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!

PA1B analyses my 137kHz WSPR results

Bert PA1B has done some interesting "reverse analysis" of the WSPR reports I've given people. Working back from these you can estimate the lowest levels (in mW) that they could have used and still been copyable with me. This also gives a good guide to the likelihood of these stations receiving my weak signal. It is clear that M0BMU should be able to copy my 50uW ERP signal frequently (which he does) but that I'd need a lot more ERP to be able to get reports from the PA stations or SM6BHZ. See attached table from Bert.

137kHz transverter update

Breadboarded 137kHz 8W transverter (ERP 50uW from antenna)

Simple 137kHz QRP transverter - click for larger image

Today I combined the RX and TX parts of my 137kHz QRP transverter for the first time and all is working although I'm losing a few dB in RX sensitivity at the moment. Copying DL, SM, PA and G stations on WSPR RX. Best DX being 148km on WSPR TX.  Who says LF has to be hard? HI.

DRM - a waste of money?

Does anyone know how much the cash-strapped BBC is spending on DRM transmissions on shortwave ? Also, does anyone actually use a proper SW receiver equipped to receive this mode? Surely this mode is a total waste of money.

4m transverter paper design

Today I have been gathering data and information for my 4m QRP transverter and started on an "on paper" design around an NE602 RX mixer, 2N3904  3rd overtone oscillator, 2N3904 driver(s) and a 2N3866 PA. It is surprising how much can be done on paper before you start by referring to datasheets and on-line RF calculators. I'm wondering if my T50-6 toroids will just stretch to 4m.

500kHz WSPR - a good evening

A decent set of reports this evening with my 1mW ERP WSPR beacon on 500kHz. Best DX DF4PV's report at 597km. Also I copied Gerhard DI2AF's WSPR beacon (just over 800km) higher up the band on 505.13kHz.

FT817 antenna pin: getting a DC voltage on the inner when on TX.

The FT817 does not have a DC voltage change between RX and TX on the antenna connector, unlike the old IC202. This voltage was very useful to switch PAs and transverters. I now know how to modify the FT817 to add this feature thanks to Chris GM4YLN who sent the link http://www.kolumbus.fi/oh5iy/HW/Yaesu.html showing one way to make the mod.. Note in this link the FT817 is wrongly called the FT718. An easier to implement link is shown at http://www.bergtag.de/download/ft817.pdf . Thanks again to Chris for this one too.

4m Chinese Multimode rig and a FT817 successor from China?

There are rumours, apparently with some substance, that a Chinese mulitmode transceiver for 4m may be being designed. This would not be too surprising, although expect some delay between "being designed" and being available in the shops.

Of course, with several Chinese FM handhelds and mobiles now available at competitive prices from 4m - 70cm it can only be a matter of time before a Chinese equivalent to the FT817's successor (yes we are still waiting, waiting, waiting Yaesu!) will hit the streets, and at a knock-out price. It would not surprise me one bit if such a rig appeared before the end of 2011. Once the Chinese realise they have a ready market for quality ham gear then look out Icom, Yaesu and Kenwood as your days may be numbered, seriously.