Steve S. Bosshard (NU5D) wrote:
>
> CARSON'S RULE
> BANDWIDTH = 2 X (PEAK DEVIATION + HIGHEST MODULATING FREQUENCY)
Thank you for quoting what I've been saying the past two posts.
> Most 2M off the shelf radios I have seen lately in wide band FM hit at
> least +/- 5kc peak deviation, and 6 to 6 ½ is not at all uncommon.
> Measurements using HP8921 or IFR COM120B.
> I have not run a swept transmit audio response test using an audio
> sweep generator into the mic input @ 60% full system deviation, but
> I suspect it would not come to a dead stop at 3 kc of audio response.
Yes, I agree that most off the shelf radios are not properly set up.
BUT, what does that have to do with a PROPERLY set up system? You don't
solve this problem by saying that 20 kHz bandwidth is OK because that's
what we are seeing as a spoon-fed limit. The minute you do that, you
will then see 25 kHz BW radios being made. Where do you stop?
The ONLY answer is to educate these so-called *trained* radio
technicians (licensed hams). If they can't solve the problem, they
should at least be taught to be able to identify a problem and take it
to someone who CAN fix it. Of course, on this list we are for the most
part preaching to the choir. It's the non-technical hams that need it.
But the point is that you NEVER cater to the lowest common denominator,
you would would never have gone below 60 kHz spacing that you had in the
60s or early 70s. If you see a problem, and can show that the TX is not
properly aligned (be it user OR repeater), you tell the operator that
and let them decide how to solve it (either by doing it themselves, or
having it aligned by someone with the proper equipment, or discontinuing
use).
I recently got an FT-736R. Nice radio, but it has no provision for
limiting the deviation to any calibrated settings. This is a
manufacturing flaw, IMHO. There should be a way to set the deviation
other than a vague meter setting. But, I got it for SSB/CW anyway, so
I'll use it there and not on FM (except perhaps on 440 where it won't
matter as much).
> Going to a Micor or M2 or adding a helical preselector will help, but
> mostly by adding insertion loss and not in bandwidth shrinkage.
You're not going to see that much insertion loss in a preselector! But,
I also agree that you're not going to solve that much with one, either.
> At best, changing the IF filters might narrow the response,
Great idea! I wish I'd said that. OH WAIT! I DID! (in my last post) 8-O
I'm surprised about the 180 turn you did from saying "Has nothing to do
with receiver" to the above comments. :-)
Joe M.
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