Wednesday, 28 July 2010

Multi Ranger 200



Watson Multi Ranger 200 on the car. I've not tried this at over 30mph but probably won't be driving very far with a HF mobile antenna on.

Tuesday, 27 July 2010

Boot Mount

I've just put a Watson boot mount on my car but I've had to put it in about the worst possible place because the car just doesn't have any edges which you can clamp something to. The top of the tailgate has an edge but when the boot opens it goes down underneath the roof so if I put something on there it would get stuck.
In the end I tried it on the left side of the tailgate, just below the back windscreen (just below the lights in this picture - that's not my car, I'll put a photo on soon!). This is about halfway between the floor and the roof but with my Watson W7900, I've still got quite a bit of antenna above the roof level. The radiation pattern is going to be weird but I can get a decent SWR with it there. Not had much chance of comparing it with anything yet, I've only been driving round town.
Being lower down, I should be able to put a HF mobile antenna on without it falling off or hitting stuff. I checked the SWR with the MultiRanger 200 and it was OK on 10MHz and upwards, but lower bands were no good, probably because it's fixed to the tailgate and not straight onto the car body.
Coax is 5D-FB which is 7.6mm so won't go through gaps in doors etc. so the boot mount has a bit of thin white coax crimped onto the end of it to stick through the gap.
I've got a Nagoya UT-108 mini magmount antenna coming too, so that'll be something to compare it against.

Why are laptop DVD drives so slow at reading discs? I'm trying to make an ISO image of a DVD and it's taking forever, doing about 2.5X.

Is the data network on 440/453MHz being closed down? Half of the base stations seem to have gone off round here, a few went off maybe about a year ago but recently more have gone including the one in Barrow on 440.4125 and Hameldon Hill on 453.3375. They were good 'beacons' for checking antennas and UHF propagation.

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.

Friday, 23 July 2010

Coax update

Made a 5 metre pl259 cable this morning from some old rg58 which i'd
had for years - i got given 2 x 100m reels. on 70cm, I was getting 6
watts out for 9 watts in so the loss was under 2db or 0.4db per metre.
That's better than the 0.6db for that rg8-mini.

--
Sent from my mobile device

Wednesday, 21 July 2010

RG8-Mini

RG8-Mini (or RG-8X) is the 50 ohm coax size which is somewhere between RG58 and RG213, 7mm diameter. You might use it where you need flexible coax but where RG58 isn't good enough. But is it really any better than RG58?
It seems to be sold more as a high power HF cable than for use where low loss matters, and I first saw it being used on CB. There were red and grey versions of this cable.
A few years ago I made up a cable of black RG8-Mini, about 11 metres long with PL259 plugs on and sometimes used it for portable operation. I thought it would probably be better than RG58 so wasn't too worried about the loss. But this week when I was on Muncaster Fell I had a listen around 433 MHz and didn't hear very much. I could hear more on my handheld's own antenna than on the 2m/70cm mobile whip that I had set up on a pole.
When I got home I measured the loss of this 11m of RG8-Mini on 2m and 70cm. With a very short piece of RG58 I was measuring 9 watts on 70cm. Replacing that with my coax cable reduced that to 2 watts! That's about 6.5dB loss or 0.6dB per metre. RG58 is supposed to be better than that on 70cm. At 144 MHz, the loss was about 2dB which is more like RG58 should be.
The official figures for RG-8X are better than this but it doesn't seem as much of a standard as RG58 or RG213. I think I bought mine at a rally and I had some on a 2m/70cm dual bander at home before I put decent coax on it so that might have been the same piece of cable.

Wednesday, 7 July 2010

70 MHz WSPR

There's some activity on 70 MHz WSPR now, on 70.0286 MHz. I can receive G0MJI from Liverpool, using my Icom IC-7000 and the dual band 2m/70cm colinear on my chimney. On the proper 70 MHz dipole in the loft, there is no improvement in S/N because there is more noise indoors. I've nothing to transmit on 70 MHz SSB though.
Alex G7RNX in Dalton was also on 70 MHz WSPR on Sunday and could be received by G0MJI and G3ZOD (Stockport).

Made a PC to radio interface for an FT-847 before finding out it wouldn't work properly because...
On the Yaesu FT-847 there are separate connectors on the back for FM and SSB data modes. The 6-pin mini DIN socket can only be used to transmit on FM (there seems to be receive audio on SSB through it though). On SSB, transmit and receive audio are through a 3-pole minijack socket. The tip of this jack is for transmit audio and PTT (ground through a resistor to transmit).
The 6-pin socket can be used for the PTT on both FM and SSB.
Connecting a cable directly between the headphone socket on a PC and the FT-847's SSB data socket made the radio stay on transmit. There needs to be a capacitor to block any DC current path which might key it up.
It seems a bit of a strange thing to have 2 data sockets but when the FT-847 was designed, people weren't using a PC sound card for data modes so would have had a standalone packet TNC.