[Lowfer] Icom R-75 Specs

[JD]

Valid enough points, Todd.  But I think the overall goal of these tests is 
not to do a conventional equipment review from an everyday operation 
standpoint.  In fact, where there already ARE reviews of that sort, John 
cites those in his articles.  Nor is the series intended as a compendium of 
receiving techniques.

The goal is simply to make repeatable, objective measurements of certain 
specific performance characteristics  --especially ones seldom shown in 
manufacturers' literature-- of a variety of gear, one by one, and let people 
make up their own minds about what is significant.  (I think it's working, 
given how many people have objected to the reference to 200 kHz. :)  When 
folks have enough measurements of different receivers to compare 
side-by-side, the points you make should become obvious to the reader. 
These are not exactly stand-alone installments, in other words, but a body 
of work.  There will eventually be a summary to tie it all together in case 
anyone misses part of the big picture.  That summary and accompanying graphs 
will go online at the conclusion of the series.

All the receivers in the series are being tested for noise floor, all the 
way from their lowest tunable frequency up to 500 kHz, and it is indeed very 
evident from the graphs that (almost) none of them are good performers on 
their own below about 50kHz, give or take.   There are a couple of 
exceptions, but certainly not among the general coverage receivers; the 
exceptions are mainly the SLMs and a specialized Watkins-Johnson LF/MF 
receiver that will all appear later.  As I think was stated in the 
introduction to the series, the noise floor and spurs will reveal a lot 
about the suitability of the radios in different band segments.

The other two performance characteristics emphasized in the series are 
filter performance and radiated noise.

As for filters...while it is true that John loves to accessorize and tweak 
receivers for maximum performance, the way some guys do their hot rods, the 
noise floor readings are being done with the most basic CW filter already in 
the set.  For the filter response itself, he does not plot a graph of every 
installed filter, and some of the ones he does plot are indeed optional 
premium ones; but the point of this exercise is to provide an illustration 
of the care --or lack thereof-- taken in the design of the filter banks. 
(Secondarily, it is also indicative of the noise of the detector and audio 
amplifier stages of the receiver.)  Clearly, there is very little leakage 
around filters in the IC-R75... much less than in some of the more expensive 
receivers that will be presented later, in fact.

John's frequent mention of loop antennas is also not intended to say 
anything one way or another about preferred antennas or matching.  It is 
mainly for the sake of evaluating residual radiation from the display, and 
sometimes other leakage from the unit.  This is another characteristic you 
seldom find evaluated in manufacturers' literature.  They do have to perform 
EMC compliance tests under Parts 2 and 15 of FCC Rules, but a radio can meet 
those requirements and still be a noise source to other gear around it.  The 
makers are not required to disclose the details to the consumers.  The 
display noise evaluations in John's articles are simply to help fill that 
gap.

I hope that clarifies what the series is about and where it's going.  I 
think it would be an even better series if we could evaluate a couple more 
of the ham radios frequently employed at LF and VLF, and one or two SDRs 
too, just for the heck of it.  As I mentioned before, you can contact me 
off-list if you might have one to spare for a few days, and we'll check it 
against the list of radios which are scheduled to appear in the series.

73
John