triax link for RF2 on skybox

Hobbsie · 18 Jul 2015 at 12:10

Hi all just fitted a triax link to plug into the port on new sky box that dont have RF2 out anymore.
All works fine and dandy until i plug the RF in which is a cable direct from aerial.
When i plug the aerial cable into triax unit so it can modulate RF with the RF2 signal the picture goes fuzzy like interference.
The 2nd i unplug the aerial cable the picture is perfect and i can still control sky etc.

DTV is fine and has a lovley picture so i know the aerial is fine which is were the confusion lies.

Im wondering that there is interference on the aerial that the digital TV is not picking up, and because im modulating the RF signal down an analogue channel its picking up interference that Digital is not?

Hope some aerial guys out there can help me
I know this is written badly but my english/spelling etc is not the best, Sorry.

thanks

lucid · 18 Jul 2015 at 16:36

The problem you have is because of a clash of frequencies.

Sky RF2 uses an analogue modulation. IOW you switch your TV to the analogue tuner to pick up the RF2 signal for the Sky box, and then go back to the digital tuner (DTV) to watch Freeview. Although we talk about different tuners and analogue and digital, both occupy the same frequency band.

A Sky box RF2 can be set to output at any frequency step from c21 to c68. Your local TV transmissions will be somewhere in the range c21-c60. If the Sky RF2 is set at a c number that is the same or close to an existing digital TV channel then the two will interfere. The result is a snowy or grainy picture on the analogue channel.

To fix this you need to move the Sky box RF2 channel to a different c number. This is done from the same menu where you turn on the Sky RF2 voltage. There's a couple of ways to tackle this.

If you have a 4G LTE filter on your aerial system, or you know for sure that 4G interference isn't a problem where you live, then try each channel number in the range 61-68. With 4G filtering in place then there should be no competing signals in that range.

The alternative is to try each c number in the 21-59 range range but avoid those you know that will clash with the Freeview channels used by your local transmitter. You also need to remember that your aerial might be picking up adjacent transmitters from neighbouring areas, so you have to account for and avoid them too.

Hobbsie · 19 Jul 2015 at 20:44

Thanks i shall try this when i can.

thanks for the info

Hobbsie · 20 Jul 2015 at 20:04

ok looked up my local transmitter and spoke to an aerial rigger and they said to put it in the 40's tried from 40-49 but still fuzzy my guessing is that i may need a 4G filter?

lucid · 20 Jul 2015 at 22:04

The area affected by 4G is at the very top of the frequency range 60-68. It won't make channels fuzzy in the 40s range. But if you mean use the filter to ensure that analogue and digital 60-68 is clear of any potential signals then yes, that should work.

Hobbsie · 21 Jul 2015 at 17:45

hmm ok so if i leave on 40 for example it shouldnt be fuzzy? iv ordered a 4g filter only a fiver so wont hurt to fit, i guess its time to jump on roof and check signal levels. oh the joy.

thanks lucid for your help.

lucid · 21 Jul 2015 at 23:24

Hobbsie said:
hmm ok so if i leave on 40 for example it shouldnt be fuzzy? iv ordered a 4g filter only a fiver so wont hurt to fit, i guess its time to jump on roof and check signal levels. oh the joy.

thanks lucid for your help.

If it's fuzzy in the 40's (or the 20's, 30's or 50's) then it's because of channel interference either at the same channel number or from adjacent channels due I guess to harmonics.

It's also worth noting that the RF2 picture won't ever be as clear as the HDMI or the SCART output from a Sky box. However, it should be passable to the casual viewer. What changes things a bit is the newer boxes that require an outboard RF2 modulator. They're not quite as good as the older Sky boxes with RF2 outputs built in. If you're continuing to have problems of a fuzzy picture then check your plug wiring or use better quality coax.Webro WF100 is the stuff to use.

Installing the 4G filter somewhere on the downlead from the aerial before it goes in to the distribution system or first receiver box will effectively clear the channels from either 59-69* or 60-69* of any signals both from 4G and any RF transmissions if they were there. That's why the filter is inserted before the Sky box rather than after it. The filter then clears the path for you to use 59-69/60-69 for Sky RF2.

* Depending on the channel allocation of the local transmitter and whether it uses ch60 then one or the other filter type should be chosen.

Hobbsie · 22 Jul 2015 at 18:30

thanks i allways use webro WF100 the job is full of it all going back to an antiferance A280 powered amp so its decent ish kit, the only thing is i put the aerial up lol leave that to the guys who can do it.
Ill think ill stick to AV

thanks again