29 Jan 2011

137kHz transverter update

Breadboarded 137kHz 8W transverter (ERP 50uW from antenna)
Simple 137kHz QRP transverter - click for larger image
Today I combined the RX and TX parts of my 137kHz QRP transverter for the first time and all is working although I'm losing a few dB in RX sensitivity at the moment. Copying DL, SM, PA and G stations on WSPR RX. Best DX being 148km on WSPR TX.  Who says LF has to be hard? HI.

28 Jan 2011

DRM - a waste of money?

Does anyone know how much the cash-strapped BBC is spending on DRM transmissions on shortwave ? Also, does anyone actually use a proper SW receiver equipped to receive this mode? Surely this mode is a total waste of money.

27 Jan 2011

4m transverter paper design

Today I have been gathering data and information for my 4m QRP transverter and started on an "on paper" design around an NE602 RX mixer, 2N3904  3rd overtone oscillator, 2N3904 driver(s) and a 2N3866 PA. It is surprising how much can be done on paper before you start by referring to datasheets and on-line RF calculators. I'm wondering if my T50-6 toroids will just stretch to 4m.

26 Jan 2011

500kHz WSPR - a good evening

A decent set of reports this evening with my 1mW ERP WSPR beacon on 500kHz. Best DX DF4PV's report at 597km. Also I copied Gerhard DI2AF's WSPR beacon (just over 800km) higher up the band on 505.13kHz.

25 Jan 2011

FT817 antenna pin: getting a DC voltage on the inner when on TX.

The FT817 does not have a DC voltage change between RX and TX on the antenna connector, unlike the old IC202. This voltage was very useful to switch PAs and transverters. I now know how to modify the FT817 to add this feature thanks to Chris GM4YLN who sent the link http://www.kolumbus.fi/oh5iy/HW/Yaesu.html showing one way to make the mod.. Note in this link the FT817 is wrongly called the FT718. An easier to implement link is shown at http://www.bergtag.de/download/ft817.pdf . Thanks again to Chris for this one too.

4m Chinese Multimode rig and a FT817 successor from China?

There are rumours, apparently with some substance, that a Chinese mulitmode transceiver for 4m may be being designed. This would not be too surprising, although expect some delay between "being designed" and being available in the shops.

Of course, with several Chinese FM handhelds and mobiles now available at competitive prices from 4m - 70cm it can only be a matter of time before a Chinese equivalent to the FT817's successor (yes we are still waiting, waiting, waiting Yaesu!) will hit the streets, and at a knock-out price. It would not surprise me one bit if such a rig appeared before the end of 2011. Once the Chinese realise they have a ready market for quality ham gear then look out Icom, Yaesu and Kenwood as your days may be numbered, seriously.

Poland soon on 4m

70.1 - 70.3 MHz will soon be available to the Polish radio amateur service on secondary basis. The maximum power will be 20W EIRP. Date of release still not known yet.

24 Jan 2011

4m transverter

It is almost certain now that my next project will be a 5W transverter for 4m. This is a band I have never used under my own call and for which I have no gear yet. The design should be straightforward transverting to 10m with the FT817 as the driver. I have started a 4m QRP transverter page on my website to track progress of this build.

22 Jan 2011

No luck with OE3GHB and G3XIZ on 8.97kHz today

Despite having my antenna and receiver system well optimised and running a Spectrum Lab configuration file allowing very sensitive detection (DFCW6000), nothing (so far) was identified from either Gerhard OE3GHB or Chris G3XIZ on 8.97kHz today. So far, the only station I have "seen" on VLF is DK7FC/P back in December. Since then I've improved the set-up. G3XIZ didn't have his "balloon extended" antenna in place, so he could be several dB stronger the next time he tries again.

21 Jan 2011

Austrian VLF tests this weekend

Gerhard OE3GHB hopes to be transmitting on VLF this Saturday (Jan 22nd) on 8.96995kHz (+/- 0.03Hz) starting between 0800-0900z. Although the chances of copying him are low, I will be monitoring and uploading what I see (or do not see) to my VLF grabber which will be active as long as possible this Saturday.

