20 Sep 2009

136kHz band WSPR reception

Jim M0BMU was firing up his transmitter on 137kHz today using WSPR. Managed very good reception of his 200mW ERP here at 69kms range. See screenshot - he is the yellow dashes. He was clearly audible by ear too, so a 12 wpm CW signal would have been copied well.

19 Sep 2009

500kHz TX transverter schematic

This is the schematic of my 500kHz QRP TX transverter (from 28MHz). The next steps are (a) to add a couple of relays and RF sensing so that I can use it as a full RX/TX transverter and (b) changing the output stage to an FET such as an IRF510 to increase the output to 5-10W from the 700mW currently.

ERP estimates on 500kHz

Just got this letter from M0BMU who has estimated my ERP on 500kHz currently .
Dear Roger, LF Group,

It is interesting to make an estimate of what G3XBM's ERP might be...

The noise level at M0BMU during relatively quiet daytime conditions I estimate to be of the order of 3uV/m in the 2.5kHz WSPR reference bandwidth. The reported SNR gets up to about -25dB, making the signal level from G3XBM about 0.18uV/m.

ERP = (Ed)^2 / 49; with E = 0.18 x 10e-6, d = 69000m , ERP is about 3uW with only "geometric spreading" propagation losses. But there is some additional reduction in field strength due to ground wave propagation losses, perhaps 3dB with "good" ground, so the ERP would then become about 6uW. Diffraction losses due to the curvature of the earth are negligible at this distance.

Obviously, this could be +/- several dB due to various uncertainties, but should be of the right order of magnitude. Plenty of potential for improvement then!

Cheers, Jim Moritz
73 de M0BMU

500kHz WSPR screenshot from G3XVL

Chris, G3XVL, in Ipswich has just sent me a screenshot of my 500kHz WSPR signal this morning when I transmitted at 100% for about 30 minutes. It clearly shows the drift when I go on TX continuously. The drift is about 40-50Hz worst case. I now suspect this is drift in the FT817's reference oscillator as the box heats up and NOT drift in the transverter. I may try using the IC703 as this has a larger mass and should drift less.

The very strong signal is M0BMU and the one towards the top is G7NKS. No new reporters overnight, so it remains at 4 reporters with best DX 69kms when using less than 1mW ERP.

18 Sep 2009

Breaking the 100kms barrier on 500kHz QRPp?

500kHz is proving quite a challenge at the moment: before I modify my set-up in a few weeks' time to increase my ERP ( less than 1mW currently) I want to get a few reports from greater than 100kms away. This target seems elusive so far, with the best DX remaining at 69kms, some 31kms short of my target.

The picture shows the longest paths my signals have spanned so far.

Sixbox 6m AM .....in Japanese

A few months ago I was asked by Junichi Nakajima-san, JL1KRA, if he could translate an entry on my blog about the Sixbox 6m AM transceiver to use in a Japanese magazine dedicated to AM and its use. Of course I said yes. A few days ago he kindly sent me a copy of the magazine. Now, I can't read Japanese, so I have no idea what the article says but it is nice to see the article in Japanese. Incidentally the magazine called 6mAM shows there is a great deal of interest in AM in Japan.

Since this blog entry was written, the design of the Sixbox has moved on and the revised schematic is on the Sixbox page of my website at http://www.g3xbm.co.uk

Junichi, I do not have your email address but thank you for sending me the magazine, the information and the 50MHz crystals.

A Brazilian Fredbox 2m AM transceiver

Hamilton, PU2XLB, has built a Fredbox 2m AM transceiver using the G4BYE adaptation of my original schematic. The G4BYE version has an LM386 audio rather than a simple stage driving a crystal earpiece. Hamilton, PU2XLB, has managed a 10km QSO already. He also has a Youtube video of it in action on RX.

17 Sep 2009

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.

16 Sep 2009

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.

15 Sep 2009

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.

14 Sep 2009

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.

13 Sep 2009

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

11 Sep 2009

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.

10 Sep 2009

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.

Electricity from trees?

A company called Voltree has some information on a system that generates electrical power from living trees. No, this is not a joke. See also the article on this in New Scientist magazine today.

Power levels are low, but the people involved believe there is enough energy to power monitoring systems and alert people of forest fires using energy derived from trees.

