each potential divider must be 8 x 75 if there is an 8 way split = 600 Ohms when the output is loaded with 75. But the two resistors must be chosen that the socket looks like 75 Ohms.

I think for 8 way*, each socket has about 80 Ohms in parallel and about 561 Ohms in series from the 75 Ohm amp.

80 in parallel with 75 Ohm load is 38.7 Ohms. The output impedance looks close to 75 Ohms as it is 80 in parallel with 560 ohms in series with 75 Ohm in parallel with 85.7 Ohms.

560 in series is 598.7, close to 600.
598.7 in parallel 8 times is 74.8 Ohms.

Probably 560 & 82 Ohms would do. Can you see what values they used? Of course the advantage of this method is that the series 560 can be adjusted for whatever output impedance the amplifier really is even if not 75 Ohms.

Loss to each port is about 14.7dB, maybe realistically 15dB at VHF and 17dB or 18dB at UHF. Mismatch at UHF will rise rapidly on increasing UHF with the Altai.

(*Calculated by using CAE program for lowest attenuation 600 Ohms to 75 Ohms matching pad).

In practice the resistive splitter is poor above 400MHz due to inductive issues and layout but perfect down to audio frequencies. The Inductive Hybrid 3 stage cascade can have a perfect layout even at 2GHz, but if good at 860MHz often deteriorates rapidly below 40MHz. Many claim to be 5MHz to 900MHz.
Above 1000 to 3000 MHz the "inductive" hybrid kind using a little ferrite is "free" as it literally is a little like a road! The microwave splitters are purely PCB tracks and can be 0.1dB loss if a Teflon substrate and silver plated.
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Re: VHF/UHF TV Distribution

Postby Chris » Sat Jan 11, 2014 5:25 pm

Test This afternoon

Current set up which is a modern Comtel cx-8 UHF/VHF dist amp in the workshop feeding Test card F to the display room, picture fine.

Disconnected the Comtel CX-8 and swapped in the Labgear, went to the display room and test card F was awful, wobbly snowy and not at all good. Why this os I've no idea I expected to see a similar picture that the comtel was providing. I then out of interest connected the display room feed to the input of the Altai, connected the TV in question to port one.... A stunning test card F!!! I think even better than I had before from the old set up.

I then connected a second UHF set to port 2 of the altai, again superb picture. A third UHF set was connected ( this was impossible under the old set up) and another good picture. Then back to the workshop to feed in the Aurora to the VHF, back to the display room. Connected a 405 set to port 3 and a good test card was presented.

The two boxes seem to have solved the problem.

I tried to photo the sets showing the test cards its a bit difficult though, but believe me the test cards are excellent. I will keep adding sets and see if it holds up. Looks like the problem has been solved though.

disp.jpg
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Re: VHF/UHF TV Distribution

Postby Terrykc » Sat Jan 11, 2014 8:56 pm

oldticktock wrote:.... Disconnected the Comtel CX-8 and swapped in the Labgear, went to the display room and test card F was awful, wobbly snowy and not at all good. Why this os I've no idea I expected to see a similar picture that the comtel was providing ...

Having never heard of a Comtel CX-8 and not coming up with anything useful on a web search, can you tell us more about it?

Is it an amplifier with a single output, by any chance? Do you know what gain it's got?

As I said earlier, the Labgear device has little overall gain whereas I suspect the Comtel has quite a lot, so that would explain why your signal levels nosedived! Having said that, the splitter outputs of the Altai only offer a 3dB boost whereas your description of improvement obtained suggests something better! Possibly something went wrong during the first test?

I'm assuming that you have no way of measuring signal levels and are relying on a plug and play approach.

If it works, you don't know why so there is little hope of working out what is wrong when it doesn't!

If you want to stumble on in this way, fine - as you say, it is working well - but if you prefer a more structured approach I will attempt to guide you from afar ...
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Re: VHF/UHF TV Distribution

Postby Michael Watterson » Sat Jan 11, 2014 9:55 pm

Most Comtel stuff I have seen makes the cheap Altai/Eagle stuff look good. There ARE decent retail VHF/UHF amp splitters with F - Connectors. I thought I was using one with 8 F, but it's in a box. The one in use is VHF & UHF inputs and 4 x out with 6MHz approx reverse and 9V DC pass through for "remote eyes", a cheap Masterplug (But better than Comtel).

But it's driven from 4 way "Proception" F-Connector UHF preamp / splitter near the aerial but in the Workshop. The other 3 ports are for Workshop. The "proception" stuff (sold by the Aerial folk I forget name of that make SR18 etc) seems not bad for cheap.

Also better than Comtel is the Global Tvlink F180 8 way amp. It's cheap and is all F-Connectors. But UHF only, which is why It's not in use I think.

