Free Uhf Channels

[sen8or]

Hi Everyone, Ive recently bought some 3 channel AV modulators and wanted to know what channels are free as to not clash with FTA channels. I have two of these modulators which iam going to feed into them f#$tel, DVD player, PVR and some other stuff. ive got it all hooked up but some channels i think have interference. Ive keep atleast 3 channel gap to stop this but still nothing, anyone able to help? Ive posted here as iam in Perth and thinking its a problem with the channels?

thanks

[dryfry]

Why not do what the broadcasters do SBS on 28 ATW on 31 Modulator 1 on 34 Mod 2 on 37 and Mod 3 on 40.

Or try 43, 46 ,49 or 52 and so on .

[wahroonga farm]

....... but still nothing, anyone able to help? ......thanks

When u say 'but still nothing'. Does that mean u can't tune the a/v modulator analogue carrier (channel) at all?

U r looking for an analogue signal ..... with an analogue tv (and not with a dig stb)?

[sen8or]

All the tv sets in the house can see the modulated channels but there is like interference over the top of the channel. Normal FTA reception is fine so i dont think its any hardward iam using.

Iam using two of these

http://webshop.cabac.com.au/webshop/public.../6213PAL-G%2fAC

and one of these to distribute it all

http://webshop.cabac.com.au/webshop/public/prodinfo/MDA-38R

This is why i thought maybe there was interference from a FTA channel or something else. any ideas would be great. thanks

[wahroonga farm]

It's possibly the way the hardware is connected, if all chosen UHF channels produce similar interference.

Can u give us a connection diagram of the MSA-38R and modulators? I guess it's simply 'Antenna', 'Mod1', 'Mod2' as the three inputs and then the eight Outputs fed to the various outlets with 4dB gain.

The correct way is to inject any modulated channel after a notch filter (or use a diplexor) before any amplification; to ensure the chosen channel slots are 'clean'.

It may be made tolerable by attenuating (also a useful method to determine the magnitude of the problem) the antenna input (within the limits of normal reception), or reducing the masthead amp gain (if there is one). A masthead amp at full gain, is a no no in this situation.

I presume if you remove the antenna input, everything is perfect.

Edited to clarify 8.00a 12/3

[alanh]

sen8or,

It depends on where you live in Perth. There is a set of translators in Rollystone which use UHF channels so if you are in the south eastern suburbs you may need to be a bit careful.

If you are near TV or Radio transmitters the problems will become worse so what suburb is this in?

I have done this and I used channels 44, 52 69, although if long cable runs are used the higher the channel the greater the loss in the cable.

You will also have to watch the signal levels.

What does the interference look like?

AlanH

[sen8or]

thanks everyone for your replies. If i disconnect the antenna it doesnt change anything, if i turn the power off one of the modulators it makes the pictures almost perfect. Iam spacing the channels 3 apart just so you know, ill post a pic of my setup tonight. Would clipsal modulators make a difference or are they all the same stuff just higher priced?

[sen8or]

here is a link to my setup, its rough but if you need more information please ask me. the splitter is the one as mentioned in my previous post and the same for the modulators

[wahroonga farm]

Tks for the pic

Unfortunately u can't imbed pics here

So it appears that the modulators themselves are overloading the amp or interfering with themselves, not the aerial input.

Perhaps if you attenuate the modulater output (is there a feature to reduce the gain of the modulator?), it may improve things. Do they both do the same thing (one 'off' = sort of OK?)

See modified pic.

What happens if you remove the video inputs to the modulators?

Why r you using two modulators? Doesn't each modulator allow for three inputs? It seems they certainly don't 'like' each other mixed on the same rf path.

Doesn't the 'fox box' have it's own inbuilt rf modulator?

[sen8or]

I removed the camera video input and the foxtel picture went downhill, not better. i think ive found a modulator adjust screw on the bottom of the modulator units, going to give me them a go. also in regards to the attenuator would this do

http://www.altronics.com.au/index.asp?area=item&id=L1706

or this

http://www.jaycar.com.au/productView.asp?I...=&SUBCATID=

but its not f connector though, hate using adaptors

[wahroonga farm]

I added a few more thoughts above, which may provide a way fwd

I'd get the Jaycar + adapters and have a play. If it proves a solution then you cud insert a fixed correct value. Always useful for the junk box.

[wahroonga farm]

So I'm thinking the two mods simply can't exist in the same spectrum. Cheaper units may be pretty messy with both sidebands present etc. Can't quite put a finger on the actual reason though. A bit of decent test gear wud soon sort it out

The slight interference with 1 x mod in cct, is most likely a product of the aerial input. Experiment with different channels and modest attenuation of the aerial input. I don't think it's useful to attenuate the mod input, but ..... ?

IMHO there r two options.

1. Simply run the A/V from the camera to a single mod which shares Fox.

2. Set up the camera with a single mod and use the Fox's internal mod (if it has one) per this pic.

[sen8or]

Ive adjusted the dials on the bottom of the mods and the picture is heaps better. I guess they were over loading the signal. Thanks heaps for your help i really thought i was going to have to spend more cash but ive got it working. Now to the next project, controlling the foxtel box in over rooms.

[wahroonga farm]

Oh well, simple is best

The 'mods' were simply driving the amp into unlinearity (too much level). Saves me worrying why both didn't work together.