Author Archives: M0TAZ

1/4 wave on 80 meters

The plan was to put up an 18 meter (60 ft) spider beam roach pole and operate a 1/4 wave on 3.7 MHz. We have used both the 12 m and 18 m roach poles from Spiderbeam with the intention of using them to support inverted V antennas and verticals. Previously we used the 12 m on a number of occasions to support a doublet for portable operating, and the 18 m to make a top loaded vertical for 1.9 MHz with an inductor.

On this occasion, we wanted to try a 1/4 wave on 80 m and the 18 m is ideal for that purpose. The pole can be fully extended and then walked up from the ground, but you will often need to use jubilee clips around the poles to stop it collapsing under its own weight. Like the smaller poles the sections do pull out and lock, but in a breeze, the sections can often rock back and forward and then without notice concertina down. Here you can see the roach pole and me for scale.

Using 6 radials and a wire fence the antenna was ready for some testing. The VSWR was 1.1.5, I think with a larger ground plane this may have been lower, but it was acceptable for our purpose.

The antenna was guyed off at 4 and 12 meters, this is essential in even the lightest of winds.

With the addition of a IC-7600 and solid state amplifier, the station was ready to go.

Unfortunately, the bands have been suffering from disturbed conditions due to solar flares, so despite our best efforts, we were unable to work big DX. We did work quite a few European stations, and also a fair few UK and Irish stations. The reports received from the antenna and the reception performance was very good, and I was able to receive stations from the USA later in the evening. Unfortunately, the USA stations were in a net, so I didn’t disturb them.

The weather also provided some anxiety, over the course of the weekend the wind picked up to a fairly constant 20 MPH breeze. Thankfully despite some groaning the guys held and the antenna came down without incident.

Over the course of the weekend, we worked 80 stations from 22 DXCC.

The first 50 MHz contest of the year

Members of the SNBCG took part in the first 50 MHz contest of the year at the Kelvedon Hatch club call M0SNB. The contest ran from for 3 hrs on Sunday morning (10 till 1) the weather was forecast to be 23C and sunny. We opted to operate outdoors using a 5e beam on a 10m pump up mast. The radio was an Icom 7600 and Expert 1.3 K-FA provided 400w power was provided by a Honda EU20 generator.

The band seemed very busy, with lots of stations taking part, and I think the good weather helped encourage more portable operating. Over the course of the next 3 hrs we worked 63 Q with our best DX into EI at 585 KM. Conditions seemed average, but we did have some very rapid QSO on some of the longer paths, sounded very much like aircraft flutter.

A very enjoyable contest in the sun, thanks to everyone we worked.

You can find the claimed scores online.

You can view the RSGB VHF contest calendar online

You can read more about the Kelvedon Hatch Secret Nuclear Bunker and the SNBCG here.

SSB AFS Contest

With snow on the ground and the sun in the sky it must be time to do some winter contesting. This weekend members took part in the RSGB affiliated society SSB contest, this takes part on 7 and 3.5 MHz from 2 till 6 PM.

With a small amount of snow on the ground, and ambient temperatures around +1C we opted for the inside operating position. The station comprised of an Icom 7600, Expert 1.3KFA solid state linear and a doublet antenna at 30m on the bunker tower.

Band conditions on 7 MHz only supported “long skip” with some good signals from Scotland and Ireland, although after a short while even these distances proved difficult. The maximum usable frequency had moved down to 4 MHz, and so a switch to 3.5 MHz was required.

A look on the Hack Green SDR confirmed 3.5 MHz was very busy, and we soon realised it was hard to find a run frequency. We also noticed a large amount of rasping electrical noise on 3.5 MHz, and so decided to investigate further. At times the signal meter was reading S9 or s9+10dB and so hearing weaker signals was proving impossible.

We changed the mains supply over from fixed to generator, and the noise floor dropped by 3 to 5 S points, interestingly it would seem the noise was coming from the mains, and so this would require some further investigation and most likely a mains filter project for Chris G8OCV.

The generator proved to be a little problematic, for some reason it was running a little lean, and so the engine was sounding rather more stressed than usual. This caused the generator to “brown out” a few times as it coughed, wheezed and spluttered in its attempt to generate circa 2KW at 240v. As they often say if something could go wrong, then it most probably would while your out in the field.

Hopefully the generator will be a simple fix, probably just needing a clean to the carburetor and no doubt another job to be added to the “to do list” before our next event.

While we had some fun, drank some tea and generally worked a few people I think its safe to say our score wont be breaking any records. As always we learnt a bit, had fun and generally tried to stay warm.

