Most other modules are functional but need some work.
PA
This module was a kit from box73. It seems to work fine.
LPF module
The band filers for all bands but one (28 MHz) are working the way they should. I may be able to increase harmonic suppression but they harmonics are below the legal limit. So no immediate need.
The 28 MHz filter is not OK. The harmonic suppression is not good enough. On 56 MHz only 30 db suppression was measured. As a temporary fix I have added a series LC circuit that short circuits the 56 MHZ signal. It works but it reduces power to 3watt.
IF strip
I use two xtal filters. One of them is used for passband tuning. Both filteres were not OK.
The one that is used to make the ssb signbal out of a dsb signal was very bad. It was very wide and it has a high attenuation. It turned out that one of the xtals was too far off frequency. This filter is now working Ok. It was needed tom measure all xtals and select the ones that have the smallest frequency difference.
The other xtal filter is a bit too narrow. I have bypassed it temporary.
TX/RX mixer and noise blanker.
This module contains the following items:
- The TX/RX mixer . This is a HPF505 diode mixer similar to the SBL1
- Amplifier for the DDS LO. It should have the same ampliufication from 1.6+9 to 29+9 MHz. It took some fiddling with capacitor get it right but it works ok now.
- Noiseblanker. This concept was 'borrowed' from the elecraft K2 design. It worked badly but I used different transitors and some other components. After some adaptions the noise detection works. I still have to see how it performs in practice.
Bandpass filter:
I did not use the filter from the Ukraine after all. I made a new one. It works Ok but at some bands the bandwidth is a bit too small. For receiving this is no big deal. I suppose A few db's will not be noticable. For transmitting it is not acceptable. Power output should be the same over the whole band. The amplifier/driver should solve this. This has to be done.
Speech compressor/clipper.
This is base on a design of PA0FRI. It is a double sideband clipper. I had some problems making it work. First off all the oscillator did not start. I fixed it by changing capacitor values.
Then I had to fiddle with the clipping. It worked but the output was not symmetrical.
After I got all issues fixed I was quite happy with the performance. The signal sounded OK when I monitored it using a PC speaker. Not really HIFI but usable. When I used it as audio source for the IF strip the resulting ssb sounded pretty good.
Driver for the PA
This module has yet to be build.
It is complicated. As the signal levels out of the band filters can vary I have to use variable gain. The output level should be the same for all bands. I think I can do it by using a detector to measure the output signal level and feed back this DC signal to a amplifier that has variable gain. This way the input level can vary while the output level remains at a fixed level.
I will use the 1350p IF amplifier for this.
