[Elecraft] dynamic range questions

[Don Wilhelm]

Geoff,

While all the situations that you pose are valid measurements, I believe 
that the 'figure of merit' that should be applied is with both signals 
within the receiver passband.  That alone will indicate the ability to 
copy a weak signal in the presence of a strong one - that is basic BDR 
(IMHO).
Third order blocking IMD is quite another thing - there are many 
variables to consider.  The best that we can hope for is that the 
'standardized' tests will provide a good indicator of the performance on 
the real world - a receiver with narrow 'roofing filters' should excel 
in that test - although the test reports should specify the filter 
widths.  The close spacing tests go a long way toward simulating the 
'real world', but are really only a set of conditions that are defined 
for lab tests - the real world operating conditions may present an 
entirely different set of parameters.

Current tests do consider MDS to be the minimum signal that can be 
demodulated with no other considerations.  Right or wrong, that is the 
way it is for now - something must be defined for lab measurements to be 
valid - we just trust that they are adequate to be useful in actual 
operating conditions.

73,
Don W3FPR


Geoffrey Mackenzie-Kennedy wrote:
> Curt,
> 
> Would you not agree that a 3rd Order dynamic range test performed with 
> both test tones placed outside of the IF filter's passband ,with a 
> product in the passband, does not provide a complete measure of a 
> receiver's odd order IMD performance but only that of its front end? A 
> receiver with a "weak" cascade following the IF filter might appear to 
> be be a good performer based on tests done this way, but will probably 
> fall apart when two or more strong signals enter the IF filter's 
> passband. During the development of high performance receivers common 
> practice in my experience was to employ multiple signal tests, two tones 
> in the IF passband and one or two placed on the skirts. I am aware of 
> suggestions that have been made during the past years regarding these 
> test procedures used to evaluate amateur receivers, likewise to restore 
> proper useage of the term MDS which is another story :-)
>