[R-390] Coil forms and more

[John KA1XC]

Hi Jim,
if I read your post correctly you are attempting to mix down 455 kc to your
Scanalyzer IF for use with a 390 rx. Cool!

In this case you want to use a low-side LO injection frequency, because if
you use a high-side LO you will end up with a spectral inversion which will
be very evident on your Scanalyser display!

The unwanted mixer products should be far enough way because with the 390
you'll only be able to see a narrow slice of the band anyway:
- if you are monitoring the IF output then the scanned bandwidth will be the
390 IF bandwidth
- if you are tapping off the 3d mixer (recommended) the bandwidth will be
only 35 to 40 kc max due to all
   the cascaded selectivity in the RF and 2nd IF stages (yes, it is that
narrow).

Also, try to use a balanced or double balanced mixer, you'll get far less
troublesome RF and especially LO feedthrough into your scanalyzer IF.

John
KA1XC

----- Original Message ----- 
From: "Jim Brannigan" <jbrannig@optonline.net>
To: <R-390@mailman.qth.net>
Sent: Wednesday, June 11, 2003 7:45 AM
Subject: [R-390] Coil forms and more


> Thanks to all for the suggestion and help with my SB-620.  After many
years
> the 455 kc. conversion project might get off the ground.
>
> Does anyone know the mixer oscillator injection frequency?  It is not
> stipulated in the manual or on-line sources.
>
> Here is my guess:
> The IF of the Heath "Scanalyzer" is 350kc.
> To convert 455kc., the oscillator may be either 805 or 105kc.
> The "high" injection of 805kc produces first order products of 350 and
> 1260kc.
> "low injection of 105kc produces 350 and 560kc.
>
> The "High" injection products are further apart and it would be easier to
> filter the unwanted sum frequency.
> So my "guess" is 805kc.
> I know the value of the parallel capacitance.  If the oscillator frequency
> is known, I can calculate the coil inductance.
>
> Any help or ideas greatly appreciated.
>
> Jim