The lowpass filter at the output is not ready yet. A PA will be build to boost the signal to 5-10 watts.
dinsdag 29 september 2009
scratch schematic diagram
Here is scratch diagram of the transverter. I will make a better drawing later.
The lowpass filter at the output is not ready yet. A PA will be build to boost the signal to 5-10 watts.
The lowpass filter at the output is not ready yet. A PA will be build to boost the signal to 5-10 watts.
maandag 28 september 2009
Super VXO
I was unable to get 20 KHz tuning range using varicaps. So I tried a variable capacitor instead (not a trimer). The tuning range increased to 14 KHz but that is not enough.Then I added a coil in serie with the varco. No luck, 16 Khz was maximum.
Finally I tried the super VXO configuration (2 xtals parallel and a coil in serie).
That did the trick. The tuning range is 25 KHz.
see http://www.qsl.net/7n3wvm/supervxo.html for information about super VXO's.
Finally I tried the super VXO configuration (2 xtals parallel and a coil in serie).
That did the trick. The tuning range is 25 KHz.
see http://www.qsl.net/7n3wvm/supervxo.html for information about super VXO's.
zondag 27 september 2009
some progress
Last weekend I did a few things. Not as much as I hoped though.
I modified the CB radio. When it transmits it also outputs a DC voltage on the antenna connector. That DC voltage will be used to switch the TX/RX relais.
The voltage is connected through a 2k2 resistor.So a transistor must be used in the transverter to switch the relais.
In the transverter the TX/RX relais circuit has been made. The TX RX switch works fine.
I made a simple lowpass filter for the audio of the CB set.
I did some experiments with varicaps to control the frequency of the LO. I did use a 35pf trimmer. The 20 MHz xtal could be varied 20 KHz using this trimmer. Unfortunately I was unable to pull the frequency more than 10 KHz using varicaps.
I modified the CB radio. When it transmits it also outputs a DC voltage on the antenna connector. That DC voltage will be used to switch the TX/RX relais.
The voltage is connected through a 2k2 resistor.So a transistor must be used in the transverter to switch the relais.
In the transverter the TX/RX relais circuit has been made. The TX RX switch works fine.
I made a simple lowpass filter for the audio of the CB set.
I did some experiments with varicaps to control the frequency of the LO. I did use a 35pf trimmer. The 20 MHz xtal could be varied 20 KHz using this trimmer. Unfortunately I was unable to pull the frequency more than 10 KHz using varicaps.
zaterdag 26 september 2009
power boosted to 5 mW
I made a small amplifier to boost the signal to 5 mw. The first amplifier is build around a bfy 90 in class a. A 2N2219 is used to boost the signal to 5 mW. This amplifier has a tuned circuit.
Initially the power output was much to high. The 2N2219 worked as class B amplifier. I measured 100 mW. So I added a resistor at the input of the first amplifier. This reduced the power to 5 mw.
Now I will add the RX TX relais.
Initially the power output was much to high. The 2N2219 worked as class B amplifier. I measured 100 mW. So I added a resistor at the input of the first amplifier. This reduced the power to 5 mw.
Now I will add the RX TX relais.
donderdag 24 september 2009
band pass filter
The bandpass filter works fine. It is 200 KHz wide now.
I measured the filtered output during transmission. The filter is terminated by a 47Ohm resistor. The signal has a value of 150 mV pp.
Today I will build amplifiers too boost this signal.
I measured the filtered output during transmission. The filter is terminated by a 47Ohm resistor. The signal has a value of 150 mV pp.
Today I will build amplifiers too boost this signal.
band filter
I made a bandfilter for 7 MHz. It should filter the input/output to/from the 7 MHz port of the mixer.
It consists of 3 tuned circuits. The coils are made by 18 turns on a T50-2 core. Coupling between then is done by a 1 turn link coupling.
