Old Rigs

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Albert H
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Old Rigs

Post by Albert H » Fri Sep 01, 2017 1:12 am

Clearing out a box of old bits today and found this:
Old 8 Watt Exciter.jpg
This was 1982 vintage, but the ICs were put in later - as I remember, the original ICs were removed for use in something else!. The only bits missing from it were the three output filter coils and their associated capacitors, and the 4 MHz crystal that should be next to the 74HC4060. I fitted a crystal, and powered it up into a dummy load. It still worked OK and tuned up to give a reasonably clean 8½ Watts at 15V supply. I wound filter coils, installed them and their capacitors and screening between the filter coils . The cleanliness is surprising (2nd is -64dBc and there's no discernible 3rd), and the carrier is beautifully quiet.

You'll see just how many stages we used to build an exciter! This one starts at ½f which allows use of the 74HC4024 as a prescaler. We used to fit all the programming diodes then, when a board was needed, it was just a question of snipping the ones we didn't want, and tuning it up.

The PLL circuit was used later on with at-frequency exciters, just using a 74F160 as the prescaler, 74HC4040 for the programmable divider, 74HC4060 for the reference oscillator and divider, and the usual 4046 for the phase comparator. The exciter was radically simplified, with a dual-gate FET (BF961) for the VCO, pair of BFR96 as the driver stage, and a 2SC1971 giving about 6 Watts. The four-chip PLL was significantly cheaper than the PIC and PLL IC version that we used later. Again, all the programming diodes were fitted, and the tracks beneath the board were configured to allow solder bridges to select the ones used. There were just two small trimmers on the board. to tweak the output match at various frequencies. The whole populated board cost about £7 at the time, and many hundred of them saw use around the world. I'll see if I can find one of these for another photographic session!
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"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Analyser
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Re: Old Rigs

Post by Analyser » Fri Sep 01, 2017 8:36 am

Photos are always good Albert. Did you etch that board yourself?

MC Spanner
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Re: Old Rigs

Post by MC Spanner » Fri Sep 01, 2017 12:30 pm

Analyser wrote: Fri Sep 01, 2017 8:36 am Photos are always good Albert. Did you etch that board yourself?
Does it remind you of something?

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Analyser
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Re: Old Rigs

Post by Analyser » Fri Sep 01, 2017 7:09 pm

MC Spanner wrote: Fri Sep 01, 2017 12:30 pm
Analyser wrote: Fri Sep 01, 2017 8:36 am Photos are always good Albert. Did you etch that board yourself?
Does it remind you of something?
Well, it looks a little Moss-esque, but apart from that not really.

You?

Albert H
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Re: Old Rigs

Post by Albert H » Sat Sep 02, 2017 1:15 am

Analyser wrote: Fri Sep 01, 2017 8:36 am Photos are always good Albert. Did you etch that board yourself?
Yep. I've found a few etched, but not drilled boards this morning. They were photo etched on double-sided PCB material. The holes were drilled by hand, using a little electric drill with a 1mm bit, and holes that weren't to be connected to the groundplane were countersunk with a bigger diameter drill bit. The results were pretty good, but we soon got p*ssed off with all the hand drilling and countersinking (and the snapped 1mm drill bits!), so the next batches were made by a PCB company in Ealing in West London.

The first commercially made batch was for 40 boards, and we soon discovered that it was much more economical to go for batches of 100 or even 120. The slightly modified version of this board (that was current for about six years) included slots to take the screens between stages. Properly constructed and aligned, this exciter was superbly clean, and because the final transistor was under-run, it was practically burst-proof. The later version of the board also had a wire-ended fuse in the supply line, and a chunky protection diode across the 15V rail, since we got two of the first run back with fried semiconductors due to reversed supply! These became very popular in Europe - I remember a friend of mine built (I think) eight of them, fitted them into nice Eddystone diecast boxes and took them over to Berlin, where a station used them as small standalone rigs.

That sort of thing has been superseded by things like this:

Bugger! I was going to upload a photo of a (nearly) current 19" 3U 400W 100% redundant rig, but the "board attachment quota has been reached" according to the error message I just got.

