Sunday, 25 July 2010

Arnside Knott

Went up Arnside Knott (SOTA G/LD-058) this afternoon. I took the half wave for 50MHz and also the Sharmans mobile antenna for 2m/70cm but after changing my coax, forgot I needed the SO239 coupler to connect it up, so ended up with nothing but the handheld except on 6m.
Made 2 QSOs on 51MHz FM with G1CCL and G1KLZ. 6m isn't really enough to qualify a summit unless it's further south (like Kinder Scout).
This was another of the G1-only activations - every station I worked had a G1 callsign:
G1OPV/P on NP-016 Dodd Fell Hill (145 MHz)
G1CCL, Morecambe (51 MHz)
G1KLZ, Ingleton (51 MHz)
G1LAT, Wennington (145 MHz)
G1OHH, Lancaster (145 MHz)

I could hear a repeater faintly on 50.800. And the Diversity FM link on 48.525 was S9, even though I was vertically polarised. Some baby monitors at S9 too.

Did some more tests on how efficient my mobile set up was, and the results weren't good. My magmount (Sirio ML-145) was giving about 7dB loss from plug to socket (it has 3.5m of RG58 coax on it) at 435 MHz. I remember measuring it 6 years ago and it was something like 3dB on 70cm so the coax must be going bad. Disconnected the coax and put a plug on the loose end. The loss of this piece was about 3dB which isn't right for 3.5m of RG58.
Yes the cable had gone bad. There was no sign of water in it or breaks in the insulation but it was getting lossy at UHF.
I'd got this magmount nearly 10 years ago at the CB shop in Lymm services while going away on holiday (to Ironbridge). At the time it made a big difference going from a 3/8 type magmount to one with a proper connector on, signals on 70cm were a lot better. I'd started to suspect that 70cm mobile wasn't what it used to be though, but not got round to actually measuring the losses.

I've got the bigger Sirio SO239 magmount which I bought in 2006, which I'll test sometime.

SWR graph of the coax (open circuit at the far end) that I removed from the Sirio magmount (3.5m of RG58). This should be a flat line near the top of the graph:

SWR graph of the magmount with no antenna plugged in (and sat on the carpet at home):

5m of RG58, straight off an old reel, with a PL259 on each end:

On 144MHz the cables look nowhere near as bad as this, it's usually a straight line around 5:1.

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