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.

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!

136kHz RX activity

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

DK7FC/P     CW/QRSS
DF6NM     QRSS
G8IMR      WSPR
M0BMU    WSPR
PA0A    WSPR
SM6BHZ     WSPR

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.

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"

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.

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.