A new reception report on 500kHz

This morning I was received on 500kHz WSPR by G7NKS near Biggleswade. This is his screen shot showing my signals. Notice my drift upwards when left on 100% TX - must do something to slow this down. It's not a problem when not on continuous TX, it's a thermal issue in the up-converter oscillator.

So far I've received reports now from 4 different stations on 500kHz, which is encouraging.

500kHz - antenna "improvements"?

This evening I am trying a different approach to the 500kHz antenna. My 15m longwire is strapped to my ground wire and now is acting as a radial. My main antenna is now the vertical coax feeder up to my 28MHz wire halo antenna. The coax has inner and outer strapped together so it is acting as just a thickish wire. The 28MHz halo will act as a top capacity hat.

The WSPR beacon will run overnight, so I will see whether the changes make my signal any different. Measured antenna current is quite a bit higher, so I am moderately hopeful a few more stations might receive my WSPR beacon if the ERP has increased a few dB. It will still be <1mW though.

After the first hour, I think my reports from M0BMU seem slightly better than before, maybe 2-3dB stronger? This is a hopeful sign, although it may just be conditions and QRN levels at the far end.

The 500kHz drifter....

G6ALB sent me a screenshot tonight of my 500kHz WSPR beacon as it was warming up. For the first 30 minutes it moved some 59Hz, not a lot really, but it looks dramatic on the WSPR waterfall. The reason is the transverter crystal oscillator settling down after first switch-on. At the moment the whole thing is a rats nest in the open on the desk: it needs putting in a box. The WSPR beacon was again heard by G3XVL at 61kms today.

Even lower power success on 500kHz

This afternoon I fired up my 700mW 500kHz WSPR beacon and wet string antenna (ERP microwatts) and got 3 reports from G3XVL at 61kms. So, I tried putting a 6dB then a 10dB attenuator between the PA and the ATU. Even with a power from the PA of just 70mW (never mind what that would be as ERP from the antenna!) he still gave me a -25dB S/N report! These were the three reports in reverse order:

2009-09-14 14:42	G3XBM	0.503829	-25	1	JO02dg	0.001	G3XVL	JO02nb	61	112
2009-09-14 14:40	G3XBM	0.503827	-23	1	JO02dg	0.001	G3XVL	JO02nb	61	112
2009-09-14 14:36	G3XBM	0.503823	-18	1	JO02dg	0.001	G3XVL	JO02nb	61	112

This suggests that just 35mW from the PA would have been enough to span this distance, even with my tiny antenna and poor ground.

More QRPpp success on 500kHz

My tiny 500kHz WSPR TX station was heard 69kms away at dawn today with a report from Jim M0BMU who spotted me several times. I also had a lot more reports from G3XVL (61kms) , some 10dB stronger than his first report last night, as well as more from G6ALB (3kms).

The picture shows my 500kHz ATU on the bedroom dressing table. This is the ONLY thing between the 700mW QRP TX and the 15m of wire dangling down the back garden - no big loading coils etc. The small toroid is a 1:50 current transformer so I can measure antenna current with a multimeter. I tune up by getting the best received signal by ear adjusting tap points used, then carefully peaking the series capacitor for maximum antenna current, which barely shows anything!

Next step is to convert the transverter to full transceive which should only need the addition of a couple of relays and an RF-sensed changeover.

500kHz QRPpp WSPR TXing - success

Well, my unbelievably simple 500kHz station DOES get out! I've now received four WSPR beacon reports from G3XVL in Ipswich some 61kms away. I've also had lots of spots from G6ALB some 3kms away.

My rig....

Antenna: 15m of wire a few metres above ground, just 2m is vertical.
Ground: The radiator in the bedroom!
ATU: A ferrite rod with coil taps and a 500pF variable capacitor
TX: 700mW out of the PA from a 2N3904/2N3906 pair
ERP: just a few microwatts (I can barely measure the antenna current!)

Sure, a big antenna, plenty of power, a loading coil the size of a dustbin would all help get further and more often, but I am TOTALLY surprised and delighted that my ultra-simple, uWs ERP, station gets out on this most interesting band.

500kHz TX transverter built

Today I completed breadboarding a very basic TX down-converter which takes a 28MHz signal from the FT817 and produces around 700mW out on 500kHz at the TX 50 ohm output. When connected to my random 15m long wire antenna the ERP is just microwatts so real QRPpp. I have managed to match my wire antenna with a tapped coil on a ferrite rod and a variable capacitor as ATU. At this stage it is not the massive loading coils that you see in the pictures of "proper" 500kHz stations but this will have to come if I am to make any real progress along with more power.

This evening I've put this TX on the air on 500kHz WSPR, more in hope than expectation! It is just possible that some of my near local 500kHz stations (around 40-60kms away) might just manage to decode me at around -30dB S/N on WSPR. A test is planned with G6ALB a few miles away on Tuesday evening when I shall try both CW and WSPR transmissions.

New (and lower) sunspot peak predicted

The latest sunspot prediction from NOAA dated Sept 8th 2009 shows a predicted peak of cycle 24 in May 2013 with a high of just 90. See http://www.swpc.noaa.gov/ftpdir/weekly/Predict.txt

500kHz WOLF - transatlantic?

This evening, I'm going to have a go at listening out for one of the USA stations on 500kHz who will be testing with WOLF (very weak signal mode) overnight. Not sure what my chances will be but it's worth a go. WE2XGR/2 (Burlington CT, USA) will be on 508.5kHz for about 4 hours from 2230z.

UPDATE: Sadly no copy. I left the rig and software running all night but clearly my system did not have enough sensitivity.

WOLF weak signal mode success

After a frustrating evening of not decoding a WOLF signal, I was told how to calibrate my PC's sound card. Then I retried decoding M0BMU's signal and met with immediate success:

2009-09-10 21:15:29 >WOLF10 -r 8100.257 -f 1000 -t 1 -w 0.0000
t: 24 f:-0.339 a:-1.5 dp: 85.6 ci: 7 cj:272 M0BMU IO91VR 2W -

It seems this mode is more critical than WSPR but offers the prospect of decoding even weaker signals on the LF bands. The calibration is easily done using the 198kHz Radio 2 signal and takes only a couple of seconds.