Making a DIY 405 TV transmitter. - UK Vintage Radio Repair and Restoration Discussion Forum

YC-156 · 18th Apr 2006, 10:09 pm

Hi folks,

Something just occured to me, given all the recent activity with 405 line TV.

I believe I read somewhere about efforts to 'resurrect' 405 line TV in the UK, possibly on one of the old TV frequencies, though I am unable to judge if this is a viable idea.

However an alternative might be of interest. I hope it isn't too obvious or has been debated to death before, but here goes: If people really want their own on-the-air transmitter, then it is quite possible for the advanced DIY radio amateur to make and run one. The 23cm (1240-1300MHz

) amateur band is sufficiently wide and the power level allowed should also suffice. The power limit here in Denmark is 1KW (PEP).

Before people dismiss the idea out of hand, it should be mentioned that commercial kits for low power transmitters and high performance down converters are readily available, and it looks like the ATV (amateur TV) is alive and well in the UK.

Here in Denmark we have guidelines for what one is allowed to transmit on the amateur frequencies re. programming. However getting a waiver on those for a special event station might be easier to obtain, compared to a commercial transmit licence for below 100MHz.

Of course getting from low- to high power at those frequencies is less than trivial, but the Earth-Moon-Earth (EME) radio amateurs have shown that it can be done 'on the kitchen table'. Then it is 'just' a matter of building the final amp for true 24/7 Continuous Commercial Service (CCS).

Now where did that spare YL1055 go...

Best regards

Frank N.

ppppenguin · 18th Apr 2006, 10:20 pm

For many years amateur TV on 405 was transmitted in the UK on the 70cm band. I think that the 70cm band has now been squeezed to the point where full bandwidth ATV is all but impossible. This makes 23cm the lowest practical band.

If we wanted to consider this seriously then we ought to be talking to the BATC where there is much expertise.

http://www.batc.org.uk

Kat Manton · 19th Apr 2006, 1:52 am

Hi,

I think I might just have a good enough reason to get my licence back; I let it lapse a while ago when I got involved in other activities.

Regards, Kat - G6DCF

Sean Williams · 19th Apr 2006, 9:01 am

Certainly far easier to achieve this than try for 45 Mhz!

I already have roughly 200w on 1296Mhz - the PA will easily remodel for the ATV segment - the UK limit is 400w PEP to the antenna, welll unless you have a special permit, but I do not think one will be issued for ATV......

As Frank mentions, down converters are no problem, however, I am unsure how a VSB transmission would be recieved in the UK amateur fraternity.....

A bit of fun trying!

Cheers
Sean

YC-156 · 19th Apr 2006, 9:36 am

Quote:

Originally Posted by m1ecy

I already have roughly 200w on 1296Mhz - the PA will easily remodel for the ATV segment...

Hi Sean,

But will it have the bandwidth? You will need something like 6-8MHz of bandwidth at around 1250MHz. My experiences with home made 23cm cavity amps goes back a few years. However I seem to recall that their bandwidth quite frequently was amazingly small, this due to the high loaded Q dictated by valve parameters.

Best regards

Frank N.

Jim - G4MEZ · 19th Apr 2006, 4:52 pm

A brilliant idea!

It may well mean there'll be something worth watching on TV again

I cannot see the amatuer fraternity being too upset about VSB transmissions, after all it's totally in the spirit of experimantal amatuer radio, or it was 15 or so years ago before I went QRT and let my licence lapse but maybe things have changed a bit these days.

This is just the kind of stimulus I need to resurrect my licence and get active again..

How about some 405 colour experiments too or is that a bit too ambitious?

Kat Manton · 19th Apr 2006, 5:06 pm

Hi Jim,

Quote:

Originally Posted by G4MEZ

How about some 405 colour experiments too or is that a bit too ambitious?

Funny you should mention that... I get 405-line RGB and seperate syncs out of my PC system; it's already colour though at present I'm adding syncs to a weighted sum of R, G and B to get composite monochrome... I was fascinated to discover that colour was tried with 405-line experimentally. I feel inclined to repeat the experiments...

Regards, Kat

PWH · 19th Apr 2006, 7:13 pm

I used to run a video recorder with an aerial connected to the RF modulator. That gave me an 'instant TV station' either playing tapes or a camera & mic in the inputs. A mate & I use to have a point to point link.

