More on the loft dipole

I added a 20m dipole to the loft fan dipole today, and fixed the leg of the 6m wire that pulled out of its crimp eyelet. I have yet to cut the coax and insert a coupler so I can use the VNA, so I installed it and hoped. The VNA gave it a SWR of just over 3 and the FT450D tuner is happy at that. But the band is absolutely dead!


Do radio amateurs develop a desire to go ferrite hunting? I’ve often wondered this. Many years ago when I used to go to radio rallies – this is when there were some close to here – there were always people wandering round examining various torrid and such. I never questioned this but always witnessed it. And I seem to have joined them! I now have four T130-2’s, one of which will be a 9:1 un-un and a box of assorted toroids on order to see if I can shut the hash up from a couple of wall warts. This is since I got my license, so it must be catching.

First loft dipole

Having acquired a FT405D from my good mate Steve over at Mullard Magic I experimented last night with a loft dipole – my aim is to make up a fan dipole for 40 thru 6 metres (for 40m it will be a zig zag). So, having measured the coax distance from the proposed centre point to the radio I made up a choke round a bit of 7″ PVC and hung it from a wire dipole centre supported by string.

Ok so far. As 6m is the shortest wire I decided to make that one up and see how it looked on the VNA.

So, two bits of PVC coated wire with crimp connectors for the dipole centre went up in a more-or-less inverted-vee stapled to the rafters. The SWR was 3-ish, not bad for a first go. Then the cable went loose but the SWR dropped – one end pulled out of its crimp! Huh. Eventually, after a bit of a fiddle I got to 2-and-a-bit SWR, fine for now. Coax pushed thru the hole in the ceiling to the little bedroom and into the radio, after merrily knocking everything over. Coax into radio, and the internal tuner is happy. But absolutely no signals! Hmmm. Well, it transmits, I can pick it up on the IC-R2. But no idea if it transmits more than 6 foot…

I tried the local repeater, no joy. Mind you, I’ve never even heard signals from that so maybe it’s just too much to ask.

Of course having made one continual length (17 metres of Westflex WF103 in all) of coax I cannot now use the VNA in the loft! So I need to cut it and add a couple of plugs so adjustments can be made up there… probably a good time to wrap the choke in tape too as I can imagine it trying to unwind itself given the chance.

Experiments with a bit of wet string

I had time the other day, surprisingly, to have a fiddle with the HF active aerial in the loft. This is a Datong AD170 that I’ve had for decades now. It feeds into a Yaseu FRG7000 and also a Watson SDR dongle.

There is a heck of a lot of noise here and the aerial is far from ideal, being mounted on a purlin in an inverted-vee formation with the ends held on the floor joists, mains and data wiring and the house alarm wiring nearby. So, noise.

But it seemed to fair reasonably well on 40 metres even so. I caught one conversation on the SDR and checked I could receive it on the FRG7000 too which sounded better, probably because the PC has dinky speakers attached. But more to the point I used the Hack Green webSDR and found the same signal. Other signals via Hack Green did not appear here, but fair enough, they won’t be using the same bit of wet string and are a way from here. But it was a useful experiment that both my bit of wet string and their setup received the same amateur signal, and neither could hear the other end of the conversation.

Next step, move the AD170 to the apex inside the roof and see if that sorts the noise out. More later.

First contact!

I got my licence on 23rd December 2016 and made my first ever QSO (other than in the Foundation training) at 12:06 to 12:09 on 27 December via the GB3HD 70cm repeater.

My only current radio is a Baofeng UV5R with just the supplied rubber-duck aerial. From our house we have a good takeoff to the south-west and this little handheld proved itself nicely. It puts out 4.5W on 70cm according to a power meter into a dummy load. GB3HD is almost 18 miles line of sight and over a hill but it made it fine with good modulation. Not bad for such a wee thing and only £21!