[minima] Re: Rx only minima for swl
- From: "Joe Rocci" <joe@xxxxxxxxxx>
- To: <minima@xxxxxxxxxxxxx>
- Date: Thu, 20 Mar 2014 16:45:32 -0400
I recall that someone actually swept that filter under different settings (or
it was possibly an Elecraft rig that uses the same technique) and verified that
the shape and loss do indeed suffer. If someone could find a way to compensate
the impedance match over the tuning range from CW bandwidth to phone bandwidth,
it would be killer. You could program a PWM in the AVR controller to produce a
variable output voltage, resulting in software controlled bandwidth selection.
----- Original Message -----
From: Lawrence Galea
To: minima@xxxxxxxxxxxxx
Sent: Thursday, March 20, 2014 4:09 PM
Subject: [minima] Re: Rx only minima for swl
You can have a look at the circuit of the multipig xcvr where instead of
capacitors in the crystal filter it uses varicaps and by changing the voltage
across the varicaps the filter bandwidth is changed.
http://kitsandparts.com/rcvr.gif
Lawrence
On Thu, Mar 20, 2014 at 7:47 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
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.
a.. Use relays or active device switches to decrease capacitor values
in the crystal filter.
b.. 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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