17 Sept 2010

Shortwave America blog

If you want to look at the quirkier side of SW radio activity check out http://www.shortwaveamerica.blogspot.com which is written by Dan KC9NCF. Most recently he's talking about pirate activity just below the 40m band.

137.5kHz WSPR 7-11pm UK time Friday

137.5kHz WSPR TX transverter
My WSPR beacon will be on-air from 7-11pm UK time Friday and any reports would be appreciated.

137.675kHz QRSS3 beacon report

The <20uW ERP 137.675kHz beacon was copied again by G3XIZ 48km to the west of me last night. I'm pleased with this report as the power from the PA was less than it was a week or so ago, yet he still managed to copy me. Work is now progressing on the class-E PA based WSPR beacon which should run about 10W from the PA (ERP around 20-50uW).

iPad case with keyboard ....but why???

http://www.senacases.com/ has a case for the Apple iPad which incorporates a Bluetooth connected full keyboard. Excuse me, but why not just buy a netbook at far less half the price in the first place? In the UK there is a range of netbooks available around £180-220 whereas the cheapest iPad is over £400.

16 Sept 2010

137.675kHz QRSS3 beacon back on

This evening I restarted beaconing with my sub-20uW ERP beacon on 137.675kHz having fixed the blown FET PA. The current design is stable and seems to be working very reliably with around 4-5W from the PA. All being well the latest version of the 137.5kHz WSPR beacon will be ready and on-air this weekend. The design of this is a class-E PA and should run around 10W from the PA with an ERP of up to 50uW.

14 Sept 2010

Sub 9kHz NoVs - a step nearer

The current UK applications for sub-9kHz NoVs have now been forwarded to the Met Office and I understand they have been received. With luck we may hear about the outcomes in the next few weeks. Currently there are 3 people appying for these G3XBM, G7NKS and G3XIZ. If these are successful I expect G3KEV and several others will also apply.

ULF/ELF/VLF radio technician job vacancy

If you fancy a job engineering radio instrumentation below 10kHz here is your chance. Armargh is in Northern Ireland, which is a truly beautiful part of the British Isles.
A research-technician-grade position is available at the Armagh Observatory funded by the EuroPlanet Research Infrastructure (RI) under the Seventh Framework Programme of the European Union (EU). Salary will be in the range £18,486 - £29,719 per annum, the exact figure depending on individual experience.
The primary aim of the project is the construction of a working instrument prototype able to (a) record and store, in digital form, electromagnetic (EM) radiation signals in the ULF/ELF/VLF frequency range (3Hz-30kHz) (b) pick up naturally-occurring radiation while screening/filtering out manmade interference in this frequency range (c) be optimised for the high-quality reception of radiation thought to originate from meteors in the Earth's upper atmosphere. In addition, the equipment should be capable of operating in the field and at remote sites with a high degree of autonomy.

 See http://star.arm.ac.uk/jobs/2010/vlf_job_announcement.html

12 Sept 2010

A nice break from the radio

For the last few days we've been looking after our 2yr 10month old grandson and this has meant a break from radio during the period as he sleeps in the room used as the shack. During the days we've been enjoying some great things including a trip to the seaside, a visit to a farm with lots of young animals, picking blackberries and similar, simple pleasures. On Wednesday it will be back on with the 136kHz experiments, but we'll miss his company.

10 Sept 2010

Heatsinks and IRF510s arrive

My heatsinks and more IRF510s have arrived in the post today. All being well I'll get these into my 136kHz QRSS3 beacon and transverter shortly and be back in business by the weekend, although operating time will be limited because my elder grandson is staying and sleeping in the shack.

8 Sept 2010

Grandchildren time

After a busy few days building LF kit (and blowing it up!) it is now time again for our grandchildren. Our younger grandson came to stay last weekend and this weekend we have our elder grandson with us. The picture here is with me in the lane close to our home on his way to feed Maggie the horse, who is a favourite with both grandchildren.

7 Sept 2010

Class E PA designs

Today I made a first proper attempt at a QRP class E PA design for 136kHz. Although the values in the output circuit seemed to tie up well with theory I wasn't able to realise the expected high efficiencies, possibly because of the gate drive design. In fact I managed to blow up my last IRF510 because it got very hot and this meant aborting a WSPR test (at a sensible power level).  One resource recommended to me is http://www.alan.melia.btinternet.co.uk/classepa.htm which has a E class design spreadsheet. 

