Upgrade-45-W-SSB-linear-Power-Amplifier-Set-for-Transceiver-Radio-HF-FM-CW-HAM

On ebay I found a 45 watt amplifier kit. It was really cheap so I bought it.
I will describe my findings here

The specifications looked good. 45 watt or more on the lower HF bands and still 25Watt at 10 meter.
I was skeptical about this. It uses 2 IRF-530 Fets. On internet I did not find an IRF-530 base amplifier that was able produce that output on 10 meter.

It was hard to get the manual. It should be supplied by email but I did not get it. The seller tries to resend but I did not receive it. I could find it on the internet on a Chinese site. It was an older manual.
It did not match the PCB. Still the schematic was simple enough so I was able to build it.
The manual is written in Chinese English. Probably translated by google translate or something similar. It is hard to read

After building it worked poorly. It worked on 80 meter and power was 5 watt. All tests were executed using a dummy load and a signal generator.

The schematic comes from a more recent version of the manual I found later.

R12 and R7 should be 5.6 Ohm. I had 100 Ohm mounted. No R6 and no R20 on my board.
After fixing this the results were better. But it did not match the specs.

Band    Power out
80        50 watt
60        50 watt
40        50 watt
30        35 watt
20        25 watt
17        15 watt
15        12 watt
12        5  watt
10        1  watt
DC was 13.8 V measured at the amplifier.

These levels are for CW only. For SSB levels should be 20 watt on the low bands. Then the 3th order intermodulation signals are 24 db down to the wanted signals. That is not really good but probably acceptable. Adjusting bias current may improve it. I intend to use it for CW and RTTY so For me it is OK.

I did some experiments with T2 to get more output. I used an additional secondary turn. That did work. I could get 25 Watt at 15 meter and 5 watt on 10 meter. Which is still not according to spec. Unfortunately it made the amplifier instable. So I went back to the single secondary turn.
The manual seems to contradict itself about the turns on the transformer. I use 4 turns primary and 1 secondary. Somewhere the manual mentioned 6  turns primary and 2 secondary. I did not try this.

On the dummyload the amplifier was stable. I needed to test what it would do when connected to an antenna. So I used a antenna tuner and a dummy load. I tuned the dummyload. This enables me to simulate several mismatches. It was a disaster. at SWR > 3 it was instable at all bands.

I was able to cure it by using an 36 Resistor at the input and a 500 Ohm resistor at the output.
Now it is quite stable. At very high SWR  at some bands some high frequency signals are seen. The lowpass filter should be able to remove this. I have to try.

So far the conclusion is that the amplifier is usable for CW  up to 15 meter. But don't expect the specified output at higher bands.

A warning. The power supply needs a current limitation as the bias current adjustment is very difficult. RV1 and RV2 are touchy  a little bit extra can cause an increase ofthe idle current of several Amperes. Better replace the trimmers by 10 turns trimmers.

60 meter transceiver power amplifier

I was able to improve the third order intermodulation. It is now almost 30 db down the wanted signals. It was done by adjusting the bias current for both IRF -510 transistors. I also increased the feedback. That lowers gain but improves linearity.

Below is a picture of the inside of the cabinet. It is getting crowded in there.

I have made an ALC circuit to control the output power. It works but is difficult to align.
That is because the 1350p has 60 db gain controlled by 2-3 volt. Here is some room for improvement.

After this it was time for some on air tests. It was stable during antenna matching.
Then I have used it to dive a external linear amplifier. That works but output power was way too high. We are allowed to use 100W. So I adjusted the power using the ALC to get the 100Watts.
It turns out I needed only 1,5 Watt input to get 100 Watts. So my 5 W amplifier is overkill.
No QSO has been made yet. It is quiet at 60 meters.

Now I am working on the CW unit. Sidetone and semi break in  are working. Now a CW signal must be added to the SSB filter input.
After that the basic functionality is present.

 

60 meter power amplifier.

I have build up the amplifier according to the schematic. And guess what , it worked.
I can get 7 Watt out of it.
No big problems encountered during building. So I continued making lowpass filters.
The work fine in combination with the amplifier. Harmonics are 60 db down.
 The amplifier stays stable when the dummy load is disconnected. So far so good. I need to test the amplifier with various load that can occur during tuning.
The amplifier needs 100 milliwatt input.

Then I builded the driver. I need to boost 3-4 mili watt up to 100 milliwatt for the final.
I used a IRF 510 for it.
Now problems start. The signal was distorted and the power is too low.
The biggest problem was the place on the driver output coil were I took the signal.
After fixing it the stability was a problem. fixed that by adding a 47Ohm resistor between the output of the driver and the input of the final.

Finally I got it working. It is stable even without load.It requires less than 2 V pp to get 5 watt out. The third order intermodulation is not that good. The levels are 20 db below carrier using 2 signals 20 KHz apart.
So There is some room for improvement. Problem is in the final. The 3th order intermodulation in the driver is acceptable (-30db)

60 meter 5 Watt PA

I have decided to change the plans for the power amplifier.
The 45 Watt amplifier may not be enough. I need 100 watt. So I will make a 5Watt amplifier and boost that signal to 100 Watts using an external amplifier.

The following amplifier will be build. I have designed it using SIMetrix. It should be able to generate 8 Watts. I hope it performs well.

Wiring modules

The cw/multi function board has been build in. Most connections to other modules are made.
Now I have:

• CW Sidetone,
• PTT switch
• TX/RX are displayed on the display.
• S meter circuit works although I have a used a led as S indicator. The brighter it is the stronger the signal strength.
• CW semi break in

The circuit to disable the bfo while transmitting CW has been made but is not wired to the modules.
Without this functionality the suppressed bfo out of the mixer would be present in the output signal.

Receiver is ready it seems to work fine. A better speaker would improve audio quality though. I may replace the small speaker by a bigger one. I could also make a connection for an external speaker.

Things to do:

• Make the power amplifier including ALC and low pass filter
• Make a CW unit to be able to TX in CW mode.
• Make a better audio filter for CW and SSB

Speech processor

A speech processor would help to cut through the QRM. So I build one.
It is a complex unit. It contains a small 12 MHz ssb transmitter and receiver for 12 MHz.
The signal out of this small SSB transceiver is limited by two diodes connected anti parallel.
Then the signal is filtered by a xtal filter that contains a single xtal. This filtered signal is detected by the SSB receiver. This results in compressed audio.

Clipping could be done on the audio signal but then only a little clipping can be done. The audio sounds distorted when more clipping is done. When clipping the SSB signal much more clipping can be done with good signal quality.

I took some ideas form the dsb clipper designed by PA0FRI. My processor makes real SSB instead. It also has a second xtal filter.

The compressed signal sounds good.

60 meter transceiver CW/multifunction board

I made a PCB with some CW functionality. And some generic functionality
It is build on a breadboards pcb with a lot of holes in it.
The functions So far:
-CW semi break in.
-CW sidetone
-TX/RX switching
-S meter circuit.
-An output when CM mode is selected and TX is working.

The board has space for more functionality. Maybe for the future