[R-390] R-390 sensitivity measurements
Bob Camp
ham at cq.nu
Mon Jan 17 11:46:38 EST 2005
Hi
The nice thing about a relative measurement as you align the radio is
that your setup stays more or less the same. For instance the output
impedance of your generator doesn't change.
The point of an absolute measurement is to know when to stop. There's
nothing wrong with working on radios but at some point you probably
should haul it of the bench and *use* it.
You can spend a couple of weeks going over all the possible variables
in an absolute sensitivity test. At some point you either need a fairly
fancy lab or you need to accept that the number may be off by 3 or even
6 db in either direction. Unfortunately 0.7 uV is a lot harder to brag
about than 0.35 uV. They both may be a reading on a radio that is
really 0.5 uV ......
The real point is how does *your* antenna work into *your* radio.
That's a tough one to characterize except by actually using the radio.
Take Care!
Bob Camp
KB8TQ
On Jan 17, 2005, at 10:54 AM, DJED1 at aol.com wrote:
> I think the test serves two functions- first, you can tell if a
> particular repair to the radio has improved the performance in a
> relative sense, and you can compare two radios in a relative sense.
> The test is probably useful in an absolute sense only if you define
> all of the test conditions- then a knowledgable person can calculate
> the differences in measured performance based on the setup. For
> example, testing at 8 Kc bandwidth versus 4 Kc gives a degradation in
> sensitivity of 3 dB.
> I think tweaking the radio for the best sensitivity has lead to its
> reputation as one of the best weak signal receivers ever made. I've
> found it to be as good as my R4C and distictly better than my SP-600.
> But I won't try and argue that its got 0.0XX microvolt sensitivity.
> Maybe the uncertainties in measurement is why the spec numbers are so
> loose.
> Ed
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