[minima] Re: New Crystal Filter
- From: Mvs Sarma <mvssarma@xxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Wed, 10 Sep 2014 08:09:25 +0530
I have few doubts.
While internationally accepted IF like 45MHz , with with ar eady made
crystal filter and oscillator crystals at 44.545 etc are available , why
we are to resort odd frequencies? Woring out around 45MHz up-conversion
would perhaps be easier. i do have few crystal 45MHz filters with me.
On Wed, Sep 10, 2014 at 3:46 AM, Joe Rocci <joe@xxxxxxxxxx> wrote:
> Here's something I've been contemplating for a long time. It's motivated
> by how we're knocking ourselves out trying to make the 'perfect' mixer so
> we won't have problems with LO & IF leakage. Well, it seems to me that the
> root of the problem is the 20 MHz IF, right in the middle of the tuning
> range. If only we could move that IF up to 30 MHz or more, our problems in
> this area would be much less.
>
> Attached is a plot of a 40 MHz 6 pole filter using very inexpensive
> fundamental mode crystals that cost a little more than $0.50 ea. These VHF
> fundamental mode crystals are now available to over 150 MHz and they've
> gotten cheap. The filter shown is about 6 KHz wide and has about 4.5 db
> loss. If we moved down to 30 Mhz, we could probably get lower loss for the
> same bandwidth or lower bandwidth for the same loss. I have some 30 Mhz
> crystals on order, so I'll find out.
>
> If this works out, we might be able to have our cake and eat it too as far
> as mixing product problems are concerned. Of course, the higher IF
> frequency will probably create some other challenges further down the IF,
> but I think they should be minimal
>
> Comments?
>
--
Regards
Sarma
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