Uhf signal too much or not enuff

fatboymsport

HI all i have finally got all the tv points working in my new house.

the system i have is as follows

antinterference 8 way distribution box (tetra model)
56 element uhf antenna
5 element VHF antenna
all coax in house is CT100 or WF100
have the RF out from sky and the uhf input T'ed together on the uhf input on the dist box.

the antennas are temp mounted in the attic i have a crystal clear picture on VHF but on UHF it is very liney when looking at tv3 tg4 is ok but no where near as good as rte1,2 on vhf. also the picture on sky isnt as good as it should be could i be getting signal overload there is an adjustment pot on the Dist box but it does not work.

i thought the uhf antenna might be mis-alligned but with sky also not 100% it cant be that

tv3 is on ch 62 and sky is ch68 surely the are far enough apart not to interfear with each other

anyone any ideas what i can check

i am in kildare and getting signal from kippure which i can see out the window upstairs

lucernarian

Is there a masthead amp present on the aerial?

See what reception is like with just the UHF aerial plugged into a TV with a single piece of cable. Short if possible.

How is reception if you disconnect the RF output from the sky box?

fatboymsport

thanks for the reply

i cant plug the antenna into a tv as it is all in the attic and there is no way to get the lead near a TV

and i will try disconnecting sky and see what happens

and no masthead amps only what ever the distribution amp has in it. think it is 8dB gain

lucernarian

You've got a bit of a problem so. But what you can do, instead of hauling a portable TV into the attic (a pain in the behind) is to simply bypass the distribution amp by joining the UHF aerial wire directly to one of the leads going to a TV socket. Use 2 f connectors and a female-female f-conn joiner if possible. Try out what the reception is like on that socket and let me know if it changes much.

Also, could you tell me how the UHF and VHF aerials are currently connected to the distribution box? Like are there 2 different inputs, one for each aerial or are they combined onto one cable which is then hooked up to the box? (with one of these: http://cpcireland.farnell.com/jsp/level5/module.jsp?moduleId=cpc/410879.xml)

Antenna

To_be_confirmed wrote: »

. Use 2 f connectors and a female-female f-conn joiner if possible.

All that's needed is the joiner, as the cables would already have the F connectors (those amps have F inputs). These Dist amps have seperate UHF and VHF inputs.

"have the RF out from sky and the uhf input T'ed together on the uhf input on the dist box."


The manner of combining Sky modulator output and the UHF aerial before the dist amp sounds dodgy!
better use a grouped diplexer to combine both (perhaps put Sky modulator on Ch21 at the low end of UHF) and perhaps use one of these
http://www.televes.com/hojastecnicas/103793.pdf
(Sky output on low channel input, UHF aerial on high channel input)

lucernarian

I thought only the more expensive Antiference dist amps have separate inputs and f-connectors. I remember looking at the antiference distribution amp range and picking the 240L because it had those features as well as a decent noise value and built-in 12V PSU.

Thanks for that bit, I overlooked that sentence when I checked to see if there was a masthead amp mentioned in the original post.

fatboymsport

have not had a chance to do anything with this in the last week i will try connecting the uhf ant straight to the tv and see what i get.

i tried to change the sky output but it would not change how is it done.

i have the thompson HD box.

im planning on mounting the antennas outside but i know its not a signal level problem as with the vhf coax disconected from the antenna i still get a perfect picture.

where would i get one of those items mentioned above

Thanks

lucernarian

Ok, to get the output changed, you have to exactly press "Services - 4 - 0 - 1 - select" quickly to access the installer menu on the sky box. In there, one of the options lets you set the output channel of the RF out. Set it to 21. As it stands, the sky box is violating the "1+5+9 rule". Here's a good website to read more: http://www.stevelarkins.freeuk.com/dtv_retuning_advice.htm

Try connecting the UHF aerial directly to a TV first and see what difference that makes, before looking for the VHF/UHF combiner. And definitely change the RF output, as it won't make anything worse and may well help.

fatboymsport

tried changing sky output to CH21 and still no improvement

there is a high gain output on the dist amp so i will try connecting that to the kitchen tv as that has the worst picture.

i still reckon there is a problem with the dist amp as the tiny screw for adjusting the gain on the uhf side does appear to be damaged.

hope to get more time at the weekend to crawl into attitc to work on this

thanks for the help so far

fatboymsport

noticed when i had the sky box plugged out that tv3 and tg4 recption was excellent all over the house. when i pluged the sky box back in evrn thou it was in stby the interference came back on TV3 and tg4.

where can i get one of those combiners mentioned above.

fatboymsport wrote: »

tried changing sky output to CH21 and still no improvement

there is a high gain output on the dist amp so i will try connecting that to the kitchen tv as that has the worst picture.

i still reckon there is a problem with the dist amp as the tiny screw for adjusting the gain on the uhf side does appear to be damaged.

hope to get more time at the weekend to crawl into attitc to work on this

thanks for the help so far