Idea for a simple 10m WSPR transceiver

GQRP club sells  inexpensive 14.060MHz crystals and these doubled would come out on 28.120MHz. I am wondering if they will pull UP to 28.1246? If so, they would make a perfect source for a DSB WSPR transceiver. Half the TX power would be wasted on a signal 3kHz lower but it would be a very simple design with just an oscillator, doubler, balanced mixer, PA and low pass filter, plus the basic audio input and DC receiver parts, which would re-use much of the TX design. Some experiments are needed!

Alternatively, can anyone suggest a more modern approach such as using a programmable reference oscillator as used in SDRs? What is the best one? Where do I get them from?

DSB mod for the Heathkit HW8

When looking around for ideas for DSB rigs I found a page which shows how to modify the HW8 for DSB operation by adding a balanced modulator and audio stages.  KL7R reports that he worked New Zealand using the modified HW8 on sideband.

Classic 10m DSB TX

There was an article, in 73 Magazine back in the early 1970s, about a simple crystal controlled, 1W 10m DSB transmitter. This was reprinted in a Dutch magazine and in RadCom. The schematic had at least one error (one diode in the mixer wrong way around, that I have corrected here), but it is a useful "ideas" starting point for a DSB transceiver. This circuit used PNP transistors. Today I'd use NPN 2N3904 devices and T37-6 toroids everywhere.

AA1TJ's Voice Powered DSB TX (El Silbo)

Mike has done it again - a superb piece of QRP creativity. This is from his email today:

"AA1MY and W1PID met with me on 3686kHz this afternoon. I was operating a new, DSB version of my "El Silbo," voice-powered transmitter. Both Seab and Jim successfully copied my/their calls and signal reports. Jim commented later that I would have been hard pressed to pick a worse day for the attempt. The propagation was producing severe QSB fading and the QRN was all over the place (peaking at S-7 to S-9 at times). I came away nearly dumbfounded that these two operators could pull enough of my 5mW DSB signal out of the mess, at distances of 100 and 67miles, to complete the QSOs."

10m or 6m QRP DSB ideas

Having finished my SixBox 6m AM transceiver, my mind is now turning to ideas for either a 10m or 6m QRP DSB transceiver. I have already breadboarded a 10m version in separate sections (RX based on the Neophyte RX, a DSB TX based on a single balanced diode mixer), but I have still to breadboard a mixer-VFO based on the NE602 which would be useful for either band. Actually a fundamental crystal x2 would give around 25-30kHz shift on 28MHz and around 50kHz on 50MHz, so this may be a simpler, and adaquate, route. However crystals "to order" are expensive these days, although the spec (temperature, cut frequency accuracy, etc) would be very low.

Today I noticed another 6m DSB schematic from a Japanese ham. There are plenty of good ideas from JA land where, despite commercial rigs, homebrewing is still in strong. See http://www6.plala.or.jp/jr8dag/micro6dsb/mi6dsb02.htm for JR8DAG's schematic. In my view, this is a rather complex schematic and I am sure it could be simplified.

SixBox 6m AM QSO

A solid QSO this evening with G6ALB (2 miles away) on 6m AM using the 50mW SixBox rig with vertical antennas at each end. In the other direction, using the super-regen RX at my end, we did some sensitivity tests with Andrew putting a signal generator on and gradually dropping his AM modulated carrier. I was able to copy his signal when it was reduced to 0.5mW.

I also tried to receive a 7dBm carrier from Andy on 70.26MHz AM using the retuned super-regen RX, but was unable to hear it, although we were both using 6m antennas which were not resonant on 4m.

Currently I am putting a rebuilt SixBox in a real box. Later, I will make a breadboarded DSB version.

More details on the SixBox page of my website.

The SixBox - A Simple 6m AM transceiver

NB There is an updated schematic uploaded June 28th 2009.

