[NJARC] Why 455?

[Jim Whartenby]

What makes you think this was the work of an engineer?

--- John Ruccolo <jr6v6gt at yahoo.com> wrote:

> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Hi Jim,
> 
> Your theory is very interesting, but that has nothing
> to do with it. The same engineer who developed the 455
> KC IF also developed the 455 cu. in. V8 for
> Oldsmobile. He had a fixation on the number 455.
> 
> I thought you knew that....
> 
> JR
> 
> 
> --- Jim Whartenby <antqradio at sbcglobal.net> wrote:
> 
> > Visit our web site - See http://www.njarc.org
> > _______________________________________________
> > Al
> > Just playing with the calculator and using
> > approximate frequencies for
> > the old AM band limits such as 500kcs and 1500kcs
> > (600 to 200 meters)
> > you get a geometric mean of 866kcs.  Divide this by
> > 2 gives 433kcs.  So
> > depending on what the frequencies actually were for
> > the old AM band,
> > you end up quite close to 455kcs.
> > Just a thought,
> > Jim
> > 
> > --- Al Klase <al at ar88.net> wrote:
> > 
> > > Visit our web site - See http://www.njarc.org
> > > _______________________________________________
> > > Every so often the question comes up: Why are all
> > the IF’s 455 KHz?
> > > I’d 
> > > like to get an article together that solves this
> > riddle while the
> > > people 
> > > who know are still with us. I know parts of the
> > story, but I need
> > > help 
> > > with a couple of issues.
> > > 
> > > There are two major consideration is the choice of
> > the intermediate 
> > > frequency used in a superheterodyne receiver. The
> > lower the
> > > frequency, 
> > > the easier it is to attain high selectivity. Also,
> > in the early days,
> > > 
> > > before tetrode and pentode tubes, it was easier to
> > achieve a high
> > > degree 
> > > of amplification at lower frequencies. Conversely,
> > a higher IF
> > > frequency 
> > > results in better image rejection.
> > > 
> > > Early superhets had the IF at 100KHz or lower in
> > order to get
> > > adequate 
> > > gain from the available triode tubes. They suffer
> > severely from 
> > > “two-spot tuning” (images). By the early 1930’s,
> > broadcast set had 
> > > settled in at 175KHz, and automobile receivers
> > would later adopt
> > > 262KHz 
> > > as a standard.
> > > 
> > > The advent of the short-wave craze, and multi-band
> > broadcast
> > > receivers 
> > > dictated a higher IF frequency to achieve adequate
> > image suppression
> > > on 
> > > the short-wave bands. The broadcast band occupied
> > 550-1500KHz at this
> > > 
> > > time, and the designer encounters sever problems
> > if his radio tunes 
> > > across it’s own IF. Some shortwave sets used
> > 1600-1700KHz for better 
> > > image rejection, but one couldn’t go higher if the
> > 160-meter ham band
> > > 
> > > (1800-2000KHZ) was to be covered. Most multi-band
> > receiver settled in
> > > 
> > > near 450KHz, a comfortable distance from the first
> > broadcast channel
> > > at 
> > > 550KHz.
> > > 
> > > Questions:
> > > 
> > > Odd multiples of 5KHz, 455, 465, etc., were
> > usually chosen so that
> > > the 
> > > image of the carrier of a broadcast-band station
> > could be zero-beat
> > > with 
> > > the carrier of the station being tuned to achieve
> > minimal
> > > interference. 
> > > (This assumes 10KHz channel spacing. Did the
> > Europeans (9KHz) do 
> > > something else?)
> > > 
> > > The Radiotron Designers Handbook, Third Edition,
> > p. 159, states “A 
> > > frequency of 455 Kc/s is receiving universal
> > acceptance as a standard
> > > 
> > > frequency, and efforts are being made to maintain
> > this frequency free
> > > 
> > > from radio interference.”
> > > 
> > > (1) Do FCC and international frequency allocations
> > reflect this?
> > > 
> > > (2) I’ve heard the term “Clear-Channel IF.” Can
> > anyone cite
> > > references?
> > > 
> > > (3) At lease one news group posting claims that
> > broadcast frequencies
> > > in 
> > > a particular market are assigned to prevent strong
> > inter-modulation 
> > > products from falling near 455KHz. Is this
> > factual? Need reference.”
> > > 
> > > (4) Was this (3) at least part of the reason for
> > “Radio Moving Day”
> > > in 
> > > 1941? See:
> > >
> >
> http://www.dcmemories.com/RadioMovingDay/032341WINXFreqChange.jpg
> > > 
> > > (5) Many National Radio sets used a 456KHz IF’s
> > and I think I
> > > remember a 
> > > 437 somewhere. Why? Are there different
> > considerations for short-wave
> > > CW 
> > > operation?
> > > 
> > > Further input, corrections, and elaborations are
> > greatly appreciated.
> > > 
> > > Scolarly reference will be looked upon with great
> > favor.
> > > 
> > > Regards,
> > > Al
> > > 
> > > -- 
> > > Al Klase - N3FRQ 
> > > Flemington, NJ 
> > > http://www.skywaves.ar88.net/
> > > 
> > > _______________________________________________
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> > > 
> > 
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> 
> 
> 
>      
>
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