Thursday, June 05, 2014

The "Trevo" works

Ok, I don't know in what frequency it his receiving, only I got my first copy of Morse signals from the ether!

The reason I don't know the frequency is simple, the only test equipment used so far is a multimeter.
After trying to figure it out the frequency of the VFO (I was suspecting that I could be receiving in the 40M or 80M band) I fired the qrss transmitter kit and set it for 3.580 Mhz, after tuning the VFO got my own test transmission (I was receiving some amateur Morse before).

The VFO (lower right on the image) is not the final design, just a quick lashed up design without great stability. Tuning is made by a varicap and a trimer cap, the two blue trimmers are for fine an coarse frequency set.



The only problems so far were:

* Incorrect publication, on the original article, of a component value on the bias of the BFO oscillator transistor which I discovered quick; the measured voltage was two low for bias and had reception for a second or so (after power on) before loosing it (was testing the BFO/product detector at 4Mhz since there's powerful AM stations around, now the BFO is back on 9Mhz)

* Thermal shutdown of the LM7912 (I'm using it so in the future I can add a 2n3055 with collector to ground) occurred on the makeshift power supply after some time of power on, now with more modules have to set another design to power the transceiver.

* Incorrect bias of microphone on the connection to the balanced modulator (still have to find out how a elect mic element does not needs power to give signal)

Work to be done:

* Decide on the VFO design
* Finish the transmit section
* Finish the band pass and low pass filters
* Adjust everything

That should be more one or two years at this rate!

Have a nice weekend.

4 comments:

Eldon R. Brown SR said...

Ricardo,

I always enjoy reading about Homebrew Projects.

Nice work on the Trevo. Are you considering a Microprocessor and Si570 for the VFO? See Farhan's Minima Transceiver.

Regards,

Ricardo - CT2GQV said...

Hello Eldon,

Thank you for the comment.

My first idea was to use the same design of the "Speaky", that is one vfo for each band and pll controlled, being the master oscillator a dds from 4-4.5Mhz. Then I thought of the Si570 since I already have two of them running, only thing is to filter/shield the "click's" that generates. Another possibility was an AD985x kit that I have already programed for 9Mhz IF tested nicely on another radio (needs an amp to level to the mixer).

Now I'm considering the same design of the K2, one VFO with switched varicaps controlled by a dual modulus pll.
The K2 design, my guess, should be a little critical to put in place since it's one coil to cover the full HF spectrum. The advantage over the "Speaky" VFO is that there are not so many coils to make. The Speaky design needs to be relay switched if more than 5 bands are used because of the load on the oscillators.

This is a design in progress but I'm considering the possibility of adding a second IF filter so I can make a shift and with control, I will have to change the BFO from crystal to pll and add a second oscillator/vfo for that.

In the end, basically I'm reinventing the wheel....anyhow it's fun.

Best Regards

pedro said...

Hello Ricardo, i prefere the Si570 VFO check the minima transceiver vfo its simple ;)


73

Pedro
ct5jzx

Ricardo - CT2GQV said...

Thank's Pedro.
The VFO is still open, considering all the options.
Regards.