diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Analog Line Level (http://www.diyaudio.com/forums/analog-line-level/)
-   -   Need help selecting FM aerial (http://www.diyaudio.com/forums/analog-line-level/76327-need-help-selecting-fm-aerial.html)

johnthedoctor 22nd March 2006 05:41 PM

Need help selecting FM aerial
 
I'm in Liverpool (England) and can't get a decent stereo signal from Radio 3 even with a Yagi type FM aerial here on the ground floor. The roof is scary high so a few fitters refused the job but a guy who will do it wanted to fit a circular 'universal' aerial and I've read that those are to be avoided. Am I right to refuse the circular aerial? He maintains it gives no problems once up high but if any kind of noise comes on top of my favourite stations I'm going to be well miffed.

All the BBC radio transmitters I can pick up are mixed polarisation, which aerial mounting would give me best/cleanest signal, horizontal or vertical?

Which cable should I ask for?

Thanks

Nigel Goodwin 22nd March 2006 05:50 PM

Re: Need help selecting FM aerial
 
Quote:

Originally posted by johnthedoctor
I'm in Liverpool (England) and can't get a decent stereo signal from Radio 3 even with a Yagi type FM aerial here on the ground floor. The roof is scary high so a few fitters refused the job but a guy who will do it wanted to fit a circular 'universal' aerial and I've read that those are to be avoided. Am I right to refuse the circular aerial? He maintains it gives no problems once up high but if any kind of noise comes on top of my favourite stations I'm going to be well miffed.




They are the lowest performing aerials you can get! - ONLY use them if you require an omnidirectional aerial. I use one, but I'm in a strong reception area, and can receive stations from all directions. When I lived at my parents (many years ago) I used an eight element yagi on a rotator - simply because my amateur band 2m ten element yagi was on it as well.

Quote:


All the BBC radio transmitters I can pick up are mixed polarisation, which aerial mounting would give me best/cleanest signal, horizontal or vertical?

FM stations usually use slant polarisation, which is in between horizontal and vertical, simply to provide the best signal for in car (vertical) and home (horizontal). Generally home FM aerials are horizontal - and the circular dipole is ONLY horizontal, you can fit yagis either way.

Quote:


Which cable should I ask for?
Just normal low-loss coax, TV coax will be fine, in older days you used to be able to buy cheaper radio coax - and for VHF TV as well, but UHF cable will give less loss, and is probably all that's available now?.

johnthedoctor 22nd March 2006 07:53 PM

Thanks for the quick reply.

My brother is in the top floor of a similar sized house near by, he's just confirmed that his FM reception is good and that's with a cheapo indoor ribbon Tee aerial. Might as well go for the circular in that case, the criticism I'd read of them failed to mention that they're OK for good reception areas.

EC8010 22nd March 2006 09:04 PM

I'd second the condemnation of circular aerials, but if you're in a good signal area, it shouldn't be a problem. The cable is important, though. The stuff most fitters use is low loss but has voids in the screen. If you've got a long cable run up to a high roof and an aerial that doesn't produce much signal, you could easily pick up more on the cable than from the aerial. The problem is that the aerial is tuned, whereas the cable isn't, so it can overload your tuner's front end with unwanted signals. RG6U (FEC 378-8106 20.30 for 100m) might do nicely - it has a foil shield as well as braid. I believe cables intended for satellite generally have foil as well as braid.

Nigel Goodwin 22nd March 2006 09:15 PM

Quote:

Originally posted by EC8010
I believe cables intended for satellite generally have foil as well as braid.
Yes they do!.

Dick West 22nd March 2006 09:42 PM

The multi-element Yagi is preferred even if you are in a strong signal area.

Are you in the city with lots of big buildings around? If so you will probably get multi-path distortion from the echoes or reflections of the original signal as it bounces of other large structure between you and the transmitter.

Multi-path distortion in TV is seen as ghosts and you can imagine how "ghosts" would sound. An FM signal will produce much clearer music if it does not have multi-path distortion. If possible, go for the Yagi and point it at the station desired to receive.

