Historic link frequencies

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Persona Non Grata
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Historic link frequencies

Post by Persona Non Grata » Mon Apr 22, 2024 8:53 pm

Anyone know the exact UHF (or Band 3 etc) link frequencies used by Irish pirates of old ?

Here's a few from the 1990's
174.6 Freedom 92.0
175.01 Jazz FM 89.8
426.85 Heartbeat FM 105.7
441 Pulse FM 99.4/103.2
490.1 (UHF Channel 23) Power FM 98.6
843.7 (UHF Channel 67) Anna Livia 103.8 (Legal)
844.7 (UHF Channel 67) Radio Limerick 95.0 (Legal)

In the 1980's Nova IIRC were up around 950 MHz but were asked (i.e. told) by the authorities to move down as they were about to start testing something called Eircell (mobile phone network) also there was a time around 1993 when Radio Dublin were plagued with breakthrough from a retail security companies two way radios on their link frequency during the daytime.

Anyone know of any others ?

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Re: Historic link frequencies

Post by Albert H » Mon Apr 22, 2024 9:23 pm

Back in the 80s - before DAB - we used Band III. It was largely empty from 175 MHz up to around 225 MHz. A favourite link frequency was 202.7 MHz - that's a 48 MHz crystal x 4 + 10.7 MHz! I also had lots of ~49 MHz radio control crystals which gave useful frequencies around 207 MHz. My receivers were (usually) a BF981 RF amp, followed by another BF981 as the mixer, feeding the 10.7 MHz IF into an "Ambit" IF board, which came as a kit for about £4.50 each if you bought a few of them. The crystal oscillator was a BSX20 Colpitts with a tuned circuit in the collector of the transistor doubling the crystal frequency, followed by another BSX20 doubling to the injection frequency. There was a further tuned circuit going into gate 2 of the mixer FET to eliminate image reception. The whole receiver went into a little tinplate box, and was happy enough in pretty close proximity to a couple of hundred Band II Watts!

My link transmitters were PLL jobs, and often included audio limiters and stereo coders in the same box. The power output of the link rig was usually a Watt or so, but on a couple of occasions, I used as much as 10 Watts.

Unfortunately, other rig builders started to use Band II for their links, and usually didn't bother with PLLs, so drifting link rigs could sometimes be a nuisance. By 1984, I'd started building only UHF links (usually around the bottom of the TV Band IV), using TV Yagis for the link aerials, and getting silly range out of just a few milliwatts!

I built a number of links for Irish stations in those days, and I'll see if I can find any records of the frequencies used.
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Re: Historic link frequencies

Post by radionortheast » Tue Apr 23, 2024 10:10 am

So what was with all the radio stations in churches over there in the past?, they would of been nice and high, they seem to like to do a similar thing in American, i've often seeing videos for church radio transmitters, guessing must be part 15

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Re: Historic link frequencies

Post by Persona Non Grata » Tue Apr 23, 2024 11:25 am

Think the previous comment was posted in the wrong thread but church FM transmitters in Ireland have not completely disappeared (although most have moved to 27 MHz) I recently attended a funeral in one which was using MY old frequency.

I haven't pirated in twenty years but still..........

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Re: Historic link frequencies

Post by radionortheast » Tue Apr 23, 2024 2:39 pm

Persona Non Grata wrote: Tue Apr 23, 2024 11:25 am Think the previous comment was posted in the wrong thread but church FM transmitters in Ireland have not completely disappeared (although most have moved to 27 MHz) I recently attended a funeral in one which was using MY old frequency.

I haven't pirated in twenty years but still..........
assuming that is an attempt to shut me down, not aware of any thread dedicated to churches, it was aimed at Albert he answers without been obtuse..seems to me to a lot of people on these forums get off on been rude, the same as when they use ban me from radiowaves just for the fact I was not in Ireland, able to receive some of the stations, I suppose trying to shut a person down and what they have to say as unimportant goes back a long way

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Re: Historic link frequencies

Post by Albert H » Wed Apr 24, 2024 12:58 am

I've been trying to find my notes on the link frequencies I used for Ireland. I still can't find those notebooks, but I did unearth the board layout (an acetate!) for my UHF PLL exciter. I sent quite a few of those to guys in Ireland. I also supplied the receivers, too.

One station in Ireland that I supplied link gear to were paranoid about their link being "overheard" on scanners. My solution was to put their audio on a subcarrier at 45 kHz, and fill the 20 Hz - 15 kHz part of their link carrier with white noise. Anyone with a scanner tuning through their link frequency might notice their "S"-Meter rise and fall as they tuned through it, but they wouldn't hear anything other than white noise!
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Re: Historic link frequencies

Post by Persona Non Grata » Wed Apr 24, 2024 1:21 pm

I used to try and listen on link frequencies wherever possible as they tended to have better audio.

The use of "covert" links like you describe was probably an anti-jamming measure as some stations experienced jamming/hijacking from RTE, rival stations or bored anoraks.

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Re: Historic link frequencies

Post by 87to108 » Thu Apr 25, 2024 1:46 pm

Albert H wrote: Wed Apr 24, 2024 12:58 am
One station in Ireland that I supplied link gear to were paranoid about their link being "overheard" on scanners. My solution was to put their audio on a subcarrier at 45 kHz, and fill the 20 Hz - 15 kHz part of their link carrier with white noise. Anyone with a scanner tuning through their link frequency might notice their "S"-Meter rise and fall as they tuned through it, but they wouldn't hear anything other than white noise!


The downside is that the link has to be significantly more powerful to achieve the same thing, as subcarrier(s) will of course be more noise prone than baseband 0-15kHz audio (filled with noise in this case).
Also the path is more critical , as multipath on the link would be more of a problem than usual. Multipath can cause crosstalk of the baseband audio (noise in this case) and subcarriers.

A more powerful link might increase the chances of affecting nearby TVs in the immediate vicinity (if linking on UHF)

what if the station is stereo?, do two separate links gets used for Left and Right, or yet another, higher and more noise prone subcarrier get used for L-R. a lot of extra complexity if stereo involved.


A casual scanner user would probably think nothing of picking up a link frequency, they are probably scanning in Narrow FM mode, a wide FM mode (for STL) will just be a distorted mess. + scanners are often prone at picking up 'images' of strong FM stations on other frequencies outside Band II anyway (especiallly common handheld ones, desktop ones would I'd expect have better performance in this regard).
Other people, who might be trying to find the studio of a station, would often have other intelligence about where it was located anyway

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Re: Historic link frequencies

Post by Albert H » Thu Apr 25, 2024 11:38 pm

You're partially right. Using the subcarrier audio system required about 4 dB more S/N ratio for the same quietening carrier. This can be achieved by increasing TX power or by making a better receiver.

The reasons given for the use of this system included trying to fool COMREG!
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Re: Historic link frequencies

Post by Persona Non Grata » Mon Jun 03, 2024 7:22 am

I'd imagine COMREG would have spectrum displays on their receieving gear so as they scanned the band they would be aware *something* was there and wouldn't be fooled by white noise even if they couldn't immediately discern actual audio.

But a lot could depend on timeframe. Back in the pre-COMREG days the old DoC investigation branch were poorly resourced and may only have had consumer level scanners and wotnot (some of them probably had amatuer radio licences) ?

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