[G0HZU_JMR]

I tried to take my mk1 290R apart to show an image of the Mutek board but I stopped part way because it proved harder than I thought to get it out! So I stopped and put it back together. But the good news is that the Mutek board now seems stable. I think by trying to remove the whip assy and the plates around the Mutek board and then refitting them I've improved the RF grounding in some way. The Mutek board seems much better behaved now as I extend the whip. Before, it would go hissy and deliver wandering birdies as the whip was extended.

However, I also took it apart to clean out the black residue from the decaying black sponge inside the top cover. This residue was falling into the radio and making a real sticky mess. This is all done now and the radio looks much cleaner inside. I've removed all of the original sponge so I'll have to find a replacement sponge from somewhere.

I think in the case of the 290R the Mutek board helps with sensitivity but the idea is to turn down the gain with the trimmer resistor so it just gives a useful improvement without causing any overload effects from local signals. I don't know what the sensitivity of an unmodified 290R is but a lot of 2m radios of this era had a NF in the region of 6-8dB. So not that great. The datasheet for the mk1 290R suggests the receiver has a NF of <= 7dB.

In 2018 I'm not sure this matters because of the higher band noise today but I recall that back in the 1980s there were several classic 2m multimode radios that were classed as deaf and this included the Trio TR9130, the Yaesu FT290R and the Yaesu FT225.

The best cure for the deafness was a masthead preamp but in those days there could be 6 operators within 2 miles of your house so overload was often an issue. So I think the more exotic Mutek boards were designed to improve the noise figure and the signal handling. They did this with a low loss TR relay, a low noise amplifier and a better mixer and sharper IF filtering. But for a portable radio like the 290R the popular choice was the little internal Mutek preamp and I do remember that most users were pleased with them. I would expect the Mutek board to improve the noise figure to somewhere close to 2dB. I could measure mine again after rebuilding it but I expect it will be somewhere around 3dB or so because I turned down the gain a fair bit on mine.