I also discovered today that 16mm diameter 3C90 toroids do NOT make good LF PA output bifilar transformers: they get very hot. The larger diameter 3C90s appear to be fine.

Overall, a frustrating day!

6 Sept 2010

Encouraging QRPp results on 136kHz tonight

This evening I had a good report and screenshot from Chris G3XIZ 48km away. This is my best report in terms of S/N and distance yet, with very clear images on the Argo screen.  I was going to try WSPR on 137.5kHz but had problems with the PA so QRSS3 beaconed instead. ERP was less than 20uW.

5 Sept 2010

Comparing 500kHz and 136kHz WSPR over a 3km path

This evening I've been running about 5W PA output (not ERP)  from IRF510 PAs on both 136 and 500kHz WSPR and getting reports from G6ALB 3km away. I'm using the same ATU (just different capacitor settings) into the same loop antenna. On 136kHz I get-20dB S/N whereas on 500kHz +10dB S/N. This is a difference of 30dB!! 136kHz seems a heck of a lot harder than 500kHz.

LATER: Just got this from Steve Olney - VK2XV:

G'day Roger,
I read with interest your observation of the behaviour of the "in the air" loop via WSPR.
"On 136kHz the best report was about -20dB S/N whereas on 500kHz it was +10dB. This is a difference of 30dB!!"
I am not surprised at the 30dB difference as the radiation resistance varies with the 4th power of frequency for the same dimensions giving 23dB difference (i.e. 10 log ((136/500)^4)). In addition WSPR reports a S/N against in-band noise.    Atmospheric noise is inversely proportional to frequency and there is about 36dB difference (500kHz being quieter) between 2200M and 600M. This difference is effectively reduced by man-made noise which is higher wrt to atmospheric noise at 500kHz compared to 136kHz. This reduces the difference in noise levels from 36dB to about 10dB to 15dB (depending on location). Therefore I would expect about (23 + 10) = 33dB to about (23 + 15) = 38db difference between WSPR reporting for 2200M and 600M.

Your measurements are reasonably close to this - given there would be other differential effects such as ground loss.

Keep the interesting stuff coming !!!
73 Steve Olney - VK2XV

4 Sept 2010

136/500kHz loop ATU

This morning I tidied up the arrangement to match my "in the air" wire loop antenna currently being used on 136kHz and 500kHz. The loop looks like a few ohms resistive when tuned so I have a 4:1 turns ratio step-down transformer wound on a 3C90 core. The loop is tuned using an old decade capacitance box and this is fine tuned with the 365pF variable capacitor. The picture shows the values needed to resonate the loop on both bands. It is simple but works fine at the QRP power levels I'm using (5W max from PAs on both bands). My report from M0BMU at 69km on 500kHz WSPR was -8/-9dB S/N which is pretty good.

3 Sept 2010

A poem that moved me

Today I went to a memorial service for a local villager who died of Parkinson's Disease after years of failing health. The church was full. This poem entitled "He Is Gone" was said at the end and I found it profoundly moving.
You can shed tears that he is gone
Or you can smile because he has lived 

You can close your eyes and pray that he will come back
Or you can open your eyes and see all that he has left

Your heart can be empty because you can't see him
Or you can be full of the love that you shared

You can turn your back on tomorrow and live yesterday
Or you can be happy for tomorrow because of yesterday

You can remember him and only that he is gone
Or you can cherish his memory and let it live on

You can cry and close your mind, be empty and turn your back
Or you can do what he would want: smile, open your eyes, love and go on.
It was written in 1981 by David Harkins. See http://www.poeticexpressions.co.uk/

2 Sept 2010

AM Day Sept 19th (info via João Costa, CT1FBF)

The ‘Associação de Radioamadores do Litoral Alentejano’ invites everyone to participate in a special Amplitude Modulation (AM) transmission commemoration, using the 80, 40, 20, 10 and 2m bands, on Sunday, Sept 19, 2010.
Frequencies and periods:

3.685 MHz - from 0600 to 0800 UTC
7.1 MHz - from 0800 to 1100 UTC *
14.286 MHz - from 1300 to 1400 UTC
29.075 MHz - from 1400 to 1500 UTC
144.575.0 MHz - from 1500 to 1600 UTC

*alternative frequency is 7.143 MHz

More loop experiments at 500 and 136kHz

Today I converted my earth electrode antenna with elevated feed wires into a full "in the air" loop for both 500kHz and 136kHz. As might be expected, tuning is now very sharp as there is no longer a 50 ohm earth resistance in circuit dampening the Q. At first I found matching and tuning impossible until I decided to match the loop with a step-down transformer (3.5:1 on a 3C90 core) and separately do the tuning. This works a treat and it is now a simple matter to tune the loop either for 500kHz or 136/137kHz.