RSGB Christmas Cumulative Contest

The RSGB have a series of Christmas Cumulative contests covering 50/70/144 and 433 MHz. The contest is a chance to put down that turkey sandwich and head out to play some radio in the winter sun. The contest run for 2 hrs, and activity is over 4 days. You can read the rules online, and activity is typically quite high.

This year I joined George M1GEO at our contest site the Secret Nuclear Bunker

The setup included.

Icom 7100, 9e Portable Tona and RF power was provided by a Linear Amp 300w solid state amplifier. The mast was a Racal PU 12 at 5m as the band was wide open with tropo propagation, this provided some interested DX. Mains power was provided by a silent running 2KW Honda generator.

We managed to work 51 stations, with our best DX into Spain, EA1FDI in IN53 at 1143 KM.

The QSO map showed some great openings to the South and East.

The temperature dropped quickly once the sun set, providing a spectacular sunset and the motivation to pack away quickly. Altogether a great afternoon playing radio, with some great propagation for a change.

Thanks to everyone we worked, and all the best in 2017.

EME and MS Weekend

Members of the Secret Nuclear Bunker Contest Group (SNBCG) assembled at Kelvendon Hatch to try 144 MHz (Earth Moon Earth) EME and MS (Meteor Scatter) over the weekend of the ARRL EME event As a group we have tried with some success MS QSO and this helped lay the foundation for this weekend’s EME event.

EME is particularly challenging due to the great distances involved and extreme path loss of the signal after its travelled close on 500,000 miles! The equipment and format of the QSO is similar to MS, we used the WSJT-X 1.7 (currently in Alpha) and WSJT provided free from Joe Taylor K1JT website.

The weekend of the ARRL EME event was selected as it provided the best chance of working some of the EME “big guns”. Our equipment was quite modest by comparison, but included a

9 Element LFA antenna designed by Justin G0KSC,

DG8 masthead preamp as designed by Ian GM3SEK with the kit available to order from hupRF.

Linear amp UK Gemini 2 VHF amplifier delivering 300w.

Low loss LBC600 / LMR600 coax.

Icom 9100.

We found we could often decode signals, and even the thrill of decoding signals from the K2VEE in EM79 via the moon was incredible…then it happened.

We answered a CQ call by HB9Q and to our surprise they replied. This was our first and it turned out only EME QSO that weekend.

We continued to have quite a few MS QSO working Italy, Slovenia, Denmark and Norway and also a number of SSB contacts with 30 or so UK stations over the course of the weekend.

It is always nice to try a new mode and to succeed, you must never underestimate how difficult it is to achieve a QSO over that incredible distance. We achieved our goal of making an EME QSO, and regular decoding of signals via the moon. If this has inspired you to have a go I would encourage you to check out K4MSG guide to small station EME. Also have a look at W5UN monster EME array that has bagged him over 11,000 EME QSO !

QST also published an interesting article “A Basic Approach to Moonbounce” that you may find interesting.

Plans are already being made for the next EME event in November…

RSGB IOTA contest

Members of the SNB Contest Group came together to play some radio in the RSGB IOTA Contest. Some stations make the trek to far flung Islands in exotic parts of the world, we opted for the contest site close to Kelvedon Hatch in Essex.

The SNB contest site has the added bonus of a 50m onsite mast, making an ideal platform to hang dipoles. George M1GEO and myself decided to operate or respective calls from the two radio setup, using 3.5, 14, 21 and 28 MHz. George also added his 50/70 MHz beam on the mast, and this provided some interesting contacts using MS and JT65.

With the able assistance of Dave G7UVW, Chris G8OCV, Peter G0IAP we soon had the antenna ready.

Two pump up masts provided the following setup.

Clark 12m: Tri-band Beam A-3S covering 14, 21 and 28 MHz, with a 50/70 MHz beam.

Clark 10m : 15m 4e homebrew monobander.

Bunker: 3.5 MHz dipole at 30m centre

At various times we added some RF power from either the solid state Expert 1.3KFA or the HAL1200_Atlantic amplifier. We had some interaction between the close sited antennas, and at times this dictated the operating modes/times.

Fred G3SVK provided joined us as our CW operator, Fred can often be found in the lower pasts of the bands chasing big DX.

No sign of the great man this weekend, but, we live in hope.

