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Re: 1967 onwards

Post by mictester on Mon Jul 28, 2014 10:17 pm

Admin wrote:I was educated on valves (tubes) in the late 60s and 70s.
My first radio transmitter was on 1.2MHz AM in 1967.
First social communications on EC in 1972.

Does this provoke any memories?



Regards Harry - SM0VPO
Harry

My first transmitter was a year later than you and was on about 1.4MHz AM.  It was a "top-band" AM circuit from Practical Wireless with an 807 final.  The first iteration was modulated using a borrowed guitar amplifier!  A mismatch (an aerial that blew down in a storm) and some ham-fisted tuning caused the output transformer of the Selmer guitar amplifier to smoke a lot!  The next version had its own modulator and a "Wotan" mod transformer.  It did about 12 Watts carrier and peaked at about 30 Watts (I like lots of positive-going mod - it sounds LOUD). 

This was the first transmitter to come to the attention of the authorities (the Dutch PTT in those days).  They turned up at my parent's house and asked to see me - the folks were entirely unaware of the pirate station that was broadcast from our spare bedroom every afternoon after school.  The men from the PTT were actually quite friendly and seemed to be impressed that a 10-year-old could build an AM transmitter (albeit one that drifted a bit!).  I ceased operations - with a promise to dismantle it - but the bug had bitten and within a week it was back on the air - on a new frequency.  It lasted about three months, then the PTT visited again and took the transmitter with them this time!

The next transmitter was an 813-based monster that could be heard all over the Benelux.  It was housed in a friend's garage down the street, and the "studio" was connected to it (initially) by about 500m of telephone cable.  The aerial was an inverted-V suspended from a housing block.  That was eventually taken by the authorities when we tried to operate into the evening, and the TVI locally was atrocious!

The last one - before "going legit" at the Big Broadcasting Concern - was two 813s, modulated by four KT88s, and fed processed audio from the studio over a UHF link.  We had reports from Poland and the USSR, from much of Europe, Tunisia and even Canada!  This was the first one to be crystal-controlled, and was loaded into a structure that was (almost) ¼-wave high - a local TV-receiving tower!  We had no TVI issues, and the transmitter was used intermittently - mostly during Public Holidays - for several years.

Professionally, I worked in broadcasting in various parts of the world for nearly 20 years, but I never had as much fun as those early schoolboy experiments!

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Re: 1967 onwards

Post by Admin on Thu Dec 13, 2012 9:53 pm

Hi Colin,
So you was a "Cosford Plumber"? Interesting! My first year at Locking didn't count - it was a No3 S-of-T.T. (medical school) 'cos they said I was colour blind "so why not be a medic?" (they were short of medics). Trouble with being a medic was I had to test aircrew colour perception and found I could read the Ishihara plates - not colour blind at all. My mother wrote to the camp commander and six months later I was back at Locking No1-S-of-T.T (radio school).

Did you know that dogs are colour blind? True - they cannot read the numbers on the colour perception plates ;-)

You certainly got that right, something has been lost over the years. I remember all the component you described, but the first transistors I ever used I sent off for ny mail order - "red spot" (audio) and "white spot" (RF).

They cost me 6d each and I spent my pocket money on those and the postal order from the post office to pay for them both. I made two transistors last me a couple of years by putting them into the electrical block connectors and attaching wires to the connector block so as not to fracture the leads.

I also took the paint off OC71s to make photo-transistors and when Mullard wised up to the trick they filled the envelope with a white opaque compount instead of the transluscent blue-grey stuff. But if you made a hole in a matchbox, fitted the transistor and taped it to the inside of the spin-drier, you could centrifuge the gel to the bottom of the envelope and expose the junction.

I stuffed a photo-transistor into a torce reflector and modulated a 6v 50mA fillament lamp (from my Philips EE set) in another reflector and made a light-beam telephone. It worked over 100 feet at night :-) I just loved playing with audio, and later RF + digital.

But if you have seen the homepages and read about me then you will have read of my exploits on EC and MW. I had loadsa fun. I once had a nice interview with my flight commander and showed him a new system on 27MHz AM where the transmitter was pulsed and sent digital data. The R/C receiver transmitted back in the time-frame created by the transmitter pulses, on the same frequency so I could get digital data from the model. I also transferred multi-channel audio data (0-1.5kHz) by the same technique to make a simultaneous 2-way radio. It used TTL.

My flight commander stated that there was no future in simultaneous multi-channel 2-way communications on one frequency, nor was there any reason for pulsed time-sharing / multiplexing due to the wide HF and VHF spectrum available. The RAF did not want to further develop the technique further. I was a lowly L-fitt(GC) and not supposed to invent things.

Later on I used a similar technique for a telephone exchange. A coaxial cable carried a pulse train at 100kHz so that there was an elongated start-pulse and 10 time-slots. The pulse train was generated by the user telephone instrument with the lowest ID number (0-9). Pull out the instrument and the next in sequence took over. I had these in the neighbours houses in Cambridge. Phone 2 put audio (am) into the timeslot of the phone to be called, which returned sliced audio in the originators timeslot. 0 and 1 was reserved for a link to a duplicate network so you could cascade several mini-exchanges. Dial 007 would connect you forward to phone 8 in network three. 007 would connect you backwatds to phone 8 in network 1. I tried to patent that but didn't have the money.

