LF – 500Khz Loading Coil

I was reading a little more in the ‘who invented the Transistor’ debate recently. It was most likely a case of parallel paths.

Likewise my Loading Coil for 600m experiments. I had seen the Air Cored Coil, the Ferrite Cored Coil, the Variometer and the variable Capacitance ATU types.

I consider the Variometer may be a lossy device, in anything other than ‘add all Inductance’ it must be lossy. When it is in a subtract situation, bucking some of the primary Inductance it must be worse.

I tried large air cored coils, these seemed less efficient maybe due to wire resistance or capacitance to ground. Smaller coils with less wire seemed better, I can use Ferrite as the QRPp levels are unlikely to cause saturatation.
With a Ferrite Cored Coil the Inductance can be varied to tune the value precisely. I designed and built a system where the main part of the Coil is air cored (on a PVC former) and a Ferrite Rod is inserted in the end for trimming the Inductance value. I even called it a Pump System due to its resemblance to a Bicycle Pump. It also resembles and uses the same construction as a small Spotter Telescope which I built many years ago.

Then someone posted a reply with reference to Litz Wire, the write up by Mitchell Lee has loading coil designs. One has an Air Core Coil with a separate Ferrite coil for adjustment this he calls a Push Rod Tuner.
Amazing, no need to draw mine, just make the Ferrite Coil the same diameter as the Main Coil and tip it up on top of the main one. Oh and mine uses a 5 turn link coupling not a tapped
Mine is out in the garden on test it will come in for waterproofing and I will take photos later.

500KHz Success

What a week, high winds torrential rain and me with Antenna work to do. I managed between the gusts and during mere showers to erect a Marconi T antenna. It’s only small simple affair 6m high at either end 10m of flat top, fed off centre. I read later (too late) that it is best to keep the top symmetrical.

Then comes the matching coil work, experimenting with different sizes and methods of tuning. Again now that has moved outside with high winds and rain, temporary, not so mechanically sound set ups are a problem.

I am not convinced that a Variometer is an efficient way of tuning, so I didn’t build one. I tried large coils, compound coils and small coils, I will go into that later with some pictures.

Aerial Current shows a nice 50ohm match on my little current meter.

For now, some results, I was pleased to see WSPR reports from my first transmission today.

2009-11-28 13:00 G4JNT 0.503850 -8 0 IO90iv 0.2 G3XVL JO02nb 212 51
2009-11-28 12:56 G3ZJO 0.503846 -26 -1 IO92ng 0.05 G3XVL JO02nb 138 99
2009-11-28 12:56 G3ZJO 0.503846 -33 -1 IO92ng 0.05 M0BMU IO91vr 76 143
2009-11-28 12:52 G4JNT 0.503850 -2 0 IO90iv 0.2 M0BMU IO91vr 119 39

It is not often that my signal has stained the database like that on this band.

The power level is neither the RF or ERP the PA gives me 160mW into 50ohms if my antenna is 1% efficient I shall be surprised so if I say 1.6mW ERP I am probably bragging.

So I now own 2 lines on the coverage map on 500KHz.

PC-less WSPR the XORgan and Timing

Most QRPp’ers will know of my method of timing in my PC-less WSPR Keyers. (look at that I am being PC and saying PC-less).
I had query the other day regarding the XORgan ‘have I considered adding GPS timing as a facility on my system’.
Well it has the facility, however my concept back in March 2008 was to abolish such things. Here were my thoughts:-
I smile at the huge power used by PC generated WSPR and a Transceiver to produce the few mW needed to span the globe. Why in a PC-less system then, add GPS timing to put the current consumption back up? Not to mention the complexity, QRPp’ers like to KISS.
Just because a Windows computer is a lousy time keeper why should we consider it impossible to keep time as accurate as the needs of WSPR. Heavens I had a fully mechanical wrist watch 40 odd years ago which kept perfectly adequate time for the purpose. Does the Quartz watch on your wrist deviate more than a second in a Month? We QRPp’ers have got to be able to do better than resorting to GPS, MSF etc.

