UHF to VHF conversion

[timohaveri]

I have my very first vintage TV under restoration at the moment. It is presumably a 1959 model Luxor (Swedish). The problem is that it has only VHF channels and every VCR, digital converter, etc seems to have the RF output in the UHF band only. There are some commercially made converters available but the prices are a bit steep for me. I was wondering what you guys use? I found some simple VHF band TV transmitter plans in the Internet but being illegal I'm not too comfortable building one. But the idea seems to be just what I need (assuming I manage to get the TV fixed eventually). Could it be possible to modify such a transmitter to have a very low output and just connect it directly into the antenna terminals so that no signal is radiated into the air? Do you have any plans for building one?

Timo

[Steve_P]

Well, is the Aurora too much?

Is it the same line standard as the sets you use now. If not then you'll need a full standards converter. Is the sound AM/FM then and now.

A transmitter is basically an amp at RF. You've got one in any video. The plans on the internet can be modified of course if needed. Then connect directly. You don't need Watts, so leave that bit off.

Where are these plans, so we can have a look?

Cheers,

Steve P.

[timohaveri]

Originally Posted by Steve_P

Well, is the Aurora too much?

I'm afraid it is

Here are the links that I've found:

This sounds the most promising to me but I'm by no means an expert:
http://web.telia.com/~u85920178/tx/tv_tx_02.htm

Another one: http://www.zen22142.zen.co.uk/Circuits/rf/tv_tx.htm

These plans seems a bit crude and also seem a bit incomplete: http://anarchy.k2.tku.ac.jp/microtv/howtotvtx.html

The plans are not that specific about the coils and other stuff so I'm not sure if I could build these without guidance. To some people this is probaly easy but not to me.

What comes to standards I'm pretty sure that they're still compatible with my TV but I'll have to find out some more info about that.

Timo

[Steve_P]

Fine, then. No worries!

The transmitting power is in the Aerial as any Radio Ham or Transmitter Engineer will tell you. Smaller aerial, less range.

The first one is from a guy in Sweden, which is also a Scandanavian Country so it should be OK for you as it stands.

Cheers,

Steve P.

[timohaveri]

OK. Thanks. I'll try to contact that swedish guy and ask some details.

Timo

[Mr Hoover]

A simple solution is to use an old Uhf to Vhf converter that was common in Germany in the early 60's-I have one here.It basically produces an output on channel 2 or 3 & you can tune it with a knob across the Uhf band.
They started on Uhf earlier than the UK in 1961 or 62 with the same TV
system as on Vhf(with different vestigial sideband) unlike the UK & there
was a great demand for older sets to get ZDF,their equivalent of BBC2

It's a Uhf tuner but with the local oscillator on the LOW side
of the RF instead of the high side so that sound and vision appear the "right way round" when converted.

Similar converters were in use in the UK in the 1950's to convert band 1
only sets to band 3 of course.

They are always available on ebay Germany cheaply.

Cheers

Hugh

[timohaveri]

Originally Posted by Mr Hoover

They are always available on ebay Germany cheaply.

Hugh, thanks very much for the hint. I just bought a Philips NT1152 converter from Germany. Quite an accomplishment since I don't speak German Fortunately there is the babelfish online translator...

I hope that the insides are as good as the outside appearance is. Should be easy to restore, though. Only two lytics judging from the schematic in radiomuseum.org.

Do I need to use some kind of impedance adapter since the UHF input seems to be 240 ohms or will it work directly with the modern 75 ohm output? Anything else I should be aware of?

Timo

[Mr Hoover]

Hi.
Glad you were able to find one,yes when I bought mine used Babelfish
translation!
It will work I'm sure putting a signal into the 240 ohms input(strange,thought most from that time was 300??)From what I remember inside mine there
was a transformer to take it back to 75 ohms anyway before it went into the
tuner & the same on the output side.

If physically on the tuner can there are two aerial pins then it's a balanced
aerial input,take one to ground (shouldn't matter which),connect the coax braid to here and the inner conductor to the other pin.

Sure you'll have great fun with it!

Cheers

Hugh

[BGmidsUK]

Out of interest, are any of these UHF→VHF channel converters single channel, i.e. filtered? I am thinking of getting a few of them as a substitute for the tuners/ modulators I currently have as the signal will be at or at least close to broadcast quality, and have proper VSB shaping - I can use these as a temporary measure whilst analogue signals are still available. The ones which shift a batch of channels are unsuitable as the channel spacing will not match the Band I/III allocations.

I do intend to build proper VSB modulators to take care of things when analogue transmissions cease, to allow the required channels to fit into bands I and III. These will be fed into the TV distribution. However as yet I do not have the parts, money or sufficient knowledge to do this


BG

[Mr Hoover]

Hi
It's just like an old band 3 to band 1 converter,Whatever comes in
is shifted to an IF in the 48 MHz upwards range.There's a tuning knob on the
box & it's effectively a rotary Uhf tuner with Local Osc on the low side.squirting out its IF into band 1

They're not single channel & freq stability will no doubt be "so so".They were
made prior to varicap tuners

There is a "potential" for patterning if the Vhf tuner in the telly
radiates a local osc harmonic into the Uhf band at the incoming Uhf freq.
In this case retune the Vhf only set to an adjacent band 1 channel & the
osc harmonic should hopefully fall somewhere else.

All good fun!

Cheers

Hugh

[garfy]

Hello Timo,
PM sent.
Regards,
Garfy.

[timohaveri]

Originally Posted by garfy

Hello Timo,
PM sent.
Regards,
Garfy.

Thanks.