[minima] Re: Rx only minima for swl
- From: Arv Evans <arvid.evans@xxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Thu, 20 Mar 2014 18:31:51 -0600
Joe
Agreed, but small impedance mismatches in crystal filters mostly causes
ripple in the passband. A quick scan of passband characteristics will
quickly tell if it is too bad to live with. I wonder if anyone has made a
study
to see how much impedance mismatch causes how much passband
deterioration? Might be interesting to know.
In the BITX group we had some fairly significant crystal filter impedance
mismatches, but the rigs still make contacts and apparently sound good.
Yes, the dual filter is the best solution. It does add to the parts count
and
space requirement, but for a receive-only version of Minima that may not
be a significant problem.
Arv
_._
On Thu, Mar 20, 2014 at 12:47 PM, Joe Rocci <joe@xxxxxxxxxx> wrote:
> "Use relays or active device switches to decrease capacitor values
> in the crystal filter"
>
> Arv
>
> Keep in mind that anything you do to change the filter bandwidth will also
> change the characteristic impedance. Impedance mismatch in bandpass filters
> usually results in distorted passband shape and increased loss. I think the
> second approach is better.
>
> Joe
> W3JDR
>
> ----- Original Message -----
>
> *From:* Arv Evans <arvid.evans@xxxxxxxxx>
> *To:* minima@xxxxxxxxxxxxx
> *Sent:* Thursday, March 20, 2014 2:31 PM
> *Subject:* [minima] Re: Rx only minima for swl
>
> Cor
>
> It really depends on whether one wants a general coverage communications
> quality receiver or a broadcast quality receiver. If wider IF bandwidth
> is
> needed then there are at least two approaches to achieving it.
>
> - Use relays or active device switches to decrease capacitor values
> in the crystal filter.
>
> - Add a second wider bandwidth IF filter and switch the filter in
> or out using relays or active device switches.
>
> Changing bandwidth of the IF filter also could be applied for CW or other
> narrow bandwidth modes.
>
> Arv K7HKL
> _._
>
>
> On Thu, Mar 20, 2014 at 12:22 PM, dx11 <dx11@xxxxxxxxx> wrote:
>
>> It crossed my mind as well to make a Rx only version with AM added. I
>> did not yet come to a solution how to widen the Xtal filter to an AM value.
>>
>>
>>
>> Cor Beijersbergen
>>
>>
>>
>>
>>
>> It appears from a quick look at the schematic that you should be able to
>>
>> add an AM detector and switch the audio amplifier input between outputs
>>
>> of SSB and AM detectors. To avoid interference you might want to switch
>>
>> the BFO oscillator power off when listening to AM.
>>
>>
>>
>> I like your idea of using this design as a general coverage receiver. May
>>
>> have to try that myself.
>>
>>
>>
>> Arv K7HKL
>>
>> _._
>>
>
>
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