[CQ-Contest] SO2R Technical Question - Round II

[Tom Rauch]

>
> and eliminating the broadband noise that synthesized 
> radios
> transmit both below and above the band they are 
> transmitting
> on.

I went through this here getting ready to duplex on 160.

In nearly all radios I've looked at the noise doesn't come 
from the synthesizers. It comes from the early IF stages in 
the transmitter just after the narrow filter if the radio 
transmits through one.

This is important to know because reducing the transmitter 
power setting often increases transmitter composite noise if 
it comes from or before the ALC gain limiting device.

I've had radios with exceptionally clean synthesizers that 
had terrible broadband noise. In the FT1000 series most of 
the noise comes from the area around the dual gate FET used 
for ALC control. Fortunately the PA filters knock the 
already low noise down to insignificant levels on the 
harmonic bands. Unfortunately it is largely a difficult to 
fix in-band problem.

It's especially important to not have any corona or arcing 
in anything from the PA stage right through to the antenna 
and everything around the antenna. A good reason to make 
solid connections and bond things.

73 Tom