Gmail Tap

OK it is April 1st but this is actually not such a daft idea http://mail.google.com/mail/help/promos/tap/index.html

Trying to see the light (very dimly)

As other nanowave enthusiasts have told me, it is very useful when experimenting with light beams at 481THz to have some sort of lab test range that allows repeatable sensitivity measurements. So, today I rigged one up.

Up on the ceiling of my "lab" I've semi-permanently fixed a standard brightness LED fed via a 1K resistor with a 1kHz tone from my 0-1MHz audio/LF generator. I can now adjust the output until the LED is only just visible to the naked eye, with difficulty,  when the room is totally dark. I then place my optical heads (without lenses) on the same spot on the workbench aiming upwards to the very very dim light. The spacing is about 1.5m. I had to check that the signal being picked up was optical and not inductive coupling from the wiring. With this setup, my most sensitive detector can detect the beam at around S2 in a pair of headphones.

I've been experimenting with the drain current of the detector FET and with optimisation of the post cascode stages of my KA7EOI head and may have made 1-2dB S/N improvement. With this test setup I can make very repeatable sensitivity measurements. However, as the tests require TOTAL darkness I have to judge the S/N by ear. My laptop could be set up outside the room with a long screened audio lead allowing Spectran to be used to measure quantitatively the S/N but I'd have to ensure the darkness of the room is preserved.  For an example of this see http://reast.asn.au/optical/Light_Preamp_Performance_Comparisons_20071119.pdf .

At least now I can do lots of initial tests at home and only venture into the field when I have good confidence in the system performance.

Elecraft KX3 - first products delivered

This email appeared on the KX3 Yahoo group today:

"I will do as I told the crew at Elecraft and help the pressure.

At 9:10 AM this morning (Sat) a nice brown truck pulled up in my drive and after I signed for it, gave me a 12"x8"x6" box that said "ELECRAFT KX3 Ultra-Portable HF/VHF Transceiver s/n 0024

Yes ... I got a call yesterday

I am hoping within a hour to be on 20 meters chasing WG0AT on his SOTA trip and putting it thru its paces on digital.

Thank you all at Elecraft ..

The game begins
You will be happy .......

Paul KB9AVO"

8.971kHz VLF earthmode test

30t loop on the ground feeding E-field probe

An 8.971kHz earth mode (VLF through the ground) test was conducted today at 1.6km and 3.5km from home. The TX was 5W QRSS3 into 20m spaced baseline earth electrodes: one a 1m copper rod at the
far end of the garden and the other end grounded to my copper hot water tank in the house.

At the RX end I was using either (a) a 30t tuned loop feeding either the PA0RDT or G3XBM tuned E-field probe, and (b) the same E-field probes but fed with a 19 inch whip instead of the loop.

Good signals were received at both locations with the loop into both probes but there was no detectable signal when receiving on the 19 inch whip into the EFPs.

It was a struggle to see the difference between the PA0RDT and G3XBM E-field probe/preamps, but I think results with my tuned drain design may have been marginally better on this test.

VLF E-field probe update

Today I compared the PA0RDT E-field probe against my own VLF design (on the sub-9kHz website) that uses an 8-9kHz tuned circuit in the FET preamp drain. To do the test I had my wife hold each E-field probe at arms length above her head in the bottom of the garden whilst I made screenshots on the PC. The S/N on Alpha beacons and 18-22kHz MSK signals is similar with the PA0RDT and mine but the PA0RDT design has a lower noise floor. So, in future I will use Roelof's design. Some measurements made by G3ZJO today compared the PA0RDT design against the narrower band VLF E-field probe by DK7FC and Eddie's results suggest comparable performance within the limits of experimental error.

E-field probe tests

This afternoon I built a version of the PA0RDT E-field probe. In the shack the interference was horrendous, but in the garden with the laptop PC just below it the reception of the VLF Alpha beacons and MSK signals around 18-22kHz was excellent. I need to do more noisefloor measurements and elevate the probe higher, but I think this is going to work well when mounted at the top of my neighbours tree that overhangs into my garden. This is a sycamore which I trimmed back a few months ago. The E-field probe can be mounted "in the clear" some 20m from the nearest house at a height of around 5m off the ground. I now need to rebuild it into a watertight box and think how I am going to get the output and power feed to the shack that is at the wrong side of the house some 30m away. Some have used CAT5 twisted wires for this purpose and I guess this would be a good, simple solution, although less suitable if I want to use the probe at 137 and 500kHz where a coax feed would be better.

ZL9 Campbell Island (near New Zealand)

There is to be a DXpedition to Campbell Island (OC-037) in November this year. See http://dx-world.net/2012/zl9hr-campbell-island-dxpedition/ .  This reminds me of the excellent conditions on 20m AM back in the 1960s when I remember hearing a station on Campbell Island working the UK with S9 signals early one morning. In those days I'm sure the prefix was ZL4 though.

Is it just me, or is it much more difficult to hear and work DX stations these days compared with back then? Some believe that the ionosphere has actually deteriorated in the last 40 odd years so that, despite rising sunspot numbers, conditions are not as good as they were years ago.

SPRAT 150 is out

The latest edition of the GQRP club's SPRAT quarterly magazine arrived on my doorstep today. As always, this is filled with a variety of interesting articles and this edition even includes one I wrote about 481THz optical comms "over the horizon", but don't let that put you off, HI.

GQRP club membership, with SPRAT 4 times a year, remains the best bargain in amateur radio in my opinion. More details on the GQRP club at www.gqrp.com .

I note that GQRP club sales is now selling fundamental crystals for 28.060MHz (suitable for my Chirpy rig) at just £2 each. This is a useful source of QRP related parts for club members.

Join!

Amateur radio postage stamps

The excellent Southgate Amateur Radio News page today mentioned that Luxemburg is bringing out a postage stamp to commemorate the 75th anniversary of the Luxemburg radio society. See http://www.southgatearc.org/news/march2012/amateur_radio_stamp_for_luxembourg.htm .  This got me wondering how many other countries have issued stamps with an amateur radio theme? I recall the USA doing a ham radio stamp in the mid-1960s.

Wondering if there were others I did a search on Google images for amateur radio postage stamps. Interesting.

VLF E-field probes compared?

Both the PA0RDT and DK7FC E-field probes antennas are suitable for detecting weak VLF amateur signals around 8-9kHz when used with the right PC software. See https://sites.google.com/site/sub9khz/antennas for the schematics of these and others.

What I'm wondering is has anyone done a "like-for-like" test to compare their performance? With a near identical test set-up (same height above ground, same ground and PSU noise conditions) it should be possible to compare noise floor, sensitivity (S/N of Alpha beacons, VLF MSK signals), and by looking for the intensity of the intermod line at 9kHz from broadcast signals in Europe get an indication of dynamic range. Has anyone done this test at VLF? If not, it looks like I shall have to do it and "suck it and see".

Incidentally, the PA0RDT voltage probe antenna makes an ideal antenna for shortwave, medium wave and long wave DX SWLs. It is essentially a high dynamic range wideband receive antenna which is tiny, yet capable of excellent results if mounted in the clear in a low noise environment ideally away from house electrical interference.