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Old 9th Jul 2020, 6:27 am   #41
Radio Wrangler
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Default Re: FM signal boosting

Some UK outlying VHF/FM stations had a receiver with an antenna aimed at a main station. This was either used as the source for rebroadcast, or as a back-up if the minor station's audio feed went down.

I wonder what sorts of distances were covered?

Of course, both antennae would be on tall masts, but the poor receiver would be very close to transmitters banging away in the same band.

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Old 9th Jul 2020, 6:46 am   #42
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Default Re: FM signal boosting

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Originally Posted by Radio Wrangler View Post
Of course, both antennae would be on tall masts, but the poor receiver would be very close to transmitters banging away in the same band.
It'd be a proper relay receiver. We use an Inovonics one to do linking between Gore and Mid Dome, but it's at an intermediate site with a view of both to save the cost of two STLs. Picks up Gore off-air, STL to Mid Dome (pic is with a temporary STL tx when our main RVR one died). Composite out, composite in to the STL so MPX and RDS are passed.

It's an oldie now, I see the current version is the 650 with more bells and whistles.

RVR used to do one as well, based on the same form factor as their RXRL-NV STL receivers, but it doesn't seem to be in their catalogue now.
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Old 9th Jul 2020, 8:43 am   #43
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Default Re: FM signal boosting

This is fascinating stuff! Mainly because of my late fathers love of classical music and R3.

He had a good enough everything (details are sketchy, but there must have been an FM antenna) to record especially interesting R3 content onto cassette and still be happy with the result.
We lived in Kent, near the top of a hill, so I guess strong signals were at hand - which from this post seems to be the best starting point.

I'm diametrically opposed here in BANES (BA1). I live in a bowl, with hills literally all around. I'd like to know where I'm actually getting a signal - it is probably bouncing off of seagulls!
I don't listen to R3 or classical music much - preferring to select the music I listen to and receive mainly talk radio (R4). This shows up interference excellently and my NAD 4020A is being fed mush from my room mounted di-pole. I've seen the stereo light go on once or twice - but that was tuning through the scale listening for something different (the Archers must have come on!).

My mind is racing (as usual) to a solution to this and the OP's issue.

If there is enough signal (enough being difficult to quantify) then there is not an issue, but when on the margins of decent reception, height seems to be important.
This height leads to long lengths of coaxial, which can negate the reasonable signal back down to marginal! I see an equation in there somewhere!
Please feel free to shoot this idea down - it no doubt has been done before, originality is difficult!

If you:
• Received the reasonable signal (at height)
• Rebroadcast it at a different frequency (double it as a poor example)
• Then with a matching receiver capture it back in the house
• Halve the signal back to originality
• Put the signal into your receiver

you surely would have the best of both worlds. Modern surface mount components could have this done in the size of a box of household matches.....
It might seem overcomplicated, but the units could be calibrated to be matched, so barely any quality loss would be added to the mix.

Possible? Well my wireless headphones work up at the end of the garden, they are the same technology . . .

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Old 9th Jul 2020, 9:02 am   #44
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Default Re: FM signal boosting

In that case, why not just use a masthead amplifier? They say in (American) motor racing circles that there is no substitute for cubic inches - in stereo FM reception there is no substitute for uV/m.
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Old 9th Jul 2020, 9:09 am   #45
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Default Re: FM signal boosting

A low NF mast head preamp would probably be a lot simpler solution to overcome feeder losses.
Crossed post with Ted but same thoughts.

Edit. There are always going to be areas where good stereo is difficult but mono requires a lot less signal, I would rather listen to clean noise free mono than hissing distortion in stereo.
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Old 9th Jul 2020, 10:06 am   #46
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Default Re: FM signal boosting

Quote:
Originally Posted by arjoll View Post
Quote:
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Of course, both antennae would be on tall masts, but the poor receiver would be very close to transmitters banging away in the same band.
It'd be a proper relay receiver.
The BBC used modified Revox B261s for their emergency backup chain for about 20 years (David owns and has restored an ex BBC example). The hops were 40-60 miles, but were in mono and they had good aerials on tall masts. Nevertheless, the signal was pretty grim by the time it got to northern Scotland.

This was actually activated in anger for several hours about a decade ago when a combination of human error and aircon failure took down the standard Nicam distribution system, which is supposed to be multiply redundant.

I think they use satellite backup now.
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Old 9th Jul 2020, 10:20 am   #47
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Default Re: FM signal boosting

The mast-head preamp has to be worth a try.

