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!

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.

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.

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/

   

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.

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.

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.