[TenTec] Orion II - Stability improvement by mixing abracadabra

[Sinisa Hristov]

Upravo sam hteo da posaljem ovo na TenTec listu,
kad se javio Jack iz TenTeca - pita gde je greska.
Poslao sam njemu.

Lista moze da saceka, a ti naravno - ne :-)


73,

Sinisa









Here's the step-by-step mixing algebra for both Orion I and Orion II.

The analysis shows that stability improvement due to the
new "mixing architecture" in Orion II is immeasurable.

To have the drift reduced by 0.1 %, 0.2 % or even 1.5 % of the original drift
is hardly worth the server space used to advertise it.

On the other hand, the new scheme caused another DDS to be added for LO3 generation,
compared to simple and clean divide by 16 in Orion I.


73,

Sinisa  YT1NT, VE3EA



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In both cases the same input frequency RF is assumed
to be converted to the same output frequency IF3.

All the names stand for respective frequencies.



For Orion I
-----------

IF1a = LO1a - RF
IF2a = LO2a - IF1a = LO2a - LO1a + RF
IF3  = LO3a - IF2a = (LO3a - LO2a + LO1a) - RF

LOa = LO1a - LO2a + LO3a   { the equivalent single-mixing LO }
IF3 = LOa - RF             { inverted sidebands at IF3 }

IF3 drift(I) = LOa drift = LOa * (TCXO drift / TCXO)



For Orion II
------------

IF1b = LO1b - RF
IF2b = IF1b - LO2b = LO1b - LO2b - RF
IF3 = LO3b - IF2b = (LO3b - LO1b + LO2b) + RF = RF - (LO1b - LO2b - LO3b)

LOb = LO1b - LO2b - LO3b    { the equivalent single-mixing LO }
IF3 = RF - LOb              { non-inverted sidebands at IF3 }

IF3 drift(II) = LOb drift = LOb * (TCXO drift / TCXO)

Here we ignore the fact that IF3 drift(II) is in the opposite direction of the TCXO drift.



Comparison
----------

IF3 = LOa - RF     RF = LOa - IF3
IF3 = RF - LOb     RF = LOb + IF3

LOb = LOa - 2 * IF3         { substitute this in the expression for IF3 drift(II) }

IF3 drift(II) = (LOa - 2 * IF3) * (TCXO drift / TCXO)

drift improvement = IF3 drift(I) - IF3 drift(II)

drift improvement = 2 * IF3 * (TCXO drift / TCXO)

(drift improvement / IF3 drift(I)) = 2 * IF3 / LOa = 2 * IF3 / (RF + IF3)

Due to extremely low IF3 compared to equivalent LO frequencies,
practically no stability improvement occurs.



Drift improvement examples
--------------------------

Drift improvement expressed as a part of the original drift:

  at RF = 1800 kHz:     2 * 14 / (1800 + 14) = 1.5 %
  at RF = 14000 kHz:    2 * 14 / (14000 + 14) = 0.2 %
  at RF = 28000 kHz:    2 * 14 / (28000 + 14) = 0.1 %



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