First reports on 136kHz with the QRSS3 beacon suggest the signal is about 6dB stronger, which is a great result. The loop is wound with quite thin wire (1-2mm diameter), so a higher efficiency is possible with thicker wire, but with even sharper tuning.

LATER: Attracting any attention is turning out to be a serious issue with real QRP on 136kHz. Even with alerts on my blog, the LF-reflector and the GQRP Yahoo groups it's hard to get that many people taking a listen/look. With uW ERPs I'm beginning to think that I'm never going to be able to get much further than my present best DX of 62km.

1 Sept 2010

Last days on 56MHz (5m) - lost recording?

Many years ago Jack Hum G5UM attended the Cambridge club and talked about VHF. During the talk he mentioned a gramaphone disc being made recording the very last night of operation on 56MHz in the London area in the 1940s. Does anyone know what happened to this most historic recording?  This would be a wonderful item of ham history if it could be located.

More results on 137kHz and a better ERP calculation

Today I managed, I believe, for the first time to accurately measure the ERP of my QRPp system on 137kHz. This is the method used:
  • Using the E-field probe, FT817 (AGC off, gain backed off as far as possible and a 10dB pad between the EFP and the FT817) and Spectran I went to my usual test site 1.5km away from the QTH, 45 degrees off the main lobe of the TX loop/earth electrode antenna.
  • Measured the signal level of DCF39 on 138.83kHz
  • Measured the signal level of G3XBM on 137.675kHz
  • Repeated this three times to reduce errors.
  • Noted the difference in FS level.
Difference in signal level = 44dB . I feel pretty confident this is an accurate figure now and not effected by AGC and overload. Assuming DCF39 is 1mV/m here (info from Alan Melia)  then my FS at the test site is 6.4uV/m.  Using the formula ERP = (E*d)^2/49 where E = 6.4*10E-6 and d=1.5*10E3 gives an ERP = 1.9uW giving an antenna efficiency of -63dB using the earth electrode antenna with the elevated feed and 4W from the PA. 

The test site is about 45 degrees off the main line of fire of the antenna, so in the best direction it could be 10dB (?) stronger, i.e. 20uW ERP giving an antenna efficiency of -53dB in the best directions. Frankly I'm amazed that anyone can copy this signal at any distance, so full marks to G3XIZ (48km) and G3XDV (62km).

Mike G3XDV sent me another screenshot of my signals this morning during the tests. if you look carefully you can just make out "G3X..." in QRSS3.

31 Aug 2010

Solar activity progress

See http://solarscience.msfc.nasa.gov/images/ssn_predict_l.gif
Sunspot cycle 24 does, at last, show signs of gathering some momentum. Despite the ups and downs in the sunspot count, there is an inexorable climb now towards the next maximum, probably on 2012 or 2013. This autumn we should start to get the regular 10m transatlantic openings again which, to me, are a sign that the new cycle is here and "good" for several years. In the press there's been some alarmist headlines about solar storms around the sunspot maximum knocking out swathes of the power systems and satellites around the world. Certainly the danger exists, but surely it is a manageable risk with planning and contingencies in place? See news.com.au on this subject.

LF/MF antenna change

Today I changed the earth electrode antenna by raising the height of the connecting wires to form a (part) loop in the air as well as in the ground. The loop part in the air has an area of >100 sq metres.  This should increase the effective loop area by a factor of at least 2, thereby improving the ERP. Later I'll repeat the tests with just the loop in the air only, so I have 3 different sets of results to compare. On 500kHz WSPR my signal with M0BMU (69km) was 6dB stronger than before with the earth electrode antenna. At the moment I am QRSS3 beaconing on 137.675kHz and seeking reports.

29 Aug 2010

136kHz WSPR - first report received

Well, it is no great DX at 3km away in the next village, but I've now received my first WSPR report on 136kHz from G6ALB. He gave me -21dB S/N when I was running 20uW ERP from the earth electrode antenna.

