What were the most commonly used IF frequencies for 405 TV?

[AdrianPH]

There is an ulterior motive for this question.

The old Ferguson I have uses 16 MHz for Vision and 19.5 MHz for sound, it is a 991T so must also cover the 99X series of the era, but what do other sets use?

My reason for asking is I need to build an RF section for vision and sound, and trying to decide if I stick to IF's in which case there is the chance of picking up a tuner when the shows start again next year?  Or building a RF deck at 41.5 -45 MHz.

Preference is to use IF frequencies, hence trying to ask what was the most popular, or I guess the most abundant still around to increase the chance of a tuner.

Cheers

Adrian

[Geordie McBoyne]

After 1955 the recommended IF frequencies were 34.65Mhz vision and 38.15Mhz sound. A few firms including Masteradio did continue to use 16.5 and 19.5Mhz. Post-war superhet TVs had intermediate frequencies determined on what what circuit designer thought was fit for at the time.

Geordie McBoyne.

[Murphyv310]

Hi Adrian.
There were a number of different IF frequencies used by different manufacturers. In the early days they were low as valves performed better at lower frequencies. I believe the EF50 was a changing point and post war IF frequencies went up into the 30mhz area. The advantage of a higher IF is bandwidth, lower frequency IF and it becomes harder to attain the required bandwidth so often another stage is needed too.
As yet we have no idea of the BHTV frequencies so for me I'd use 34.65 mhz vision and 38.15 mhz sound plus a tunable front end from most likely 46mhz to 66mhz, I belive the old Ch1 won't be used.

[Kalee20]

I've got an idea that one of the early Bush VHF radios used an IF of 19.5MHz. It starts to make a bit of sense now - maybe Bush already had 19.5MHz IFT's for its televisions, and just repurposed them for the new radio.

Though, it also seems rather unlikely at the same time...

[radioman]

Yes, the Bush VHF41 used an I.F. of 19.5MHz.

Andy

[AdrianPH]

OK thanks for the responses, I will have a go at the 34.65 MHz vision IF, in the hope of a later tuner.

Thanks for that information , it was confusing looking at service sheets around the 54/55 years, Ferguson, Bush and Pye all seemed to be the lower, with the TV22/24/34/36 sets, 991/992 series and VT4, but as you say Pye CTM21 and Murphy V310 in 57 were on the higher frequencies.

As to British Heritage TV, I have my doubts if it will ever get a licence to broadcast and if it does it it will be picked up in the Northwest.

Adrian

[Geordie McBoyne]

Earlier versions of the Pye V4 and VT4 had 16 and 19.5Mc/s IFs.
Later production VT4 and VT7 models have the BREMA intermediate frequencies of 34.65 and 38.15Mc/s.

Geordie McBoyne.

[Murphyv310]

As to British Heritage TV, I have my doubts if it will ever get a licence to broadcast and if it does it it will be picked up in the Northwest.

Adrian

I'm pretty sure that they wouldn't have spent countless hours and huge amounts of money on the transmitters, modulators, combiners and aerial if they hadn't got confirmation of licence conditions.
I'm sure if in the end it was rejected some other alternative would have to be thought out, a ship comes to mind

[AdrianPH]

It is the selling off of frequencies that is my main concern, after Ofcom realised the commercial trading value of the radio spectrum. Millions of pounds can change hands for swathes of frequencies.

As the frequencies can be turned in to revenue streams the cost of having 3 or 4 MHz of exclusive bandwidth must be astronomical. Band III went from TV to Private mobile radio, now to DAB.

Band I where BHTV seem to be going for to me is an unknown, there was Low Band PMR which was once the remit of many of the local authorities and utilities such as Water, Electricity etc going back years ago was in the 70 to 87 MHz area, and was generally phased out with licences gradually moving up the frequency band.

Do not get me wrong I would be very pleased to see 405 TV on air again, but it will only be as an oddity for many, and viewers would be the likes of us interested and dwindling collectors. Perhaps if it is done as a low power system just around London to start the system off.

What I could envisage on the back of BHTV is a internet streaming service of programs going to be displayed on Computer screens or to perhaps a 'Hedghog III' able to take the stream and push it out through the modulator to a 405 TV. With suitable compression such as H265 I would think the IP bandwidth would be reasonable compared even to the music streams we have today.

I like working with valves, I like making things with valves, but from some of my peers I get why, things advance just accept it move on, perhaps not all want to see the nostalgia of a bygone period.

Adrian

[Murphyv310]

Band 1 though is reserved in some parts for military use, although it's not used virtually at all. I did some research a few years ago and it was only for times of conflict. So it's doubtful it would be sold off.
The best man here to confirm about band 1 use is Panrock (Steve Ostler) who is also involved with BHTV.