Modifying a 1.2 GHz Receiver to Pick Up 1.3 GHz

The potentiometer out out is a variable, stabilised DC out put that is applied across a varicap capacitor. When the capacitance is varied, the tuned frequency varies. Your circuit may br different. Do you have the schematic by any chance?

I have no schematics. The black Toshiba component has nothing to do with tuning. The potentiometer is a 10K one. I tried several other potentiometers and they had no effect on the frequency range.

Changing the potentiometer will not help. What needs changing, is the varicap diode. Measure the variable output of potentiometer at the highest level. Select a varicap giving higher capacitance change, for the same voltage, than the one used presently. You have to lift part no. of present varicap, look-up in relevant data sheets etc. If you can increase the out put of potentiometer slightly, it will help. But I would advise against it, unless you have lot of experience of PCB repair.

I have had a close look at it and it appears that the tuning system is made up of tiny unmarked surface mount components.

What is the make & model of the receiver? Please give all the detail that you have. Are you an electronics man?

It is a rf1200-051212

That did not help. Who/company has manufactured this video receiver & the type/model number of the receiver.

It is a generic unbranded one.

If there is any forum for these receivers, it may be useful. You track back to your source. What is the range of the receiver? Without spec. of the receiver it is impossible to go further.

Have a look at some video receivers in the link & identify if your receiver was part of those.

http://www.readymaderc.com/store/index.p...ts_id=1015

http://www.readymaderc.com/store/ind...roducts_id=629

UHF messed up my 1.2G lawmate video and RVGS tracking on Vimeo

Your two readymaderc links don't work.

http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_34_44&products_id=629

http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_34_44&products_id=1015

You must increase the frequency of your local oscillator of the super-heterodyne receiver. Likely the non-linear components of the mixer will operate at the higher frequency. You may not be as lucky getting your local oscillator to operate 100Mhz higher than it was designed to operate.

I don't think that the frequency of the receiver is crystal controlled. The frequency is probably being generated by an oscillator consisting of capacitors and transistors.

Sigh

I did not use the word "crystal" anywhere in my reply. A super-heterodyne receiver may use a crystal for stabilizing an oscillator or to select a bandwidth, but they do not always have a crystal. (Except of course for the semiconductor crystals.) I cannot help you if you add erroneous information and then complain that your added term is wrong.

I was only detailing how I think the frequency is generated. I bought a 500mw 1.2 GHz transmitter from Ebay so it doesn't matter any more.

What is your setup? Where & how do you use this receiver? What video signals, from what distance, do you receive? Why do you want, change of frequency? There are too many question marks. Sorry.

I have no setup as of yet. I saw a powerful transmitter for a good price but its frequency was too high. I then decided to buy thishttp://www.ebay.co.uk/itm/280812953845?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 It will probably take 2 months to arrive as it is from china and I now have to type the rest of my post as a hyperling and can no longer correct my mistakes because of bugs in this editor we are forced to use. I will be lucky if it even arrives at all.

As & when you have time, please PM me, all your project details. Will be glad to help.

I intend to have the transmitter and camera inside my shed being powered by a solar panel and battery. I once had a 10mw transmitter which worked well with a direct line of sight of about 20m so this 500mw one will be far better.

You will receive a four channel 1.2 Ghz transmitter. Your on hand receiver is tunable 1.2 Ghz. Why do you need to increase receiver frequency to 1.3 Ghz? Wait & see what are the frequency out put on each of the four channel 1.2 Ghz TX.

I was wanting to modify the frequency to start with because the original transmitter I wanted to buy was more powerful but it was slightly out with my receivers range. I decided to buy a slightly lower frequency one from China, but it will probably never arrive.

Wait with your fingers crossed!

I will just file a claim against them and tear them up for arse paper if it doesn't arrive.

I think the given picture is for a channel tuner . the SAW filter is called trap filter which is used to determined or trap)the bandwidth of an useful signal(signal want to detect) for example in TV(s) the bandwidth of the composed video signal is 34.5MHZ to 41.5MHZ . if you want to increase the receiving UHF-signal you need to make some changes in the filters of the UHF preamplifier if there is no transistor is used as preamplifier back to DATASHEET of the I.C tuner(search google) which is used in your video receiver.good luck

Here is the transmitter circuit which burned out. I think it might have been a transistor or inductor which failed.

Most likely your transistors are dead. These are the three lead devices. (Excuse me if you already knew that.) The resistors are the numbered two lead devices. The numbers indicate their nominal value in a simple code similar to the original color bands for resistors. So the ones labeled 104 are 100k (100,000 ohm) resistors and the 223 is 22k resistors. The two lead parts without a label are capacitors. They cannot be labeled because the ink will cause a leakage resistive path in parallel with the capacitors. Unfortunately for you it is very likely that one of these capacitors shorted and took out the transistors in a cascading failure. So it will naturally be difficult to determine what capacitance value the shorted capacitor should have. I do not see any inductors in the circuitry except for the natural inductance of wire paths. Oh, the wiggly circuit path under the YZ1.2GAV1 label is actually a technique to make a low inductance path between two non-adjacent nodes.

PS This circuitry has already been repaired once and not very well repaired.

Good Luck

Yes, I tried to remove a bad component which looked damaged. Chances are, I will never be able to find any replacement components. It is a real shame that they do not sell these tiny transmitters on their own because it was such a simple and good quality transmitter which transmitted the audio and video clearly.

If there is a bad component it will be the transistor because it,s fast damage and be sure from the test of the transistor after remove it from the tuner and recognise to the type of the transistor bipolar TR. or MOSFET TR. i think it is MOSFET TR. from the mark number (9F or w2w) you will know the real number of the transistor (write to google those two mark number).

regarding to modifying a 1.2GHZ to 1.3GHZ i knew you receive 1.2GHZ from transmission this frequency is a central Carrier frequency and this frequency is add with local frequency of the tuner to produce the IF-Carrier so if you want to receive 1.3GHZ you have to know the IF-carrier frequent and then make some changes in the local frequency to get the same IF-carrier frequency. for example

if the

local frq.=1.1GHZ

the IF-carrier =1.2GHZ-1.1GHZ=0.1GHZ

if you want to receive 1.3GHZ the local freq must be 1.2GHZ

i think the task is need to high skills

As redfred rightly said, the wavy green coloured copper track is an inductor. Lots of TX kits for 1.2 Ghz are available. Look around, you may find something similar.

THIS will throw lot of info. on the subject.