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

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.

Rotary encoder

I bought a COPAL rotary encoder on Ebay. This encoder is used in several Japanese transceivers. It uses magnets instead of switches. It is an expensive part.

Now it is installed in the transceiver. It works fine. Only a small hardware change was needed.
I do need a better spinner for it. Unfortunately those things  are expensive too.

Some planned software updates:
Tuning is faster now. It can be improved  even mode by improving the software. It takes too much time to update the frequency after each change. An solution can be to limit the frequency  updates while spinning the knob fast.

Changing band is also done by turning the knob. It is too touchy now. The encoder produces more pulsed per rotation than the previous one. Apart from that it has no clickes. It can be solved by counting the pulses. Band chang  is done after for example 100 pulses.

home made HF transceiver continued

I worked on the homemade HF transceiver.
When connecting an antenna I heard noise increase. However on the higher bands I needed to open the volume fully to hear it. Weak stations were hard to copy.
So I build a preamp. It is placed after the band filters. Before the first mixer.
I used the following amplifier as base http://www.hamlan.org/tech/w7iuvpreamp/
Difference is that I use a 2N2219. I use relays to bypass the filter when needed.
I get 12 db gain out of it when terminated with 50 Ohm. That is enough for most bands. For 12 and 10 meter It is probably enough. I need to wait for weak signals to appear.
I have tried it on 40 meter. No signs of intermodulation.

This is close up of the panel. The awful stickers will be replaced soon.

HF homemade transceiver

I worked on the HF homemade transceiver.  See my separate blog about this project

It is now in a usable state. Still a lot of work has to be done before it is finished.
I had a few contacts with it in SSB and CW. The signal was also received by various reversed beacon receivers. I am happy with that.

As mentioned before it needs more work.
Some of the open issues are:

• Improve power output. It should be the same on all bands. The driver needs improvements and some LPF's
• Calibrate frequency. The displayed frequency is at least 10 KHz off. It could be frequency dependent. 
• Changing from TX to RX takes to long (1-2 seconds). AGC voltage is at maximum after a TX-RX switch. This is strange it must be checked.
• The filter that is used for passband tuning is too narrow.

80 /20 MHz transceiver fan problem audio problem

I have decided to make the transceiver for 80 meter only. I may reconsider but I don't want to spend too much time on this radio
I intend to use it as a signals source for experiments with IRF510 based amplifier for 80 meter.

The power amplifier need some cooling. I have some PC fans that should be usable. They work great but they introduce hum in the audio. It comes via the power supply. No problem was seen when the fan was powered from outside the enclosure. Even when using the same power supply. Getting the fan power from within the radio causes a big hum. Adding capacitors does not help. I don't understand this.

One of the problems with this radio is that the audio is low in volume. So I have added an additional preamp. It works audio is at an acceptable level. I would like a bit more but it is Ok for now.
Unfortunately

My 20Ampere power supply has a problem. Once in a while it is not 13.8 V as it should be but 18+ V instead. That power is then stable at 18V for a while. Unfortunately this broke the audio PA. Smoke can out of it,

80/20 mhz transceiver

I found out what the reason was for the bad carrier suppression at 20 meter. The problem is the sideband oscillator.  I did not have the xtal for usb. so I have use a 27 MHz  on its fundamental frequency of 9 MHz. I had to make provisions to tune it to the right frequency. That worked but the signal shape is not a nice sine wave. This causes bad suppression of the carrier.
I will make an separate sideband oscillator with some filtering. That should fix the problem.

I have made an enclosure for the radiomyself. Using some laminated wooden furniture plate and some PCB plates. A picture will follow soon.
A metal case would look better but I don't want to spend too much money on this radio . However it is retro style. That suits the radio fine.

I will make a separate box with a PLL synthesizer to improve the stability. The PLL is working. It was leftover from another project. I need to make a  controller for it using a microcontroller.

CHN 80-20 tranceiver continued

I fixed the problem with the RIT. It was wired incorrectly.

The TX/Rx leds now work for both 80 and 20 meter. These too were wired incorrectly.

Somehow I made shortcircuit somewhere. This blew a BD137 power transistor.
Fortunately I had a few more in the junk box.

At 80 meters I was able to get a bit more than 10 Watts CW. SSB however was at 3 Watt max.
I have checked all circuits. They seem ok. I fixed it by making a small mar 4 based amplifier. Now I get 10 Watt PEP out. Current is 3 Ampere at 13.8 Volt

On 20 meter it does not work that well. Output is 3 Watt PEP. The input signal is according to spec.
Looking at the signal levels in the PA module it seems that I cannot input more signal.
More signal will cause an distorted output signal. It should be possible to get 10 watts at 20 meter though. I have another power module without transistors. I will try 27 MHZ transistors instead of the BD137. I hope that does the trick.

One of the remaining problems is the enclosure. I need to make a cover for the top left right and the bottom. I hope I can get some aluminum cheap.



 

a new toy

I have a new toy. A HP spectrum analyzer that works up to 350 MHz.

I already own a spectrum analyzer. It is an Atten that works from 0 to 1000MHz. It only has 1 filter that is  more than 200 KHz wide. It is usable but this HP is much better.

TR7200

Two years ago I bought a Kenwood TR7200. It is a well know 2 meter FM radio. It uses xtals

 I did not use it much as I only have 2 channels that are usable.
The other xtals were for USA frequencies  in the 146 MHz range.

Now I bought some xtals for it. Now I can use the following frequencies.

• 145.500
• 145.550
• 145.400
• 145.350

I also have a set for 145.325. Unfortunately the TX xtal works on 145,300. Although 145.325 is written on it. I can adjust the frequency a bit using the trimmers in the set. However 25 KHz is too much.

CHN transceiver update

I did some rpairs on the CHN transceiver.

• -X/RX relais was wired incorrectly. Fixed that
• It contains a variable capacitor at the front. It is used to peak output for the 80 meter band.This capacitor was not working correctly. Fortunately I had a similar capacitor in the junkbox box.That one worked OK.
• The IF board needed alignment. Fixed that.
• Improved decoupling of PA board.

HF PA's usually causes head ages. This one is no exception.
I can get 14 watts CW on 80 meters. On 20 meter it was just 4-5 watts. SSB PEP is lower.
at 80 meter I can get 6 watt. on 20 meter it is about 2 Watt max.
In CW mode the signal does not go through the xtal filter. It is much stronger than the SSB signal.
So I need to get some more gain of the ssb signal.

The PA suffered from some strange distortion. At full power It works for 1 second. then the sinus starts to deteriorate. It does not seem to be oscillation. After a small pause I can get another second with a clean signal.
I tried to solve  it using forced cooling. It helped but it is was not enough.

The power transistors  6xBD137 were mounted on a small heatsink. No cooling paste was used.
I think this causes the problem. A hotspot temperature is getting to high. That may be the reason for the deteriorated signal. So I applied some paste.
I also mounted two 10 Ohm resistors in series over the input transformer of the PA.
This reduces the power to 7-8 Watt but the signal is clean. It looked OK even when the dummyload was removed. Usually PA's start to oscillate when I try this.
I don't need a lot of power though. I need only a few watts as input for a bigger amplifier. So I won';t try to getr max power out of it

Things to do.

• Get more gain for SSB.
• Carrier is not suppression is not good om 20 meter. It is quite allright on 80 meter though.
• RIT works but I can not tune  to the same frequency I had when RIT is off.
• Find an enclosure for the set.