Old Rig

THE GOVERNOR · Post by **THE GOVERNOR** » Thu Jan 17, 2019 9:47 pm

20190117_213433.jpg

I wonder who made this

teckniqs · Post by **teckniqs** » Fri Jan 18, 2019 10:32 am

^^ With equipment like that, it's no surprise to see articles like this....

https://www.gazette-news.co.uk/news/551 ... air-alert/

nrgkits.nz · Post by **nrgkits.nz** » Fri Jan 18, 2019 7:53 pm

They’ve soldered it together straight on top of copper clad, which is ok but it looks quite messy giving the impression that it won’t work properly. However as long as the design is correct, and they’ve followed all the standard rules for RF then there shouldn’t be any problems. I solder my designs straight onto copper clad like that for testing purposes as it’s the easiest and cheapest way to get a good ground plane without having to spend extra time etching or money on prototype boards.

Albert H · Post by **Albert H** » Sat Jan 19, 2019 5:07 am

Looking at the PA end of that board, there's no proper lowpass filter. There's also no screening between stages - not good with the kind of gain that the "engineer" is trying to get from his critically tuned stages! The transmitter itself is using a free-running oscillator - no PLL here - so it will drift and be temperature sensitive. The receiver at the left end of the box is a pretty nasty, VFO-tuned Band I job. It will suffer from de-sensing problems because of the unscreened proximity of the PA stage.

This is nearly as bad as the "frying pan" rigs that were around in Birmingham a few years ago. Some "engineer" didn't want to spend out on heatsinks, so bolted his PAs to cheap frying pans! Those rigs looked even worse than this one.

One of the "arts" of good RF electronic construction is to keep all component leads as short as possible (every piece of wire will exhibit both inductance and capacitance to ground and to other nearby components). It's also quite important to be neat too.

It's not really possible to build a frequency-stable rig without the use of a PLL. The Phase-Locked Loop compares the transmitter frequency with a very stable reference (usually a crystal). The PLL continually re-tunes the rig to keep it in exactly the right place on the dial.

It's also essential to have a lowpass filter on the output of the rig, to prevent harmonics being radiated. This filter should be separated by metal screening from the rest of the PA.

Modern designs tend to use broadband amplifier stages, so that adjustments aren't necessary and one significant point of failure (the trimmer capacitors) can be eliminated from the design. My latest design uses just four on-board preset resistor adjustments - modulation level, power level, output FET bias and SWR trip point. Frequency is set by four screwdriver-adjusted rotary switches and once they're set, and the four pots tweaked, it never requires further adjustment. The rig includes thermal protection, and the Radiotext content of the RDS signal can be configured to broadcast error messages (like SWR and overheat warnings).

The funny thing is that a properly constructed rig with all the right parts doesn't cost much more to build that that heap at the top of this thread!

nrgkits.nz · Post by **nrgkits.nz** » Sat Jan 19, 2019 7:07 am

Albert H wrote: ↑Sat Jan 19, 2019 5:07 am This is nearly as bad as the "frying pan" rigs that were around in Birmingham a few years ago. Some "engineer" didn't want to spend out on heatsinks, so bolted his PAs to cheap frying pans! Those rigs looked even worse than this one.

You could probably fry bacon and eggs while the rig is running!

THE GOVERNOR · Post by **THE GOVERNOR** » Sat Jan 19, 2019 8:54 am

I believe it's from the 90s, when I get a chance I plug it in and see what it does, it looks like the PLL is wrapped up in tin foil. The builder is still about

teckniqs · Post by **teckniqs** » Sat Jan 19, 2019 3:22 pm

Be insteresting to see more pictures of the exciter and the receiver.

MC Spanner · Post by **MC Spanner** » Sun Jan 20, 2019 5:16 pm

It looks to me like the engineer has a degree of understanding in what he's doing but as Albert says he's made some negligent errors which have got to be through laziness or cost cutting!! No it wasn't me!!!

