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I don't think D51 is there for it's voltage drop, its there to prevent the TX voltage that goes to the varactors (during TX) from going back into the RX supply via the voltage divider at the clarifier. Having the RX chain go active during TX, even a little bit, would be a bad thing. D51 stops that from happening.

IC4 already regulates the voltage to the varactors, so adding a "stable" voltage drop in series with that regulator voltage will still pass any variation with temperature from the regulator to the varactors. The voltage would only be stable across the diodes, but since they are not in a zener configuration, it can still pass any variation from the supply (while only remaining stable across the diodes themselves). Thats just my take on it anyhow.

Edit: i initially misunderstood nomad and took it as voltage stabilization, not voltage compensation to offset a variation from a different part. I'd love to understand how that configuration achieves it.

<blockquote data-quote="brandon7861" data-source="post: 812467" data-attributes="member: 53724">I don&#039;t think D51 is there for it&#039;s voltage drop, its there to prevent the TX voltage that goes to the varactors (during TX) from going back into the RX supply via the voltage divider at the clarifier.&nbsp; Having the RX chain go active during TX, even a little bit, would be a bad thing.&nbsp; D51 stops that from happening. IC4 already regulates the voltage to the varactors, so adding a &quot;stable&quot; voltage drop in series with that regulator voltage will still pass any variation with temperature from the regulator to the varactors.&nbsp; The voltage would only be stable across the diodes, but since they are not in a zener configuration, it can still pass any variation from the supply (while only remaining stable across the diodes themselves).&nbsp; Thats just my take on it anyhow.&nbsp;Edit: i initially misunderstood nomad and took it as voltage stabilization, not voltage compensation to offset a variation from a different part.&nbsp; I&#039;d love to understand how that configuration achieves it.</blockquote>

[QUOTE="brandon7861, post: 812467, member: 53724"] I don't think D51 is there for it's voltage drop, its there to prevent the TX voltage that goes to the varactors (during TX) from going back into the RX supply via the voltage divider at the clarifier. Having the RX chain go active during TX, even a little bit, would be a bad thing. D51 stops that from happening. IC4 already regulates the voltage to the varactors, so adding a "stable" voltage drop in series with that regulator voltage will still pass any variation with temperature from the regulator to the varactors. The voltage would only be stable across the diodes, but since they are not in a zener configuration, it can still pass any variation from the supply (while only remaining stable across the diodes themselves). Thats just my take on it anyhow. [B]Edit: i initially misunderstood nomad and took it as voltage stabilization, not voltage compensation to offset a variation from a different part. [/B]I'd love to understand how that configuration achieves it. [/QUOTE]

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