Month: September 2015

Practical Wireless 70MHz Contest

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70MHz DK7ZB 12.5r Yagi on Racal PU12 mast.We had a fun day up at Kelvedon Hatch on Sunday for the Practical Wireless 70MHz contest with fantastic weather yet again!

Dave M0TAZ was operating with his Racal PU12 mast and IC-7100 and I brought along my amplifier and Yagi for this once a year event. There was good activity although as predicted, the final hour was a bit slow going.

We were operating for the whole four hours, running 160W into an 8.24dB Yagi giving an ERP of ~1kW and we worked a total of 47 stations, of which the best DX was GM4JR at 454km. We also worked into Wales and The Netherlands.

As PW contests do not give you a QSO map, I plotted my own in Google Maps by exporting a KML file from the Minos logging software. The QSO map can be seen here.

A photo of the field can be seen below…

PW 70MHz Contest 2015 at Kelvedon Hatch

PW 70MHz Contest 2015 at Kelvedon Hatch

I also took some video on my phone, which can be seen below…

You can also read Dave’s article on his website. George M1GEO, Chris G8OCV, Dave M0YOL and some others also attended to play some radio so it was a good day all round!

RSGB 2nd 70MHz Contest

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2015_70MHz2_1

M0UKD/P – 70MHz

We had some great September weather today for the 2nd 70MHz contest. We setup at the Kelvedon Hatch ‘Secret Nuclear Bunker’ as seen above, using my new 70MHz amplifier at 160w and my 4 element DK7ZB 12.5Ω Yagi.

QSO Map

QSO Map

Conditions seemed quite normal, we worked no Scotland or Ireland but our best DX (as many others) was PA4VHF at 449km. Other highlights were GJ3YHU in Jersey and M1CJN/P in the North York Moors. Total contacts was 46.

A very enjoyable day of operating and testing the new amplifier. Next week, it’s the Practical Wireless 70MHz contest, so lets hope for the same weather and some band openings perhaps? Maybe I’m asking too much 🙂

The Claimed Scores are available. Thanks to Dave M0TAZ, George M1GEO, Dave M0YOL and Chris G8OCV for help & company, and of course everyone we worked (or tried to work!).

RSGB 2nd 70MHz Contest at Kelvedon Hatch

RSGB 2nd 70MHz Contest at Kelvedon Hatch

Two years in the making – 70MHz 300w Amplifier

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70MHz 300w MOSFET Linear Amplifier

Today, I finished a project I started over two years ago. It’s not that it took two years to build, it’s just that its taken me two years to get the parts together and build in my spare time! The upcoming 2nd 70MHz contest and PW 70MHz contest prompted me to get this finished.

Its a 300w 70MHz amplifier, using a BLF 278 MOSFET. Power supply is 50v @ 10A. The amplifier has 9dB attenuation at the PA input to bring the gain down to something usable, as without the attenuation, 2.5w input gives 300w output (21dB gain)! The input & output power, with 9dB ATT (total 12dB gain) is:

  • 5w = 100w
  • 7.5w = 150w
  • 10w = 200w
  • 15w = 300w

The amplifier uses ~7.5a @ 48v for 200w O/P, so it’s around 80% efficient. Bias is set to 750mA. The maximum power here in the UK on 70MHz is 160w, for which this amplifier requires 8w of input. Below is a picture of the inside. I will tidy up the cables at some point!

300w PA & LPF

300w PA & LPF

Bird 43 - 70MHz 250w+

I need a larger Bird element to measure the 300w output on the Bird 43!

5th 144MHz Backpackers Contest

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On Sunday, Dave and I went to South Weald to take part in the 144MHz Backpackers Contest. We used Dave’s 9 element Tonna 6m AGL and 10w from the Icom IC-7100. The weather was perfect, blue skies and sunshine and hardly a breeze! Dave worked 51 stations and some good DX for low power, due to the big stations competing in the 144MHz Trophy contest. We managed contacts with England, Wales, Scotland, France, Germany, Belgium and The Netherlands. Our best DX was DR4X at 648 KM. The QSO map can be seen below.

5th Backpackers 2015 QSO map

5th Backpackers 2015 QSO map

I brought along some 70MHz equipment, which I set up after packing away the 144MHz gear and spent about an hour on 4m working 8 stations. All in all, a good days operating in the sun!

Backpackers in the September sunshine!

Backpackers in the September sunshine!