Building a 477kHz receive loop

With the approach of the winter LF season it was time to look at building an LF receive antenna to put on the apartment balcony. My attention was drawn to the design by wa1zms A Simple Loop Antenna for 500 kHz. It looked straightforward to build. The half inch wood was available at the local hardware store. The hard question was how to cross the wood at the centre. Luckily Bob WA5YWC stepped in and milled the crossover portion to be a snug fit, solving that issue. Each arm had 8 holes (for the 8 turns of wire) spaced at 0.5". The two arms were secured with a brass screw to allow dismantling

I had found some 10/46 Litz wire on ebay. It soon became very apparent that this was too fragile to use as it snagged and broke with ease. A further internet search revealed a supply of the more robust 10/26 Litz wire from scotts electronic Parts It was not cheap but it would do the job. The wire was mounted on the frame easily and terminated with two brass nails. I measured the inducance and found it was 65uH, meaning around 1700pF would be needed to resonate the loop at around 475kHz. This value was soldered across the brass pins.

A visit to the local emporium produced all the components for the preamp including a box and stripboard. This was assembled and attached to the mast with adhesive backed velcro and a 9V battery attached. . I hooked it up to the ANAN-10 and took a listen around 475kHz.  but I noticed that the PowerSDR software was indicating an A/D overload. The preamp was acting as a wideband power oscillator! I re-examined the wiring finding a couple of extra short circuits which were fixed. Reconnecting it to the receiver I could hear the WG2XIQ on 475.7kHz and the antenna showed the expected very sharp nulls

131028 0152  25  -7  0.3   0.475663  WG2XIQ EM12 30
131028 0156  24  -8  0.5   0.475663  WG2XIQ EM12 30
131028 0200  23  -9 -2.0   0.475663  WG2XIQ EM12 30
131028 0208  10 -21 -1.4   0.475663  WG2XIQ EM12 30
131028 0212  10 -21 -0.3   0.475663  WG2XIQ EM12 30
131028 0216  11 -20 -0.2   0.475664  WG2XIQ EM12 30

Hamcom 2013

June brings the annual Hamcom hamfest to Dallas, which as always clashed with the ARRL June VHF contest.

As in the last three years I volunteered to help man the Elecraft Booth, but this year there was a change as Eric WA6HHQ and wife would not be attending, but I would get to work with Lisa, who I had spoken to a lot while placing orders over the phone, Dave  and Bob K6XX who I had spoken to but never met.

The trade show exhibitors this year started earlier at 0800 and officially closed at 1800, making a long day. Lots of questions, the most popular being "When can i get the KXPA100 100W PA for the KX3" , which was on display. The other new Elecraft item for me was the K3/0 mini, which is a remote front panel for remoting the K3 in a just sufficient box; you wont need to carry a full size k3 box in future. Bob was remoting his HF station in California using one, which worked as well as the Plano conference centre's wired internet would allow (horrible latency/reliability). The ISDR app for the Ipad to produce a panadaptor display (demonstrated by Eric at last years Hamcom) for the KX3 also generated a lot of interest, but a lot wanted an Android app!

I did see a useful  aftermarket product for the KX3 which was an extended pair of sidepanels and a perspex cover to protect the front panel knobs on the KX3. http://gemsproducts.com/covers.html So useful i ordered a set Sunday morning

The outside flea market wasnt too exciting, but i did get a GPS board with CDMA modem assembly for $1. The Inside Fleamarket produced a couple of the HP 12V 47A PSU (like i used to power my 100W 3400MHz PA) for $20 each and a Flexible solar panel. I also discovered that Buddipole now have a "knurled whip sleeve" to put over the telescopic whips with the 1/4-20 thread (as I use on my PAC-12 HF antenna) to stop the whip assembly wobbling in its ferrule, so I ordered a few

I did get to meet John Langridge. KB5NJD who also operates on LF as WG2XIQ, a station i hear often on 474.2kHz. Unfortunately I could not get to his talk, but I did persuade him to email me his Powerpoint which made for interesting reading.

500kHz in USA

From the LF reflectors I had noticed new LF licences had been issued in the USA and new modes had appeared so it was time to take a look with my HPSDR and DX-B wire antenna

Monday night I looked on 474.2kHz and saw a signal from WG2XIQ (identified by his 12wpm ID) but couldnt decode as WSPR or the new JT9-2 digital mode, indeed they didnt look on the panadaptor like either mode. It was late so I switched off

Tuesday morning I tried the setup on 30m QRSS and noticed a lot of jitter on the Argo display. I was suspicious of the VAC connection between PowerSDR and WSJT-X so I ran a cable from the headphone output of the HPSDR to the computer mic input. QRSS looked fine and was easy to copy

Tuesday evening listened on WSPR on 474.2MHz. saw 2 signals

WG2XIQ in Fort Worth 0520 to 1432z

121121 814 30 0 -0.5 0.475686 WG2XIQ EM12 30 0 1 0

WG2XJM in PA from 0606 to 1156z

121121  820  8    -24      -0.5  0.475775  WG2XJM  EN91    37      0       1       0

Wednesday evening listened on the new JT9-2 (-2 is 2 second transmissions) on 474.2MHz. saw 2 signals

WG2XIQ in Fort Worth 2352 to 0532z

0820

10

-5

0.1

1420.6

0

14

WG2XIQ EM12

WG2XJM in PA was also seen at -33dB at 0254.

I also heard the "local" WD2XSH/6 and WD2XSH/7 beacons and the WD2XSH/31 beacon in Virginia