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Modifying Yagi Dipole
anon_private
Posts: 96 Forum Member
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I receive good reception from the local 'light' transmitter.
For geographical and atmospheric reasons, I receive poor reception for the 'main' transmitter, located about 90 degrees from the current direction of the aerial.
If I point the aerial towards the main transmitte, I receive no signal, so I must rely on reflected signals..
I was wondering if I connected a wire, say about 6 inches in length to the dipole, then this might increase the signal reception (strength and quality) from the main transmitter, while essentially leaving the local transmitters unaffected.
Before attempting this, I am looking for opinions. Is this idea likely to work, make little difference, or likely to make things worse?
If if it is likely to work, can someone advise regarding connection of the wire.
The aerial encloses the dipole in a plastic casing. I assume that this can be opened, would I simply be able to attach the wire, wound around the top of the dipole and pointing upwards. And perhaps another wire fixed similarly to the bottom of the dipole, pointing downwards?
Thanks
UK user
For geographical and atmospheric reasons, I receive poor reception for the 'main' transmitter, located about 90 degrees from the current direction of the aerial.
If I point the aerial towards the main transmitte, I receive no signal, so I must rely on reflected signals..
I was wondering if I connected a wire, say about 6 inches in length to the dipole, then this might increase the signal reception (strength and quality) from the main transmitter, while essentially leaving the local transmitters unaffected.
Before attempting this, I am looking for opinions. Is this idea likely to work, make little difference, or likely to make things worse?
If if it is likely to work, can someone advise regarding connection of the wire.
The aerial encloses the dipole in a plastic casing. I assume that this can be opened, would I simply be able to attach the wire, wound around the top of the dipole and pointing upwards. And perhaps another wire fixed similarly to the bottom of the dipole, pointing downwards?
Thanks
UK user
0
Comments
What two transmitters are you talking about? In general a main transmitter use horizontal polarisation and it's relays use vertical polarization. Plus they are very likely to be in different aerial groups.
So if you have a vertical aerial pointing to a relay transmitter and swivel it round to a horizontal main you will get a much reduced signal compared to turning the aerial horizontal as well. And if you are using a grouped aerial as well then the main transmitter could be out of band for the aerial reducing signal even more.
The best option is to get a decent aerial properly mounted and aligned on the main transmitter rather than try and bodge something that is unlikely to work.
My Grandparents live in Cirencester and used to be on the relay which is an A band, when they wanted to use Mendip they had to have a new aerial as Mendip is C/D.
Oh and While a C/D aerial will receive A band signals they will be weak, so a booster would be needed if you were to go down that route, using the band below would be less of an issue.
You'll stuff it up completely!
The dipole in a Yagi array has to be shorter than the reflector, always, otherwise the aerial will fire backwards.
Also the spacing of elements has to be in precise proportion to the length of the dipole.
http://www.changpuak.ch/electronics/yagi_uda_antenna.php
The aerial may already be a wideband version .
But the reality us a few dBs of lost gain on the antenna is insignificant in most cases as the power uplift at most main transmitter sites to overcome terrain impediments is considerable.
As much as 20dB ,certainly 10 dB .
What is relevent is how much the signal us being impeded by the terrain between the receive antenna and a main station in a area that has a relay.
The reason for the relay in the first place will be due to crap coverage on analogue due to a hill or other obstruction in the way.
Digital of course will propagate better ,due to the type of modulation and works in many areas were previously analogue wouldn't .
This is the reason why in my opinion our monopoly broadcaster only provided 3 multiplexes on most relays as the cost diffrence of providing 6 muxes compared 3 on relays is chicken shit and less ,so most viewers would eventually have a new antenna installed on the main transmitter .
http://www.aerialsandtv.com
I will not be trying the modification.
Both the main transmitter and the 'light' transmitter are vertically polarised as is my aerial. I believe that my aerial is wideband.
The relay was established because people in my vicinity could not receive the signals from the main transmitter - due to the geography.