Feeder cable loss before you get any amplification in has exactly the same effect as path loss. So 3dB cable loss is the same as living 41.4% further from the transmitter. If you then add a masthead preamp, you take out this much loss. If your preamp has a lower noise figure than the tuner (not usually very difficult) then you gain even more.

Unlike bigger, gainier antennae, the preamp doesn't take any significant space.

So the priority is to get the best antenna you can, pointed accurately or on a rotator, have it up outside in the clear with minimum cable length to a weather sealed preamp (possibly peaked for the stations you want) and then good quality cable to the tuner indoors.

Look for cable with a foil layer under the braid. Satellite TV grade.

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Old 9th Jul 2020, 5:18 pm   #48
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Default Re: FM signal boosting

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Originally Posted by arjoll View Post
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Originally Posted by paulsherwin View Post
75 miles is a very big distance for FM, even with a good external aerial and a big transmitter.
I've just done a quick calculation, that's 120km.
I've checked on a map and its not 75 miles/120km, its 40 miles/64km.
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Old 9th Jul 2020, 10:11 pm   #49
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Default Re: FM signal boosting

It's what lies in between that can be the make-or-break issue.

Where I live, some of the houses do not have a clear path to the nearest TV transmitter and therefore use a more distant one, without any problems. Along came channel 5 and their retuners. In these houses they swung the aerials round to the one they'd been told to use in that postcode. No signal. So they sent round an aerial fitter who tore down the perfectly fine antenna in bent pieces and fitted a broadband lower gain one. Still no signal, but with careful adjustment an unwatchable picture was achieved on the 3 higher power channels. They beggered off muttering about sending a specialist. Aye, right.

I sorted a couple of neighbours out. Straightening and welding back together the remains of the antennae which had been literally torn out. Then with the greatest precision, and photographs, I tore out the new antennae exactly as the old ones had been. I tried to get them out in as many pieces. It had been fitted by driving nails through some of the elements into the attic framing.

A quick bit of aiming, being able to see all signal strengths at once on the spectrum analyser, then tune the telly onto a sig gen and I could then do the bit of showmanship of plugging the antenna cable into the telly to have all five channels working with no further twiddling. They had offset the VCR reasonably well, but I provided a few SCART leads and showed people the difference in quality.

All because of someone's over simplification of a coverage area map. And it being blindly followed.

Grrr. One of my neighbours said if the channel 5 people ever came to get their aerial back, she would show him an entirely new way of carrying it back to his van.

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Old 10th Jul 2020, 7:13 pm   #50
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Default Re: FM signal boosting

I spent time this week in the middle of Dorset. In some idle hours I was doing some SDR experiments with GNU radio and Band 2 FM was the most convenient source of signals - with a helical whip indoors at ground level I didn't expect much.

All I could find were the BBC national stations. Hardly surprising except the frequencies matched the Wenvoe transmitter. Well that just couldn't be - there is steep rising ground in every direction except a gap to the South. The frequency groups of main stations do tend to be re-used on relays but none of the local Dorset ones matched.

The only station I could find that has the correct frequency group is Ivybridge but that is just outside Plymouth. It's a very long path 100km + to the SW but quite a bit is over the sea.

No sign at all of the intended relay for the area which is about 10km South through the gap in the hills. Strange stuff RF.

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Old 31st Mar 2021, 11:15 pm   #51
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Default FM signal strength

I have a Linn Kudos AM/FM tuner. This is fed from a four element yagi style external aerial mounted at the roof apex to the flank wall of my house. It’s aimed at Wrotham in Kent, I live in Tiptree, Essex.
I’m experiencing what I consider (and the signal strength on the Kudos bears out) a low signal strength signal. There is nothing of any consequence; buildings, trees, hills, etc in the immediate line of sight of the aerial.
The Kudos states that a signal strength of >70dBuV is required to achieve the best results. I’m getting 60dBuV, approx 12% down, give or take. What would be the best way of boosting this signal to the suggested level?
Any suggestions would be very welcome.
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Old 31st Mar 2021, 11:37 pm   #52
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Default Re: FM signal strength

That isn't a 12% change.
60 dBuV= 1.12 millivolts and
70 dBuv= 3.16 mV
It is impossible to answer your question (not knowing the receiver path, distance antenna height etc. etc. etc.) but, both levels are more than enough I reckon.
Don't take too much notice of some of those spec's you read.