Well, I've completed a breadboarded version of the SixBox, an ultra-simple 6m QRP AM transceiver which I've had in my mind for some time. As it stands, without a linear, it produces around 50mW AM (200mW peak) from the 2N3904 series modulated PA. It is not in a box, just a rats nest on a piece of copper clad board, but it works. The receiver is a super-regen using MPF102s with an isolating RF amplifier loosely coupled to the super-regen detector. A varicap diode (to be added) is used to tune across the band. The TX consists of a 25MHz xtal, a x2 multiplier and PA both of which are series modulated. Ubiquitous 2N3904 transistors are used throughout apart from the super-regen stages.

Click on the schematic to see what it consists of. It would readily scale for 4m although the T37-6 toroids would be a bit marginal this high. I was surprised how well they worked at 50MHz.

I should be DELIGHTED if someone wanted to develop this circuit further and maybe produce a small PCB and case.

On reflection, I think the DSB version of this would be a better bet. Much of the TX line-up can be re-used for this but I would use a DC receiver. 200mW pep of DSB (equivalent to 100mW SSB) would be quite a useful power. My next project will be to complete the DSB version, either for 6m or 10m.

10m RX using 14.3MHz ceramic resonator

Tried using a 14.3MHz ceramic resonator (in a x2 oscillator circuit selecting x2 at the collector) with the Neophyte derived 10m RX today. Applied the external oscillator to pin 6 of the NE602 and used the on-chip LO as a buffer.

With a 60pF variable capacitor I could pull the oscillator from 28.563-28.641MHz i.e. about 80kHz shift. Adding some inductance in series with the resonator allowed it to pull lower, but I could not make the circuit work reliably with too much inductance. Conclusion so far is that with a ceramic resonator at a better frequency (e.g. 14.23 or 14.24MHz) this would make a neat 10m SSB RX with the Neophyte. A small amount of series inductance would allow around 100kHz shift around the main SSB part of the band.

Next I'm going to try the mixer-VFO using a 32MHz xtal and a 3.58MHz ceramic resonator. This should cover around 28.40 - 28.46 I think.

Ceramic resonator VFOs

David W Searle ZL3DWS sent me a very useful link about the use of ceramic resonators in VFOs. These can be pulled more than crystals but the pulled stability is still better than a VFO. I am trying to use these in a mixer-VFO for my 10m DSB rig. See the webpage by Jack Ponton GM0RWU at the address below. I think taking the output differentially from a tuned circuit across the output pins of the NE602 would be better with a simple link winding down to 50 ohms. http://eweb.chemeng.ed.ac.uk/jack/radio/projects/resnote3.html .

10m (and 15m) DSB rig ideas

The GQRP club sell xtals for 24.906MHz for £2 each. They also sell 3.58 and 3.68MHz ceramic resonators at 50p each. Now, mix 24.906 with either 3.58 o 3.68 with an NE/SE602 and you end up with a stable and simple mixer-VFO (when the ceramic resonator is pulled in a VXO) covering two very useful parts of the 10m SSB band or the 15m SSB band. All it needs is a filter on the output to select 10m or 15m injection. I have ordered the xtals and ceramic resonators and will start on the mixer-VFO when the parts come.

My idea is to use the VFO with a simple DSB TX and DC receiver. Such an arrangement will give a simple 10m (or 15m) DSB transceiver covering very useful parts of either band, but with few parts.

DSB transceiver circuits - 10m and 6m

Michele IZ8JJI has just sent me a link to a neat, very simple, DSB transceiver suitable for either 10m or 6m. It is from a Japanese magazine (CQ?). See http://www.cqpub.co.jp/hanbai/books/15/15061/15061_p.180-181.pdf

I am not sure of the power (milliwatts I think) but WHAT a neat circuit!

6m Lunchbox - further thoughts

Further thoughts on the G3XBM answer to the Benton Harbor Lunchbox for 6m. Maybe it would be better to make the rig DSB instead of AM? The design is almost as easy and a VXO crystal at 25.08 or close would give some 50kHz VXO range (50.15-50.20) in a useful part of the band. Also, it would be more efficient than AM. In sporadic-E openings it would produce some DX contacts too if the power out was around 0.5 to 1W pep.