Rather better are my 2 Chinese Cable /Broadband amps (4 port) but you'd not like them as they are fixed 5 to 65MHz upstream and 88 to 1000MHz downstream. They are very good and can handle more than 80 downstream 8MHz channels (any mix Analogue / Digital / Broadband Modem) at +8dB. Heavy diecast boxes and power either on one tap out or on dedicated F-Connector. 12V 500mA (6W!)

Slightly more use for VHF TV is a Polytron Trunk amp probably for apartments (easily drive an 8 port passive splitter) it's only 4 to 30MHz upstream (-1dB) (older Broadband systems) but 47MHz to 862MHz downstream (20dB gain). variable attenuator on input. 3.5W consumption built in mains PSU (outdoor trunk more likely separate PSU or line power?).

But my EMP Centauri four off Quattro LNB in and 16 outlets multiswitch is a good passive splitter for TV. Works 1MHz to 900MHz any mix upstream or down (I tested it with Cable Broadband, off Air Analogue & Digital TV, Band II FM Radio and Band III DAB). At each outlet you fit a 900/950MHz diplex TV/Sat splitter. Currently a VHS with a low light B&W security camera at back of garden feeds the Terrestrial port. (Sat ports are 28.2E, 19E, 13E and 9E with 28.2E on port one so Sky or Freesat boxes with no DISEQC work.

If I had some 405 and vintage 625 I might fit up with mix of 405 and 625 on Band1 and BandIII (RTE1 405, BBCI 405, UTV 405 RTE1 & RTE 2 625) and put BBC1, BBC2, UTV, C4 and Five on UHF (five cheap HD Sat receivers, I have 16 sat feeds + 2 x cheap DVB-T MPEG4 HD boxes for RTE). To simulate the Analogue Era of 1962 to 2009 inclusive. Maybe a 6th UHF channel simulating Limerick RLO who had local radio licence and a licence to retransmit UK Ch5 locally (really!) and the first people to LOSE a licence! They thought it would be great to "opt out" of some of C5's adverts for local ones and also even entire programs by local live sport! After losing licence they popped up occasionally as Pirate Radio and also on Satellite Radio about a year. C5 was uniquely on Analogue Astra 19E with an encryption flag and no encryption! So not hard to receive in Limerick. I think that closed about 1 year after they launched on Sky Digital.

But I only have one near vintage TV so far.
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Re: VHF/UHF TV Distribution

Postby Chris » Sat Jan 11, 2014 10:48 pm

Terrykc wrote:Having never heard of a Comtel CX-8 and not coming up with anything useful on a web search, can you tell us more about it?


Not much to tell Terry, two inputs VHF and UHF each has a variable gain control. There are then 8 outputs.

Here's some pics of the now removed amp, I attempted a tear down to see what's what but there was little point as it contained a sealed unit.

comt1.jpg

comt2.jpg

comt3.jpg

comt4.jpg


I didn't stumble by accident on my new set up, I saw a similar config in an old redundant TV shop a couple of months ago. The chap was not selling any of it but I made a mental note of how it roughly connected and what units were employed, then it was a case of finding suitable boxes on e-bay.
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Re: VHF/UHF TV Distribution

Postby Malc Scott » Sat Jan 11, 2014 10:50 pm

Well, i didn,t understand a word of Michaels last post! :ccb
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Re: VHF/UHF TV Distribution

Postby Chris » Sat Jan 11, 2014 10:52 pm

Well I'm glad you're honest enough to say so Malc, I was beginning to think I was the only thicko on the forum :qq1

This is the trouble with threads like this they need to stay on track rather than tangent knowledge demonstrations.

The post you mention does nothing other than glaze me over to the extreme as well. I think we all know by now Mike has a vast knowledge on most subjects but after I suggested this needs to be tempered for mere mortals like myself, it obviously goes unheeded.

"Mwarrr!..... Mwarrr!..... Mwarrr!......" So yep I'm switched off!

As Terry pointed out I've learnt nothing but hey my new distribution system works until it breaks, then I can fumble around again. Still I'm not a museum, I don't have customers and nobody gets miffed other than I if things go wrong. At least I can get back to my telly restores/rebuilds.
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Re: VHF/UHF TV Distribution

Postby Refugee » Sun Jan 12, 2014 1:24 am

Yes indeed Chris things can get complicated.
If I do maths I try to keep it running in the background and come back if I am asked to explain how I worked something out.
If I am seen to quote a range of values for a component it is likely that I am running the maths behind the scenes.
Keeping things simple is also good. If you are working on circuits with transistors that have a gain of 40 to 150 on 12 volts do I really need to worry about the base drive voltage of 0.6 volts when all the resistors are 10% tolerance anyway. It is only needed if you are making a currant limiter for a series regulator or instrument biasing.
Running the thing on 3 volts is a different matter though.
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Re: VHF/UHF TV Distribution

Postby Terrykc » Sun Jan 12, 2014 2:01 am

Ah! Commtel with two 'm's - that makes all the difference to the search engine (much to my surprise!)