20 Jan 2011

Optical DXing at around 460THz

Until I read the webpage below I didn't know that the record for optical morse DX goes back to 1896 and was an astounding distance of 183 miles using a Heliograph between Colorado and Utah in the USA. This link about the heliograph makes fascinating reading. The heliograph is essentially a keyed mirror that reflects sunlight and uses it to send morse code over long distances.  Modern versions of heliograph mirrors are available on eBay for emergency communications. See for example eBay item 250681260168. A good article about heliographs is on Wikipedia, see http://en.wikipedia.org/wiki/Heliograph.

Modern amateur optical DXing uses either lasers or high intensity LEDs. There is a piece about this on p51-52 of the Feb 2011 RSGB RadCom in Sam Jewell's "GHz Bands" column with further links including http://www.lasercomms.org.uk/index.htm which looks like a useful resource.  There was also a funny article in the RSGB Bulletin of April 1962 called "Getting Going on Bottom Band".  

Dreamer's Band activity around 8.97kHz

In the last few days OE3GHB and OE5ODL have been testing close to 8.97kHz with their signals (from home QTHs) being received at considerable distances across Western Europe. DK7FC was planning his 10th kite VLF test this weekend but has had to postpone this until Jan 29/30 because of the weather. My grabber is currently looking around 8.97kHz and seeing a strong signal, although I suspect this is a locally generated interferer. See http://dl.dropbox.com/u/15047843/xbm_grab.jpg for the grabber as it updates. This is not on all the time, just when I am testing or listening.

Corporate Greed

I don't usually get political on my blog, but something has incensed me this week. Goldman Sachs, the huge multi-national finance company, has declared huge bonuses for its staff. In the press yesterday it was reported that their staff now have an average salary+bonus package of $430000 a year!  At the same time I've read that they've slashed their corporate charity giving by a large amount. If these figures are correct, then I believe them to be obscene and a prime example of the corporate greed of some big financial institutions. I am not sure how to respond, but want to email their CEO, but haven't managed to find his email address on the swish corporate website!  In the end, such greed cannot be acceptable. This is the sort of behaviour that festered revolutions a century ago: the seeds are there for it to happen again within 10 years when the ordinary man says, "no more".

19 Jan 2011

5mW on 80m - best DX 1310km

80m WSPR with 5mW output
This evening I ran 5mW output on 80m WSPR to see what sort of distance I could achieve. It was quite an eye-opener with lots of reports and some good DX, the best being LA2XPA at 1310km. The report from LA3JJ suggests that almost 1000km would have been possible with 500uW. And it is not as if the antenna here is anything: just 5m of coax to the 10m halo with inner and outer joined together as a vertical and tuned through a tiny T1 auto-ATU!

FT817 lowest power setting at 500mW

Do you know, I've only just realised something about my FT817 having owned it for almost 10 years: as someone pointed out to me, the lowest setting on the FT817 is always 500mW whether on an external supply or internal batteries. For some reason I had believed "1 dash" on the display was 500mW on batteries and 1W on a mains PSU. I just checked and it really is 500mW out.

So, my recent WSPR DX spots with 10mW and 1mW were actually at 5mW and 500uW!

Reverse Beacon Network

Thanks to Mike Rainey AA1TJ for putting me on to this. The Reverse Beacon Network is a revolutionary new idea. Instead of beacons actively transmitting signals, the RBN is a network of stations listening to the bands and reporting what stations they hear, when and how well. It works by using skimmers to check activity and then uploading spots to an internet database much like WSPRnet for WSPR spots. Using it you can see if your signals are making it to a given spotting location.

18 Jan 2011

1mW DXing on 40m

Today I reduced the power from my 40m WSPR beacon TX from 10mW down to just 1mW. The FT817 is run at minimum power setting (1W) then via a 20dB attenuator within a few cm of the antenna connector and then into a 10dB stepped attenuator. My antenna is the 5m coax feeder (inner and outer strapped together) up to my 10m halo and tuned via the Elecraft T1 auto-ATU. The first report received at 1436 today was from DC4FS at 523km (-28dB S/N).

