[Boatanchors] Why 455?

Tue Jan 29 15:08:01 EST 2008

BTW:

In the late 50's I worked on 20KW and 35KW RF furnaces in the semiconductor
industry, These units worked around 500KC.

But 500KC was a Marine International Distress Frequency! We had to keep
these units below 490KC or above 510KC.

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message -----
From: "jeremy-ca" <km1h at jeremy.mv.com>
To: "Bob Macklin" <macklinbob at msn.com>; "Al Klase" <al at ar88.net>;
"Boatanchors" <boatanchors at theporch.com>; "Boatanchors List"
<boatanchors at mailman.qth.net>; "New Jersey Antique Radio Club"
<njarc at mailman.qth.net>; "Delaware Valley Historic Radio Club"
<dvhrc at mailman.qth.net>
Sent: Tuesday, January 29, 2008 11:59 AM
Subject: Re: [Boatanchors] Why 455?

> I believe that 455 became a standard for 2 main reasons.
>
> 1. To provide a standard that made purchasing cheaper. The set
manufacturers
> bought a catalog transformer and had their part # stenciled on it if at
all.
> Naturally there were custom made exceptions.
>
> 2. The set manufacturers discovered that if the LO section of the tuning
> variable was made smaller it saved them the cost of a padder trimmer as
well
> as alignment time. In order to save money again a standardized LO section
> became the norm.
>
> This all took place in the mid-late 30's as near as I can tell by looking
at
> several home type radios I have here.
>
> Dual conversion was available in the early 30's for some high end console
> receivers that covered several SW bands.
>
> National went their own way as they manufactured their own variables and
IF
> transformers well into the 50's & even the 60's for some models. The
> original HRO established the 465 Kc wheras the earlier FB-7 was 500. (the
> 51J4 mechanical filters do wonders in that radio)
>
> The cheap sets (AC-DC, etc) and eventually most others used RCC variables
as
> did most other companies and those used 455 Kc IF's.
>
> Carl
> KM1H
> National Radio 1963-69
>
>
>
>
>
> ----- Original Message -----
> From: "Bob Macklin" <macklinbob at msn.com>
> To: "Al Klase" <al at ar88.net>; "Boatanchors" <boatanchors at theporch.com>;
> "Boatanchors List" <boatanchors at mailman.qth.net>; "New Jersey Antique
Radio
> Club" <njarc at mailman.qth.net>; "Delaware Valley Historic Radio Club"
> <dvhrc at mailman.qth.net>
> Sent: Tuesday, January 29, 2008 1:58 PM
> Subject: Re: [Boatanchors] Why 455?
>
>
> > Not all IFs are 455. But 455 was the most common.
> >
> > There were some that were 465. These were not just retuned 455s. They
were
> > manufactured as 465.
> >
> > There were also 265KC IFs used in auto radios.
> >
> > But I believe that the choice of 455KC was because Miller produced them
in
> > very high quantities for a very low price. Up to the late 70's you could
> > still by the Miller transformers over the counter at most
> > Radio/Electronics
> > supply dealers.
> >
> > Also the BCB variable capacitors were made in large quantity to use with
a
> > 455KC IF.
> >
> > Bob Macklin
> > K5MYJ
> > Seattle, Wa,
> > "Real Radios Glow in the Dark"
> >
> >
> > ----- Original Message -----
> > From: "Al Klase" <al at ar88.net>
> > To: "Boatanchors" <boatanchors at theporch.com>; "Boatanchors List"
> > <boatanchors at mailman.qth.net>; "New Jersey Antique Radio Club"
> > <njarc at mailman.qth.net>; "Delaware Valley Historic Radio Club"
> > <dvhrc at mailman.qth.net>
> > Sent: Tuesday, January 29, 2008 10:44 AM
> > Subject: [Boatanchors] Why 455?
> >
> >
> >> 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/
> >>
> >> _______________________________________________
> >>
> >
> > _______________________________________________
> >
>
>