Sunday, June 04, 2006

I though Magnum was a TV cowboy, or an ice cream?

With all this commuting I though its time to go mobile!

I picked up a Magnum 257 on eBay for 10m mobile, it had an audio problem but that was easily sorted with a bit of switch cleaner.

It looks like a bit of an unusual rig but searching about I can see its sold under different badges. It’s a multi-mode transceiver with 30watts out on SSB AM and FM and was obviously originally built for the CB market. I stuck it on the Thruline and it delivers a comfy 32watts output.

It’s been in the shack for the last month whilst I sort out how it works.

Pros –

  • Cheap as chips 10m multi-mode
  • Reasonable power out
  • A small light-weight unit (I won’t be leaving it in the car for any tea leafs so it has to be carried)
  • Variable power out 6 – 30Watts on all modes (Very useful)


  • The RX audio quality could do with improving
  • Best used mobile as it looks a bit dirty on the spectrum analyser
  • The 10KHz steps show its CB heritage?

I started tuning about on FM using a dipole in the loft and soon encountered a local who gave it a good report. FM was Okay, SSB was good, AM was dire (More to do with the mode than the rig?)

The next day I could hear a Swedish repeater on 29.620 with some locals rag-chewing. Managed to work through using the repeater shift and have had a few simplex QSO since - 59+40 into OE land (Austria) on FM so this is going to be fun!

The 10Khz steps are a bit annoying on SSB, to get 1Khz you have to press a button or two, which is a bit fiddly. It comes with a combined TX/RX clarifier (No RIT), but the range of this is only +- 1.5khz

If anyone knows of a mod to take this to +-5Khz or just a circuit diagram get in touch!

I think I will stick to FM when mobile, and maybe sideband when parked up.

One advantage of 10m is all the CB stuff you can pick up. This either works on 10M or just requires a minor re-tune. I decided an amplifier would be useful and picked up one for £26. Again this is meant to be 150watts or something silly. I checked it out on the power meter and it gives a reasonable 80 watts out for about 6 watts in so I guess these CB watts drop off as the power level increases?

Anyway 2 minutes at 70 watts and the unit was hot to the touch, 4 minutes and you could leave your fingerprints (Plus skin) on the heat sink. Another 2 and I think the unit would have automatically un-soldered itself.

I had a little 12-volt fan going spare in the shack, so this was wired into the unit and tie-wrapped to the heat sink. It will be on all the time the amp is running but won’t be noticeable in the car, and should keep it from going into thermal meltdown?

I have the aerial ordered (a sort of springy 1.5m loaded whip thing) and will soon be able to create a bit of noise on 10m.

That should give me something to do whilst driving home through Richmond Park in the evening. I wonder how long before I get pulled over by some over enthusiastic pimply policeman hoping to nab a cb’er?