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

60 meter trx audio

I made the audio amplifier for the transceiver. It uses a LM386 as amplifier.
In front of this amplifier I have added several RC filters with buffers between them.
It works, Although the suppression of signal above 3 KHz could be better.

The circuits were build in a tin box. I still has room for a CW audio filter or a better audio filter for speech I may add that later.

The speaker that I use is small. Sound is way better when a bigger one is used. I have tested this. So I may replace it.An improvement could be the mounting of the small speaker. Now I have a acoustic short circuit.

The speaker is thin. I was able to mound it on the front of the radio. Then the cover was placed over it . This way I did not have to drill holes in the stainless steel of the front.
Unfortunately volume is low with this setup because of the acoustic short circuit.

60 meter transceiver concept

This is the concept of the transceiver

TX/RX switching is done by switching LO and BFO to the mixers.
AGC and ALC can be done with a single IF amp.
Note that it has 2 bandpass filters for 5.4 MHz. It could be done with a single filter and two relays.

Most items have been  I still need to build:
Speech Compressor.
Diver for the PA.
Lowpass filter 5.5 MHz.
Audio power amplifier (not in drawing).
CW unit  ( Not in drawing).

I can receive and transmit using a signal generator a LO and another generator as audio source. Now it is time to build the DDS unit and the microprocessor board together. Then I have a working LO.
After that I can add the audio amplifier. Then the receiver should be working.

The PA has been assembled except for the power transistors. I bought the kit on ebay. It should be able to deliver 45 Watts.

60 meter transceiver amplifier and agc

The unit that provides 5 mili watt on 8 MHz and 13.350 -13.450 MHz is working. It is connected to the main board. The 13 MHz signal comes out of a signal generator. Later the signal generator will be replaced by a DDS board.

On the main board I have build the amplifier for the tiny 5.4 MHz signal out of the mixer. I can get 5-10 milli Watt out of it. That is enough for now.
In receive mode I can get 8V pp audio with 2 uV 5.4 MHz signal input. This signal is rectified and used for the AGC. It works, from 2uV to 30 mV the signal level of the audio is constant. I cannot get more than 30 mV from the generator.
The time constants for the AGC must be improved though. I want fast attack and slow release.
So some more experiments are. needed.

60 Meter homemade transceiver

In Holland we got access to 60 Meter We can use 5.350 to 5.450.
The band looks interesting. I have IC-718 that can be used at 60 meter.
It works fine.

I prefer homemade radio's so I have started to build a 60 meter Transceiver.
Desired specs:
-SSB CW
-8 MHz IF
-50 Watts output
-Controlled by a micro controller.
-DDS as LO. Maybe a cleanup PLL.

Concept is to use a SSB filter in one direction. In front this filter a mixer is placed. After the filter an IF amplifier is placed followed by another mixer.
The role of the mixers depend on RX or TX. The LO switches between 8 MHz and 13.350-13450 MHZ. If one of the mixers LO is 8 MHz ,the other gets 13.4 a LO.

This is the heart of the transceiver. It contains 2 mixers, the Xtal filter, IF amplifier and AGC amplifier, and  Two 5.4 MHz band bass filters.

This is the oscillator board. It contains a 8 MHz oscillator including amplifier and filter.
The amplifier for the 13.350 13.450 DDS signal is not ready. Only the low pass filter is build.

This is the box that I plan to use. It came from another transceiver project but that did not fit in.