[time-nuts] Cutler NAA on 24.0kHz....

Alexander Pummer alexpcs at ieee.org
Sun Aug 17 17:27:02 EDT 2014


if you use analog way to divide the 120kHz that will prevent an 
incidentally flip of the phase
73
Alex
On 8/17/2014 2:21 PM, paul swed wrote:
> Robert
> Yes indeed the lm3900 is a great part. The last opamp is a 100hz BPF.
> The RCs perform a phase shift and I will tend to believe that at the
> bandpass filter it is a full wave rectified signal. Only a guess.
> Here is the part I don't get. How does that remove the msk? Mask is FSK and
> you can see the shifts in spectrumlab.
> Rick per your comment yes the doubling of the carrier does remove the BPSK
> that was the earliest approach studied applied and then rejected as when
> teh carrier was returned to 60KHz any method used left an ambiguity that in
> fact could flip randomly due to noise. Not pretty on the strip chart.
> But back to this its msk. I am missing the secret math or something.
> Do I believe this will work if I build it. Absolutely and a 24 Khz rcvr
> ain't all that bad to build.
> Regards
> Paul
> WB8TSL/1
>
>
> On Sun, Aug 17, 2014 at 4:35 PM, Robert LaJeunesse <lajeunesse at mail.com>
> wrote:
>
>> It's simple, but not obvious. The LM3900 is a Norton amplifier, and while
>> it has differential inputs they are current driven. (Most older op amps are
>> voltage driven.) The LM3900 is powered from 10V, so I think of that as just
>> above the maximimum output voltage. Both the upper amplifier and the second
>> lower amplifier have 1M feedback resistors, and + inputs fed 10V by 1M bias
>> resistors. That would bias the output at near the supply rail, turning
>> these stages into something like half-wave rectifiers. Since the first
>> lower stage has a 2M bias resistor it idles at about half supply, and
>> behaves as a simple inverter. If my analysis is correct (and I worked at
>> National when the LM3900 came out, a friend did apps for this odd new part)
>> then the combining of the two outputs produces a negative going full wave
>> rectification of the signal. The fourth LM3900 stage looks like an
>> inverting bandpass filter, but I'd have to dig out some reference books to
>> determine its behavior in more detail. As for the 100-200 switch I'm
>> confused, why would the bandpass frequency be lowered for the higher
>> modulation rate?
>>
>> Bob LaJeunesse
>>
>>
>> Sent: Saturday, August 16, 2014 at 2:56 PM
>> From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
>> To: "paul swed" <paulswedb at gmail.com>
>> Cc: time-nuts at febo.com
>> Subject: Re: [time-nuts] Cutler NAA on 24.0kHz....
>> On 16 Aug 2014 at 13:35, paul swed wrote:
>>
>>> Kenneth on the opamps that is correct.
>>> But I put little U's to indicate phase. They actually represent the top
>> half of
>>> the input cycle.
>> Yes, I saw those, but unless I am mistaken, you didn't add a "U" after the
>> second opamp, which would have returned the phase to the input's.
>>
>>> In the top path it inverts once.
>> I see twice: once through the first op amp and again through the second
>> one.
>> The second one then outputs to the IF.
>>
>> Anyway, to me, it is a very interesting and simple circuit.
>>
>> I LIKE "simple". I am a great believer in the KISS principle.
>>
>> Ken W7EKB
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