RadioBanter - View Single Post - Is FM performance on modern PLL radios "rap" with a capital "C"?

January 1st 04, 05:15 PM

In article ,=20
says...
Michael Black wrote:
=20
You've made a classic mistake, that because shortwave receivers carry
relatively high price tags, that they then offer superior FM broadcast
reception.

In the first place, a higher price tag may reflect the limited interest
in shortwave. If you have to design something out of the ordinary,
it will cost more than an average design. And if fewer people are
interested, then you have to recoup the cost by a higher price.

But more important, any design concerns will be put into what
the radio is intended for, ie shortwave. And for anyone
who understands radio design, there is virtually no overlap
between what's good for an FM broadcast receiver in the 88 to 108MHz
range, and a shortwave receiver. One is for FM reception, the other
is for AM reception. One is for wideband signals relative far
apart in a part of the spectrum that is at least three times the
upper frequency of the other, while the other is for narrow signals
with narrow spacing between channels and still at a relatively low
frequency. Shortwave and the FM broadcast band are not close
together. All of this means that there is very little where
the designs overlap. What you are buying is a shortwave radio
(and maybe/likely that circuitry is used to tune the AM broadcast
band since the frequencies are adjacent and the mode and signal
bandwidth would be the same) and an FM broadcast radio in
the same box. Traditionally, shortwave radios did not include
an FM band, with a few exceptions; it changed as small shortwave
receivers from Asian companies became the norm. In other words,
the FM BCB section is thrown in as a marketing matter.

Since that FM section does nothing for the main selling point
of the radio, that shortwave reception, then any money put
into that section will take away from the design of the
shortwave section. So realistically, one might as well
put in as cheap an FM section as possible, since it's just
added circuitry, and one can so very easily pick the
same sort of circuit that is in any average FM radio.

Buying a shortwave radio will not automatically give better
FM reception, and depending on specific design, it may be
inferior to what you could find elsewhere.

Car radios are often good, because they require sensitivity yet
also the ability to withstand strong signals. FM reception is
a key part of the design, so it gets the attention. I have various
digitally tuned Delco car radios around the house, and they are
the best FM radios I've ever had. I have no idea of the absolute
performance, just that in my passing contact with relatively low
end receivers the FM section is great. On FM, the PLL is well
designed so I don't get spurious responses. The sensitivity seems
good, yet it doesn't overload. It is rare to find a station where
it doesn't belong. Selectivity is pretty good. The other day,
conditions were great and a non-local station was booming in.
It's adjacent to another non-local station but which comes in
regular (though it's strength varies). There was no problem
that day from adjacent channel interference.

FM broadcast receivers intended for good performance will also
be good contenders. Note that you have to go for something
with a beyond average design. Just as in those shortwave radios,
FM (and AM even moreso) are considered not so important in a "hifi"
situation, so they put little money into the tuner section. You would
have lousy FM radios in consumer equipment twenty and thirty years
ago, and you have it today, whether they are digitally tuned or
not. Such receivers are intended for local reception (who would
be interested in that noisy signal from a bit further out, especially
since the ads and traffic reports aren't local?) so weak signal
reception is not a concern in the design. And as with a lot of
FM receivers, they tend to be too sensitive, but that never becomes
useful for weak signal reception because that sensitivity also
means a tendency to overload on the local and strong signals.

Michael
=20
Points:
=20
I think some of the the points you raise are probably applicable to any
radio that is not FM only.
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I do not think I can buy a PLL FM only RX, and besides I'd want AM broadc=
ast
band at least, in addition.
=20
One would imagine a portable that was just FM and broadcast band (no
shortwave) the money would be spent on better FM performance. But, I
suspect that in many cases that might not be the case.
=20
Not sure whether poor FM perfornance is related to PLL. Maybe not, but
generally to use of IC's.
=20
Maybe biggest reason that the the ICFM33RDS FM performance at FM might no=
t
be that good is because it's an inexpensive set. Maybe.
=20
Maybe no modern worldband RX will be that good on FM. Then again maybe so=
me
are at least as good as (say) an old Grundig. Perhaps the likely candida=
tes
would be FM/Broadcast band ony RX. Or the more expensive worldband. As
usual, you get what you pay for.
=20
Bottom line for me I guess is that I'd like to feel that if I went ahead=
an
spent say =A380 to =A3100 on a PLL radio, that FM performance would be as=
good
as an old Grundig. Worldband RX or no. Or is it the case that I could
spend much more than this and still not get the old Grundig performance. =
If
that was the case, surely that would say something about modern FM design=
?
=20
I could end up with two radios, a FM/Broadcast band RX. Plus a worldband
set.
=20
That article really does scathe rec.radio,shortwave"!! Ha!! That was jus=
t
unfortunate, I was not concentrating on that part of the article. Just ca=
me
with the bit I was interested in.:c)
=20
=20
=20

My Panasonic RF-2200 was fantastic on FM, I could hear stations 50+=20
miles away on it, and it actually sounded good too. The next best one I=20
ever had was an old Delco car radio, with the "wonderbar" seek deal that=20
I bought at a garage sale for 10 bucks. I ran it off a 12V power supply.

I had it for about 20 years, then it suddenly died without warning. It=20
was playing away, I went to get something to snack on, and when I came=20
back it was sizzling away. It really smoked itself. I ended up tossing=20
it out in the yard so it wouldn't stink the place up.=20

I miss that thing.

BDK