[ARC5] Crystal Filters in BC-455

[Fuqua, Bill L]

  I had used the "phasing filter" design in my WWV receiver. 
The 2-3 MHz crystals that cost from $0.40 to $1 each are amazingly precise 
and high Q with a series resistance "measured" about 70 Ohms. 
  In my case I needed very narrow bandpasses but it is easy to increase the Q.
For those interested I can send a image of the response curve. 
I will be  away from my computer until late tonight but I will get back to it
after 10PM EST.
73
Bill wa4lav

________________________________________
From: ARC5 [arc5-bounces at mailman.qth.net] on behalf of Kenneth G. Gordon [kgordon2006 at frontier.com]
Sent: Thursday, October 29, 2015 12:21 PM
To: Arc5 at mailman.qth.net
Subject: Re: [ARC5] Crystal Filters in BC-455

On 29 Oct 2015 at 16:14, Fuqua, Bill L wrote:

>   I have been working on a homebrew receiver for the ARRL Frequency Measurement
>   Test.
> There are two receivers, one has crystal filters for 4 WWV frequencies. The
> other is the test signal receiver Anyway, I have used 2.5 MHz crystals from
> mouser to make a filter with less than 100 Hz bandwidth. Naturally that can be
> widened by lowering the Q.
>   It occurred to me that 2.5 MHz is not far from the IF frequency of the BC-455.
>   In fact
> Digikey has a 2.949 MHz crystal which is even closer to the 2.830 MHz IF.
> Naturally the Local oscillator would have to be aligned but being only 4% shift
> in IF it should still track and match dial fairly good.
>   I remember some earlier discussions about using crystals in ARC5 receiver IF's
>   but don't recall the
> outcome.
>
> 73
> Bill wa4lav

Hello, Bill:

I had thought of that idea too, and, in fact, Mike Murphy WU2D has a
youtube video of a BC-455 in which he did exactly that and the video shows
the very effective results.

He, apparently, found a 2830 KHz crystal, and although I have been
searching for one, I have, so far, never found one that was inexpensive.

Your idea has great merit, and I thank you for it.

Be aware that the BC-455 and the R-27/ARC-5 have two different kinds of IF
transformers: I forget the models, but the IF transformers in one model
consist of only one coil, whereas those in another model consist of two coils
like the lower frequency models have.

vy 73,

Ken W7EKB
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