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

paul swed paulswedb at gmail.com
Sun Aug 17 19:16:34 EDT 2014


Actually I built analog dividers and it doesn't fix the issue at all as
itsthe relationship from local to the reference. A slip is a slip and the
chart recorders track them. But we stray from the question on msk.
Regards


On Sun, Aug 17, 2014 at 5:27 PM, Alexander Pummer <alexpcs at ieee.org> wrote:

>
> 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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