It works but I am not satisfied. It is probably good enough but it can be made sharper. I think the link coupling is too tight. The link coupling is a piece of wire (ring) between two cores. This coupling is good, probably too good.
I will change the coupling by a capacitor coupling.
It consists of 3 tuned circuits. The coils are made by 18 turns on a T50-2 core. Coupling between then is done by a 1 turn link coupling.
It works but I am not satisfied. It is probably good enough but it can be made sharper. I think the link coupling is too tight. The link coupling is a piece of wire (ring) between two cores. This coupling is good, probably too good.
I will change the coupling by a capacitor coupling.
woensdag 23 september 2009
dinsdag 22 september 2009
some results
Last night I reduced the power of the LO amplifier to 5 mw.
Then I mounted the mixer (HPF-505). Now I have a basic transverter.
No band filters were build yet.
I was curious if stations could be received using this setup.After all 40 meter contains a lot of broadcast stations. So I hooked up the cb set to the IF port of the mixer. My antenna was just 50 cm of wire.
I did receive a lot of broadcast stations. I was even able to hear a lot of ammateur stations. That is a nice result. Connecting the antenna increased the noise to S5 level. So a preamp may not be necessary. I'll check again when the bandfilters are ready.
Then I tried to transmit. Success, the LSB signal sounded good on my FT-950.
Of course the output signal is small, a few 100 mv at the non terminated IF output.
During reception I found out that The CB sets produces too much high tones. I already expected this. So I'll have to add a LC lowpass filter with a cutoff frequency of 2200 Hz. I will put it between the amplifier and the speaker. That is not the best solution. However it requires only a small modification of the CB radio.
I started building the band filter and the attenuators. I hope I can finish it today. Soon I will upload some pictures and a schematic diagram.
Then I mounted the mixer (HPF-505). Now I have a basic transverter.
No band filters were build yet.
I was curious if stations could be received using this setup.After all 40 meter contains a lot of broadcast stations. So I hooked up the cb set to the IF port of the mixer. My antenna was just 50 cm of wire.
I did receive a lot of broadcast stations. I was even able to hear a lot of ammateur stations. That is a nice result. Connecting the antenna increased the noise to S5 level. So a preamp may not be necessary. I'll check again when the bandfilters are ready.
Then I tried to transmit. Success, the LSB signal sounded good on my FT-950.
Of course the output signal is small, a few 100 mv at the non terminated IF output.
During reception I found out that The CB sets produces too much high tones. I already expected this. So I'll have to add a LC lowpass filter with a cutoff frequency of 2200 Hz. I will put it between the amplifier and the speaker. That is not the best solution. However it requires only a small modification of the CB radio.
I started building the band filter and the attenuators. I hope I can finish it today. Soon I will upload some pictures and a schematic diagram.
Building VXO
Last night I built the VXO I also made an amplifier for this VXO.
The VXO can be pulled 20 KHz up with a single xtal and a 35 pf trimmer. Twenty KHz is enough so I may not need the super VXO configuration at all. However the tuning is not lineair. Maybe the super VXO has better lineairty, I will try it later.
For testing a use a trimmer to set the frequency.It will be replaced by a varicap eventally.
The signal out of the VXO is amplified by a 2N2219 amplifier. I delivers 80 mili watt. That is too much, the mixer needs 5 mw. I will reduce the power to 10 mili watt. The output signal will be fed to the mixer via a 3db attenuator. This attenuator wil improve the termination of the mixer.
The VXO can be pulled 20 KHz up with a single xtal and a 35 pf trimmer. Twenty KHz is enough so I may not need the super VXO configuration at all. However the tuning is not lineair. Maybe the super VXO has better lineairty, I will try it later.
For testing a use a trimmer to set the frequency.It will be replaced by a varicap eventally.
