EMRFD Message Archive 4414
Message Date From Subject 4414 2010-03-06 11:12:47 Phil Sittner Fw: Re:W7ZOI 14Mhz receiver ----- Original Message -----
From: "Phil Sittner" <sittners@sbcglobal.net>
To: <leinwebe@mcmaster.ca>
Sent: Saturday, March 06, 2010 11:06 AM
Subject: Re: Re:W7ZOI 14Mhz receiver
> Glen-
>
> Here's the results from my experiment and I'm very pleased. I used 200
> ohms
> as the design impedance and the results have great correlation to those
> predicted by Ladpac. The VNWA curves aren't up to laboratory standards but
> sure work great in the shack. Thanks again for your comments.
>
> Phil kd6rm
> ----- Original Message -----
> From: "Glen Leinweber" <leinwebe@mcmaster.ca>
> To: <sittners@sbcglobal.net>
> Sent: Tuesday, March 02, 2010 12:19 PM
> Subject: Re:W7ZOI 14Mhz receiver
>
>
>> Phil,
>> Best wishes in doing a homebrew receiver, and in trying
>> a "tweak" on a good design - you'll have all the more
>> satisfaction when you're successful...
>> For such a narrow bandwidth of 500 Hz, with nearly 9MHz.
>> center frequency, crystal Q will be somewhat important.
>> You are designing a filter having Q of 18000. Crystal Q
>> should be roughly 10x this figure (180000). My junkbox
>> crystals may be roughly cut (coming from mass-produced
>> microprocessor market), and none approach this figure.
>>
>> You can still make a filter with these crystals even if they
>> have Q in the 100000 ballpark, if you use more complex
>> design process outlined by Zverev in his "predistorted"
>> filter tables.
>> Just for laughs, tried entering a 5 crystal filter @ 9 MHz
>> with Q=100000 into Wes' "XLAD08". It came up with
>> termination R of about 125 ohms. This is just a bit low. You
>> should really characterize your crystals with care before
>> trying a design. If I were to build a ladder filter with crystals
>> of a caibre similar to those from *my* junkbox, the filter
>> would likely have a lot of loss in the passband, poorly shaped
>> filter sides, and a bandwidth narrower than I'd wanted.
>>
>> You may have to tweak the I.F. amp design a bit to
>> accommodate a filter having low termination resistance.
>>
>> Note that if you build a filter having crystals whose unloaded
>> Q is marginal, you tend to get filter shapes with tops that
>> look somewhat gaussian, with ill-defined edges.
>>
>
[Non-text portions of this message have been removed]4415 2010-03-06 11:43:40 Phil Sittner Fw: Re:W7ZOI 14Mhz receiver ----- Original Message -----
From: "Phil Sittner" <sittners@sbcglobal.net>
To: <leinwebe@mcmaster.ca>
Sent: Saturday, March 06, 2010 11:06 AM
Subject: Re: Re:W7ZOI 14Mhz receiver
> Glen-
>
> Here's the results from my experiment and I'm very pleased. I used 200
> ohms
> as the design impedance and the results have great correlation to those
> predicted by Ladpac. The VNWA curves aren't up to laboratory standards but
> sure work great in the shack. Thanks again for your comments.
>
> Phil kd6rm
> ----- Original Message -----
> From: "Glen Leinweber" <leinwebe@mcmaster.ca>
> To: <sittners@sbcglobal.net>
> Sent: Tuesday, March 02, 2010 12:19 PM
> Subject: Re:W7ZOI 14Mhz receiver
>
>
>> Phil,
>> Best wishes in doing a homebrew receiver, and in trying
>> a "tweak" on a good design - you'll have all the more
>> satisfaction when you're successful...
>> For such a narrow bandwidth of 500 Hz, with nearly 9MHz.
>> center frequency, crystal Q will be somewhat important.
>> You are designing a filter having Q of 18000. Crystal Q
>> should be roughly 10x this figure (180000). My junkbox
>> crystals may be roughly cut (coming from mass-produced
>> microprocessor market), and none approach this figure.
>>
>> You can still make a filter with these crystals even if they
>> have Q in the 100000 ballpark, if you use more complex
>> design process outlined by Zverev in his "predistorted"
>> filter tables.
>> Just for laughs, tried entering a 5 crystal filter @ 9 MHz
>> with Q=100000 into Wes' "XLAD08". It came up with
>> termination R of about 125 ohms. This is just a bit low. You
>> should really characterize your crystals with care before
>> trying a design. If I were to build a ladder filter with crystals
>> of a caibre similar to those from *my* junkbox, the filter
>> would likely have a lot of loss in the passband, poorly shaped
>> filter sides, and a bandwidth narrower than I'd wanted.
>>
>> You may have to tweak the I.F. amp design a bit to
>> accommodate a filter having low termination resistance.
>>
>> Note that if you build a filter having crystals whose unloaded
>> Q is marginal, you tend to get filter shapes with tops that
>> look somewhat gaussian, with ill-defined edges.
>>
>
[Non-text portions of this message have been removed]