Is the stereo fully quieting (no noticeable hiss)?
Is the antenna in good nick (Is it old)?
Is the Yagi pointing in the right direction?
Is the coax in good nick?
Is the plug fitted with a good crimp or solder joint?
Those are the first questions I would ask.
You could buy an line line amplifier and try that of course.

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Old 1st Apr 2021, 6:37 am   #53
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Default Re: FM signal strength

Hi cruisinradio, thank you for responding and correcting. Just showing my ignorance in all things dB. That still seems a big difference in what Linn specify wouldn’t you think?
To answer your questions though:
No, there is no noticeable hiss or distortion.
The Antenna is in good nick, it’s only four years old.
As far as I’m aware it is pointing in the right direction.
The cable has one join which is made with two F type plugs with a screw together connector. This was to replace a wall socket outlet that the aerial fitter installed. The plug to the tuner is a normal aluminium coax plug. Neither soldered or crimped (although I always give the conductor tube a nip with side cutters to ensure a good contact with the cable).
Perhaps I am indulging in a degree of navel gazing (blame the Covid, everyone else does).
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Old 1st Apr 2021, 6:57 am   #54
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Default Re: FM signal strength

It could all simply be the Signal Strength meter is out of calibration for some reason of course.
If it sounds good and you can pick quite a few stations up, it must all be OK.
Perhaps someone here may know the unit you use and could advise?
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Old 1st Apr 2021, 8:55 am   #55
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Default Re: FM signal strength

i assume you are using a low loss 75 ohm coax - CT100 semi air spaced with copper foil
is what I would use.
Wrotham has the same power in both polarisations, so you could try mounting the
aerial vertically.
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Old 1st Apr 2021, 9:56 am   #56
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Default Re: FM signal strength

You are some way from Wrotham, so expecting a very strong signal even with a good aerial installation is asking a lot.
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Old 1st Apr 2021, 10:03 am   #57
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Default Re: FM signal strength

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You are some way from Wrotham, so expecting a very strong signal even with a good aerial installation is asking a lot.
Hmm, I was wondering about that. There is another transmitter out towards Bury St Edmunds but I don’t believe it’s of equal strength.

Yes, it is a 75ohm cable, one with the central core surrounded by a nylon honeycomb affair. I presume that is as suggested?
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Old 1st Apr 2021, 10:05 am   #58
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Default Re: FM signal strength

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It could all simply be the Signal Strength meter is out of calibration for some reason of course.
If it sounds good and you can pick quite a few stations up, it must all be OK.
Perhaps someone here may know the unit you use and could advise?
I don’t think it’s that. I have a second unit which reads the same give or take.
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Old 1st Apr 2021, 10:13 am   #59
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Default Re: FM signal strength

I have attached use guide as references for the thread-But when you had or installed the Yagi as a DIY was it set up with an Analyser or Signal strength meter etc that and reputable professional Aerial installation company would employ to set up? At the moment it kind of reads point and play but just thought to ask in the meantime. Even after 4years taking into account external weathering Pigeon wear and tear etc You may consider a complete recheck and possibly might be worth some basic PSU checks etc for caps etc that might be holding things up with ageing etc? Just general thoughts at this stage. I would ask if you may have contacted Linn Technical but I'm guessing that all goes back to dealers with service trained techs etc and there rates etc to test the equipment and your wallet!
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Old 1st Apr 2021, 10:39 am   #60
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Default Re: FM signal strength

Coaxial cable can become very lossy if moisture gets in. The low loss sort with air spaces in the polythene dielectric can take in water, there have even been cases where leaky connection boxes at the antenna end have collected rainwater and the coax has piped it into people's living rooms, prompting customer complaints that there is water coming out of their telly!

But the real situation making domestic coax lossy is if water gets into the space between the dielectric and the outer jacket, tarnishing the copper braid.

If any of the coax is able to flap around in the wind, the braid will eventually fray, leading to increased loss.

For this reason, it's usually good practice to renew the coax to outside antennae periodically. On the scale of these things, 10dB increase in loss is small compared to many cases. 10dB could also be accounted for quite easily by inaccurate aiming of a typical three-element antenna.

Also, signal strength indicators in FM tuners aren't precision measuring instruments, and considering the range they have to work over, being within 10dB of right would be unexpected, particularly towards the low end of their range. They're really just a relative indicator to help someone swinging an antenna around find the peak.

It's also possible that the antenna aim was done as a compromise to allow reception of stations from other transmitter sites. THe posh way out of this dilemma is to mount the antenna on a rotator and have remote control from a control box by the tuner.

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