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Looking for resources for TV RF delay line?


I haven't done any construction since school days but really loved doing it.

I have an idea for a project which will solve an AV issue I have at home.

I use the powered RF2 output on my Sky+HD box to to distribute my Digital TV aerial signal and my Sky output to 3 TV's in my house.

I've just bought a new (4th) main TV and that receives the HDMI output from the Sky Box.

The decryption of the HDMI in the TV leads to a delay in this main TV which causes an echo around the house. It's a fraction of a second of about 100 to 300ms. The analogue signal getting to the 3 peripheral TV's first!

I imagine that I can put a simple resistance/capacitance circuit in the RF2 output, inline, but don't know quite where to start looking for resources.

Would any one be prepared to guide me?

So I need to learn a bit about the AV RF signal and I'll need some maths to calculate component values?


0 Votes


December 7, 2018 08:45

Hi Phil,
I've written a long comment, but having problems posting it directly, so I'm putting it in a text file attached to this message. (I'll replace with a direct comment when the system lets me do so without error message.)

0 Votes

December 5, 2018 13:08

Hi Phil, I confess to no experience in this area and will be interested to hear any expert opinions, however from memory communications with geostationary satellites cause a delay of about 250mS. I mention this as coaxial delay line will need to be about 0.6 of this distance! So way out from any LC delay line possibility.
Regarding an RC delay you will probably require a gain element to restore the signal between delays, this will obviously introduce noise as the signal is restored, what is required is beyond my knowledge but you could start investigating this area.
My initial thought was a digital delay, but the buffer will have to be huge (and fast) and require video ADC's and DAC's which will be expensive.
The above is not very useful regarding a solution, but my thoughts are this is a non-trivial issue you are trying to resolve. I look forward to any other answers on this topic.

0 Votes

December 6, 2018 08:58

@Boss Thanks for your thoughts. I have read that 100's of meters of coax cable can introduce nanosec delays. I have also noted that commercially available RF delay lines provide very accurate delays of pico and nano sec ranges but they are used for much more demanding applications. I have to do much more reading and your suggestions are helpful. Ta.

December 7, 2018 08:45

@PhilButton Being fascinated by the issue I explored a bit more. Have you looked at the HDMI setting in that TV? I did a search "video signal delay HDMI" and one result mentions IFC (Intelligent Frame Creation) which can cause about 100mS delay. Could be worth exploring any options available in the settings for their effect. However another post stated "Most displays have a minimum of 1 frame and at 1080i that's 33ms. Add a video processor that's another frame or more.", so I'm not sure what if anything you will achieve in the TV settings. Just to make things worse.... there are many posts related to audio/video lag and it appears we are more sensitive to video lagging audio. This leads to one possible solution if you can possibly split the audio and video on your other TV's and delay the audio a little to see if you get something acceptable. I have no experience as to what the impact on the entertainment experience will be, but as a quick test turn down the local sound and listen to the HD TV sound (with every possible HDMI delay feature turned off). If you find anything usable, then we can discuss audio delay circuits if you can split the audio and video.