[Premium-Rx] real basic question on stability etc.

[Ahmet Gundes]

Hi Eugene,

I don't know what was going thru my mind when i wrote this. but i think a
lot of the FM receivers had this AFC back in those days. I remember when
I was little, around mid 70s - 80s most of the FM home receivers and even
TVs had AFC buttons that you can switch in if you would want it. Perhaps
it is the nature of Frequency Modulation coupled with less reliable
tuning curcuitry in those equipment lead to the use of AFC.  I remember a
lot of the TVs actually had this and when you presses the button, it
would pick up the weak signal nearby and center it.  Maybe this was used
with Varactor tuning circuitry which easily changed voltage to find the
maximum strength of signal.

But the idea of "Jurrasic Frequency Hopping System" just sounded better
to me at that time.  If I am not mistaken, Frequency Hopping was invented
by a Hollywood actress whose husband was a German scientist. I don't know
how she came up with the idea ( or am I thinking of something else ) !...

In modern Frequency Hopping Transmitter and Receivers, there are
algorithms used in order to eliminate errors of signals appearing in the
hopping range but not actually belonging to the intended transmission. 
So my proposed freq hop would be an unreliable one, simply relying on
signal strength / signal in the Bandwidth, making it Jurrasic for sure (
unless there is an audio decoding in the receiver )!...

It would be interesting to know the +/- frequency range swing.  Please
let us know. 

Ahmet


it is a very interesting thought indeed. I will try to make some
measurements as to how much it will actually track. I dont know if its
+/-Hz, or +/-Khz or +/-Mhz or what. I will check it out. might send
results to the premium-rx list in case others are interested

interesting idea tho!
Eugene

    -----Original Message-----
    From: Ahmet Gundes [mailto:ahmet-m at usa.com]
    Sent: Friday, September 2, 2005 03:37 PM
    To: 'Eugene Hertz'
    Subject: Re: [Premium-Rx] real basic question on stability etc.

    just an idea, but this might even be the beginnings of Frequency
    Hopping scheme ...

    Perhaps they used the receiver for receiving transmissions of a
    Jurrasic version of Frequency Hopping Transmitter.  Everytime the
    transmitter hopped to different frequency within a very limited
    bandwidth, receiver AFC'ed to get best signal reception !.. 
    well, maybe this is not the case but just a thought.
    ahmet


      Ok, here's a novice question. I know that receiver stability
      is a big topic of discussion. The more stable the better. But
      it seems to me stability for a receiver is only as useful as
      the stability on the transmitter?! Of course, if both Tx and
      Rx are drifting, then unless they are drifting in the same
      direction at the same rate it certainly would be better to
      have only one node drifting as opposed to both. I recently
      acquired a receiver (not premium) P-1524(P)/WRR submarine
      countermeasures receiver 30Mhz-1,000Mhz with plug in RF
      tuning stages and it has this neat feature (probably common,
      but new to me) where it has AFC automatic frequency control.
      It works pretty well (to my unsophisticated mind).
      Essentially adjusts the LO up or down to match the carrier of
      the transmitter.  I would imagine a feature like that to
      perhaps be more valuable than stability. Who cares what the
      LO of the receiver actually is, as long as its locked onto
      the transmitter.  Imagine being able to track the tx no
      matter how much it is drifiting. That to me should be a great
      design goal. Now, I would imagine AFC would be darn near
      impossible for ssb. But FM, AM and maybe even CW could
      benefit. I am sure I am missing something.  Why the emphasis
      on stability and not tracking?

      Eugene _______________________________________________
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