WOLF mode on 500kHz

Just set up my PC to receive and decode LF signals on 136kHz and 500kHz using a very weak signal mode called WOLF. DL4YHF, has written a GUI program to run WOLF and it's available at: http://freenet-homepage.de/dl4yhf/wolf/index.html . The program itself is available at: http://freenet-homepage.de/dl4yhf/wolf/wolf_gui_060118.zip . You need to unzip this and run the WOLF_GUI.exe file. Having set this up I am now waiting for some activity in this mode to take place so I can see if it all works. Last night M0BMU was active on the mode on 503.5kHz and was widely reported around the UK and Europe.

9 Sep 2009

Human hair solar panel??

The Daily Mail carried an article yesterday about an invention by a boy from Nepal for a solar cell array using human hair. The article claimed huge cost reductions compared with conventional solar panels. This sounds a bit like cold fusion and needs peer reviews by respected scientists in the developed world. It would be nice if was true.

BTW, do YOU still believe there was something in cold fusion?

10m WSPR (inter-G)

This afternoon I left the WSPR beacon running on 10m. Although the band was quiet, there was a weak trace that appeared and then faded out. It turned out to be G3JKV some 123kms away by tropo. On the stronger traces around 1422z you can see additional Doppler shifted lines as a result of aircraft reflection.

8 Sep 2009

160m WSPR

On 160m I have an almost useless antenna by accepted standards: just 15m of low wire down the garden and a central heating ground. Not only that, but my Elecraft auto-ATU cannot find a match on 160m. So, I get around this crudely by putting a 1dB pad between the antenna and the auto-ATU and it then manages to find a match. OK, I lose another 1dB but that is a fraction of an S-point.

Now, even with this crude set-up I have had reports from G, GM and PA0 on WSPR running 5W (less 1dB) into the antenna, proving that a piece of wet string is very nearly all you need to get out. Clearly, with a bit of effort I could make at least 10-20dB improvement on my signal - adding loading coils in the antenna, running out more wire and higher up, improving the ground system etc. I shall need to all of these if my efforts on 500kHz are to come to anything.

10m short skip still about

Although the main sporadic-E season is drawing to a close now, there are still some useful openings to be found, especially around lunchtimes and early evening. Lunchtime Sept 8th the band was open to central Europe with several 5W QRP SSB contacts possible, one to a mobile on the move in E. Berlin.

Never give up on 10m. If all else fails, you can always do a bit of WSPRing and see what surprise openings appear.

7 Sep 2009

500kHz TX activities - closer

In recent days there has been an upsurge in interest in WSPR beaconing on 136 and 500kHz with loggings now running into thousands whereas only 1 month ago there was hardly any WSPR activity on these LF bands. I am now regularly listening on both 136kHz and 500kHz WSPR.

My next priority is to get a basic 500kHz WSPR TX capability in place, if only a few watts to my very inefficient antenna. Once I get a signal of any kind I can start to improve the antenna and ground system and see how reports develop. The most probable route will be a transverter using the FT817 as the prime mover using an SBL1 mixer and a small IRF5xx FET PA This may take a few weeks, but I hope to have something on the air in October.

2 Sep 2009

6m aircraft scatter

Just been WSPRing on 6m and spotted G3ZJO, who is 79kms from here, by aircraft scatter. This is clear from the WSPR waterfall display which shows all sorts of Doppler shifted traces as well as the one that was successfully decoded. I suspect this is aircraft stacked over, or approaching or leaving, Stansted or Luton Airports.

1 Sep 2009

More on the active LF antenna

Yesterday I used a PA0RDT designed active antenna (but with MPF102 and 2N3904 devices and a 9V supply from a PP3 battery)to listen successfully on both 500kHz and 136kHz. This is a bit better picture of the antenna. Although it is recommended it is mounted well in the clear and away from the house (feeding the power up the coax), I just stuck mine onto my double glazed window - it still worked and heard stations on both LF bands. This is the ENTIRE antenna - no wire is needed down the garden.

In the last few days SM6BHZ has been heard in central Bejing China using a version of this antenna.

Guess what? A SUNSPOT!!!!

Hang out the flags - there is a sunspot on the surface today!