A bit illegal but no more so that the AM transmitters we used for rebroadcasting FM. & If you don't cause interference, who will know?

The beauty of this was you did not have to tweak the receivers!! It is surprising how far the signal will go too!

18th Apr 2006, 10:09 pm	#1
YC-156 Retired Dormant Member Join Date: May 2005 Location: Aarhus, Denmark Posts: 281	Making a DIY 405 TV transmitter. Hi folks, Something just occured to me, given all the recent activity with 405 line TV. I believe I read somewhere about efforts to 'resurrect' 405 line TV in the UK, possibly on one of the old TV frequencies, though I am unable to judge if this is a viable idea. However an alternative might be of interest. I hope it isn't too obvious or has been debated to death before, but here goes: If people really want their own on-the-air transmitter, then it is quite possible for the advanced DIY radio amateur to make and run one. The 23cm (1240-1300MHz ) amateur band is sufficiently wide and the power level allowed should also suffice. The power limit here in Denmark is 1KW (PEP). Before people dismiss the idea out of hand, it should be mentioned that commercial kits for low power transmitters and high performance down converters are readily available, and it looks like the ATV (amateur TV) is alive and well in the UK. Here in Denmark we have guidelines for what one is allowed to transmit on the amateur frequencies re. programming. However getting a waiver on those for a special event station might be easier to obtain, compared to a commercial transmit licence for below 100MHz. Of course getting from low- to high power at those frequencies is less than trivial, but the Earth-Moon-Earth (EME) radio amateurs have shown that it can be done 'on the kitchen table'. Then it is 'just' a matter of building the final amp for true 24/7 Continuous Commercial Service (CCS). Now where did that spare YL1055 go... Best regards Frank N.

18th Apr 2006, 10:20 pm	#2
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Making a DIY 405 TV transmitter. For many years amateur TV on 405 was transmitted in the UK on the 70cm band. I think that the 70cm band has now been squeezed to the point where full bandwidth ATV is all but impossible. This makes 23cm the lowest practical band. If we wanted to consider this seriously then we ought to be talking to the BATC where there is much expertise. http://www.batc.org.uk

19th Apr 2006, 1:52 am	#3
Kat Manton Retired Dormant Member Join Date: Jul 2005 Location: West Yorkshire, UK. Posts: 1,700	Re: Making a DIY 405 TV transmitter. Hi, I think I might just have a good enough reason to get my licence back; I let it lapse a while ago when I got involved in other activities. Regards, Kat - G6DCF

19th Apr 2006, 9:01 am	#4
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: Making a DIY 405 TV transmitter. Certainly far easier to achieve this than try for 45 Mhz! I already have roughly 200w on 1296Mhz - the PA will easily remodel for the ATV segment - the UK limit is 400w PEP to the antenna, welll unless you have a special permit, but I do not think one will be issued for ATV...... As Frank mentions, down converters are no problem, however, I am unsure how a VSB transmission would be recieved in the UK amateur fraternity..... A bit of fun trying! Cheers Sean __________________ Engineers make things work and have spare bits when finished

19th Apr 2006, 4:52 pm	#6
Jim - G4MEZ Tetrode Join Date: Feb 2006 Location: Newport Pagnell, Buckinghamshire, UK. Posts: 95	Re: Making a DIY 405 TV transmitter. A brilliant idea! It may well mean there'll be something worth watching on TV again I cannot see the amatuer fraternity being too upset about VSB transmissions, after all it's totally in the spirit of experimantal amatuer radio, or it was 15 or so years ago before I went QRT and let my licence lapse but maybe things have changed a bit these days. This is just the kind of stimulus I need to resurrect my licence and get active again.. How about some 405 colour experiments too or is that a bit too ambitious? __________________ Jim G4MEZ

19th Apr 2006, 7:13 pm	#8
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Making a DIY 405 TV transmitter. I used to run a video recorder with an aerial connected to the RF modulator. That gave me an 'instant TV station' either playing tapes or a camera & mic in the inputs. A mate & I use to have a point to point link. A bit illegal but no more so that the AM transmitters we used for rebroadcasting FM. & If you don't cause interference, who will know? The beauty of this was you did not have to tweak the receivers!! It is surprising how far the signal will go too!