From London to Birmingham with 16,75MHz!

[oldeurope]

Good morning,

what do you think about this idea?

I tested the circuit with the SO42P and it seems to be
a possible alternative to upgrade your London modulator
for the Birmingham channel.

The thing in the picture is broadband test circuit to
look what else is produced and to find a way to get
the best signal.

Kind regards
Darius

[flyback]

Hi Darius..and telly folks,

Funny you should be doing that, I'm playing with a SA602A (Philips) similar type of device but it has the oscillator built in.

I have discussed the idea of having a tunable 'up-converter' to provide other channels with a few people but had never got around to trying it out.
Its only this week when I'm testing other devices that might be suitable for use in a modulator that I had revived the idea... great minds think alike!

Link to SA602 on Philips site.. http://www.semiconductors.philips.com/pip/SA602AD.html
Link to PDF.. http://www.semiconductors.philips.co...ets/SA602A.pdf


Malcolm

[flyback]

Just an addition to what I said...

Had I looked at the datasheet for the SO42P I would have seen it has the capability to be configured to have an internal oscillator!...silly me.

Malcolm

[oldeurope]

No, not silly.
If you want to mix with 16,75MHz you can not use the thing
as a self oscillating mixer. Even with the SA602 you will fail.
A special trick must be used!

Maybe you see it if you look at the picture!

Kind regards
Darius

[oldeurope]

Hi,
now the idea is reality.

I have no filter at the output now because I want to make sure
that the signals produced by the mixer makes no noise in the
picture.
I'll make a broad band high pass transformer at the output
because there is a level loss at the moment.

In the pictures you see the FV1 tuned to ch4 and the mixer
with an external 5V supply and the standart converter with
ch1 output.

The other picture showes a noise free picture without noise.
(Sorry free hand without flash.)

Kind regards
Darius

[DoctorWho]

What a fantastic idea. I'd love equipment enable to perform this. Would this mean you could use Channel 1 & 4 at the sae time. Are these readily available?


I've been interested in Malcolm,s Domino converter for some time, but I've been holding back on ordering until a version is available that operates on both Channels 1 & 4

[oldeurope]

Good morning DoctorWho

It is possible if you make sure that your London modulator only produces
a signal at the London channel. To make this you need a good RF-filter
at the output.

You have to split the signal from your London modulator to get
an input for the Birmingham mixer. Then you must add and ampliefy
the signals.

I stopped the development because there was no interest.

My idea was to put it in a little battery case with a 9V block
and put this into the coax cable in front of the antenna input of
the Birmingham set.
The current consumption is ca. 10mA so it works more than 10 hours.

What kind of modulator do you use at the moment?

Kind regards
Darius

[DoctorWho]

I have a rather antiquated modulator which works excedingly well on Channel 1, I think it is designed around David Loosers version, I have had it since the late 1980's. It puts out such a high strength signal that you can receive the output on a 405-line set down at the end of the garden with just a length of wire! The only problem with it though is that it causes interference on all UHF channels when on, so I suspect it has no filtering at all.

[oldeurope]

hm,
You must make sure that the output level is more than 60dBuV and
less than 80dBuV!
When the output is terminated with 75 Ohms there must be no signal
"on air".

Kind regards
Darius