UPDATED 20170416

Last update: On new amplifier page.

I should continue tradition and find something to moan about on my front page…

Dirty Transmitters!
The 40m and 20m amateur bands are not just crowded because of contests at the weekends. There is a lot of "splatter" and noise generated by our transmitters. If you tune off the top end of 20m the noise level drops noticeably. As a power limited mobile operator, it's worse than frustrating to call a 'CQ' then un-key to find a noisy mess and have to QSY. Here in the UK we have a legal limit of 400W which is a lot less than other countries.

Some of it is due to people who crank their power up to 11 and shout two letters of their callsign over and over. Some of it is due to bad intermodulation performance of semiconductors running at 12V. Over the past 10 years most 100W radios used the Mitsubishi "RD" range which are pretty poor running at 12V, they need a bit more voltage, and even then are not good. But there is one aspect of transmitter performance which has escaped scrutiny, and it's very important.

There is a broadband noise issue with many radios. It takes the form of a raised noise floor which is difficult to pin down to a particular signal on the chaotic HF bands, but it is there. Look at the output spectrum of two commonly used radios (data from Sherwood engineering).

K3 spectral outputFT1000

It's clear the FT1000 is over 30dB (100x) worse than the Elecraft K3. Yes indeed I do compare one of the best with one of the worst, but the Yaesu FT1000 is in widespread use, without a doubt there are many out there driving 1kW amplifiers - so there's your problem. And that's without compounding it by anything being overdriven!

Unfortunately there are a number of middle aged and still-sold rigs that are nearly as bad. In particular Yaesu pay little attention to their transmitted noise. Sherwood engineering has some reports on this at
their website. Also see this report from Leif Asbrink of LinRadio fame. An expensive radio doesn't buy a clean radio!

There is also the odd radio they (the manufacturers) let slip knowing they will probably never be found out. The Flexradio Flex-1500 is an example quoted by Sherwood. It uses a QSE (Quadrature Sampling Exciter) similar to the SoftRock type radios, but has a rather noisy unfiltered ADC. As individual amateurs there is little we can do but try and persuade the transceiver OEMs to fix this type of problem. The ARRL and RSGB are not going to help. They avoid disputes with the OEMs from fear of losing advertising revenue.

All we can do is vote with our feet and don't buy the polluting radios. That said perhaps
some manufacturers are getting a bit better - the Icom IC7300 is notably better than their older offerings. The IC7610 has just been announced which replaces their flagship radio with IC7300 technology.


My amateur radio details are listed at
QRZ.com. My locator in the world is IO90LU, Cosham near Portsmouth, as shown in this map:

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The other website that I manage is: www.sortedentertainments.com