So last Saturday I drove to the woods and parked in a convenient lay-by near the mountain bike centre. It was a beautiful sunny day – lovely to be in the open air playing radio! A short walk to the trig point and I set up the antenna and rig – after some adventures trying to guy the sotapole I eventually just secured it to the trig point with bungee cords.
I started out on 40m with a bandhopper two dipole antenna and conditions were actually very good. I used the sota goat app on my iPhone to spot myself (self-spotting is acceptable and recommended for sota) and the hamlog app on the iPhone to log contacts as I had forgotten a pen or pencil!). I worked stations in England, Wales, Germany, Netherlands, Belgium and Scotland – see full log below. I then switched to 60m using a half-wave end-fed dipole and had another few contacts. 60m conditions were much noisier and difficult compared to 40m which was quiet with most calling stations being 59+. You need 4 contacts to officially activate a summit.
The scenery around the trig point is very beautiful – here’s a few more pics. Unlike the actual Wendover Woods centre, which was packed to bursting with picnicking families and activities, the trig point field was empty – a solitary walker and two mountain bikers were the only visitors in over two hours.
I recently revamped my Flag antenna which has served me so well for MF dxing in this very suburban London location. It was around 8m by 3m but I made the vertical sections longer and the horizontal section slightly longer as well so it is now 9m x 4m.
The major change was that I constructed a balun. I had been using a balun made for the Flag antenna by eBay seller kafa2500 which was well made, waterproof and reasonably priced – however i thought I would have a go myself. In the end I ended up making two baluns which i’ll describe and show here.
Remember the purpose of the balun is two fold – primarily to transfer the wave energy of the desired signal from the antenna to the feeder cable – RG58 in my case. The second purpose is to prevent common-mode currents flowing along the balun which could cause RF problems in the shack. The latter is not an important consideration for the receive only paradigm. The balun will not help with directivity or nulling. The energy is transferred by the balun using magnetic induction which is a manifestation of the Work form of energy transfer – http://en.wikipedia.org/wiki/Energy_transfer
The first balun was constructed using a pair of largish monocular toroids picked up a the Kempton ham rally, bound together in a box picked up for £1 at the same rally. The windings ratio is 11:3 using 24 swg magnet wire from Maplins. I was intending for 12:3 following advice from N2VV but could not get the 12th turn through! Believe me it’s not critical. The SO239 and phono antenna sockets I had in stock. Here’s a close-up picture of the beast:
and here is how it looks with the box top screwed down- all connections are wrapped with self-amalgamating tape with black electrical tape on top and liberally smeared with vasoline to further combat water ingress, especially the box top screw holes.
For context a picture of the garden showing part of the Flag antenna wires and balun box:
This new Flag antenna works very well with excellent signal/noise characteristics from LF up to 26 Mhz and beyond. It also delivers a decent signal strength hence not necessitating the use of a pre-amp.
I also made a similar balun with an Amidon binocular toroid BN-73-202 kindly sent to me by N2VV. The BN-73-202 is very highly thought of by serious low band dxers. I aimed for the same turn ratio but think I ended up with 10:3 – again it works very well but for the moment I am long-term testing the larger toroid model. Here’s a picture:
I think the reason people complain about low signal strengths from Flags and lack of coverage above 4-6 MHz is purely down to the choice of toroid and the turns ratio used. You can’t just use any old toroid and a random turns ratio – source a proper high quality toroid and use an appropriate turns ratio.
I had a play in last weekend’s major CQ WW CW contest – staying on 10m all the time. Goal was to work as many DXCC and CQ zones as I could. I ended up with 28 zones and 79 DXCC worked. The link below shows the QSOs graphically:
Hard rocking and propagating well into London this early afternoon.
The station is run by students of the Moscow Technical University of Communications and Informatics (MTUCI). Rig is the Perseus SDR with 10x5m Flag antenna. Home-brew bi-monocular balun is used with 10:3 ratio of turns with 24 swg magnet wire. The balun performs really well at MF and extends up to 26 MHz and beyond.