My GMC 950w generator which has powered about 5 of the last few years’ VHF field days, refused to start last week when I set out to change its oil.

There have been a number of GMC branded generators on the Australian market.  GMC (Global Machinery Company) was based in China, or was it just an Australian importer of various GMC-branded items?

Mine is rated 950watts, which should really be called 950 VA (volt-amperes) and is powered by a small 4 stroke engine.  My experience of it is that it is a quiet and reliable engine, and the generator produces enough power for my modest VHF/UHF portable station, which requires power for an IC910H and a TS670S plus some minor items like a 40w light globe and a couple of antenna rotators.

My only problem with it was that it produced radio noise at a quite high level, sufficient to require a noise blanker to be run on 144 and be noticeable on 432 MHz.  On 50 MHz it was S9, at a distance of 25 metres between the generator and the 6 metre antenna, an omnidirectional vertical. I tried shielding the entire generator by wrapping it in chicken wire connected to the frame of the generator.  No improvement.

Several other radio amateurs have suggested the noise from the generator is transmitted along the 240V cable.  I haven’t yet proved where the noise is being radiated from.

Last week I put oil into a new Chinese built inverter generator and started it for the first time.  It ran fine and the voltage output displayed as 237 on a DVM.

I found a small engine mechanic willing to look at the GMC generator.  He said the magneto assembly was touching the shaft and preventing it from moving.  He has readjusted it so that it runs smoothly and at about the right RPM.  I have yet to try to calibrate the speed for 50 Hz output but I have a DVM that does frequency among other things, so I should be able to take a low voltage out of my scope soldering iron transformer and see what the frequency is.  For that matter I should check the inverter generator.