[Boatanchors] oscillator waveform

[James Liles]

Hi Paul:
Very few if any tube vintage radios will display what appears to be a clean 
sine wave from the first local oscillator or even the BFO.  Loading is the 
issue and what looks to have a very negative effect may not be a problem at 
all specifically within the mixer that it is driving.  Careful though, in a 
poorly shielded, discretely wired radio, that mutant sine and it's rubbish 
can couple to other circuits.

Look at any radio that uses an overtone crystal for the local oscillator and 
you will find some of the shabbiest junk known to man --- with no 
measureable negative effect.

What radio are you working with?  If we know the heterodyne scheme we can 
predict the presence of birdies, or spurs if it's a transceiver.  Look at 
the romance sheet for Collins, Hallicrafters etc. and you will find a BIRDIE 
disclaimer usually equal to or less that a 1 uv signal for most if not all.

Kindest regards Jim K9AXN



----- Original Message ----- 
From: "Paul Kraemer" <elespe at lisco.com>
To: <boatanchors at qth.net>
Sent: Sunday, December 12, 2010 2:05 PM
Subject: [Boatanchors] oscillator waveform


>A tecnical question for the group:
> Should the waveform from a hetrodyne oscillator in a
> receiver front-end be a
> clean sine wave? Does it matter if it is a skewed or not
> symmetrical
> waveform?
> I'm working on a receiver which seems (to me) to have a
> lot of birdies or
> tweets and I'm wondering if that waveform could be
> significant contributing
> factor.
> Alignment of the xtal oscillator "by the book" looking for
> maximum voltage
> produces somewhat distorted waveform.
> A slight mis-tuning while observing the scope to make the
> waveform more pure
> is possible on some bands but not all.
> Paul K0UYA
>