[Collins] 75S3-B is receiving different bands

[Osamu Hazawa]

Hi Jerry,

Thank you very much for your detailed description.
The Calibration Preselector Curves was surely at the back
of my mind but I didn't know it tunes on the fundamental frequency as well.

Now that I know it, I'm looking forward to digging (searching) unknown BC 
bands :D

73's
Osamu

----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at storm.weather.net>
To: <collins at mailman.qth.net>
Sent: Monday, March 31, 2008 12:40 AM
Subject: Re: [Collins] 75S3-B is receiving different bands


> On Sun, 2008-03-30 at 16:14 +0900, Osamu Hazawa wrote:
>> Hello All,
>>
>> My 75S3-B seems to receive different bands, other than normal bands.
>>
>> 1. No modification but SB_2 has been made (by me).
>> 2. It occurs on 7MHz band and above.
>> 3. It occurs when the preselector indicates about half position it 
>> should.
>> 4. e.g. on 21.4MHz position, the preselector is set at about 5, it 
>> receives
>>     BBC and Radio Australia on the same band. They seem to be of 
>> 21.660MHz
>> and 21.725MHz.
>
> Perfectly normal. At the higher bands the second harmonic of the crystal
> is used for the first injection. Tuning the preselector to the lower
> frequency uses the fundamental of the oscillator. For the 21.4 band that
> crystal frequency is 12277.5 Khz, normally doubled to 24.555 Mhz, 3.155
> above the selected lower band edge. When you use the fundamental of that
> crystal, your band (from 0 to 200 on the dial) covers 9.1225 to 9.3225
> MHz or possibly 15.4325 to 15.2325 MHz, depending on how the preselector
> is tracking.
>
>> 5. CAL tone is heard at different position it should (30kHz away from the
>> tone).
>>
>> Of course, it receives very good on normal bands with proper preselector
>> position.
>> Yes, I'm very happy with that situation but very curious.
>> Could this happen logically?
>
> Yes. Covered at the end of section 2 of the operator's manual which
> shows that band D tunes to about 15 MHz at a position of 5 on the
> preselector scale, so it will be receiving 15 MHz SW BC band. If tuned
> to 1, it may also receive the 9 MHz range I computed above.
>>
>> 73's
>> Osamu
>>
>>
>
> -- 
> 73, Jerry, K0CQ, Technical Advisor to the CRA
> All content copyright Dr. Gerald N. Johnson, electrical engineer
>
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