The Horror-Mitters

This page commemorates (for me at least) a project I completed in 1978.
A working tuneable FM transmitter for the two meter amatuer using only found junk and components scavanged from old television sets
by VK3ZZC  Oct 2016

This transmitter project was started in the summer holidays of 1977 when I was still in high school  to use with my new Ham licence that
was issued in 1976.  It produced its first signal in March 1978  when the Melbourne VK3RML repeater's squelch opened  in response to me crossing two bits of wire together to activate the TX circuits.  To say that I was astonished as "my abomination"  came to life is not to understate the emotion.  It went through a number of revisions and was last used sometime in 1984 when I left home to establish my own life.  With this device I spoke to people that I would never otherwise have spoken to, and spoke to people that resulted in doors being opened ,  the consequence of that was the launch of my career in High Technology.  My late father kept this device for me, even though most of my stuff had been discarded, I think he appreciated the significance of this device to me.

There are no surviving schematics, the circuit is its own "self documenting" circuit.  Valve circuits  are simple and repetitive enough  to not really require a circuit, allthough now I wish I had made one. The circuit is remarkably advanced and very ambitious to the then 18 year old something me way back then.  The rationale for this transmitter was that back in 1978  I had the so called AOLCP licence which only permitted operation above 52Mhz, as I was one of the lesser men  who could not learn Morse Code ! I also had no money to purchase a ready made 2M rig,  back then they were expensive ! My only source of components back then was discarded valve television sets of which there was a steady supply on municipal hard rubbish collections .  The other source was the significant number of second hand electronic junk retailers  of which Melbourne had about five.  Even most junk transmitters were still out of reach to me financially at that time.

The images show  the 2nd version of the horror-mitters, the revision being required after one of the mains power transformers caught fire while I was on air. The circuit consists of a solid state vfo that tuned from 5 to 9 Mhz.  This was mixed with the output of a multiplier chain  that multiplied a random crystal  thought I had purchased for forty cents  to about 157Mhz.  This was mixed down to  144-148Mhz  in a balanced mixer using two sharp cutoff pentodes followed by two stages of amplification using originally a 12BY7 to drive an RCA  832 tube.  This tube was replaced with a pair of 2E26s.  The FM modulation was achieved by direct audio drive of a varicap diode  in the VFO.  There was no pre-emphasis, compression or clipping.  A  if strip from another discarded television set was used as my off-air monitor.  I measured the frequency of my VFO  using my prized ex-army C13 set. Thus , after doing bit of arithmetic  I could reliably put myself on chanel at 2 Meters using only my HF set as the main frequency reference.

Initial alignement and tuning was done with a long gone  grid dip oscillator  that had been callibrated with lecher lines !  Many other amatuers, wealthier than me,  came to visit with their digital frquency counters and were allways astonished  that with even this primitive setup  it was possible to be on frequency with free running oscillators  on 2 Meters.  My main problem was drift. At that age I did not yet understand  how to mitigate thermal drift or the need for regulated power supplys  for my vfo.  I had to use the "armstrong" method of frequency lock !  The other significant problem  was the lack of sheilding  in the main chassis.  My transmitter was only just barely stable as a result and a number of QSOs had to be terminated when others informed me that not only was  I triggering VK3RML  but Geelong and Ballarat and others all at the same time !  The other highlight was exhibiting my complete setup at an 1978 open day at Monash University in front of an incredulous public.  Golly, that was a long time ago.

The reciever part of the horror-mitters was somewhat remarkable in its own right.  The Army C13 wireless set that had served so well as a frequency reference  was used as the reciever,  The RX signal  was mixed down  with pre-drive transmitter  signal  to produce an IF  signal on the same chanel tuned on the C13.  Thus I had automatic off air monitoring and a fairly sensitive reciever as well.  The original down converter had used a rebiult televsion set  tuner  with a twin triode cascode preamp and a pentode mixer.   The C13 set had a phase demodulator  that was really too narrow for amatuer FM,  so I used AM slope detection most of the time, but could change to Phase Mod  when  the signal fm deviation was small.   It was a hard slog.  The pinacle for me was having a two way contact on the distant Ballarat repeater with this setup. That was rare DX , at least for me ! 


finally its the year 2016.  This object had served its creator with a dividend  that I am not capable of computing.  I removed a few souvenirs from the chassis, took these pictures and put it outside on a hard rubbish collection.  There was someone in my neibourhood  that scavanges electronic parts , just like I did 40 years ago. The chassis vanished in a few hours as I bade a fond farewell to the past and a prayer of thanks and praise.