[Elecraft] K3 & ADAT ADT-200A by HB9CBU

[Geoffrey Mackenzie-Kennedy]

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.