Roger said:
>Only recently have SS rigs began to approach the IM figures of the old
Collins S-Line. Even some of the mighty expensive rigs have pretty
crappy IM figures.<
SM5BSZ has done some work on this, and let me use some of his data for my
presentation at the RSGB Convention last year - which I called 'Spreading the
Sewage' as 'Slinging the s**t' wouldn't have been acceptable! In it, I used an
analysis of published equipment reviews back to 1972 (123 transmitters) to look
at how the IMD performance of transmitters has degraded with the move to solid
state. What is especially bad is the big increase in high order IMD, in some
cases up to the 11th order. The rigs that were really clean were those Yaesu
rigs where the PA could operate in a heat producing, lower power, very low IMD,
Class A!
>They have receivers that have passed the point of
practical numbers for intercept points, dynamic range, selectivity, and
have a sensitivity that is far, far below the band noise, yet they seem
to be ignoring the transmitted signal which is one of my pet peeves.<
I am somewhat amazed that the manufacturers appear not to realise that the
intermodulation limited dynamic range and the phase noise limited dynamic range
need to be comparable, although the phase noise limited one can arguably be
required to be better by about 10dB. This is because the phase noise moves
linearly with signal level, dB for dB, while IMD drops faster with reduction in
signal level - often not the theoretical 3dB/dB but usually more than 2dB/dB.
The analysis I did that were published in QEX and NCJ some years apart (sunspot
cycle peak and trough) showed that in the UK at least, in a situation with
noise meeting ITU 'rural' levels, about 95 to 100dB of DR (phase noise or IMD)
was all that was needed. I did a paper on this subject at RF Expo in Anaheim in
1986 (Phase Noise Intermodulation and Dynamic Range in Receivers), so it's
hardly new. There was a ham radio reception at that RF Expo with door prizes
and I was a lucky guy - a nice new Bird 43 with 1kW HF slug
came my way!
So, Roger, you aren't a lone voice crying in the wilderness, but the number of
voices is very low.....
73
Peter G3RZP
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|