28 Aug 2010

WSPRing on 137.5kHz at last

136kHz TX transverter
Having got the TX part of the 136kHz transverter going today I am, for the first time, putting out a WSPR signal on 137.5kHz. Power from the PA is around 4W and the ERP from the earth electrode antenna is around 20uW. I am hopeful that Chris G3XIZ in Biggleswade may be able to decode the signal, possibly others not too far away. In the picture the transverting bit (from the 10MHz band) is on the right and the PA in the top left with low pass filter visible using the T106-2 toroid. Note the heatsink for the IRF510 - a couple of crock clips being all I could find in the junk box!

My 20uW ERP QRSS3 signal as received by G3XIZ
This was the signal G3XIZ got today 48km away on QRSS3 from me on 137.675kHz.  It is somewhat stronger than earlier in the week, confirming the few dB extra ERP.

27 Aug 2010

136kHz TX transverter almost ready (5W from PA)

Today I should complete the first breadboard version of my QRP TX transverter for 136kHz. It mixes down from 10MHz in a similar arrangement to my 500kHz unit, which transverted down from 28MHz. ERP on the original 137.675kHz QRSS3 beacon has been increased by 3dB to 20uW. The ERP from the transverter into the earth electrode "antenna" will be about the same level initially. I'll run WSPR tests for the first time on 136kHz this weekend.

25 Aug 2010

Another report on the 136kHz QRPp beacon

G3XIZ has sent me a nice screenshot of my 10uW ERP 136kHz beacon as received in Biggleswade, about 35km away. Chris believes I'd be perfect copy with QRSS10 (10 second dots).

24 Aug 2010

62km with QRPp and earth electrodes on 137.675kHz

Today I ran an earth electrode transmission test with Mike G3XDV in Welwyn Garden City 62km away. I put my QRSS3 8-10uW ERP beacon on and Mike took regular screen shots through the day until mid afternoon. Although unable to copy the message in QRSS3, when using QRSS30 speed for reception the start and end of the message sequences (9 mins 7 seconds apart) could clearly be seen. He was able to precisely detect when the beacon was turned off. Mike estimates another 6-10dB should allow him to read the message properly. Signals were weaker later, possibly because of rain here altering the effective loop size within the ground.

22 Aug 2010

136kHz RX loop calibration

Today I attempted to calibrate my 136kHz 80cm loop antenna by measuring the signal strength of DCF39 in Germany on 138.83kHz. I'm told that the field strength of this signal in daytime in this area is around 1mV/m. The level of DCF39 was -4.5dB on the Spectran screen with the settings I used. So, by extrapolation 0dB on the screen should be close to 1.7mV/m.

I then measured the signal level of my QRSS3 beacon on 137.675kHz  to see how much lower the level was at the same point about 1.5km away from the home QTH. My QRSS3 beacon was measuring -42dB approximately, corresponding to a field strength level of 12uV/m at 1.5km.

To work back to my ERP from the earth electrode antenna I used the formula ERP = (E * d)^2 /49 and this gives a result of 6.3uW and an antenna "loss" factor of 56dB (power in to RF out).

There are several sources of error:
  • loop orientation +/-3dB
  • loop Q/tuning +/-3dB
  • measurement accuracy +/-2dB
So, the ERP could be as high as 40uW or as low as 1uW.

17 Aug 2010

Chinese SSB and CW transceiver kits/built

YouKits of China is advertising a new 6 band HF SSB transceiver, the TJ6A that is available both in kit form and ready built. Prices look very attractive for a 10W transceiver. Well worth a look at their website.  This last year we have begun to see Chinese ham products appearing. It is only a matter of time before a Chinese manufacturer will produce quality transceivers to seriously rival Icom and Yaesu, and at unbelievable prices.

Pakistan Floods

This map appeared on the Oxfam site today and gives a graphic indication of how much land is affected by the floods in Pakistan when overlaid on a map of the UK.  It must be truly awful for the poor people there affected by this with crops, homes and businesses in ruin. Just imagine if this happened here (see map) and think how we would like the rest of the world's governments and peoples to help.

Help here: http://www.oxfam.org.uk/get_involved/campaign/actions/pakistan_response.html

ICQ Podcast: LF/VLF and QRP stuff

Last week Martin M1MRB interviewed me by Skype for an ICQ Podcast mainly about LF/VLF and QRP . My contribution starts about half way through the podcast. Thankfully Martin edited out many of the "ums" and "errs" that littered the piece!