The signal out of the VXO is amplified by a 2N2219 amplifier. I delivers 80 mili watt. That is too much, the mixer needs 5 mw. I will reduce the power to 10 mili watt. The output signal will be fed to the mixer via a 3db attenuator. This attenuator wil improve the termination of the mixer.
maandag 21 september 2009
zondag 20 september 2009
Start blog
I have a few CB ssb sets in my junk box.
It is time to use them for ham operation.
Those CB radios can be converted to 10 meter. However 10 meter propagation is poor.So I will make a transvererter to 40 meters.It should not take too much time to build. I have a few other projects that need to be finished.
Building a transverter from cb to one of the lower ham bands has been done before. I found a few examples on the Internet. I expected to find more though, After all a lot of these sets are available at low prices.maybe the quality of the cb sets is not good enough.
The CB radio that I will use is an Uniden 5500. This is supposed to be one of the better CB sets.A transverter needs just a few milli watts so I have disconnected the final and the driver stage. The radio now produces 1,5 milli watts. This signal sounds good on a hf receiver so the basics are ok. I think I will add 12 volts DC to the output signal while transmitting. That DC signal can be used to switch the transverter between TX and RX. AM transmission does not work anymore. That is fine, I don't need AM. Transmitting in AM mode produces a carrier. That is great for tuning the antenna.
A CB radio has a 10 KHz channel raster. However sometimes the space between two adjacent channels is 20 KHz. This raster is unusable so some kind of finetuning is required. The set has a clarifier we hams call it RIT. Maybe it can be modified to work during transmit. However it won't span 10 KHz let alone 20 KHz. So finetuning will be build in the transverter.
Design ideas:
I will build a (super) VXO at 20 MHz. This signal goes to one of the RF pins of a diode mixer. The transceiver is connected to the other RF port of the mixer.
The IF port of the mixer is connected to a band pass filter for 7 MHz. That is basically It. This transverter is bidirectional, no TX/RX switch is needed.
Of course the output is low, I expect 0.5 milli watts. The received 7 MHz signal will be attenuated as well but I guess that won't be a problem.
During TX the signal is amplified to 5 watts. Relais are used to switch between RX and TX. The 3db attenuators are used provide proper match for the mixer.
It is time to use them for ham operation.
Those CB radios can be converted to 10 meter. However 10 meter propagation is poor.So I will make a transvererter to 40 meters.It should not take too much time to build. I have a few other projects that need to be finished.
Building a transverter from cb to one of the lower ham bands has been done before. I found a few examples on the Internet. I expected to find more though, After all a lot of these sets are available at low prices.maybe the quality of the cb sets is not good enough.
The CB radio that I will use is an Uniden 5500. This is supposed to be one of the better CB sets.A transverter needs just a few milli watts so I have disconnected the final and the driver stage. The radio now produces 1,5 milli watts. This signal sounds good on a hf receiver so the basics are ok. I think I will add 12 volts DC to the output signal while transmitting. That DC signal can be used to switch the transverter between TX and RX. AM transmission does not work anymore. That is fine, I don't need AM. Transmitting in AM mode produces a carrier. That is great for tuning the antenna.
A CB radio has a 10 KHz channel raster. However sometimes the space between two adjacent channels is 20 KHz. This raster is unusable so some kind of finetuning is required. The set has a clarifier we hams call it RIT. Maybe it can be modified to work during transmit. However it won't span 10 KHz let alone 20 KHz. So finetuning will be build in the transverter.
Design ideas:
I will build a (super) VXO at 20 MHz. This signal goes to one of the RF pins of a diode mixer. The transceiver is connected to the other RF port of the mixer.
The IF port of the mixer is connected to a band pass filter for 7 MHz. That is basically It. This transverter is bidirectional, no TX/RX switch is needed.
Of course the output is low, I expect 0.5 milli watts. The received 7 MHz signal will be attenuated as well but I guess that won't be a problem.
During TX the signal is amplified to 5 watts. Relais are used to switch between RX and TX. The 3db attenuators are used provide proper match for the mixer.
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