Author Archives: Gavin, M1BXF

VHF Station Going Well

May 10th, 2017 | Posted by Gavin, M1BXF in General - (0 Comments)

The VHF station has been running well since the day we arrived.  It was setup and making QSO’s by 19:00z on Saturday.

The VHF Antennas

As usual, the Camb-Hams trailer mast has been used for the VHF antennas. The G1000 rotator is in a cage this year to help reduce the strain on it, especially when lidting to the vertical position.

From bottom to top the antennas are;

  • 6m:  6ele YU7EF EF0606
  • 2m: 17ele Tonna + DG8 preamp
  • 4m: 7ele YU7EF EF0707

4m and 2m are fed by LBC-400 coax, and 6m is using H2020 coax.

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The VHF Operating Position

The VHF desk runs all 3 VHF bands, at the same time usually.  The setup here is;

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To work 3 stations there is a need for 2 laptops + a 21” monitor, The monitor allows 2 MSHV windows (2m + 6m) to be shown side-by side, with the main laptop display to be used for KST chat and other computer activities. The 3rd MSHV (4M) window is running on the netbook (above the Pro3).

At the time of writing this, on VHF we have made 96 QSOs; 42 on 6m, 14 on 4m and 40 on 2m, including 16 on 2m EME.

EME Activity

April 30th, 2014 | Posted by Gavin, M1BXF in General - (0 Comments)

We came to Lewis with a low ERP 23cm EME system with hopes of making a handfull of QSOs.  We up till now we have 9 EME initials on 23cm with a few days to go.

Here are a couple of screenshots of some of the QSOs.



2m EME has been impossible due to local high noise levels on 2m.

Main HF Station

April 29th, 2014 | Posted by Gavin, M1BXF in General - (0 Comments)

HF1 station

This is the the room used as the main HF operating, typically SSB.

The Decca is symmetrical with opposite layouts at each end of the building. At the other end, in the opposite room, is another HF station mainly used for CW, an HF data station and the VHF/UHF satellite station.

VHF and Up Stations

April 29th, 2014 | Posted by Gavin, M1BXF in General - (0 Comments)

This year we have again put all the VHF and up stations together in Flossie, These are;

  • 6m = JT6m, ISCAT-B & SSB
  • 4m = FSK & SSB
  • 2m = MS and JT65 (EME)
  • 23cm = JT65 (EME)


This makes sense as we find the same stations usually want to work us back to back on all the different bands and with 2 operators we can run 2 bands each (6m + 4m) & (2m + 23cm).

Find us ON4KST chat.

4m Update

April 29th, 2014 | Posted by Gavin, M1BXF in General - (0 Comments)

So 4m has not had the best start.  We are experiencing higher than usual inter-station breakthrough from HF into the 4m RX, here is an example of it at its worst;


This is a combination of about 3 HF stations, and as you can well see it’s impossible to work anything on 4m through this QRM.

Lots of investigations ensued and found that even at low power levels, 100w, and with all stations using band-pass filters, the interference was still apparent and we had no way to cure it, the only conclusion is we have something nearby which is causing a “rusty bolt effect”, there is little chance of curing it.

The site we are operating from is an old Decca transmitter site used for navigation and we believe there is a network of ground radials underfoot and the building has an integrated faraday screen, and probably many other pieces of metalwork we have yet to see.

The good news is we have found a combination of bands which work now well with 4m and 4m operation is yielding QSOs again, so if you see us on the band, or on ON4KST chat, then give us a call.

One issue though, and it’s a biggie, is during the investigation phase, alignment of a backup transverter was in progress when it went into TX oscillation which resulted in too much RF power being delivered into the MRF-151G final PA which in turn destroyed the device.  The workaround has been to use the Yaesu Quadra on 4m as the final PA driven from the G4DDK 7w RA07H0608M pre-drive PA, this setup can achive 80w out the Quadra on 4m, this isn’t so bad as it’s only 3dB down on the MRF-151G output.  It does mean however 6m must run barefoot (80w) from the K3 when 4m is using the Quadra but can be set back to 400w when 4m is not in use.

