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.

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

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.

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.

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.

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!

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.

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

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.