When the atmospheric conditions allow I get strong but poor quality digital signals from the main transmitter, which I assume are reflected signals because the main transmitter points towards the back or side of my aerial. On other days, I receive no signal from the main transmitter. I believe that I have optimised the position of my aerial so that I get good quality all the time from the 'light' transmitter and some signals form the main transmitter (atmosphere permitting).
My aim was to try and boost the reflected signals
Best wishes
Ps.
'light' = freeview light.
main = all multiplexes.
In aerial terms, what does Antiference mean?
Just point the antenna to the main transmitter .
This will lift the signal by about 100 times from the main transmitter
As well as this, having a good aerial up on the rooftop would improve your chances of getting a good signal. I have a recollection that you are using an aerial in the loft, something which is fraught with potential problems.
By the way, Antiference is just the name of a manufacturer. The word has no technical significance.
Which transmitters are you getting?, it's unusual for a main transmitter to be vertical.
Edit: Yes, checking my list, I think they are the only ones in the eastern part of the Meridian area, though they are all fairly low power for main transmitters.
Hastings PSB 1kW, COM 500W
Whitehawk Hill and Tunbridge Wells both 4kW
Problem is even with digital switchover, many relay masts are still needed due to poor or variable reception from a main mast. I live in one such area - only last week end one lady in the older age group was telling me how many of her freeview chs were troublesome and had been even after digital switchover. She has a large aerial on a high pole, and to try and resolve the random picture break up, several local aerial suppliers have sold her different signal amplifiers, but none of them have cured the problem. She asked my advice, and I recommended she change the aerial for a smaller Grouped one and pointing at the relay.....I said she would lose the troublesome chs altogether, but as these were troublesome anyway it wouldn't be any big loss.
Part of the issue with marginal or variable reception is that the aerial company can come on a day when the signal is stable, fit a new signal amp, leave, everything working. Then 2 days later the problem comes back.
See my first post:
'If I point the aerial towards the main transmitter, I receive no signal, so I must rely on reflected signals'.
'As well as this, having a good aerial up on the rooftop would improve your chances of getting a good signal. I have a recollection that you are using an aerial in the loft, something which is fraught with potential problems.'
Not an option
At DSO then I'm surprised that they didn't start shutting down some redundant relays which surely would free up some frequencies for the other relays to have 6 MUXs?
If the aerial is in the loft then the "correct" direction for the aerial might not be what you think it is. It can be a large dollop of trial and error aligning a loft aerial properly and you might find that pointing the aerial in some random direction other than the direct route to the transmitter pulls in a good signal. Equally you might find that no direction works.
However the fact you get some sniff of a signal off the main with the aerial pointing at the relay does suggest there could be a signal there. Just hunting the beastie down might take some doing.
Yes.
I tried positioning the aerial in all manner of directions and orientations.
I believe that I have the best compromise.
I get excellent reception form a relay, and on 'good days' satisfactory reception (poor quality) from the main transmitter and on all multiplexes. But on 'bad days' I see nothing from the main transmitter.
I think this is the best that I can hope for.
I even considered the possibility of reflecting signals on to the aerial. But, of course, I can't see them. So this idea is not feasible and would probably make things worse (destroy signals).
Thank you your interest.
Best wishes
Have you tried putting your postcode into the checker (selecting "detailed view") to see what standard of service should be available where you are, admittedly with a roof aerial?
That low a power they are probably still relays, just relays that carry more channels - not all relays are only Freeview Lite.
At DSO the number of 6 Mux site was limited by economics not spectrum...
There was also a policy that minimal home aerial changes .. To keep the cost to the country down ..... So it was seen to be cheaper to retain a relay...
At DSO 2 there may be some tidying up and relays removed as reception of main site DVB T2 can be measured not just predicted.
Ah I see so there could be a good number of relays disappearing, that can only be a good thing in the long run as transmission costs will drop especially for the BBC!
After all a relay existed in analogue days to serve down to ( often below) 100 houses
and that sort of number will still need to be served ...even if most of gage viewers are moved to receve from a mian site
So not a significant change in costs....
But more viewersof comm muxes
Or Freesat, no need for Sky.