Category Archives: Informal Activity

Easter Field Weekend

During the long Easter weekend members of the SNBCG came together for a radio weekend. Over the course of the four days, two HF stations were set up; one on 7 MHz and the other roaming between 1.8 and 28 MHz depending on propagation.

Dave M0TAZ decided he would try a 1/4 wave vertical on 7 MHz and use his recently purchased push-together fibreglass poles. These poles are often sold at radio rallies in packs of 5 (each pole 1.3 metres) to give an overall height of 6.5 meters. Using two packs of the poles, the required height of 10 metres was achieved.

Chris G8OCV had made some supporting guy rings, these provided anchor points for the guy lines at approximately 4 and 8 meters. The first attempt didn’t quite go to plan, it simply wasn’t possible to walk up the 10m pole, as we found out when we exceed the bend radius of one of the poles. Lesson learned it didn’t make any difference as the fracture was in the joining section that was simply moved to the first section. In the end, we used 9 poles, giving us a total height of 11 meters with a simple wire running down the side for the radiator.

Six 6 radials were cut, each around 10 meters in length, and the antenna was mounted at the base of a wire fence. The earthing system included the 6 radials and the wire fence, and this provided a reasonable match around 1.5:1 at 7.150 MHz. It would have been much easier to use a push-up fishing/roach style pole but experience has taught Dave that these can be tricky to keep up without guying and tapeing over the joints. As we wanted to run linear amplifiers this weekend, the prospect of the pole moving in the wind and/or falling down made, we made up our minds to use push together poles as the first choice. The antenna was fed with coax with a choke unun (or balun) at its base to stop the coax radiating, and this needed to be capable of high power.

The antenna provided reliable service all weekend, and with the addition of 400W yielded over 200 contacts in 40 DXCC countries. An enjoyable part of the weekend was working DX stations later in the evenings, including the USA, Chile, Mozambique, Guinea-Bissau, Israel, UAE, Armenia and Asiatic Russia all on the 40 metre vertical.

DXCC Breakdown on 40 metre vertical

George M1GEO, Fred G3SVK and others operated the other station. George chased some good DX and Fred worked several hundred stations as “GB0SNB” in CW.

Below we see the DXCC breakdown of the second station using the mast doublet on 160 and 80 metres, and the beam (pictured above) on the higher bands. Some of the DX on the doublet and beam included several QSOs into Japan, Fiji, Trinidad, Guinea-Bissau, Cayman Islands and Argentina.

DXCC Breakdown on 160m doublet and HF beam

We also had time for a BBQ and some excellent curries provided by Fred G3SVK. It was nice to see Camb Hams members Geoff G0DDX and Linda G0TPX, and LEFARS members Derek M0XDC, Dave M0MBD and Dave M0VID. RSGB regional man Peter G0DZB also joined us for the afternoon, making the most of the good weather for a ride on his motorbike, and Bill G0IQK popped in on the Sunday afternoon.

Dave M0YOL worked some data modes using his portable setup. All in all, a good weekend was had by all.

RSGB AFS Phone Contest

On Saturday 16th January George M1GEO, Chris G8OCV and Dave M0TAZ took part in the RSGB AFS phone contest. The idea was to give the Secret Nuclear Bunker Contest Groups first outing of the clubs call MX0SNB. The clubs contest site benefits from having a large doublet antenna (40m per leg) 30m up on the large onsite mast.

Using the Icom 7100 and 100w we noticed quickly while it was possible to match the antenna it didn’t seem to be working very effectively.  The shack is located 20m below ground, in the original Home Office radio room. Once inside the bunker you have no idea what may have occurred. We decided to go back up to the mast and check, and on taking the doublet down we discovered one of the 300 Ohm feeder legs had become detached.

The antenna is located close to 30m above the ground, and the mast is already very well elevated, making it sometimes hard to maintain a working HF antenna in the winter weather. A quick fix later and we was soon back on the air.

George M1GEO

We operated from 3 till 5 PM and managed to work over 100 stations. The contest was well supported with many club stations and members from around the country. It was just a casual entry, but enabled us to get our club call on the air. Thanks to everyone we worked. 73 MX0SNB

50/70/144/432MHz Christmas Cumulatives

The RSGB 50/70/144/432MHz Christmas Cumulatives Contest series run from the 26th to the 29th of December each year and are intended as a bit of fun in the contester’s calendar.  The contest exchange is the usual RS(T), Serial Number and 6 character locator (e.g. JO01DQ).  These contests are really easy to become involved in, and often provide a good excuse to escape the house after Christmas.

This year, Dave M0TAZ, Dave M0YOL and George M1GEO decided to operate alfresco from the Bunker for the final two days (George having put in token entries on the 26th and 27th for 144 MHz from Home).  We operated on 50 MHz, 70 MHz and 144 MHz for the full 2 hours on a picnic table, in large overcoats on cold winter afternoons, packing up in the dark!


144 MHz was to be our main band. For that we used an Icom IC7100 transceiver, DG-8 masthead-preamplifier (GM3SEK design/M1GEO construction), and 9-element tonna (10m AGL), powered from a large 60 Ah sealed lead acid battery.


50 MHz and 70 MHz were run as a sub station. Again, using an Icom IC7100 transceiver and an InnovAntennas 6-element dual band (50/70MHz) yagi (7m AGL), with an 85 Ah leisure battery. The battery also provided mains power via a small inverter, which charged the logging laptops.


