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.

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!

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.