The transverter works but the the lowpass filters are a problem.
I will need to make them myself.
The attenuation on the second harmonic is just about acceptable on most bands (-40db). on some bands it less (35db). I think I understand the reason why.
It was intended for a amplifier that uses a push pull configuration. The second harmonic is suppressed much more. in such a amplifier. I am using a class B amplifier that has a strong 2nd harmonic.
Input Impedances don't seem to be 50 Ohm for all bands. Fortunately I was able to tune it a bit by adding capacitors. That even improved the 2nd harmonic suppression.
maandag 6 oktober 2014
maandag 15 september 2014
picked it up again
This project was on the shelf for a long time.
Now I have picked it up again.
the transverter basically work. Reception is Ok. Listening on the 40M band during night condition is a good test. The transverter seems to work well under those conditions.
after smome test I found that a variable attenuator is not really needed. I have used 2 resistors to reduce the gain until I got 4 watts on 80 meter. On other band the output is between 3 and 4.5 watts.
That is Ok for now,
TX caused more trouble. It has some oscillations that were hard to find.
I have improved the wiring and made a separate 12V supply (7812) for the PA.
The amplifier without low pass filter produces harmonics at -15dbc for the second harmonic.
After I got the amplifier working I connected the LPF. Now the second harmonic is at -40dbc. This is just enough according our regulations. I had expected a bit more from this filter. Another problem is that at some bands the attenuation is a bit high. I loose 2 of the 4 watts. The filter came from a commercial transceiver. It may be tweaked for that transceiver. Input and output impedance may not be 50 Ohm.
The band pass filter causes some problems. After some tests 14 MHz stopped working.
One of the relays is not working well. I tried to resolder it but no luck. Once in a while it works on 14MHz but it stops after changing band and the change back to 14MHz. I need to replace the relay but this is a Russian type that cannot be found easily here. In fact I have never seen anything that looks like it.
The after a while another problem with the bandpass filter popped up. Somehow the center frequency of 40 30 meters has moved up a few 100 KHz. I have no idea why. I did improve soldering of some components that is the only reason I can think off. Strange, I have never seen this happening. The tunable cores are glued in place so I don't see any problem there. I will try to tune it by adding small capacitors.
Now I have picked it up again.
the transverter basically work. Reception is Ok. Listening on the 40M band during night condition is a good test. The transverter seems to work well under those conditions.
after smome test I found that a variable attenuator is not really needed. I have used 2 resistors to reduce the gain until I got 4 watts on 80 meter. On other band the output is between 3 and 4.5 watts.
That is Ok for now,
TX caused more trouble. It has some oscillations that were hard to find.
I have improved the wiring and made a separate 12V supply (7812) for the PA.
The amplifier without low pass filter produces harmonics at -15dbc for the second harmonic.
After I got the amplifier working I connected the LPF. Now the second harmonic is at -40dbc. This is just enough according our regulations. I had expected a bit more from this filter. Another problem is that at some bands the attenuation is a bit high. I loose 2 of the 4 watts. The filter came from a commercial transceiver. It may be tweaked for that transceiver. Input and output impedance may not be 50 Ohm.
The band pass filter causes some problems. After some tests 14 MHz stopped working.
One of the relays is not working well. I tried to resolder it but no luck. Once in a while it works on 14MHz but it stops after changing band and the change back to 14MHz. I need to replace the relay but this is a Russian type that cannot be found easily here. In fact I have never seen anything that looks like it.
The after a while another problem with the bandpass filter popped up. Somehow the center frequency of 40 30 meters has moved up a few 100 KHz. I have no idea why. I did improve soldering of some components that is the only reason I can think off. Strange, I have never seen this happening. The tunable cores are glued in place so I don't see any problem there. I will try to tune it by adding small capacitors.
Abonneren op:
Posts (Atom)