UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > General Vintage Technology Discussions

Notices

General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc.

Reply
 
Thread Tools
Old 9th Jul 2020, 6:27 am   #41
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 15,288
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.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 9th Jul 2020, 6:46 am   #42
arjoll
Nonode
 
arjoll's Avatar
 
Join Date: May 2006
Location: Invercargill, New Zealand
Posts: 2,843
Default Re: FM signal boosting

Quote:
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.
Attached Thumbnails
Click image for larger version

Name:	WP_20130725_005.jpg
Views:	38
Size:	76.3 KB
ID:	210612  
arjoll is offline   Reply With Quote
Old 9th Jul 2020, 8:43 am   #43
SeanStevens
Heptode
 
SeanStevens's Avatar
 
Join Date: Sep 2009
Location: Bath, Somerset, UK.
Posts: 877
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 . . .

SEAN
__________________
There are only 10 types of people, those who understand the binary system, and those who don't.
SeanStevens is offline   Reply With Quote
Old 9th Jul 2020, 9:02 am   #44
Ted Kendall
Nonode
 
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 2,294
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.
Ted Kendall is offline   Reply With Quote
Old 9th Jul 2020, 9:09 am   #45
Nuvistor
Dekatron
 
Nuvistor's Avatar
 
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 8,010
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.
__________________
Frank

Last edited by Nuvistor; 9th Jul 2020 at 9:12 am. Reason: Info about stereo reception.
Nuvistor is offline   Reply With Quote
Old 9th Jul 2020, 10:06 am   #46
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 20,312
Default Re: FM signal boosting

Quote:
Originally Posted by arjoll View Post
Quote:
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.
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.
paulsherwin is offline   Reply With Quote
Old 9th Jul 2020, 10:20 am   #47
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 15,288
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.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 9th Jul 2020, 5:18 pm   #48
Jonster
Heptode
 
Join Date: Apr 2008
Location: Eastbourne, East Sussex, UK.
Posts: 594
Default Re: FM signal boosting

Quote:
Originally Posted by arjoll View Post
Quote:
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.
Jonster is offline   Reply With Quote
Old 9th Jul 2020, 10:11 pm   #49
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 15,288
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.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 10th Jul 2020, 7:13 pm   #50
Jon_G4MDC
Octode
 
Jon_G4MDC's Avatar
 
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 1,036
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.

Last edited by Jon_G4MDC; 10th Jul 2020 at 7:22 pm.
Jon_G4MDC is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 2:31 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.