[SOLVED] Can I use a frequency converter to impliment a Local oscillator

[obrien135]

Hello,

I have been trying to get a 10MHz local oscillator to work for quite a while. I have tried about 15 or 20 different designs and even a kit, but none of them worked reliably. I was wondering if it is feasable to use the frequency converter kit shown at the link below , with a 10MHz crystal, and a very low frequency variable oscillator to generate the 10kHz to 300KHz input for a resulting range of 10.01 to 10.3MHz.

LF Converter - Ham Radio Kits

 

[FvM]

The converter will generate a double side band signal, which you won't want, as I guess.

 

[obrien135]

The IF I am aiming for is 3MHz. Its for a 40M SSB transceiver.

 

[BigBoss]

The IF I am aiming for is 3MHz. Its for a 40M SSB transceiver.

What is your target ??? To get a Stable Local Oscillator that will work 10MHz or another particular specification ??

 

[obrien135]

Yes that first one you mentioned is the target. I just want to get a stable 10 to 10.3 MHz oscillator.

 

[FvM]

The IF I am aiming for is 3MHz.

Yes, but mixing 10 MHz with a low frequency oscillator in a regular mixer produces 10 MHz +/- LF, so you get at least images at 2*LF in your receiver.

 

[obrien135]

What if I put a crystal filter on the output of the mixer (the mixer kit for the 10MHz and 10-300kHz)? Would the +/- LF foul up the IF on receive and the RF output on transmit?

 

[tony_lth]

In one of our design, we used one LO (2310M) for both RX RF(2450M) and TX RF(2660M), so we got RX IF (140M) and used TX IF (350M).
Actually, I don't understand your question. maybe you should clarify what's your TX RF, TX IF, RX RF, RX IF, etc.

 

[obrien135]

OK. The IF is 3MHz. It is mixed with mic audio to produce TX IF. This is mixed with LO which is 10.1 - 10.3MHz to produce 7.3MHz RFOUT. The same LO is used for RX and is mixed with 7.1 - 7.3MHz from RF input amp output coming from antenna and tuning resonant circuit. This produces RX IF of 3MHz. To generate the 10.1 to 10.3MHz is the problem. I thought this third mixer kit and the 10 to 300kHz oscillator might answer the problem. I was wondering if I am on the right track, or if , as the gentleman from Bochum mentioned, there might be problems with the +/- LF, (LF = 10 to 300kHz).

 

[tony_lth]

This should be some clock recovery circuit or clock lock from receiver circuit, but I am not familiar with that.

 

[betwixt]

I think what you need is a tunable oscillator covering 10.1 to 10.3MHZ and a fixed oscillator at 3.0MHz

On receive, you mix the input between 7.1 to 7.3MHz with the oscillator to produce a fixed 3MHz IF output which you can filter, amplify and demodulate to recover the signal.

On transmit, you generate a modulated signal at fixed 3MHz, mix it with the oscillator to shift it up to 7.1 - 7.3MHz where you filter it, power amplify it and feed it to the antenna.

Generating the oscillator frequency should be very simple, personally I would use a PLL to make it as stable as possible. I think I would be tempted to look at alternative frequencies for the IF though, you will have difficulty finding ready made filters for 3MHz, it you went for something higher you could probably find off-the-shelf filters which would save you lots of work. If you plan to use narrow bandwidth for CW or SSB modes this would definitely be advantageous.

Brian.

 

[BigBoss]

Yes that first one you mentioned is the target. I just want to get a stable 10 to 10.3 MHz oscillator.

Why don't you use a PLL+VCO ?? A simple integer PLL will give you very stable and programmable Frequency Source..
The best solution is the simplest one..

 

[obrien135]

Yes I will look into the PLL. Thank you. The main problem I was having was, actually not the drifting but the intermittance of the oscillation. That's why I thought the kit would help since it uses a crystal and can be varyed easily with the LF input. But as The gentleman from Germany was mentioning the +/- LF may cause some kind of interference with the wanted signals. I was wondering if this would be a problem and if so, how to get around it. I was hoping to find out before I invest the money in the kit. Do you think the kit is a waste of money and the wrong way to go?

 

[FvM]

A single sideband mixer, that generates e.g. 10.01 without 9.99 MHz at the same time would involve a much more complex circuit. I also opt for a VCO/PLL design.

 

[obrien135]

Thank you , all for your feedback. I think I know how to proceed now.