I'm thinking, there's a man who knows his portable radios 
Thanks Mike for passing on some of your knowledge. Much appreciated.
Not obvious, and I hadn't said - but the K is running from a 6V SLA battery, driving a switching power converter providing LT and HT. It has copious filtering, and it's heavily screened (sits in a cavity machined in a solid block of aluminium, walls 10mm thick), but in the K the frame aerial is wrapped round everything. And there are slight whistles audible with weak stations.
Hence, rather than have the RFI generator sitting right in the middle of the frame aerial, I wanted to try ferrite rod aerials where this wouldn't be the case. I wasn't expecting quite such an improvement in performance as I'm seeing.
Incidentally, the CN420a is powered by the same converter, but as the aerial is in the lid it's hinged up out of the way, and it runs as quiet as batteries (despite, in the CN420a, being housed in a, off-the-shelf diecast box).
(And, the irony of using a lead-acid battery to run a radio using valves expressly designed for all-dry operation is not lost on me)
Thanks Mike for passing on some of your knowledge. Much appreciated.
Mike Watterson Wrote:I'm not sure why you'd replace the frame aerial in a K with a ferrite Rod.
Not obvious, and I hadn't said - but the K is running from a 6V SLA battery, driving a switching power converter providing LT and HT. It has copious filtering, and it's heavily screened (sits in a cavity machined in a solid block of aluminium, walls 10mm thick), but in the K the frame aerial is wrapped round everything. And there are slight whistles audible with weak stations.
Hence, rather than have the RFI generator sitting right in the middle of the frame aerial, I wanted to try ferrite rod aerials where this wouldn't be the case. I wasn't expecting quite such an improvement in performance as I'm seeing.
Incidentally, the CN420a is powered by the same converter, but as the aerial is in the lid it's hinged up out of the way, and it runs as quiet as batteries (despite, in the CN420a, being housed in a, off-the-shelf diecast box).
(And, the irony of using a lead-acid battery to run a radio using valves expressly designed for all-dry operation is not lost on me)
