Hi John,
In this part of Scotland (approx 56N 3W), the carrier levels of many of the
BC stations at 7100 kHz and above get up to +5dbm / +10dbm if propagation is
"normal". These are measured levels at the shack end of a coax feeder with
my backup 40m dipole at 70ft selected and in use. It is possible to work SSB
DX among these BC stations, most of which are spaced by 5 kHz, but it does
require a receiver whose close in *and* far out performance is good in terms
of Spurious Free Dynamic Range etc. BC TX phase noise has not appeared to be
a problem, but I hope to receive a plot of a particular BC TX's phase noise
to help me fully understand why BC TX phase noise has not been a problem
here.
On the other hand legitimate modulation sidebands produced by these BC
stations can be a problem in terms of raw QRM, but there might be a way to
deal with this type of QRM.
I do not have any neighbours who are hams, so I cannot comment on phase
noise problems from nearby ham TXs. Methods to solve the key click problem
at the receiving end are being investigated.
I have a Perseus which appears to perform well in this signal environment,
but since this is a subjective observation I need to run suitable multitone
IMD tests to simulate the effect of BC stations and obtain real data.
Perseus performs very well indeed when used as an auxiliary IF behind a
H-Mode mixer and quadrature 2.5 kHz roofing filter front end that has small
negative gain for reasons of large spurious free dynamic range at all
spacings. A post mixer amplifier is not required in this front end whose
noise figure is 10db when followed by a low noise IF. Perseus performs very
well when used as a panadapter after the H-Mode mixer with the transfer gain
set to 0db, but again these comments about Perseus are based on use not
measurement.
As I do not have a K3 I cannot make any comparisons between the K3 and
Perseus based on use.
73,
Geoff
GM4ESD
John A. McCabe wrote on Wednesday, December 03, 2008 at 1:11 AM
Hi David,
Yes I can see your point, and I am certainly not questioning the benefit
of High Dynamic range receivers in those situations. I guess what I am
having a hard time understanding how it would be possible for any
receiver, regardless of the dynamic range of the receiver, to receive a
weak signal 2 Khz away from, say a 80db over 9 broadcast or other signal.
Would not the IMD, sidebands, and splatter from the broadcast station
itself be so severe as to prevent this? Or am I overstating the effects of
transmitted phase noise and IMD? As I mentioned in my previous post, there
is no way I could see operating 2 Khz away from the very strong signal of
my ham neighbor. His transmitted IMD would be way too severe. But I can
easily operate 20 Khz or more away with the K3. To me, any minor
difference in close in dynamic range between say the Perseus and the K3 is
of little or no importance in this situation. I could not receive a weak
signal so close to such a strong signal anyhow because of his transmitted
IMD. But the wider spaced number's matter a great deal, and that is what
concerns me when I see a 117-123db BDR as compared to 140db at wider
spacings.
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