Category Archives: Flag

New Baluns for Flag Antenna

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  –

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.


Radio North 846

Radio North 846 from the Irish/Northern Ireland border area (Donegal?) is a consistently good signal into London these days. It is audible from mid-afternoon and as late as 09/10.00 in the morning.

Here’s how it was sounding this early evening just after 18.15:

If YouTube has blocked the video due to the brief Glen Campbell song then try this one:

The signal is so consistent it is my MF beacon with which I test the Flag antenna and various baluns.



Rare Peruvian Radio Carraviz heard in London

Yesterday I heard the rare Peruvian Radio Carraviz OAU72 from Juliaca at 0357 on 1570 kHz following a tip-off from Paul C:

Despite the distorted audio you can clearly hear the “La Voz de la Liberacion” id at 03:57:55. Receiver as ever was the Perseus SDR and a 10x4m Flag antenna with home-brew dual binocular toroid balun.

Beauty of MF dxing is that you never know when a new rare one will pop up. Normally 1570 is dominated by the Canadian French popster CJLV out of Laval. If Latin America dominates it is usually Bethel Radio from Lima.

NA MF DX Back with a Bang – Zer Radio Mexico heard in London

After almost a  month of very poor or non-existent NA DX  conditions came back this week down south (Scottish dxers  saw a return last week).  On 25 November at 0629 I had a personal first – XEARZ-AM Zer Radio was coming into London on 1650 kHz with easy listening music and “Zer Radio 16-50” ids as can be seen below:

Finally, a welcome back home to Paul C after his hospital stay. Take it easy Paul but keep those dx-ears of yours available!




Moscow Technical University Student Station 25900 kHz

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.