Can the admins give us some more attachment space, please? I was going to provide some nice circuit diagrams, PCB layouts and construction instructions for a simple, cheap, clean and reliable 5W exciter.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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yellowbeard
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Re: Old Rigs

Post by yellowbeard » Sat Sep 02, 2017 6:14 am

An experiment: That worked. You can add files from an external host, photobucket, imgur etc. :tup
Image
Nasty huh? This belonged to a buddy back in the 80's, its biggest claim to fame is it is the medium wave transmitter that got radio nova back on the air after they were raided in 1983. From a 50Kw RCA rig to this...

sde-1104
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Re: Old Rigs

Post by sde-1104 » Sat Sep 02, 2017 8:23 am

Albert H wrote: Sat Sep 02, 2017 1:15 am
Analyser wrote: Fri Sep 01, 2017 8:36 am Photos are always good Albert. Did you etch that board yourself?
Yep. I've found a few etched, but not drilled boards this morning. They were photo etched on double-sided PCB material. The holes were drilled by hand, using a little electric drill with a 1mm bit, and holes that weren't to be connected to the groundplane were countersunk with a bigger diameter drill bit. The results were pretty good, but we soon got p*ssed off with all the hand drilling and countersinking (and the snapped 1mm drill bits!), so the next batches were made by a PCB company in Ealing in West London.

The first commercially made batch was for 40 boards, and we soon discovered that it was much more economical to go for batches of 100 or even 120. The slightly modified version of this board (that was current for about six years) included slots to take the screens between stages. Properly constructed and aligned, this exciter was superbly clean, and because the final transistor was under-run, it was practically burst-proof. The later version of the board also had a wire-ended fuse in the supply line, and a chunky protection diode across the 15V rail, since we got two of the first run back with fried semiconductors due to reversed supply! These became very popular in Europe - I remember a friend of mine built (I think) eight of them, fitted them into nice Eddystone diecast boxes and took them over to Berlin, where a station used them as small standalone rigs.

That sort of thing has been superseded by things like this:

Bugger! I was going to upload a photo of a (nearly) current 19" 3U 400W 100% redundant rig, but the "board attachment quota has been reached" according to the error message I just got.

Can the admins give us some more attachment space, please? I was going to provide some nice circuit diagrams, PCB layouts and construction instructions for a simple, cheap, clean and reliable 5W exciter.
Try it now :tup

MC Spanner
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Re: Old Rigs

Post by MC Spanner » Sat Sep 02, 2017 10:07 am

Analyser wrote: Fri Sep 01, 2017 7:09 pmYou?
No, I was just wondering why you asked, knowing you've seen a lot of these sorts of exciter. It looks like something I would have made in the early 90s! I was going to ask Albert if it was a nail varnish job like mine would have been but he answered it later.

MC Spanner
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Re: Old Rigs

Post by MC Spanner » Sat Sep 02, 2017 10:29 am

yellowbeard wrote: Sat Sep 02, 2017 6:14 amNasty huh? This belonged to a buddy back in the 80's, its biggest claim to fame is it is the medium wave transmitter that got radio nova back on the air after they were raided in 1983. From a 50Kw RCA rig to this...
I love it. That was a pretty common arrangement on MW back in the day using a pair of 813s, so 800W or 900W out I'd guess.

Albert H
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Re: Old Rigs

Post by Albert H » Sat Sep 02, 2017 3:00 pm

There was a very famous capacitor used by one of the Irish pirates back in those days - made out of a glass-topped coffee table! It was a huge compression trimmer and was part of the aerial matching circuit!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

Albert H
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Re: Old Rigs

Post by Albert H » Sat Sep 02, 2017 3:09 pm

A more recent rig:
2012-rig.jpg
The module cases were made for another radio company, but we found that they were ideal for our PA boards. The metalworking company were happy to enlarge their production run of all the sub-cases. The main box is just a standard 3U 19" rack case.

The power supply was a nightmare - we had a series of PSUs from companies like "Advance", and all of them failed in no time. One installation had to go ahead without a PSU, running from a couple of big truck batteries with a charger strapped across the one that wasn't being used. It automatically switched batteries over every few hours!

There are two bits missing - the front panel and the logic and switching module (that fitted behind the front panel) which monitored the operation of the box and switched to the reserve parts in the event of failure.
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"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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