The high shortwave bands 24 and 28 MHz are difficult when using 27 MHz as IF.
I am considering to build a simple transverter to a high frequency. I can be made similar to the one described in this blog.
The 27 MHz trx transverter combo can be used as IF for the shortwave transverters.
50 MHz could be used as IF. All I need is a 23 MHz xtal, a mixer and some filters.
A preamp may be needed as well .This way I have a 50 MHz radio too.
A better option is to build a transverter to 70 MHz. Currently PA land does not have an 70 MHz Ham allocation. This may change in the future though. 70 MHz Is a better IF than 50 MHz. Besides, SAW filters are available for this frequency. Those could be used as roofing filter.
A lot of conversion is done in this concept. The SSB signal will surely degrade by those conversions. It should be possible though after all some ham radio's use 4 conversion too.
maandag 26 april 2010
maandag 29 maart 2010
USB synthesizer
At the annual radio market in Rosmalen I bought a USB synthesizer kit.
See SDR-KITS
It uses the si570 to generate signal between 3.5 MHz and 180 MHz.
This unit can provide all frequencies I need for the all-band version.
Power output is a bit low. I will amplify it using a MAR amplifier. That should not be a problem.
The synthesizer is USB controlled. I will use a PC to control it. I might add a micro controller board later.
However, I am considering to make it a PC controllable Transverter.
To do that I need some USB controllable I/O ports. I could even make a PC controllable transceiver.
The power amplifier I will use is 5 Watt amp box73 it is a 5 watt amplifier that works from 1.8 to 144 MHz. So I can even add 50 Mhz an 144 MHz.
More design considerations later.
See SDR-KITS
It uses the si570 to generate signal between 3.5 MHz and 180 MHz.
This unit can provide all frequencies I need for the all-band version.
Power output is a bit low. I will amplify it using a MAR amplifier. That should not be a problem.
The synthesizer is USB controlled. I will use a PC to control it. I might add a micro controller board later.
However, I am considering to make it a PC controllable Transverter.
To do that I need some USB controllable I/O ports. I could even make a PC controllable transceiver.
The power amplifier I will use is 5 Watt amp box73 it is a 5 watt amplifier that works from 1.8 to 144 MHz. So I can even add 50 Mhz an 144 MHz.
More design considerations later.
vrijdag 20 november 2009
allband version
I have investigated the possibility to build an allband version.
A device Si570 could be used to generate all signals. The CB set can be set to a fixed frequency. A microcontroller, LCD and rotary encoder can be used to control the Si570.
It should be possible to build one for most HF bands. However 28 MHz will be difficult. The Mixer will leak some 27 MHz. A suppression of 40 db is possible but it is hard to accieve. The 28 MHz bandpass filter won't provide enough attenuation.
I think that 24 MHz will be difficult too.
For 14 MHz and higher a preamp between the mixer and the bandfilter may be needed for reception.
Using a Lo signal that is higher than the reception frequency is needed for bands > 10 MHz. LSB and USB will be switched. I better use it for all bands. it will reduce software complexity. An additional advantage is that the Lowpass filters can be used to reduce mirror image reception.
A device Si570 could be used to generate all signals. The CB set can be set to a fixed frequency. A microcontroller, LCD and rotary encoder can be used to control the Si570.
It should be possible to build one for most HF bands. However 28 MHz will be difficult. The Mixer will leak some 27 MHz. A suppression of 40 db is possible but it is hard to accieve. The 28 MHz bandpass filter won't provide enough attenuation.
I think that 24 MHz will be difficult too.
For 14 MHz and higher a preamp between the mixer and the bandfilter may be needed for reception.
Using a Lo signal that is higher than the reception frequency is needed for bands > 10 MHz. LSB and USB will be switched. I better use it for all bands. it will reduce software complexity. An additional advantage is that the Lowpass filters can be used to reduce mirror image reception.
donderdag 12 november 2009
80 meter version
The design can be adapted to 80 Meter. making a suitable LO signal may be a bit difficult though.
Two 23.5 MHz xtals are required (27-3.5). These are non standard as far as I know. 30.5 (27+3.5) MHz can be used instead. Those are nonstandard frequencies too.
using 30.5 inverts LSB and USB.
23.5 MHz can be generated by dividing 47 MHz by 2. You could try to use a VXO at 20 MHz. Then double this signal and mix it with 7 MHz.
A band 300 KHz wide band filter for 80 meter can be found in the Elecraft K2 design.