My KISS approach:-
Use a good quality Quartz Crystal for the PIC timing oscillator, pre age the Xtal. Write the WSPR PIC code timing for that Crystal. Sounds easy, you will have to work out the figures needed and a method of checking the accuracy of the result. Of course I cant supply the code to do it for your Crystal. I suggest that if you don’t already have a PIC WSPR generator you start with the SM6LKM code which is on the web.

Does it work:-
Well I have had an MEPT QRSS with WSPR ident on 10.140073MHz running 24/7 since early April 2008 I try to visit it every so often to push the manual re-set, other than that it is Quartz timed.

Results on 500KHz

My NOV (Notice Of Variation) Permit for Research on the 500KHz Band arrived on the Friday 20th November. I have not yet produced a specific Antenna for the band so I tried the Transmitter into my Doublet with the Twin Feeder strapped to use it as a Marconi T. I tune this with an inductor and the good old No19 Set Variometer which can add or subtract from the inductance. Alternatively I used a plunger arrangement to adjust a Ferrite Rod into and out of the Inductor.

I stripped and cleaned the Variometer, The smells were wonderful, the construction interesting, particularly the anti vibration clutch on the knob, it is a dual plate circular clutch using Greased Cork Discs either side of the casing. The disc plates looked as good as the day they were made. Pretty good going as my specimen is a bit ‘well used’. Made in 1944 I wonder if it went into service.

Fridays tests brought no results at all. Good show, this makes it a challenge to be seen on the band using QRPp.

On Saturday I made a slight adjustment to the Loading Coil, in the evening on air I could not make any impression on the Grabbers in the band and there were no reports.

Until gone midnight.

2009-11-22 00:48 G3ZJO 0.503814 -30 0 IO92ng +17 0.050 M0BMU IO91vr 76 47

Apart from my insistence on minuscule power levels, I am sure the Antenna used is the main problem. It is not ‘far from ideal’, it is nowhere near. The Top Load drops dramatically to get it into my available space, this lowers efficiency, I have not got power to spare.

What I do have is my starting point -30dB at 76Kilometers is my 0dB reference point.

Transmitter details.
TX power RF Output into 50 Ohms = 160mW
Total Power consumption including PIC Keyer = 76mA at 13.8 Volts
Frequency = 503.805 KHz
Modulation = QRSS Morse, Hellschreiber, WSPR

WSPR2 – Whisper V2

WSPR2 will be on full release shortly. I have run it for several hours and it seems to work just fine.

Several new features are included. At last we can use /P when we are out Portable and a proper prefix in a foreign country i.e. F/G3ZJO, and a full 6 figure QRA Locator. This has been a constant source of embarrassment for me, sitting on a Ski slope in France using my Home Call and two thirds of a Locator which was exactly the same as when I was in a town several Km away at the foot of the Mountain Range.

In addition there is a version for Linux. I can see a huge expansion now in the use of Linux, particularly Ubuntu in the Ham Shack.
Well done Joe and the Team.

Hypersonic XORgan on 500KHz

The XOR Subtractive Mixer is ideal for higher frequencies too. I built this 500KHz version for QRP on the 501KHz to 504KHz Band.

A 13.5MHz Crystal Oscillator is configured as a VXO this is subtracted from a 14.0MHz Modulated Crystal Oscillator to produce 500KHz. This goes via an LPF to an Inverter PA, on the underside of the board, which produces 150mW of RF via a further LPF.

The Output signal is very Pure and Stable. Frequency stability can be seen from the following decodes in a 5 hour period.

091113 1050 13 -17 -0.1 0.503923 G3ZJO IO92 17 0 1 0
091113 1250 14 -18 0.8 0.503923 G3ZJO IO92 17 0 1 0
091113 1520 14 -18 1.8 0.503923 G3ZJO IO92 17 0 1 0