Building a set of 5B4AGN bandpass filters

For the Martello Tower DXpedition to Herm, I borrowed two complete switchable 5B4AGN bandpass filters, we had one connected to each radio to prevent the two stations interfering with each other and they worked very well.  I’d decided before we went to Herm that I wanted to build a set of these filters myself and seeing how effective they were really cemented that decision.  I’d planned that rather than have the big switchable unit that I’d build individual filters which would allow two or three stations to be used simultaneously with no problems. This would only require one set of filters because no two stations would be on the same band at the same time.

Bob, 5B4AGN recently announced a group buy and so I declared myself ‘in’ for the purpose of the individual PCBs and filter capacitors.  I sourced the wire and the toroids myself.

So I’ve got everything ready to go and in the near future I’ll be building these filters.  I’ll be sure to post updates here as I do them but one thing is for sure – I’m going to have sore fingers after winding the coils!

Some of the parts to build a set of 5B4AGN bandpass filters

Some of the parts to build a set of 5B4AGN bandpass filters



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  1. I’d like some more info on these filters. If these kits are available I’d like to source some for our clubs ( Radio Society of Tucson ) up coming ARRL Field Day.

    73′ Bob

    1. Hi Bob,

      They’re not available as a kit but 5B4AGN sometimes organises a ‘group buy’ of everything needed to put together a set of filters. You can find out all about them at his web site – and there’s a Yahoo group that’s worth joining because that’s where the group buys are organised and discussed (

  2. Well, It looks like I’m going to have to revert back to an old QST article and build my own. I put dome together a few years ago using plans from the ‘Ugly Filter project’, But they were a pain to construct. I’ve ordered the Toriods and have to get the Micas yet.

    Cheers Mate and 73’s

  3. Bob, I did email you earlier today because a new group buy has been mentioned on the Yahoo group I linked above so if you’re after these filters then it’s worth joining the group and getting involved.


  4. Is there a schematic available for the 5B4AGN kit

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