70MHz M1BXF Transverter–Based on G4DDK’s Nacton

April 24th, 2014 | Posted by Gavin, M1BXF in General - (0 Comments)

This year we have an updated 4m transverter based on Sam G4DDK’s Nacton transverter. 

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The transverter can receive signals from the generator down to, and beyond, –140dBm and can output 300w meaning running data modes at 50% duty cycle at 150w is easily possible.

A full write-up of the transverter, and it’s history, is available on Gavin M1BXF’s  webpage.

Mast Bearing for 6m

April 21st, 2014 | Posted by Gavin, M1BXF in General - (0 Comments)

Tis year the 6m beam will be mounted on the Camb-Hams /P trailer mast at 13m AGL.  The mast itself is 10m and it is at this point we mount the Ham IV rotator and above the rotator will be a 4m pole which we normally put both the 6m and 4m beams on.  This year we are putting 4m beam onto Flossie’s 20m mast and will mount the 6m beam near the top of the trailer mast pole at about 13m and above it a Solarcom imax-2000 vertical for 10m.

This leaves lots of potential movement above the rotator on a windy day so we have decided to support it using a slip-ring.

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We are using a Yaesu GS-065 which comes with handy guy rope mounts and to connect to them 4 runs of 8mm nylon rope terminated with thimbles and D shackles which will make assembly much easier.

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This preparatory work I can not stress enough.  The few hours effort back home means we know the guy connections will be good whoever connects them to the guy points, no worries about bad knots, and the time to assemble and pack away is much reduced, which if the weather is poor at setup or teardown you’ll be very much appreciative of the effort you put in before setting off.

As there are 2 guy points on the 6m mast, the lower one is at the rotator 10m up and the second will be at the guy slip ring 3.5m above that.  As such we have 2 different lengths of guy rope, the tops ones are 23m and are marked with “TOP”, the bottom ones are 20m.

Originally John G4BAO made this up a guys slip ring before I opened my new GS-065 box to find Yaesu supplies the rope attachments.

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My only concern with Johns design is the stress on the right angles, this thickness of extruded aluminium should be OK, however the supplied Yaesu parts seem better and less likely to fail, this is just me being over cautious.

GM3SEK HF Chokes

April 21st, 2014 | Posted by Gavin, M1BXF in General - (6 Comments)

We find that vertical antennas work for us on most bands.  We also use vertical Dipoles for HF bands above 20m, there are a few reasons why verticals should be considered for a DX’Pedition;

  • Low weight to transport
  • Small size requirements to transport
  • Quick and easy to setup
  • Easy to tune and change as required
  • Minimal guying needed (3 only)

The only draw back is RF can flow back down the outer of the coax radiating in places it shouldn’t.  This is acceptable (but not ideal) in a single station environment but can be a contributing factor to breakthrough issues in a multi station operation like we normally run, this year upto 5 HF and 4 VHF stations running at one time.

The way to solve this is to add a choke to the coax.  Some people just make 6 turns of coax at about 5 inch diameter but this is not always sufficient.  Ian GM3SEK has written lots on the subject of chokes and  this year we have made some to help improve our station.

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6m Rotator Upgrade

April 21st, 2014 | Posted by Gavin, M1BXF in General - (0 Comments)


One thing which was noticed in the Mull2013 DX’Pedition was how annoying a south stop rotator was on 6m. Moving between SP and CT was via north and *very* slow.

We use Gavin M1BXF HAM IV rotator and this year he’s done some updates to it.

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The Decca’s Original Purpose

January 23rd, 2014 | Posted by Gavin, M1BXF in General - (0 Comments)

The cottage we are staying in for the 2014 DX’Pedition, The Decca, is so named for its original purpose.

The Decca Navigator System was a hyperbolic radio navigation system which allowed ships and aircraft to determine their position by receiving radio signals from fixed navigational beacons. The system used low frequencies from 70 to 129 kHz. It was first deployed by theRoyal Navy during World War II when the Allied forces needed a system which could be used to achieve accurate landings. After the war it was extensively developed around the UK and later used in many areas around the world.