An experiment with the Aurora 30 & 32 Line standards converter.

[DoctorWho]

I decided on a quick experiment with the Aurora 30 & 32-Line standards converter with the converter running on a 32-line output.

I have a small 'Gizmo' AM transmitter which is available on-line, and which allows you to re-transmit pretty much anything on to a MW frequency of your choice. These are very useful to re-transmit VHF BBC stations back on to MW. If you use the aerial wire supplied with it then you remain within the limits set by law, and so it is completely legal. They do sell an aerial for longer distance transmitting, but its use is not legal in this country, and so I stuck with the basic wire aerial.

I fed the output from the converter in to a small pre-amp made from one channel of an old set of computer speakers, this then gave a little gain to amplify the signal before transmission.

I then connected the extension speaker output from a pre-war Ekco radio (connected to the secondary of the audio output transformer) to the Televisor input. When I made sure that the signal was properly tuned in I muted the speaker so that the only load on the output transformer was the Televisor. It would be essential to make sure that the Televisor was connected to the secondary and NOT the primary of an audio output transformer otherwise you'd have a fried Televisor!

Amazingly it worked, 32 line pictures via Medium Wave - and all legal!

It was not such good quality as direct connection to the converter and the lock was not very stable, but you could get something recognisable through.

I shall still be running the Televisors by direct connection to the converter as a rule, but it was, none the less, a fascinating experiment. The setting of the gain control on the input, and the radio's volume control on the output side of things needs quite fine adjustment.

Has anyone else tried anything quite so daft? I somehow doubt that anyone else locally were tuning in to watch 30 lines.

[ppppenguin]

Originally Posted by DoctorWho

It was not such good quality as direct connection to the converter and the lock was not very stable, but you could get something recognisable through.

It would be interesting to use a dual beam scope to monitor the vision waveform before the TX and after the RX. There will obviously be loss of the DC component and any frequency/phase distortions imposed by the TX/RX. Should be possible to track down the worst of the problems and get a much improved picture.

Originally Posted by DoctorWho

I then connected the extension speaker output from a pre-war Ekco radio (connected to the secondary of the audio output transformer) to the Televisor input.

I hope you kept a low-ish impedance load on the radio's output transformer. You can do damage if you don't and it won't help the frequency or phase response either.

[DoctorWho]

Good point about the load on the output transformer, the honest answer is no, I didn't. Should I have left the speaker connected and running instead of disconnecting the speech coil?

It would be good to be able to improve the TV signal to get it as good as the direct connection to the converter. This was only an experiement of course, but it would be interesting to see it transmitted and received without any real loss of quality.

[ppppenguin]

A dummy load would be more comfortable than the speaker. A resistor between 15 and 50 ohms should be fine.

[mickjjo]

I recall from reading books and magazines of the period when 30 line TV was current that broadly tuned T.R.F. receiver circuits with anode bend detectors with R/C coupled audio stages gave much better picture quality than the average superhet. .

Regards, Mick.

[DoctorWho]

Jeffrey - That's useful, thank you. If I set it all up to try again then I'll experiment along these lines.

Mick - That's interesting. I was using a Superhet, but I will try it another time with a TRF and see how it performs.

[Ghostuser]

Probably a TRF had wider bandwidth than a superhet, particularly if the reaction control was set fairly well back from the point of oscillation. My experience of leaky grid and anode bend detectors is that they distort like crazy on music signals, creating all sorts of intermodulation. Maybe you could lash a diode detector to a TRF or use a superhet with variable IF selectivity on the 'wide' setting.
Keep on playing with crazy ideas, its what fun is all about.
Cheers
Nigel

[DoctorWho]

Sounds like a good theory Nigel, I'll have to play about with this again and see how things improve with a TRF.

All the best,

Peter.

[HMV 1120]

I think I remember PM'ing you an age ago about a similar project. I used a very simple twin transister transmitter on 1590 khz and got a signal that barely managed to cover the house. For NBTV work the 'breadboard' set with red LED's and cardboard disks was connected via a disected headphone lead to a roberts portable, and a recognisable signal was had for about 30 feet.

Nothing impressive, but it was fun!

[DoctorWho]

Yes indeed Rob, it's real fun.

Have you played the 32 line footage I sent you?

[HMV 1120]

Sorry for the long delay, been offline for quite a while! I must say, I had forgotten about the CD, but in any case it failed to turn up?