Most of this stuff was done with TTL, germanium and early silicon transistors. The displays were Minitron-3015 (7-segment fillament). Remember those?

When did TTL first appear? I remeber ordering the chips in 1973/4 when I was exiled to Masirah. I built a TTL frequency counter and learned about multiplexing to reduce component count (and current - the first counter took about 1.5A at 5v!!).

Oh dear, I seem to be rambling on. But you was into the larger tubes, I was into the battery tubes, like DF91 and then the more modern DF96 with much better performance.

Yes, I remember bias batteries very well. But now I have to get ready for bed. I have to be at work early tomorrow and Saturday. Hope this has provoked a few comments ;-)

BR Harry - SM0VPO

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Re: 1967 onwards

Post by electrosys on Wed Dec 12, 2012 7:13 pm

Ah - Locking - a mate of mine went there ... Ground Comms IIRC.

Myself - I went to Cosford to learn all about Airborne Radar - only to discover that it was mainly about plumbing ! (waveguides etc)

First played with octal-based valves in the 60's (6L6's 6V6's etc).
Beam tetrodes as big as jam jars, all that sort of stuff, great fun. Once made a push-pull amp using a pair of 807's - promptly blew the cone out of a 15" bass loudspeaker ...

I well remember that many capacitors in those days were coated in wax - bit of use and they became absolutely filthy. Not forgetting tag boards, and resistors made from carbon rods with thick wires wrapped around their ends - and a weird colour coding scheme with dots placed in the middle of 'em. Paper capacitors in tins, the size of fag packets, and bigger ...

Remember those salmon-pink hi-stability resistors ? And grid-leak batteries ?

First transistors I came across were Mullard OC71's and 72's - and found that if you scraped the paint off the ends they became photo-transistors - and at half the cost.

Much later on, I remember the first available 'computers' (if you can call them that) - one was called 'Scrumpi' - data had to be loaded in by discrete switches, one byte at a time, and couldn't be saved afterwards. "Them there 'computers' will never catch on", says I. Got that a little bit wrong ...

And then came along 8" floppy disks, the drives of which could be adjusted with a carpenter's screwdriver ... Followed shortly afterwards by CP/M and the Z80, and the early days of the computer hobbyist.

I think it was at about this time that the world of electronics started to change significantly - for it wasn't too long before SMD components and multi-layer PCBs came onto the scene ...

Progress ? Oh sure - but I rather think that something got lost along the way.

'best
Colin

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Re: 1967 onwards

Post by Admin on Tue Nov 27, 2012 7:00 pm

Yes, that supository, good buddy! Even if ya had your ears on the breakers were in the back of the box, even with a good twig like the Ringo Ranger.

I was in the RAF in 1970 when I lived in a barrack block top floor. So I slung a wire out of the window, across the lawn, to the next barrack block top-floor window. I ran my first ever HF contact.

On my Heathkit RG1 I heard a voice saying "Testing 123", so I netted my TX in to his carrier and replied "Testing 456". Naturally I got back a "Who dat dere?" and I was asked for my callsign. I didb't know where to look, so I just blurted out "It's EL84". Bet you cannot guess where I got that? That was on 6.5MHz AM.

After that weekend the guy in the room across the lawn went sick so I could not take the antenna down. My commanding officer was not so pleased when he inspected the barrack room on Monday morning.

I remember my first CB contact in 1981. The guy asked me for my "handle" so I said it's Harry. "No", he said "that's you personal. Ya gotta have a handle". So I replied, "Uh! er! that's Harry as well!".

Incidentally, in 1970 I was at RAF Locking technical training school and I was taking lesson during the day in such subjects as "AC theory". In the evening I was building my first HF transmitter. 3.5MHz VFO and doubler to 7MHz. Those were the days!!

Anyway, Maj-Lis is calling me. Gotta go to watch Äntligen Hemma on the telly. Our idol Martin Timell will be installing a heat exchanger in a typical Swedish country cottage, or is it a wood-shed? Then the skinny bird with the pony tail will be sticking silly sticky-backed plastic cutouts of cats on plantpots, or something equally silly.

Best regards from Harry - SM0VPO
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Re: 1967 onwards

Post by DragonForce on Tue Nov 27, 2012 9:11 am

lol no, not really - I may be an old man now, but I was only 10 years old in 1972. My first experience with a real radio transmitter was in 1981, with a CB radio. I had played around with several low power devices before then, but they had a range no further than I could lob a decent sized rock Smile
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1967 onwards

Post by Admin on Sun Nov 25, 2012 9:44 am

I was educated on valves (tubes) in the late 60s and 70s.
My forst radio transmitter was on 1.2MHz AM in 1967.
First social communications on EC in 1972.

Does this provoke any memories?



Regards Harry - SM0VPO
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Re: 1967 onwards

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