Resonant antenna tests on WSPR 472 KHz

At the SNBCG operating site we have the opportunity to out up some large antenna, and for some time we had wanted to try 472 KHz using George M1GEO WSPR transmitter.

The plan was using the onsite 50m cellphone mast* to pull up some wire, and with some work hopefully, enough wire to have a 1/4 wave on 472 kHz. We calculated it would require around 150m of wire, and we had a pully on the mast at 42m, so we could pull up the first 50m as a vertical, and then have the next 100m sloping down from the last forming an “L” shape as best as we could into the next field.

The transmitter would be grounded to the mast earthing point, and we would run the 10w transmitter at the base of the mast overnight.

*for the avoidance of doubt we have permission to use the mast from the site owner.

The antenna slops down from 42m towards the ground.With a little bit of tinkering, we had a resonant antenna on 472 KHz

We left the transmitter running overnight from JO01DQ with the call GB0SNB, and was delighted to see a number of reports all around Europe.

Here you can see the tower and yellow wire making its was up from the base, and then into an adjacent field.


Timestamp Call SNR Pwr Reporter RGrid km az
 2018-05-06 01:12  GB0SNB -28 0.01  SM2DJK  KP03au 1774 33
 2018-05-06 01:12  GB0SNB -18 0.01  SM3LNM  JP82qg 1558 34
 2018-05-06 00:50  GB0SNB -28 0.01  EA1FAQ  IN71pn 1188 201
 2018-05-05 23:22  GB0SNB -22 0.01  LA8AV  JO59cs 1090 31
 2018-05-05 22:14  GB0SNB -26 0.01  EA2HB  IN93ah 946 191
 2018-05-05 23:34  GB0SNB -24 0.01  LA3EQ  JO28xj 828 24
 2018-05-06 00:10  GB0SNB -15 0.01  GM4OAS  IO76cx 708 329
 2018-05-05 22:08  GB0SNB -23 0.01  DL1KAI  JO42vj 654 79
 2018-05-06 02:56  GB0SNB -28 0.01  EI2KK  IO65ca 651 308
 2018-05-06 00:22  GB0SNB -28 0.01  DF5FH  JO42um 649 78
 2018-05-06 01:16  GB0SNB -21 0.01  DK7FC  JN49ik 645 110
 2018-05-05 23:22  GB0SNB -28 0.01  DL1GCD/1  JN48ar 642 118
 2018-05-05 22:08  GB0SNB -27 0.01  DK6UG  JN49cm 608 110
 2018-05-06 00:16  GB0SNB -25 0.01  DL0HT  JO43jb 597 72
 2018-05-05 23:34  GB0SNB -20 0.01  F6GEX  IN97na 526 190
 2018-05-05 21:38  GB0SNB -28 0.01  DF1VB/15  JO33pl 513 64
 2018-05-06 11:58  GB0SNB -25 0.01  DL/PA0EHG  JO32sq 506 74
 2018-05-05 23:34  GB0SNB -17 0.01  F59706  JN07th 496 168
 2018-05-06 00:10  GB0SNB -24 0.01  DL6II  JO30nx 481 97
 2018-05-05 23:22  GB0SNB -27 0.01  LX1DQ  JN39cq 472 116
 2018-05-05 23:22  GB0SNB -29 0.01  DC0DX/RF  JO31lk 462 91
 2018-05-05 22:14  GB0SNB -28 0.01  DC0DX/MW2  JO31lk 462 91
 2018-05-06 01:24  GB0SNB -24 0.01  DL2ZZ  JO31lo 460 89
 2018-05-06 04:38  GB0SNB -25 0.01  PI4THT  JO32kf 455 80
 2018-05-05 22:00  GB0SNB -29 0.01  PA0SLT/A  JO22xx 411 67
 2018-05-05 21:38  GB0SNB -22 0.01  G0LUJ  IO83ls 322 317
 2018-05-05 23:22  GB0SNB -23 0.01  G3WCB  IO80ei 311 243
 2018-05-05 21:56  GB0SNB -10 0.01  PA3ABK  JO21it 304 86
 2018-05-06 01:40  GB0SNB -28 0.01  PH2M  JO22hc 301 79
 2018-05-06 01:04  GB0SNB -15 0.01  PA0EHG  JO22hb 300 80
 2018-05-05 23:22  GB0SNB -13 0.01  G3KEV  IO94sh 296 351
 2018-05-06 11:58  GB0SNB -17 0.01  PI9ESA  JO22ff 292 76
 2018-05-05 21:38  GB0SNB -12 0.01  PA0RDT  JO11tm 231 93
 2018-05-06 11:52  GB0SNB -12 0.01  G6KSN  IO82xj 178 297
 2018-05-05 23:34  GB0SNB -13 0.01  G4ZFQ  IO90ir 153 227
 2018-05-06 01:16  GB0SNB -18 0.01  M0XDK  IO92ne 97 305
 2018-05-06 13:32  GB0SNB 11 0.01  G4GIR  IO92sd 72 315
 2018-05-06 00:10  GB0SNB -4 0.01  G4FKI  IO92sa 63 306
 2018-05-06 14:22  GB0SNB 1 0.01  G8EMO  IO92uc 61 319
 2018-05-06 04:16  GB0SNB -26 0.01  G3YMN  IO91tj 56 235
 2018-05-05 20:56  GB0SNB 4 0.01  G6AVK  JO01ho 25 112
 2018-05-05 22:14  GB0SNB 1 0.01  M0TAZ  JO01cn 15 203

How good is that choke?

