scratch schematic diagram

Here is scratch diagram of the transverter. I will make a better drawing later.

The lowpass filter at the output is not ready yet. A PA will be build to boost the signal to 5-10 watts.

Super VXO

I was unable to get 20 KHz tuning range using varicaps. So I tried a variable capacitor instead (not a trimer). The tuning range increased to 14 KHz but that is not enough.Then I added a coil in serie with the varco. No luck, 16 Khz was maximum.

Finally I tried the super VXO configuration (2 xtals parallel and a coil in serie).
That did the trick. The tuning range is 25 KHz.
see http://www.qsl.net/7n3wvm/supervxo.html for information about super VXO's.

some progress

Last weekend I did a few things. Not as much as I hoped though.

I modified the CB radio. When it transmits it also outputs a DC voltage on the antenna connector. That DC voltage will be used to switch the TX/RX relais.
The voltage is connected through a 2k2 resistor.So a transistor must be used in the transverter to switch the relais.

In the transverter the TX/RX relais circuit has been made. The TX RX switch works fine.

I made a simple lowpass filter for the audio of the CB set.

I did some experiments with varicaps to control the frequency of the LO. I did use a 35pf trimmer. The 20 MHz xtal could be varied 20 KHz using this trimmer. Unfortunately I was unable to pull the frequency more than 10 KHz using varicaps.

power boosted to 5 mW

I made a small amplifier to boost the signal to 5 mw. The first amplifier is build around a bfy 90 in class a. A 2N2219 is used to boost the signal to 5 mW. This amplifier has a tuned circuit.

Initially the power output was much to high. The 2N2219 worked as class B amplifier. I measured 100 mW. So I added a resistor at the input of the first amplifier. This reduced the power to 5 mw.

Now I will add the RX TX relais.

band pass filter

The bandpass filter works fine. It is 200 KHz wide now.

I measured the filtered output during transmission. The filter is terminated by a 47Ohm resistor. The signal has a value of 150 mV pp.

Today I will build amplifiers too boost this signal.

band filter

I made a bandfilter for 7 MHz. It should filter the input/output to/from the 7 MHz port of the mixer.

It consists of 3 tuned circuits. The coils are made by 18 turns on a T50-2 core. Coupling between then is done by a 1 turn link coupling.

It works but I am not satisfied. It is probably good enough but it can be made sharper. I think the link coupling is too tight. The link coupling is a piece of wire (ring) between two cores. This coupling is good, probably too good.
I will change the coupling by a capacitor coupling.

pictures