Two 23.5 MHz xtals are required (27-3.5). These are non standard as far as I know. 30.5 (27+3.5) MHz can be used instead. Those are nonstandard frequencies too.
using 30.5 inverts LSB and USB.
23.5 MHz can be generated by dividing 47 MHz by 2. You could try to use a VXO at 20 MHz. Then double this signal and mix it with 7 MHz.
A band 300 KHz wide band filter for 80 meter can be found in the Elecraft K2 design.
maandag 19 oktober 2009
Almost ready
The transverter is almost ready. I could add the bias current temperature stabilizer.
I might do that in the future. It may be good enough though. I have reduce the power to 5 Watt so it is not getting that hot anymore. Five watt is enough to drive my lineair amplifier.
I tried to make contacts using it bare bones. So far I have not had any luck. It should be possible though. I have a lineair amplifier that can provide 200 watt PEP using 5-10 watt drive. I will use that amplifier to boost the signal. It should make things easier. In the future I may build a PA for the lower bands using IRF510 fets.
I will try to make a movie clip showing its receive capabilities.
I might do that in the future. It may be good enough though. I have reduce the power to 5 Watt so it is not getting that hot anymore. Five watt is enough to drive my lineair amplifier.
I tried to make contacts using it bare bones. So far I have not had any luck. It should be possible though. I have a lineair amplifier that can provide 200 watt PEP using 5-10 watt drive. I will use that amplifier to boost the signal. It should make things easier. In the future I may build a PA for the lower bands using IRF510 fets.
I will try to make a movie clip showing its receive capabilities.
vrijdag 9 oktober 2009
New output transformer
I made a new output transformer for the PA. I used less turns and more ferrite.So I was able to use wire with a larger diameter.It worked out fine. I can get a bit more than 10 Watt output, measured after the low pass filter. Input current was 1,8 Ampere. This result is OK.
The transformer has 2*2 turns primary and 9 turns secondary. SM0VPO uses 3*3 turns primay and 16 secondary.My transformer is made by 3 2 hole ferrite cores. Brand is unknown. This is the third transformer I tried. My maximum power is limited to 12 Watt theoretically. That is OK I will use the PA at 7-8 Watts maximum. The SSB signal sounds good on my receiver. I didn't notice splatter on nearby frequencies.
I really have to implement temperature compensation. Now It suffers from thermal runaway (DC bias current increases when temperatere rises). For SSB speach it is not a problem. It is a problem when a carrier at full power is being transmitted (AM mode). AM is not needed ,I (mis)use it for tuning the antenna though.
The transformer has 2*2 turns primary and 9 turns secondary. SM0VPO uses 3*3 turns primay and 16 secondary.My transformer is made by 3 2 hole ferrite cores. Brand is unknown. This is the third transformer I tried. My maximum power is limited to 12 Watt theoretically. That is OK I will use the PA at 7-8 Watts maximum. The SSB signal sounds good on my receiver. I didn't notice splatter on nearby frequencies.
I really have to implement temperature compensation. Now It suffers from thermal runaway (DC bias current increases when temperatere rises). For SSB speach it is not a problem. It is a problem when a carrier at full power is being transmitted (AM mode). AM is not needed ,I (mis)use it for tuning the antenna though.
dinsdag 6 oktober 2009
Low pass filter and fan regulator
I just built the Lowpass filter using info from the ARRL handbook. I have used the 5 pole Chebychev filter. That sould be enough. It seems to work although I can not measure its characteristics yet. The output signal is not attenuated much. the output looks clean on a 100 MHz scope. I have to wait until my spectrum analyser project has finished. Than I can be sure.
The PA does not have enough cooling, so I added a fan. The fan starts when a transmission starts. After the transmission stops, it stays on for a few secons. I made a circuit to accomplish that.
After pushing the PTT switch I hear a tjoep signal on my SW receiver. I will have to find out why that happens. It is a bit anoying.
I found a similar power amplifier in a previous project. That PA has a better output transformer. It puts out 5 watts too but the efficiency is much better. I 'll rebuild the transformer using the same ferrite core type.Then I may get out a bit more power. That would be nice.
The PA does not have enough cooling, so I added a fan. The fan starts when a transmission starts. After the transmission stops, it stays on for a few secons. I made a circuit to accomplish that.
After pushing the PTT switch I hear a tjoep signal on my SW receiver. I will have to find out why that happens. It is a bit anoying.
I found a similar power amplifier in a previous project. That PA has a better output transformer. It puts out 5 watts too but the efficiency is much better. I 'll rebuild the transformer using the same ferrite core type.Then I may get out a bit more power. That would be nice.
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