4m transverter boxed and finished (for now)

G3XBM 4m transverter - finished (for now) with 2-3W pep

Another good day today saw the 4m transverter completed and even boxed. I also did the FT817 DC switching mod  to put 5V DC on the antenna pins when on TX. It was easy to do, with care, and made the transverter switching so much easier. Don't understand why it was not there as standard for the sake of 1 capacitor and 1 resistor. The limitations with the current design are:

• IF breakthrough rejection at 28MHz is not brilliant, as one would expect from a single tuned circuit on the NE602 input. I can change the input to a top coupled pair to help, but will see how it behaves on-air first.
  
• LPF on the PA is just a single 3 component Butterworth. At some point I should add another section, but as the drivers/PA are linear all the way through, the 2nd/3rd harmonics should be reasonable already.



GB3BAA 4m as received

• The TX strip has DC power on it even on RX. I need to arrange to switch this off later, but I am not worried that there is another 50mA or so when on RX at the moment.

This evening I have rigged up a horizontal dipole for 70MHz in the loft and am ready to find some locals to work. So far just the 70.016MHz GB3BAA beacon 89km away visible well with Spectran (20dB S/N).

4m QRP transverter progressing well

4m QRP transverter (so far)

Today I got on with the 4m transverter build adding the TX LO buffer, the TX mixer, drivers and PA. Output power is around 2-3W pep from an MRF237 PA device (SD1127 equivalent) I had in the junk box. All seems stable and well. All that now remains is to add the TX-RX switching circuit and put it in a box. At the current rate of progress, and barring disasters (like blowing up the PA - my last MRF237) the project could be completed next week.

DK7FC's report on his 10th VLF test

This is an extract of the note from Stefan to the LF-reflector about his tests last weekend:

"Dear LF/VLF group and further VLF watchers :-)

After another very successful, exciting and fascinating /p VLF experiment i want, as usual, thank all the many (>=24) receiving stations who took the time to arrange a suitable antenna/receiver, PC and to watch the experiment and take some interesting captures. The transmissions took place on 2 VLF bands, 33km (8970 Hz) and 58km (5170 Hz).

So, thanks to TF3HZ, SQ5BPF, G4WGT, G3KEV, Daniele Tincani, G3WCD, G3XDV,M0BMU, G3XBM, OK2BVG, OE3GHB, G4AYT, IK1QFK, DL3ZID, F4DTL, OE5ODL, PA3CPM, PA3FNY, DL4YHF, DF6NM, DJ2LF, DD7PC (bold = 1st positive reception on VLF).

Special thanks to Halldor/TF3HZ who wasn't member of this group before but set up a very sensitive VLF receiver and even a most intersting grabber just by my email request. This is the first VLF detection between DL and TF. My signal appeared at up to 15 dB SNR in 4.5 mHz in 2404 km. This helps a bit to get some imagination how far a transatlantic detection is away.

Sorry to those who tried without success this time, like 4X1RF. The next experiment will come soon, maybe in about one month.

So, see you in the 11th experiment. :-)

Vy 73, Stefan/DK7FC'

HamSphere internet ham radio system

How HamSphere works

When band conditions are poor or you feel like a change, you may like to have a go at a different sort of amateur radio experience by trying HamSphere, which is a virtual ham radio service using the internet to replicate HF bands and operation.

User interface is via a simulated HF transceiver presented on the computer screen. The "feel" of the transceiver is remarkably good. Of course, being an internet based virtual amateur radio system, no amateur radio equipment is needed and no RF is radiated, yet the experience is very close to that of operating a real HF radio on the HF bands. For those unable to operate real radios because of planning restrictions or other problems, this system offers some of the fun of amateur radio again. It is like CQ100, but in my opinion better.

The transceiver uses Java technology and simulates all amateur radio bands from 160 to 6 meters. The software, plus a lot more information about this service, is available from http://www.hamsphere.com/ .  The software works in Windows, Mac and Linux.

Using the system I just had a QSO with ZS4CCM in South Africa. It felt like a real "on air" HF QSO. It's no substitute for the real thing, but fun to use on occasions and when HF conditions are appalling.

DK7FC copied well here on 8.97kHz

After a few false starts and faulty kit, I managed good copy of Stefan DK7FC's signals on 8.97kHz this afternoon with my loop in the garden and this simple preamp into Spectrum Lab running on the PC. S/N was around 5-7dB in a 4.52mHz bandwidth. He was also copied in Iceland at over 2400kms.

JT65A on HF

Having seen the article on how to do this in the latest edition of Practical Wireless, I have installed the software and taken a listen/look. Main issue seems to be that the AGC in the FT817 is fierce and with close-by PSK31 signals it kills the gain of weak JT65A signals nearby. Anyway, it looks a useful mode. For HF use, download the HF tailored version at http://jt65-hf.sourceforge.net/. Not yet had a 2-way QSO but will soon when I've got the hang of this.

DK7FC/P active on VLF this Sunday

Stefan plans to be out with his kite antenna and around 100mW ERP on the VLF bands this weekend from 0700-1630utc transmitting on 3 frequencies starting with 8.970000kHz.  Progress can be monitored on his grabber located 40km from the /P location. I am hoping to copy Stefan on 8.97kHz again as I managed it back in December.

These grabbers will show when he is active:
8.97kHz http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html .
6.47kHz/5.17kHz  http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html

4m transverter - stage 1

4m converter breadboard (2N3904 oscillator and NE602)

This afternoon I breadboarded up my 4m RX converter using a 42MHz 3rd overtone oscillator and an NE602 RF amp/mixer. Surprisingly for me, all worked first time and I was rewarded with the sound of the GB3BAA beacon in Tring on 70.016MHz 90km away using my 10m halo as the antenna for now. Signal levels with this antenna were not great, but heck it works.

Next stage is to breadboard the TX mixer and buffer stages.

E-field probe test on 8.76kHz away from home

G3XBM E-field probe for 8-9kHz

With my 5W QRSS3 beacon on 8.76kHz I went out looking for my signal at the local National trust car park 1.6km from home. On the 80cm loop signals were as expected but on the E-field probe disappointing when compared with the results with G6ALB's signal at the home QTH a few evenings ago. Although I could detect my earth-mode signal using the EFP with it flat on the ground there was no copy with the probe handheld in the air. The e-field probe schematic is attached.

VLF earth-mode success: G6ALB copied at 3km on 8.76kHz

Spectran trace of G6ALB on 8.76kHz at 3km

This evening G6ALB fired up his 8.760kHz earth-mode TX at his home QTH running QRSS3 and 40W into earth electrodes spaced 25m apart. We started listening outside his QTH with a colossal signal, moving to the next village (Reach - about 2km) where the signal was still good copy. Finally we parked up outside my QTH in Burwell exactly 3km from Andrew's TX. Signals picked up in the road with my 80cm portable loop into the tuned preamp were still strong - at least 20dB S/N on QRSS3 (see attached). For some reason I was unable to copy Andrew's signals on my own earth electrode pair: I may have had a fault and need to check why, as I was expecting this to give the best result. Andrew's signal was so strong on the 80cm loop that 12 wpm CW would have been copied. His keyer and 8.760kHz signal were generated using "Direct Digital Synthesis" from a 25 MHz clock using my Digilent Spartan S3 FPGA board.

This is the first time I've received another amateur by earth-mode (conduction). The result suggests much further is possible. Experiments continue!