BATC Forum

Im after some help, Long shot on equipment this old.
I picked up a Fortop TVT1300 locally, a 24cm FM ATV TX.
It has two xtal positions both empty for two tx channels.
Does anyone know anything about this tx? are they 96mhz xtals?

If you have one of these I would appreciate if you could check the xtal values.
Better still does anyone have a manual / circuits etc.


Thank
Terry G1LPS

Hi Terry,

I've just obtained one and it's got 2 crystals fitted; 96.00000 and 93.70833 MHz. At the moment I don't know what the actual TX frequencies are as I haven't had a chance to fire it up, but according to the paperwork it a x12 multiplier. That gives frequencies of 1152.00 and 1124.50 MHz respectively.
I'm not sure at the moment whether there's another internal oscillator which mixes with the crystal generated signal to give the final o/p, but I won't know until I fire it up and check the output frequency.
I'll post the info on here when I've checked it, assuming it works.

Regards,

Frank.

Further to my above post, I've now had a chance to check the operation of the TX and have found there is an internal LO running at about 120MHz. This appears to be modulated by the video and mixed with the derived x12 crystal frequency giving the required o/p frequency. The 120MHz oscillator seems to drift markedly on start-up and I've noted one of the crystals that came fitted gives a very reduced final o/p power of about 0.5 Watt compared to the other one which gives about 1.0 Watt. This is despite retuning the complete string and trying to find a compromise setting, so I suspect the low o/p crystal is either lazy or not cut for the oscillator circuit it's fitted into.

Thanks Frank for the replies and help
Missed your earlier post.
That gives me the information I was after.


Terry

Hi Terry,
No problem. I hope the info is of some use.
I seem to remember reading the crystals are 5th overtone but can't remember whether it said series or parallel resonant. I'm sure for that frequency though it will be enough just to specify the crystal frequency required, i.e 96.xxxxx 5th overtone. Maybe someone else can comment if need be.
Regards,
Frank.