70 MHz Trophy Contest and CW QRP HF

George M1GEO and Dave M0TAZ took part in the RSGB 70 MHz trophy contest this weekend at the Kelvedon hatch Secret Nuclear Bunker contest site. The weather was ideal for alfresco operating, using the Icom IC-7100 and homebrew 6e beam at 10m on the Racal PU12 mast. Using 50W and a 85Ah leisure battery we operated from 11am till 4 am.

Here you can see the PU12 and home-brew 6e 70 MHz beam. Operating from the base of the mast provided quick access to turn the beam. We managed to work 59 QSO with best DX into Scotland at 518 KM. The QSO map is shown here.

Meanwhile Rob M0VFC was operating QRP HF on 3.5, 7 and 14 MHz using a range of dipoles. Unfortunately the HF bands have been a challenge at the best of times during the day, and QRP provided to be interesting. After a few hrs operating Rob had completed 30 QSO, and under the conditions that counts as a sterling effort! Here you can see Rob operating from the boot of his car. No appearance from the great man.

Altogether another great weekend of alfresco operating in the sunshine.

LEFARS Bank Holiday Radio Weekend

Everyone loves a bank holiday weekend (unless you happen to be working) and last weekend was a 3 day radio event run by LEFARS. The event is based at the Rainbow and Dove PH, yes really a radio event in a pub garden !

The event used the special event call GB2LRS on 7 and 144 MHz, while 21 MHz used the Secret Bunker Club call M0SNB. On 7 MHz the club used a doublet antenna, on 21 MHz we used 400w and 4e home-brew beam aerial. The beam was mounted on a 10m Clark pump up past, with a recently purchased Yaesu G1000S rotator. The linear amplifier was a solid state by Expert 1.3K providing flawless power on the Honda generator.

While the band conditions did provide a challenge, we did prove that even on a quiet band its possible to work DX with some power and a good antenna. We worked some nice DX including Uruguay, Brazil and Philippines to name a few.

In the evenings we turned our hand to 3.5 MHz, and I made a simple dipole to hang from the mast. We placed a 1:1 Balun at the feed point, and fed the antenna with coax. The antenna was cut to provide a match on 3.7 MHz, so no ATU was required. The addition of 400w allowed us to put out what many described as a phenomenal signal. I checked the signal on the Hack Green SDR, and from this screenshot you can judge for yourself. The signal reported by Hack Green was -42 dBm.

Fred G3SVK also guest operated, working over 100 station on CW including some USA stations. The total number of QSO over the weekend was 320 mostly on SSB. The conditions at times did throw up a few surprises, at one stage I could hear and worked stations in Ireland at 59 on 21 MHz !

It was also nice to see Charlie M0PZT and Peter G0DZB operating portable both using Elecraft KX3s although both torturing their radios with some old school on-off keying ?

Thanks to the LEFARS team for organising another great weekend of radio.

Upminster Windmill on the air

National Mills on the air weekend is a chance to combine amateur radio with the national windmills open day. Although not directly related to the bunker, the SNBCG decided to activate Upminster windmill as it is our local mill – it was a delight to operate on the green opposite the mill once again! The mill has stood on the green in various guises since 1803, and recently thanks to the National Lottery Heritage Fund its just secured large grant to complete some restoration and the building of a education and visitors centre.

Unfortunately due to the ongoing building work members of the public were not able to visit the mill this year, but that didn’t stop them coming to visit us operating radio in the field.

(Back Left Dave M0YOL, From Left John 9H5G, Peter G0IAP, Chris G8OCV and George M1GEO)

This years event was well attending, with our furthest operator travelling from Malta to guest operate. John 9H5G operating (left station) retired to Malta, but often travels back to the UK. We were delighted to welcome him to the team, and he was soon pressed into service on 7 MHz managing the pile-up.

We operated using 2 x Icom 7100, making use of 5, 7, and 14 MHz on HF and 70 and 144 MHz on VHF. Over the course of the weekend we contacted over 30 mills and 150 others stations from all over Europe.

Thanks to everyone we worked, QSL is via eqsl.cc 73

Flight around GB0SNB Kelvedon Hatch SNB contest site

The following video is a unique view around the GB0SNB contest home of the Kelvedon Hatch SNB . Using the DJI Phantom 3 and recorded in UHD 4K. The mast on site is home to the GB7KH DSTAR repeater and stands at around 50m high.

GB0SNB/MX0SNB/M0SNB – Kelvedon Hatch Secret Nuclear Bunker

RSGB affiliated amateur radio contest group & special event station in a RGHQ 5.1 Cold War Nuclear Bunker, hidden in the depths of Essex!