With field days just on the horizon, I decided to make a couple of Balun (common mode choke) for field day use. I often use a vertical for 7 or 3.5 MHz, and a 1:1 choke is needed to stop the feeder becoming part of the antenna system. Sure you can purchase them online, but your never sure of the quality or the power handling and they are easy to make.

You will need a suitable box, ferrite toroid (FT240-31) is good for the lower HF bands and some coax. The type of coax you use will depend on the power handling, RG58/RG316 would be fine for 400w but if you want some margin for error then RG142 is a better choice.

The RG142 is quite expensive, but its capable of much higher power handling and it has a PTFE centre insulator. The coax typically costs around £5 per meter, and 1 meter should be sufficient for a single core balun.

FT240-31 Toroids cost around  £9 each, so a typical project would cost around £20 for a single toroid or £30 for a double toroid QRO version.

If you purchase one already made they cost around £40 to £60 depending on the power handling.

Once assembled you should have something like this. The “QRP” version is good for 400w, the QRO version is good for 1KW.

The subject of choke may need some further explanation, so you may want to watch this video by Callum M0MCX. I would also suggest reading this excellent article by Steve G3TXQ

Steve explains in his article how you can measure the choke impedance, and he provides some measured data showing the effectiveness of various combinations of ferrite and number of turns. This gave me the idea, how hard would it be to measure the choke impedance at various frequencies?

Turns out it’s not as simple as you think, the first try with a VNA produced some interesting but mostly meaningless figures. It turns out you cant just sweep the choke with the VNA as it presents very high impedances outside the range where the analyser can be expected to be accurate. The VNA can be used, but the results will require some further maths before meaningful data can be obtained. At our recent radio pub meeting, I asked Dr David Mills (G7UVW) if he could assist, and he completed the measurements and the maths! Thanks, Dave.

VNA plot QRP single 240-31 Torroid

VNA plot QRO 2x 240-31 Torroid.

And now for the measured data, you are looking at the frequency on the left, and choke impedance in ohms on the right. We would typically say anything over 3,000 is very good.

As you can see both the chokes work very well over most of the HF spectrum. The target for me was to have something with very high choking impedance below 14 MHz.

Thanks to Dave G7UVW for his assistance, and I leave you with a picture from our radio pub meeting.

Summer 2018 has arrived (almost)

At last, the warmer weather has arrived, today gave me the first opportunity to operate outdoors without a coat.

It was a pleasant sunny afternoon so I decided to operate outdoors and make the most of the nice weather. Using the Icom 7100 and 65Ah leisure battery and a white stick for 145 MHz and slim jim for 70 MHz allowed me to work a number of local stations.

The 70 MHz Slim Jim is mounted on the fibreglass pole on the right.


















The metal mast on the right had been given to me by Richard G4DDP and it was its first chance to try it out in the field. Its very heavy duty, and I think would have originally been designed to take a speaker at a gig, now upscaled to amateur radio.

On 145 MHz I worked M0FAQ Martin in Braintree, M0WJL Gordon in Corringham.

On 70 MHz I worked 2E0HPA/M Andy in Tadlow, G4YBI Paul Rainham, M0XTA Selim, G0ENN Southend.

Here you can see the Icom 7100 setup and operating on 70 MHz

The Icom 7100 all packed up in its travel box.


Easter Weekend Radio Fun

Easter weekend is often the start of the better weather and lighter evenings, so provides a chance to go out portable for the first time in the year. Unfortunately, this bank holiday weekend in true British tradition was wet and cold with rain forecast and temperatures soaring to a tropical 7C.

This didn’t stop  Chris G8OCV, George M1GEO and myself from camping over although it required careful positioning of the tents to prevent localised flooding!

We set up an 80m doublet sloping from 35 meters off the tower, and a 40m ground mounted vertical with elevated radials. The 40m vertical used a 12m spidebeam pole, although we sometimes used the green push together army poles depending on the weather.

We also had the chance to try out the new Icom 7610 transceiver, and this performed very well on both receive and transmit.

I concentrated on 40m, using the 7610 and expert linear amplifier to develop 400w, and found band conditions to be very good in the late evening and early mornings. On Sunday morning I decided to get up around 6.45am and was really pleased to work some nice early morning DX.