The table below shows the number of QSOs made per band on each day, as well as the best DX station callsign, locator and distance. In order of fairness, we switched callsigns on the second day, all points awarded to the SNBCG.

Band  Info 28 Dec 2015 (M0TAZ/p) 29 Dec 2015 (M1GEO/p)
144 MHz # QSOs 30 40
(IO64XL 525km)
(IO74PC 430km)
70 MHz # QSOs 7 10
(IO81MX 226km)
(IO92XW 141km)
50 MHz # QSOs 8 13
(IO81KQ 236km)
(IO74PC 430km)

The map below (click to zoom) shows the worked locators for the Contest. Almost all of the DX was worked on 144 MHz. Produced by OpenContest’s EDI Visualiser.


A very enjoyable activation.  Even if it was a little cold! Lots more photographs here.


Casual Operating in the Shack

This weekend a few of us decided to head down in to the Shack at GB0SNB to do some operating.  The HF bands were full of stations in the Worked All Germany and BARTG RTTY contest, as well as JOTA activation stations.

In between working a few on HF, we managed to pull around 20 contacts on 2 metres, and had a nice pileup on 145.400 MHz.


Above Chis G8OCV and Dave M0TAZ operate on HF.


Here we see Dave M0TAZ operating on 145 MHz FM.

Antenna Maintenance

Exposed on the side of a 50 meter mast the antenna often requires maintenance. George M1GEO and Chris G8OCV have over the years perfected the best way to mount the antenna, and on this occasion is had lasted close on 2 years. Antenna maintenance in the afternoon sun is much preferable to winter rain, so we too advantage of the weather to pull up the new doublet antenna. The doublet is 40m per leg, into 300 Ohm ladder line and then a 4:1 Balun.

The doublet is 40m per leg, into 300 Ohm ladder line and then a 4:1 Balun.


The centre of the antenna is made from a plastic chopping board from one of the discount value stores, ideal for insulators. The wire is multi strand 13A flex, ideal for antennas and hopefully robust enough to survive the winter weather.

The centre of the antenna is pulled up onto the mast, elevated to 20m and the ends are on one side into a tree and the other a warning siren. Its quite difficult to locate suitable points for the antenna ends, and elevation without snagging in the local trees is always a challenge. Once setup we managed a couple of QSO on 80m.

73 Dave M0TAZ, George M1GEO, Chris G8OCV

Meteor Scatter Experiments

This weekend was very close to the peak meteor shower from Perseid. This gave us an ideal opportunity to try meteor scatter for the very first time, using a 9-element G0KSC antenna at 10m and 100w amplifier. The antenna had G7UVW‘s LNA adding a further 20dB of gain to the receive path at the mast-head.


Using WSJT we were able to decode a number of stations, although it took some reading, and trial and error to make our first QSO. The first QSO was with OK1UGA in JO80dd, some 1137 km. Through the course of the evening we completed the following QSO.

Callsign QRA Locator Distance (km) Freq (MHz) Mode
OK1UGA JO80dd 1137 144 FSK441
DF5NK JN59PM 812 144 FSK441
SP2FRY JO83WR 1215 144 FSK441
S56P JN76PO 1225 144 FSK441
OK1DQT JO70IB 1027 144 FSK441
YU7TT KN05FW 1662 144 FSK441
M1BXF JO02FE 71 144 JT6M
F8DYR JN07WL 487 144 JT65A
I6BQI JN72AK 1456 144 FSK441
SM7FWZ JO78MM 1134 144 FSK441
IZ3WQO JN65CL 1110 144 FSK441


Since the use of WSJT is not much of a spectator sport, we also had a 20 metre beam up to shout on HF, which was later changed to 17 metres to avoid the ongoing CW contest. Full log breakdown here. Best DX was CE6SAX (12320 km) and YB3HJM (12280 km).




In the afternoon, John M0UKD arrived with a homebrew 4 metre beam which he built on the Saturday (8th Aug 15) to a DK7ZB design.



We worked 40 stations in 2 hours, which I think is good for 70MHz. Our best DX was PA4VHF at 449km.



Portable Weekend

The weekend of the 1st and 2nd of August 2015 saw an informal activation at the Bunker.  Dave M0TAZ operated in the 2m low-power contest, while George M1GEO and Fred G3SVK operated in the European HF Championships.


The event gave us an opportunity to dry out some of the equipment from the previous weekend (RSGB IOTA) where we packed away in heavy rain.

A simple station setup consisting of Icom IC7100, SB200 amp and 3-element monobander for 20 metres. This was later swapped for a 4-element monobander for 15 metres.

A breakdown of the European HF Championships log can be found here, for those interested, and some maps here:

Screenshot - 100815 - 21:30:21



Meanwhile, Dave M0TAZ operated the 144 and 432 MHz low power contest (anything up to 25w from the transmitter), using a 12m mast and the 9-element portable Tonna beam.



The weather was ideal for sitting outside, and the activity levels were best described as moderate. Not as busy as the shorter UKAC contests, but the first 1 hour did coincide with the backpackers contest.



We managed to work into IN88, a first for M0TAZ. A few French stations, We didn’t hear any GW, GM, GD or GI.