Cambridge Radio Club is 90

Today, the Cambridge and District Amateur Radio Club held a 90th birthday picnic at the village hall in Foxton, Cambridgeshire. The weather was good and there were plenty people there. The club put up antennas for HF plus 2m and 6m with the aid of the Cam Hams group recently back from Harris in the Hebrides. I managed to get along for a couple of hours in the morning and rejoined the club. It was nice to operate on 6m with a big station (QRO and a big, high yagi) for a change. The band was open to Europe and there were plenty of stations to work. In the afternoon, at home, I worked their special call GB0CAM on 2m FM. A nice friendly day.

The CDARC website is http://www.cdarc.org.uk/
Cam Hams website is http://www.camb-hams.com/

Transatlantic 6m summer super DX - what mode?

The usual assumption for the super-DX across the Atlantic from Europe to the Caribbean and S.America is multi-hop sporadic-E. Certainly the contact to K1TOL that I made a few years ago was by this mode.

But, with the recent questioning of the mode for the Europe to JA path on 6m in summertime, I am wondering if mesospheric cloud reflection is a possiblity for other extremely long paths too? YV and other places on the north of South America is some 8000kms away from here, yet people seem to work such distances every summer on 6m.

I'd welcome your comments and views.

QRP 6m multi-hop Es SSB QSO

Just switched on the FT817 at 0820z and worked EA8CQS (Canary Is) on 6m SSB with 5W to the vertical. DX was 3010kms. He was quite weak so surprised he got me so well.

Noctilucent cloud DX - microwave mega DX mode?

There was a MOST interesting note on the ARRL propagation report tonight:

"Noctilucent Clouds Return - As reported at spaceweather.com on June 1, the first noctilucent clouds (NLC) of the 2009 season were sighted over Russia on May 27. NLCs typically appear about 20 days prior to the summer solstice, increase quickly to a high summer level, and then disappear about 50 days after the summer solstice. These clouds are mostly a high latitude phenomenon, and are believed to be composed of ice crystals. VHF radars see very strong echoes from these clouds, and since they are at mesospheric heights (80 to 90 km), they are also known as polar mesosphere summer echoes (PMSE). These clouds are hypothesized by JE1BMJ and others to be responsible for 6m propagation across high latitudes (for example,
from the East Coast of North America to Japan) during the northern hemisphere summer. This mode of propagation has been dubbed Summer Solstice Short-path Propagation (SSSP). Check out page 34 of the February 2009 issue of WorldRadio Online (available free at
www.cq-amateur-radio.com/wr_back_issues.html) for a general discussion of PMSE and SSSP and for references in the technical literature. To reiterate, SSSP is still just a theory,
but the occurrences of QSOs appear to match the occurrence pattern of PMSE."

Now, there is also evidence (from radar returns) that microwave DX might be possible using the same noctilucent clouds, possibly allowing superb DX possibilities on 10GHz possibly even with low power.

This is a whole area of future ham research just waiting to be exploited. It may be one upside of global warming as these high altitude clouds are now more common than hitherto.

For more on these mesospheric clouds see http://www.chiandh.me.uk/p/Noctilucent_cloud#Results

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.

6m (4m?) distraction

OK, I'm about 40 years out of date with my technology, so if I live to be 100 you may just find me getting excited by SDRs and the like when the rest of you are busy with thought and matter transfer. Who cares, it keeps me happy and doesn't cost a lot :-)

This last week I have had a spurt of creative (?) energy and have been building. Firstly I started work on the 10m DSB rig. The RX is fully working using the Neophyte as a basis. Next I tried the 14.3MHz ceramic resonator-doubler idea for the LO but was disappointed that I couldn't get it to reliably pull down to a useful part of the 10m SSB band. The plan was to look at a mixer-VFO and then put the whole breadboard together with the DSB TX. But I got distracted....

Instead, I built a simple super-regen AM RX for 6m (or 4m), which works well using T37-6 toroids. All that I need to do is arrange for the RX tuning across the chosen band with a varicap. Next I built a simple series modulator (even simpler than the Fredbox one) and now I've started on a very simple AM TX strip and small linear. The idea is to do a Heathkit Lunchbox "Sixer" AM transceiver replacement but in a very simple solid state and no-IC design. The design is likely to produce around 100mW of AM and can be completed for either 6m or 4m. I haven't decided which yet.

There is not a lot of AM on 6m, but a bit in pockets on 70.26MHz. I know 100mW is not much. But, this is a project I've just wanted to do for years and you'll have to bear with me. When this is done I'll get back to the serious stuff - the proper DSB transceiver that is!

Colpitts VFO parts value calculator

PY2OHH is a very creative ham with an excellent website full of good circuit ideas. I noticed a neat Colpitts VFO calculator there today. You put in the frequency range needed and the variable capacitor range available and out pop all the capacitor values in the tank circuit.

Since including this link the original site has removed the schematic.

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.

10m Neophyte RX

Today I breadboarded a 10m version of the Neophyte direct conversion RX from a 1988 QST. The Neophyte uses an NE602 as the RF amp, LO and mixer and with the output fed differentially into an LM386 audio amp. In my version I used a single toroid 10m tuned circuit and a free running LC oscillator using the oscillator onboard the NE602. As it was a lash-up, frequency stability was a bit average, but it had good sensitivity and allowed plenty of Europeans to be copied on 10m CW and SSB. I used an 8 ohm LS and there was plenty of audio. Overall I was impressed that something this simple worked so well.

Tomorrow I want to try the same circuit but using an external VFO using a VXOed 14.3MHz ceramic resonator in an oscillator/doubler. I am hoping that the resonator will pull well over 100kHz so that it covers a useful part of the 10m SSB band. The same LO will be used for the DSB transmitter assuming it pulls OK and is sufficiently frequency stable.

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 .