ZL3CHE Willem was the first DX of the morning, located near Christchurch. Willem was using 600w to a ground mounted vertical and was a great signal.

ZL3CHE Willem in Christchurch New Zealand

VK4PDX Colin using just 100w in Brisbane Australia

VK3FT Keith was very strong from near Melbourne Australia, and he was using a rotary dipole at 20m on his tower.

A very enjoyable weekend, and always nice to get some DX on 40m over the weekend I was able to work around 27 DXCC.

PI4 next generation VHF/UHF beacons?

Beacons have like other digital modes moved with the times, making use of the latest digital modulation techniques to improve detectability far beyond the human ear and CW.

The name PI4- PharusIgnis4 comes from the ancient words for a beacon, lighthouse and fire and is a digital modulation that is compliant with the IARU Region 1 VHF Committee accepted 1 minute mixed mode beacon sequence.

The sequence of events is illustrated below, and always starts on a full 1-minute cycle.0 to 24 seconds PI callsign


25 sends CW ident callsign and locator


carrier until 59.5 seconds


To decode the PI4 beacons you can download software PI-RX by Poul-Erik OZ1CKG or MSHV by Christo LZ2HV, they both report being compatible with Linux and Windows.

OZ7IGY beacons date back to 1957, and they are now QRV from 28 MHz to 24 GHz. You can review the dial frequencies and check the operational status online.

Frequency [MHz] USB dial* ERP [W] ASL [m] 99% accuracy [mHz] Year QRV
28,271 28.270.200 10 95 1 2009
40,071 40.070.200 10 97 1 2007
50,471 50.470.200 25 98 1 1990
70,021 70.020.200 25 100 1 2003
144,471 144.470.200 50 102 3 1957
432,471 432.470.200 75 103 9 1958
1 296,930 1.296.929.200 90 95 26 1978
2 320,930 2.320.929.200 30 98 46 1985
3 400,930 3.400.929.200 50 96 68 2006
5 760,930 5.760.929.200 50 98 115 1992
10 368,930 10.368.929.200 80 97 237 1999
24 048,930 24.048.929.200 20 97 481 2012

To support the PI4 beacon project, or to see a technical description of the modulation technique read more on their website.

Other becons to look out for.

PI4 + CW + carrier/Next Generation Beacons platforms
4O0BCG in JP92PK – 70,048 MHz
DB0HRF in JO40FF – 144,475 MHz
DB0IH in JN39HJ – 432,447 MHz
DB0JG in JO31HS – 432,412 MHz
DB0LTG in JO31TB – 1296,7435 MHz
DB0MMO in JN49RV – 144,455 MHz and 432,425 MHz
EI0SIX in IO63VE – 50,005 MHz, SBP 5/0
GB3CFG in IO74CR – 70,027 MHz and 1296,905 MHz
GB3MCB in IO70OJ – 50,443 MHz and 50,005 MHz SBP 5/1 and 3
GB3MHZ in JO02PB – 10 368,830 MHz
GB3UHF in JO01EH – 432,430 MHz
IW9GDC/B in JM78SD – 50,006 MHz (Later SBP 6/4)
KG4BYN in EM75RV – 28,2368 MHz
ON0EME in JO21JG – 10 368,875 MHz and 24 048,875 MHz
ON0SNW in JO21BE – 10 368,965 MHz
OX4M and OX6M in HQ90AL – 70,047 MHz and 50,047 MHz
OZ4BHM in JO75KB – 50,005 MHz, SBP 5/4, later also 50,466 MHz
OZ7IGY in JO55WM – 28 MHz to 24 GHz
PA0AG in JO32GH – 70,095 MHz (personal beacon, 07-21 UTC)
SK4MPI in JP70NJ – 144,412 MHz
TF1VHF in HP94AC – 50,457 MHz
UA1ZFG/B in KP69AK – 144,425 MHz
VA2NQ in FN35NL – 50,295 MHz, 144,491 MHz, 222,295 MHz and 432,302 MHz

FT8 on 144 MHz

FT8 has taken the HF bands by storm, a bit like PSK did in the early 2000s. These days it seems the mode of choice for DX stations, allowing them to make a number of QSO is a short duration. If you haven’t checked out FT8 then I would suggest you head over to Joe Taylor website and have a look at some of the weak signal propagation modes available.

If you are new to FT8 you may find this operating guide helpful.

Connecting my Icom 7100 to Ham Radio Deluxe, and then WSJT-X to “Ham Radio Delux” works just fine for me. It should be possible to connect WSJT directly to the Icom radio, but a lot will depend on your operating preferences.


The agreed dial frequency is 144.174 USB and you will see activity most of the time, probably more in the evenings and weekends


Its quite common to see Germany, France, Belgium, Ireland, Wales and Scotland in a few hrs of monitoring under flat conditions.

50 MHz is also popular and works well under short sporadic E opening.

© 2015 Dave, M0TAZ