If you want to receive several different stations with transmitters located at different points of the compass then you might have to use the circular antenna and accept poorer sounding signal -- unless you use a rotor. You can't fool mother nature or physics.

johnthedoctor 23rd March 2006 05:16 AM

I've got a rotator (ebay bargain) and a cheapo Yagi in the loft. (Wierd house, every floor has loft space.)

The only reason I'd want the rotator on the roof is in case the aerial shifts in a gale although I'd probably check out just what I can get with a full rotation for novelty value.

How many elements on the Yagi is best for me? I'd guess it's a compromise between big for signal strength and small to survive the high winds.

Any opinions on horizontal/vertical mounting? With a rotator which would give the clearest signal? Or would it make no difference?

I can only afford to have this done the once and the advice is much appreciated.

Nigel Goodwin 23rd March 2006 09:58 AM

It won't really make any difference, but you should use horizontal polarisation for a home FM aerial.

As you are after Radio 3, have you considered a satellite dish?, there are many radio stations (including Radio 3) available from Astra 28.2E. These are also the highest quality radio transmissions available in the UK - don't bother with DAB, it's considerably lower quality than FM radio!.

Jack Crow 23rd March 2006 12:47 PM

Antenna stuff
 
Dr John,

I spent a wonderful two weeks in the UK during the summer of 05 while on R and R from the war. So please forgive me if I mess up a few tech details.

First guess is that your FM band is similar to the US. 88 to 108.

So far these guys are on the 'beam' about getting you some better rececption.

The problem is multipath.

If you drive in traffic, ever notice how the signal can fade in and out as you creep along at very low speed.

Your moving into and out of null areas. Where signals are in phase and out of phase. The deepest nulls are where the phase cancels exactly.

I see it more often in two way radio than entertainment because the power levels are lower.

What you need is a way to move your antenna away from the phase cancelation spots on the roof.

You won't know until you spend the money if your in one or not for your favorite channel. Then someone moves a fridge , changes the pattern of nulls and your back in cancel city again.

My idea is to have your service vendor install two antennas. First would be your H Beam, and then an omni on a 40 inch stand off away from the beams mounting pipe. As you rotate the beam, the other antenna can be pulled out of phase nulls and into clear air. It will have an 80 inch swing, more than a few 1/4 waves away from the nulls.

Your spending twice for antennas, and feed cables. Once for labor. A simple CATV A/B switch at your receiver can do wonders. It's a cheap form of diversity rececption.

Some two way people do this with V and H antennas or two V antennas at different heights or locations. So if the mobile transmitter is in a null for one, it's in the clear for the other.

Even some car receivers do this. A V antenna on the fender, and an H antenna on the back glass.

This may be the way to go if your labor is expensive and the parts are fairly cheap.

Most entertainment receivers are not the best RF wise. They are wide band, in wooden cases, and they will collect noise.

You might want to look at a pre amp band pass filter.

I had the Ramsey Electronics unit for a while and found it to be good. Since there will be expense in servicing it, put the amp down stairs rather than up stairs.

Also consider that modern electronics make a lot of RF trash. Your signal might just be fine and the receiver is being creamed by a computer or some other digital gizmo.

Much luck
Later dude
Mike Chisena
TDY Camp Arifjan, Kuwait

johnthedoctor 23rd March 2006 02:33 PM

Nigel, I already knew that radio was available from sat dishes but assumed it was DAB quality so dismissed it.

I can get a good analogue radio signal from a satellite dish? I'm not so keen if it's digital and has to go through a DAC, the aerial is to get the full benefit of my AKAI tuner.

Jack, my tuner has 2 aerial inputs and it works out for itself which is the best signal to use. It also decides whether wide or narrow band, stereo blend etc.
Specs here:

http://www.fmtunerinfo.com/AT-93review.pdf

Reception is good here once you've the height so I probably don't need the 2nd aerial, tempting all the same. My brother gets a good signal from a £3 ribbon aerial by living on the top floor of a large house. The FM bands are similar, high 80's, low 90's for the main stations.


All times are GMT. The time now is 08:15 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2