VLF earth-mode tests legal without NoV

Today I received a letter from OFCOM, which clarifies the legality of operating so called "earth mode" (conduction/induction via the ground) experiments at frequencies below 9kHz in the UK. In it, the official from OFCOM stated, "We would not normally issue NoVs for communications using non-wireless telegraphy apparatus/stations i.e.  where you rely only on conducted emissions and where there are no intentional radiated emissions.".

Wanting to check earth mode propagation behaviour at a series of frequencies below 9kHz to see how results compared (earlier tests at 0.838kHz seemed around 10dB better than at 8.76kHz), I asked OFCOM if I needed an NoV extension to be legal. One could reasonably also argue that such through the ground conduction tests at frequencies above 9kHz would also be legal as long as they don't
cause any "Undue Interference to any wireless telegraphy" and one was not intending to radiate.

This sounds a wholly pragmatic answer from a government body.

17 Jan 2011

PA1B's QRPp website

Whilst looking at the links on PC4T's blog I noticed Bert PA1B's excellent website all about QRPp operating with lots of tips on how to produce mW power levels and have real fun on the HF bands.

This has encouraged me to have a go, so I am currently WSPR beaconing on various HF bands using 10mW out from the FT817 via a 20dB attenuator right next to the rig.These were the results from 40m late this afternoon and into the early evening. Encouraging!
Best DX 983km with 10mW in just a few hours!

15 Jan 2011

136kHz RX activity

In the last few weeks I've received 136kHz signals from several different countries and stations:


Certainly my receiving system is now up with the best since adding the tuned preamp. My main drawback is the TX/RX loop's directionality which reduces signal levels in a N-S direction. We just need a lot more stations active on the band, especially on WSPR.

13 Jan 2011

Further 8.76kHz VLF test transmissions today

8.76kHz earth mode tests - best DX 5.1km and 4.75km
Today being mild and dry (for the first time in almost 6 weeks) I decided to do a field test with my improved 8-9kHz tuned preamp and loop antenna. A 5W "earth mode" (through the ground) test signal was emitted on 8.760kHz from the Burwell QTH and I ventured out into the countryside armed with the 80cm loop and preamp to see where the signal could be copied. In addition to my usual test sites at 1.6 and 5.1km I tried other directions and sites today. The map attached shows where signals were received and where no copy was achieved. The signal does seem to travel along the metal water pipes, which must be absent to the east where I assume they must be plastic, at least in places.

A 4th UK station with VLF NoV

Just received this from Gary G4WGT:
"Today I received my SRP from Ofcom to carry out research and experiments on the 9kHz band. The NoV is effective immediately and expires on 10th January 2012. The allocated frequency, power and additional conditions are the same as for other UK 9kHz operators, ie. 8.700kHz to 9.100 kHz with a maximum of 100mW (-10dBW) e.i.r.p. I am not ready to transmit a signal yet but it will be quite soon. I will make an announcement through the usual channels.

73  Gary - G4WGT"

12 Jan 2011

What next at G3XBM?

With my recent semi-successful WSPR transmissions on 136kHz and a few outings on 500kHz I feel I'm at a crossroads now: do I go on with the LF experiments or do I have a change and do something completely different? My original aim on the LF bands was to see what could be done "simply" i.e. without large antennas and with real 5W or less QRP power from the PA. Already I have the measure of this and I doubt I'll prove much more to myself by striving further.

Next challenge? Ideas please.

On-line CW training

If, like me, your CW is not as good as it could be, then you may want to visit http://lcwo.net/ where you can both train yourself and test yourself. On plain callsigns I could read 22-23wpm on average, but I still made mistakes at much slower speeds. 30 minutes a day on this site and anyone's speed would rapidly improve.

Short Marconi vertical on 136kHz - forget it!

