History of early pirate transmitters

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Gigahertz
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History of early pirate transmitters

Post by Gigahertz » Tue Nov 23, 2021 9:57 pm

Hi fellow necks!
It’s good to see illegal stations are still battling on after decades for the fight to provide radio listeners a choice of different genres of music, program ideas and over the years how people have be initiative to stay on the air.

Its definitely apparent pirate radio has really changed the broadcast industry even though many would say it causes nothing but nuisance. It has opened the doors for many people and brought so much pleasure to others. Music and radio has definitely made a big impact in my life and even after all these years it still fascinates me, I recently came across something that spiked my interest to start this thread and hopefully its in the right place (admin please move if not) but hopefully will encourage others to share details of any history pieces they have tucked away gathering dust somewhere???
Last edited by Gigahertz on Tue Nov 23, 2021 10:02 pm, edited 1 time in total.

Gigahertz
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Re: History of early pirate transmitters

Post by Gigahertz » Tue Nov 23, 2021 9:58 pm

Below is transmitter I acquired off someone and they gave me this information about it, who bought it back in the mid 80’s. It’s one of the early phased lock loop designs as there weren’t many about back then as most were VFO’s. It originally came from a shop in Chelmsford and cost in the region of £200 back then, Approx 10watts when supplied with 11v – 14v not sure if it was a one off or who the builder was!

As you can see from the pictures, all built into a diecast box with stages separated with copper board. There is a printed board which is the PLL, unfortunately the IC’s have been coloured with black marker pen but been advised that the crystal on this board needed changing along with the adjustments on the slug of the exciter.
(Frez divided by 10.25 will give the crystal frequency required)

The exciter is made on double side copper clad board with the small can transistors being 4 x 2N2369A and the final MRF237 (delivers 600mW).

Pre-emphasis board, using what looks like TL0*10JG (* is either 8 or 9)

The amplifier stage is using a MRF314 and as mention produces about 10watts (brief look online shows 30watt device 30MHz – 200MHz at 28volts)

Shame it doesn’t have the diagrams as mentioned on the sheet!

Hopefully an interesting read/pictures for most and if anyone knows more about it please share and I can add some more history to it.

Gigahertz
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Re: History of early pirate transmitters

Post by Gigahertz » Tue Nov 23, 2021 10:00 pm

Main
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Gigahertz
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Re: History of early pirate transmitters

Post by Gigahertz » Tue Nov 23, 2021 10:01 pm

Inside
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Re: History of early pirate transmitters

Post by Gigahertz » Tue Nov 23, 2021 10:04 pm

Paper info
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Albert H
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Re: History of early pirate transmitters

Post by Albert H » Wed Nov 24, 2021 4:21 am

The PLL in that thing looks a bit like the early "rockbound" ones that I made - it used a Plessey SP8629 prescaler (/100), looking at the output frequency. That fed a 4024, dividing by 8, and the reference crystal was divided down in a 4060 (which included the crystal oscillator) to match the output of the divider chain. The phase comparator was a 4046, and there was a CA3130 op-amp used as the loop filter. Later versions used a dual bistable and a few NAND gates for the phase comparator, as this would also give a reliable lock detection as a bonus!
After lots of hassle getting crystals cut, I deided to move to a variable divider circuit, using the 4059 (which had just become available).

I used an SL560 as my oscillator and buffer. This was a little 8-pin VHF amplifier IC with both the base and the emitter of the first transistor available on pins (so a Colpitts oscillator was trivially easy). My VCO ran at either half or one quarter of the output frequency (according to the logic I was using), and when the 74F series of ICs became available, I could get rid of the prescaler.

I was an early adopter of the all-in-one PLL ICs, and made a board that used the venerable PLL02 (found in lots of CB rigs) for a while. I moved to the MC145170 as soon as it became available, and my first ever PIC project was to develop a way to load the PLL registers at power-up, using the 16C54.

I've got some photos somewhere....
"Why is my rig humming?"
"Because it doesn't know the words!"
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Gigahertz
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Re: History of early pirate transmitters

Post by Gigahertz » Wed Nov 24, 2021 11:08 am

Thanks for the information about the PLL very interesting!

Can you put a rough year when this was made?

Albert H
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Re: History of early pirate transmitters

Post by Albert H » Thu Nov 25, 2021 3:37 am

That one looks like it's probably from around '82. It's a bit of a blob-fest! I don't recognise the handiwork.
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teckniqs
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Re: History of early pirate transmitters

Post by teckniqs » Thu Nov 25, 2021 10:32 am

Albert H wrote: Thu Nov 25, 2021 3:37 am That one looks like it's probably from around '82. It's a bit of a blob-fest! I don't recognise the handiwork.
The MRF237 batchcode is quite hard to read but looks like that was manufactured in 1987. :tup

Gigahertz
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Re: History of early pirate transmitters

Post by Gigahertz » Thu Nov 25, 2021 1:41 pm

teckniqs wrote: Thu Nov 25, 2021 10:32 am
Albert H wrote: Thu Nov 25, 2021 3:37 am That one looks like it's probably from around '82. It's a bit of a blob-fest! I don't recognise the handiwork.
The MRF237 batchcode is quite hard to read but looks like that was manufactured in 1987. :tup
Thanks for that Teckniqs :tup

The 2N2369A are marked "8326" so assume 26th week of 1983, MRF237 marked 8748 (48th week 1987)
and MRF314 marked with "8604" (4th week of 1986)???

So roughly puts it where the guy said when he bought it. Was tempted to pull the boards to see if there's any writing or other markings, but to me it's part of radio history so leaving it be.

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Re: History of early pirate transmitters

Post by Albert H » Sat Dec 04, 2021 4:47 am

Here's a circuit that was frequently used in the late 70s onwards.....
Ancient Exciter.jpg
The buffer transformer was usually 12 turns of enamelled copper wire for the primary and 6 turns on the secondary wound on a ferrite bead. The oscillator components were chosen fro stability, and if built carefully, the rig would be stable (without a PLL) to about 10 kHz! The next stage after this board was a 2N4427 for a Watt out. We used to build these into small diecast boxes, with feedthroughs for the mod and the 12V supply, and a BNC for the RF out. The exciter box would often then be housed in offcuts of polystyrene ceiling tile to try to keep the temperature stable!

Pretty soon I added a PLL to this circuit, using an extra winding on the buffer coil to feed the divider chain. The original PLL used the Plessey prescaler and TTL logic.
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