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 Post subject: what are the common IF frequencies?
PostPosted: Feb Sat 16, 2019 11:11 pm 
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I know about 10.7 MHz for FM, and 455 kHz for AM. I think some AM sets are also 450 or 460 kHz. I'm curious what other IF frequencies you have seen, and how common they are in restoration?


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sat 16, 2019 11:15 pm 
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50 KHz, 175 KHz, 262 KHz, 370 KHz, and 1500 KHz all for AM, and 9.1 MhZ for FM.

How common they are depends on what kind of radios you work on. For decades 262 was the standard for auto radios and there are many millions of them out there. You see 175, 370, and others used in more than just a few pre-WW2 AM sets. 50 and 1500 are commonly seen in communications receivers. Some earlier FM sets used 9.1.

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sat 16, 2019 11:27 pm 
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I suspect that if you work on postwar radios, you probably will only see 455 in broadcast radios. Prewar that was common but then there are plenty with the oddballs. Especially early thirties. If you get into communications receivers, both solid state and tube, you may see a variety of frequencies. And double conversion types two per radio. If you built a ceramic resonator controlled modulated 455 oscillator circuit for IF alignment, that would get the most workout by far.


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 2:40 am 
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As Dennis and wazz pointed out, IF frequencies are all over the place on prewar sets. To make matters even more confusing, many had padders and compensators to adjust for tracking errors over certain parts of the dial.

The big takeaway here is to make sure you have detailed service info for your set before attempting an alignment.

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 3:22 am 
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Prewar FM IF frequencies were all over the place.

I've seen them anywhere from 2.1 MHz in the GE HM136 to 13.7 MHz in the Crosley 22CA.

-Steve

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 3:37 am 
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175 khz was common in many early 1930s radios. Most had a padder to set the low end tracking, usually at 600 khz.

There were plenty of other oddball frequencies in use during the 1930s, and it's best to have the service literature on hand before doing any alignment. The Ghirardi Radio Troubleshooter's Encyclopedia lists the IF frequencies of most prewar models.

The Philco 90 is a special case; they changed the IF frequency in the middle of the model run. The version with two 47 output tubes is peaked at 260 khz, while the previous versions used 175.

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 4:19 am 
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If you get into other types of equipment than radios other frequencies were also used. Intercarrier TV sets used 4.5 MHz as the sound IF. Video IF was 21 MHz on early post-war sets and 45 MHz on later sets. Radar sets frequently used 30 MHz or 60 MHz.

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 5:26 pm 
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In Europe due to a strong Longwave station at 232kHz and later moved to 234 kHz, 468, 470 and 473 kHz were also used.
First FM receivers also used 6.75 MHz.


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 9:50 pm 
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Don't forget 456. This one is sort of curious in that ordinary analog signal generators of the day had frequency accuracies of at best 1% and usually less, so that 456 could be anywhere from 451.44 to 460.56 with the best generators (and we worry about a few cycles now days).

RRM


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 11:08 pm 
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Retired Radio Man wrote:
Don't forget 456. This one is sort of curious in that ordinary analog signal generators of the day had frequency accuracies of at best 1% and usually less, so that 456 could be anywhere from 451.44 to 460.56 with the best generators (and we worry about a few cycles now days).

RRM



That's the important part - the IF doesn't actually care too much what frequency you tune it to, and the performance of the radio is the same if you get them all the same, rather than all right on the 455 (or whatever). The dial tracking may suffer, but the radio will work almost the same as long as they are all lined up on each other.

If you have some sort of a filter instead of just IF transformers, then, it matters that you line them up on the filter frequency.

Brett


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 11:09 pm 
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Yes, I have often wondered about that. Why 456 and not 455?

456 was in use as far back as 1934, according to Rider's "Servicing Superhetrodynes" book, published that year.

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 11:29 pm 
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The Regency TR-1 Transistor Radio (1954-'55) used 262 kilocycles as it's IF frequency.

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Sun 17, 2019 11:50 pm 
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My Supreme 582 signal generator has a set of preset frequencies for Broadcast band and IF alignments.
Why 455 isn't one of them, I'm not sure...

-Steve


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Mon 18, 2019 1:01 am 
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Mallory-Yaxley lists IF as part of their receiver data. They're all over the place. 456, 172.5, 345, 252.5, 262.5, 262, 465, 175, 470, 180, 450, 250, 458, 432, 458,170, 115, 181.5 etc.

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Mon 18, 2019 1:09 am 
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And Atwater Kent had some models with 130kc IFs and some with 472 1/2kc IFs, and probably others as well.

Jeff


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Mon 18, 2019 3:49 am 
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I seem to recall 465 was it for some Silvertone radios.
Mark Oppat


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Mon 18, 2019 4:53 am 
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oldradioparts wrote:
I seem to recall 465 was it for some Silvertone radios.
Mark Oppat
... and, IIRC, some UK radios had a 465 KHz IF.
Cheers,
Roger

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Mon 18, 2019 9:42 am 
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A ham friend clued me on buying a Heathkit Model TO-1.
It has the IF frequencies controlled by a rotary switch. and if you need different frequencies other than those provided, there are two extra crystal sockets if you need them.

Image

The Heathkit TO-1 test oscillator can provide a 400HZ variable audio signal and RF signal up to 18.25MHZ

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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Mon 18, 2019 9:55 pm 
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Here is another product similar to the Heathkit TO-1, but with more selection of frequencies.

-Steve


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 Post subject: Re: what are the common IF frequencies?
PostPosted: Feb Tue 19, 2019 12:27 am 
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Have you considered the reason for selecting the IF's?
For prewar fm, the IF was typically 4.3MHz. This was to ensure no rf image frequency would be received across the band. E.g. with IF at 4.3MHz and the FM Band extending from 42 to 50 MHz, to receive the lowest allocation at 42.1MHz, the local oscillator would be 42.1 + 4.3 = 46.4MHz. The image would appear at 46.4 + 4.3 = 50.7MHz which is outside the band.

The same reasoning applies to the new FM Band. AM broadcast with 456kHz IF has the same image problem and so the solution was to push it as high as practicable.

The ultimate standard TV IF range of 41 to 47MHz was chosen to make the local oscillator fall between channel 6 and 7 when receiving channel 2 to 6 and to put it always above channel 13 when receiving channels 7 to 13. I just want to point this out because there are always carefully considered reasons for the choice.

That said, what was the advantage of originally choosing 50kHz or 175kHz for the earlier superhets?


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