MC Spanner · Post by **MC Spanner** » Sun Jan 20, 2019 5:21 pm

I loved the saucepan rigs, they were a classic. I don't know about Birmingham but there was a guy doing this in the early 90s in London. The rigs were built on half aluminium frames upside down with the PA stud through the bottom of the box and the bottom of a saucepan. The transistor nut held the whole thing together. The rigs typically went outside on the roof of the block and when it rained, you'd get extra heatsinking capability when the pans would fill up! I don't think the guy's mum was too pleased when she found out he'd nicked all her saucepans though!

Albert H · Post by **Albert H** » Mon Jan 21, 2019 1:29 am

I admit to building a pretty powerful rig without a heatsink, because I'd run out of them! We needed to get a station back on in a hurry, so went up the block (in Shepherd's Bush) with a drill and self-tapping screws. We bolted the rig to the underside of the cold water tank, and sealed each screw with Araldite Rapid. We fired it all up and we had a whacking great signal into most of London and the link was coming in nicely. The rig remained nicely cold!

It stayed there for about three months - used every weekend and some midweek nights. Of course, eventually Gotts and his pals turned up to remove it. He just unscrewed the whole thing from the bottom of the tank.....

.... and flooded the top three floors of the block!

It was probably the most effective heatsinking I ever used!

mixfm · Post by **mixfm** » Mon Jan 21, 2019 3:22 pm

seen a few of these rigs in birmingham. on well known stations. also i remember seeing a news report on itv 1 or central news about causing music on birmingham airport planes. lol. i know one of the builders was mark s. he had a bit of an idea how 2 build transmitters vfo jobs, with the swann sauspan heatsinks, no big fans to cool them, ive searched the net for the news clip. no joy. lol...

trancetechnic · Post by **trancetechnic** » Mon Jan 21, 2019 5:54 pm

Better using one of these!.

pirateaddict · Post by **pirateaddict** » Mon Jan 21, 2019 8:19 pm

Now that looks clean.. Are they any good and how much they go for. What's the output power?

nrgkits.nz · Post by **nrgkits.nz** » Mon Jan 21, 2019 8:44 pm

It looks like one of the old 1980’s transistors that Hollings uses and needs about 8watts of drive for 30watt out. I would be going for something using the latest LDMOS technology - it’s so much more efficient and easy to get 300w with just 1watt of input

trancetechnic · Post by **trancetechnic** » Mon Jan 21, 2019 10:32 pm

pirateaddict wrote: ↑Mon Jan 21, 2019 8:19 pm Now that looks clean.. Are they any good and how much they go for. What's the output power?

Late 90's Veronica PLL 30 Watt TX. The transmitter cost me £300.

wazza · Post by **wazza** » Tue Jan 22, 2019 8:55 pm

mixfm wrote: ↑Mon Jan 21, 2019 3:22 pm seen a few of these rigs in birmingham. on well known stations. also i remember seeing a news report on itv 1 or central news about causing music on birmingham airport planes. lol. i know one of the builders was mark s. he had a bit of an idea how 2 build transmitters vfo jobs, with the swann sauspan heatsinks, no big fans to cool them, ive searched the net for the news clip. no joy. lol...

Was that Silk City who caused problems with air traffic control? I have a feeling it was them. I remember back in their early days when they were up at the top end of the dial they used to drift all over the place...

mixfm · Post by **mixfm** » Wed Jan 23, 2019 7:24 pm

it was premiair, from a block in highgate. offcom came out in force, to remove the rig, it put every station on top for a few days.... memories,

wazza · Post by **wazza** » Thu Jan 24, 2019 8:56 pm

Oh yeah I remember them, I think there were a couple of stations with that name, or maybe just different frequencies for the same station. Something to do with chicken george?

Live2SX · Post by **Live2SX** » Fri Jan 25, 2019 6:34 pm

LOL that rigs a heep of shit Bruv

MC Spanner · Post by **MC Spanner** » Fri Jan 25, 2019 10:51 pm

Live2SX wrote: ↑Fri Jan 25, 2019 6:34 pmLOL that rigs a heep of shit Bruv

Which one, I like both!

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