16 Aug 2010

Resonating the earth electrode antenna on 136kHz

The 20m spaced earth electrodes "antenna" has about 30m of wire coming back ato low height to the feedpoint upstairs. I wondered if I could increase the current flowing into this structure by tuning out the small inductance presented by the wire. Using a small capacitance switching box I selected the value that gave most current with the 2W beacon TX. It was 100nF although because of the resistance of the ground return path the Q is low and the peak small. This suggests the inductance of the feed wire is only 13.5uH. I also tried matching the loop using a 3C90 transformer with various secondary taps but this made little difference. So, conclusion is that resonating the loop and matching it makes very little difference to the current (and ERP) because of the low Q.

15 Aug 2010

136kHz with a vertical antenna ....8uW ERP


Having simply tuned and matched my 5m coax feed to the 28MHz halo (the halo is used as a top capacity hat) I'm now putting out the grand level of 8uW (+/-3dB) on 137.675kHz in QRSS3 from my 2W out beacon TX.  Tuning was with 1.2mH wound on a small piece of ferrite in parallel with some fixed and variable capacitance. Matching was via a 3C90 toroid transformer. Field strength tests a few km away from the QTH suggest that the ERP from the earth electrode antenna is higher than this vertical, which is a bit disappointing as it suggests the vertical is, well, poor.

14 Aug 2010

Old UK radio and TV clips

If you were young in the UK in the 1950s you may be interested in these two sites dealing with radio and TV in the 1950s. There are many old clips that take you back nearly 60 years.

http://www.whirligig-tv.co.uk/radio/index.htm  
http://www.whirligig-tv.co.uk/
   

13 Aug 2010

Back on the vertical on 500kHz

WSPR Reports today
This afternoon I fired up the 5m long feeder (inner and outer strapped together) running up the pole to the 28MHz halo (used as a top loaded vertical) on 500kHz. Tuning was with a tapped inductor on a ferrite rod and matching using a 3C90 toroid with multiple tapped secondary winding. This works well and the signal reports on WSPR from M0BMU are 18dB stronger than on the earth electrode antenna. Also had reports from GW3UCJ, PA0A, OR7T and M0LMH so far this evening. If I can create a suitable loading coil (4-6mH needed I think) I will try this vertical with the 136kHz QRSS3 beacon as see what the signal is like.

300% more efficient wind turbine?

Japanese professor Yuji Ohya and his team have investgated the design of wind turbines and suggested a honeycomb-like structure could triple the amount of wind energy that can be produced by offshore turbines. See Tech Future site for more information.

12 Aug 2010

Perseids meteor shower tonight

The Perseids meteor shower is supposed to be a strong one peaking this evening. I may run the WSPR software overnight on 10m to see if any bursts are long enough to support a 2 minute WSPR transmission.

LATER: Overnight I copied PA0PSY at 0044z by what looked like MS: quite strong signal, seen once only, with Doppler, over a 300km path, although it could also have been aircraft reflection. Unfortunately I didn't see the WSPR screen to examine the actual screen trace.

Sunspots - high 60s

Have you noticed how high the sunspot count is climbing? Today it is 66 or 70 depending on which measure you take. This is not far off the sunspot count predicted at the peak of cycle 24 in about 3 years' time. If this trend continues, we could be in for a bigger peak than some were predicting. It could by just a blip.

10m halo re-erected

Today I rebuilt my Homebase10 10m wire halo and put it back up on the pole. I was going to erect a spiral top hat vertical for LF but decided instead to go HF. VSWR was good from 28-29MHz and WSPR reports from G4IKZ (18km west) good with just 1W out. I can use this antenna, with feeder strapped, as a vertical on 500kHz. For 136kHz I've decided to erect a wire loop rather than a Marconi and will support this from the 10m antenna mast.

10 Aug 2010

417km on 500kHz QRP ....with just earth electrode antenna!

Just been received in Holland by PA0A on 500kHz WSPR when using just the 20m spaced earth electrodes! The ERP is around 250uW and I am amazed that this non-antenna is able to work so well. I've also been emailed by Victor PA3FNY to say he also copied me at -27dB S/N.

500kHz WSPR with 20m spaced earth electrode antenna

The effectiveness of the 20m spaced earth electrode "antenna" (virtually nothing is in the air) continues to amaze me. Last night I copied PA0O on 500kHz WSPR and this morning I've got 4 reports of my sub-1mW ERP signal from M0BMU around -19dB S/N at a distance of 69km. This level suggests the (non) antenna is only around 6-8dB down on my best top loaded  short vertical used to get reports from OK2BVG 1232kms away last winter and the ERP is around 200-250uW.