ATU for 136kHz. Antenna connected to top of ferrite rod
Disappointing results yesterday with a very short Marconi vertical tuned using a ferrite rod loading coil and variable capacitor. ERP was calculated as around 200uW, but in reality the ERP was around 10dB down on the vertical loop (based on WSPR reports locally), so the ERP was around 5uW only. Most of this can be put down to the coil losses and to tiny current actually flowing in the antenna part actually radiating. A much more efficient antenna for the band will require a BIG loading coil outside and more wire in the air with some top loading. I could erect a 6m vertical antenna with a sloping top capacity hat horizontal section with an overall vertical rise of 10-12m. Antenna improvement could increase ERP by >6dB. TX power could be raised by 6dB. Taken together this would make a difference, but it would not meet my QRP ethos.

My conclusions are that an ultra-simple QRP approach to 136kHz TX is just not possible if one is to achieve useful results consistently.

11 Jan 2011

ERP with the loop on 136kHz

Today I did a recalculation of my 136kHz ERP using the loop antenna with my WSPR transverter. I have a small RF ammeter in series with the loop wire and I measured the current as 1.3A.

For 136kHz the ERP of a loop is = (I^2 * A^2) / (205 * 10^6)
where I = loop current and A = loop area (see "LF Today" RSGB book p101)

Putting in the numbers ERP = 1.3^2 * 80^2 (205 * 10^6)

So my ERP = 52uW on 136kHz.

A further 3dB could be obtained by thickening up the wire used in the loop taking the ERP up to around 100uW. Other improvements could come from increasing the TX power output from the present 5W. Later today I will work on a small ATU to resonate my 5m feeder to the 28MHz halo as a Marconi vertical. First I will work out the antenna current needed to beat the ERP of the loop. At least a Marconi will not be directional, which is a drawback of the loop.

9 Jan 2011

Reports on 137.5kHz WSPR and QRSS3

In the last couple of days I have managed to get a couple of reports on 136/137kHz. Yesterday G3UUT copied my QRSS3 beacon and today G3XIZ copied the WSPR beacon. Neither represent any great distance - G3XIZ is 46km and G3UUT about 18km - but these are my first reports since getting back on the band after a few months of absence. ERP was about 10-20uW. G3XIZ was getting me at about -22dB S/N suggesting that around 100km may be possible on WSPR with the current kit (I did get a few spots from G3YXM at 148km last autumn with the same set-up), so I hope a few more stations in range can manage to detect me. I really must increase the ERP by 10dB: I have been saying this for too long and not doing anything about it!

8 Jan 2011

DK7FC/P on 136.8kHz normal CW

DK7FC/P very strong on 136.8kHz CW today
Stefan has been out /P with his 100m long kite antenna, this time on 136.8kHz CW. He was excellent copy here in the UK (JO02dg) with a signal some 20-30dB over the noise floor even when sending fast CW. Attached is a screen shot from Spectran showing him working DF6NM at 1715 this evening. Distance is around 649km.

6 Jan 2011

Improved E-field probe for VLF

Today I made an improved version of my VLF E-field probe. The first hi-Z FET input stage now an amplifier with an 8-9kHz tuned circuit in the drain. Sensitivity is now much better than before with strong Alpha beacon reception. It works well with the 80cm loop too and with the large TX loop in the garden via a step-up transformer. I'm looking forward to further tests by DK7FC and G3XIZ on 8.97kHz as my sensitivity is now better.  I hope to test this out in the field with my 8.76kHz transmitter over the weekend.

5 Jan 2011

136kHz WSPR DX reception

Today there were several stations active on 136kHz WSPR with best DX heard the 50mW ERP beacon of SM6BHZ. Also copied PA0A and G8IMR. So far this evening no-one has heard my own modest (10-20uW ERP) WSPR beacon on 137.5kHz though. I'll keep trying.....

4 Jan 2011

SAQ Jan 3rd

SAQ was audible well last night around 2330z tuning up for a transmission on 17.2kHz CW at midnight. The signal was about 20dB above noise using the 20m spaced earth electrodes as an antenna.