I bought a Funcube dongle to have a play with SDR and also a secondhand Realistic PRO-2006 scanner (pages on these to follow) so I needed a wideband antenna and decided on a discone which is a genuine wideband design rather than use a vertical which would basically be just a random wire. Originally I was going to build my own having done so before for a UHF version many years ago but baulked at the engineering job that would be required for one which covered VHF so instead I bought a cheap one labelled SE-900 off eBay. I think this was probably a mistake.
It has the usual optimistic performance claims…
Receive 1-900 MHz
Transmit 70-500 Mhz
Power Handling 200 Watts
Dimensions 0.88 m (H) x 0.72 m
Impedance 50 Ohms
Measuring the impedance from 25 to 175MHz shows it is never better than a 2.5:1 VSWR and is more often over 5:1 so I’d be disinclined to transmit on it on the VHF amateur bands and doubt it’s much use at UHF either. For receive of course it’s a lump of metal in the air and will produce some sort of signal.
There were mechanical issues too. The threaded holes for the grub screws securing the long elements didn’t really weren’t deep enough and some didn’t grip at all. I filed flats on the elements which allowed the grub screws to go a little deeper with more thread in use. Even so at least one element wasn’t secured well enough because it fell out which was potentially dangerous. I bodged around this by Aralditing the elements in as well as using the grub screws plus I drilled a small hole in each near the top and threaded a wire through making a loop right around the top. Now it one comes loose it can’t fall and will just hang on the wire until I can attend to it. I hasten to add that the VSWR measurements were taken before I had to use araldite and wire to hold the thing together to prevent a re-run of The Omen with a family member starring as the impaled priest.
I think on reflection I would have been better off just using my old dual band collinear.
I like long walks especially when they are taken by people who annoy me.