However, Chris, you've got me really puzzled now! Can you explain why you ditched this flexible bit of kit with its inbuilt ability to balance the UHF and VHF input levels ...

Commtel.PNG
Commtel.PNG (9.29 KiB) Viewed 312 times

and replace it with this bit of unbalanced, inflexible c**p ...?

Labgear_Amp.PNG

Was it intended as some kind of intelligence test?

Please tell me I passed ...
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Re: VHF/UHF TV Distribution

Postby Michael Watterson » Sun Jan 12, 2014 11:01 am

The summary of my post:

The Commtel stuff isn't very good. It might be flexible, but doesn't work very well. Very many retail models of distribution amp/splitter are poor. Easily overloaded.

Belling Lee plug/sockets bad at distribution head end as they are unreliable & poor compared to F-Connectors. Good VHF/UHF distribution amp / splitters are not expensive.

A Multiswitch with 16 outputs is very good for Distribution, better to buy "passive" terrestrial port kind and add own driver amp(s). But one with inputs for four Quattro LNBs (one can be Quad) on dish(es) is over £180. However it's a future proof solution for SIXTEEN outlets with virtually any signal from 5MHz to 900MHz on terrestrial port and 950MHz to 2200MHz on LNB inputs. Can be expanded up to 1000 outlets.

Plan for future, not just what you want today. Having ability for 4 VHF channels (one or two 625 for VHF 625 stuff (Ex Cable or non-UK TV), maybe London & Birmingham on Band I for old TRF TVs) and 5 or 6 UHF channels isn't unreasonable. Most really cheap amps and certainly the old Labgear can't manage that. I'm not sure how good the Altai is. There is a way to test.

Not only can you feed VHF TV and UHF TV down the cables, but it might be useful to feed VHF Band II and Satellite IF down them too.
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Re: VHF/UHF TV Distribution

Postby ppppenguin » Sun Jan 12, 2014 11:04 am

Not sure whaty use an RF switch is in this sort of setup. The need for switching is at baseband audio and video. An RF switch won't do that.
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Re: VHF/UHF TV Distribution

Postby Chris » Sun Jan 12, 2014 11:20 am

Terrykc wrote:However, Chris, you've got me really puzzled now! Can you explain why you ditched this flexible bit of kit with its inbuilt ability to balance the UHF and VHF input levels ...

and replace it with this bit of unbalanced, inflexible c**p ...?

Was it intended as some kind of intelligence test?

Please tell me I passed ...


That will be because the pictures with the commtel in place are dire beyond belief, grainy with patterning running all over the place, colours a mess. With the labgear replacing the commtel the picture is clean as a whistle and I can run many sets. But of course being a complete idiot I can't tell the difference. I know I don't know anything when it comes to aerial systems and I took a poke and hope approach.

ppppenguin wrote:Not sure whaty use an RF switch is in this sort of setup. The need for switching is at baseband audio and video. An RF switch won't do that.

I assume you are referring to the switcher on my "Pretty Picture", its a composite switch not an RF switch and is very useful for me, I can run many devices (4) in with one output to the aurora.

Anyway enough ticktock bashing, this thread has come to an end as far as I'm concerned.
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Re: VHF/UHF TV Distribution

Postby Murphyv310 » Sun Jan 12, 2014 11:23 am

Terrykc wrote:Ah! Commtel with two 'm's - that makes all the difference to the search engine (much to my surprise!)

However, Chris, you've got me really puzzled now! Can you explain why you ditched this flexible bit of kit with its inbuilt ability to balance the UHF and VHF input levels ...

Commtel.PNG

and replace it with this bit of unbalanced, inflexible c**p ...?

Labgear_Amp.PNG

Was it intended as some kind of intelligence test?

Please tell me I passed ...

Hi.
I don't have a commtel amp but I do have an unknown 70s amp with seperate gain controls for VHF & UHF. I have used it for many years and having the ability to balance the system is great, I think I would be sticking with the commtel.
Grain and noise can be caused by excess signal, cross mod and other reasons. I would try one set from the commtel and gradually back off the gain and see what happens.
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Re: VHF/UHF TV Distribution

Postby Michael Watterson » Sun Jan 12, 2014 11:33 am

Yes, good plan.

But maybe the Commtel is faulty?
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Re: VHF/UHF TV Distribution

Postby Murphyv310 » Sun Jan 12, 2014 11:46 am

Michael Watterson wrote:Yes, good plan.

But maybe the Commtel is faulty?


Quite possible.
At least if Chris tries it this way with one input and output and all is well then he can add other input channels, adjust the gains and then he will find out when the amp falls over, again as I've said before often these things can be trial and error plus its all experience and learning.
Nae point in chucking yer toys oot the pram :qq1
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