[minima] Re: Experimenting with the crystal filter
- From: Adrian Preda <ady.preda@xxxxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Fri, 24 Jan 2014 01:52:23 -0800 (PST)
Hi,
What caps values can be used for a CW filter, like 300-400Hz?
Adrian
YO4HHP
________________________________
From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
To: minima@xxxxxxxxxxxxx
Sent: Friday, January 24, 2014 11:42 AM
Subject: [minima] Re: Experimenting with the crystal filter
Interesting reading list!
Just shows you - I suspect the filter you have now is just great.
M
On 24/01/2014 09:34, Thomas Sarlandie wrote:
Mark,
>
>
>No, I had not. I have a bag coming. I will experiment with the circuit and
>method (inspired by g3uur) shown in the ARRL handbook. I also found some
>interesting doc online:
>http://pages.suddenlink.net/wa5bdu/crystal_slide_show.pdf and
>http://openqrp.org/?p=418. I am traveling this weekend but that should give me
>some good theory to be ready when I come back.
>
>
>I will probably move on to another stage before I get back to it though.
>
>
>thomas
>
>
>
>On Fri, Jan 24, 2014 at 1:28 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:
>
>Hi Thomas
>>
>>That looks much better!
>>
>>I don't remember if you said you had matched the crystals
or not?
>>
>>Mark
>>G0MGX
>>
>>
>>
>>On 24/01/2014 09:24, Thomas Sarlandie wrote:
>>
>>Hey,
>>>
>>>
>>>It occurred to me this morning that I had measured the output peak-to-peak
>>>voltage of the DDS in open circuit and calculated the power like if it was
>>>50 ohm terminated...
>>>
>>>
>>>Sure enough with a 50 ohm termination (after the L-match), the output power
>>>of the circuit is -5.9 dBm and the characteristic of my filter much more
>>>normal:
>>>
>>>
>>>2 dB bandwidth: 4.50 khz
>>>Insertion loss: -5 dB
>>>
>>>
>>>https://docs.google.com/spreadsheet/ccc?key=0As9CZnZ-A5a2dEZaM1dlWVdVX3pXaUlJMXd0cHNscHc#gid=1
>>>
>>>
>>>
>>>lesson learnt!
>>>
>>>
>>>thomas
>>>
>>>
>>>
>>>
>>>On Thu, Jan 23, 2014 at 3:56 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:
>>>
>>>Hi Gang
>>>>
>>>>I just pulled 8 crystals out of the bag and
built another crystal filter without
attempting to match them - just out of
curiosity.
>>>>
>>>>The sweep is attached, the -2dB bandwidth is
3.5KHz and the insertion loss 4dB (the
tracking generator is at -20dBm).
>>>>
>>>>The sides of the filter don't look quite as
steep but it still looks pretty good without
any matching - maybe I got lucky? Certainly
can't explain why you are seeing a 10dB
insertion loss - that's very high.
>>>>
>>>>Mark
>>>>G0MGX
>>>>
>>>>
>>>>
>>>>On 23/01/2014 10:42, Thomas Sarlandie wrote:
>>>>
>>>>Clark: I had a face-palm moment when I got your email. This is obviously a
>>>>much simpler solution. Thanks a lot.
>>>>>
>>>>>
>>>>>Farhan/Jerry: I read EMRFD on return loss bridge and this page too:
>>>>>http://www.qrp.pops.net/RF-workbench-3.asp but I am still not sure how I
>>>>>would measure the output impedance of the dds. If you have some more links
>>>>>or quick suggestion, that would be very helpful. Thank you.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>I used Clark technique to measure the output impedance of the DDS and
>>>>>found 100 ohm again (not a big surprise). I then built an L circuit to
>>>>>match it to 50 ohms. I did not have the perfect parts available so I ended
>>>>>up with 39+i.14 calculated (66 ohms measured with the pot).
>>>>>
>>>>>
>>>>>I took the time to graph the filter response:
>>>>>https://docs.google.com/spreadsheet/ccc?key=0As9CZnZ-A5a2dEZaM1dlWVdVX3pXaUlJMXd0cHNscHc#gid=1
>>>>>
>>>>>
>>>>>I get a center freq of 20,002.5 kHz, a 3dB bw of 5 kHz and a ripple of 2.2
>>>>>dB. If you have feedbacks on my method or if you think I goofed somewhere
>>>>>please feel free to point it out. I will probably try again with matched
>>>>>crystals ... and a better idea of what I am aiming for.
>>>>>
>>>>>
>>>>>One thing that still puzzles me is the insertion loss. I get about 10dB
>>>>>when Mark reported 3 dB. I am not sure what could explain such a big
>>>>>difference.
>>>>>
>>>>>
>>>>>thomas
>>>>>
>>>>>
>>>>>
>>>>>On Wed, Jan 22, 2014 at 2:18 AM, <jerry@xxxxxxxxxxxxxxxx> wrote:
>>>>>
>>>>>The return loss bridge is one of the handiest tools on my workbench. I
>>>>>>got my design from chapter 7
of EMRFD.
>>>>>>
>>>>>>
>>>>>>
>>>>>>-------- Original Message
--------
>>>>>>Subject: [minima] Re:
Experimenting with the
crystal filter
>>>>>>From: Ashhar Farhan <farhanbox@xxxxxxxxx>
>>>>>>Date: Wed, January 22,
2014 4:04 am
>>>>>>To: minima@xxxxxxxxxxxxx
>>>>>>
>>>>>>the correct way, is really
to measure it with an RLB.
six resistors and
>>>>>>a balun will go a long way
in helping us measure
these impedances. oh,
>>>>>>btw, u can measure the
input and output
impedances with the RLB.
>>>>>>
>>>>>>- f
>>>>>>
>>>>>>
>>>>>>
>>>>>>On Wed, Jan 22, 2014 at
3:08 PM, Clark Martin
<cmmac@xxxxxxxxx> wrote:
>>>>>>
>>>>>>
>>>>>> Sent from an iPhone,
don't ask whose.
>>>>>>
>>>>>> > On Jan 22, 2014, at
1:34 AM, Thomas Sarlandie
<thomas@xxxxxxxxxxxxx>
>>>>>>wrote:
>>>>>> >
>>>>>> > I am using an ad9850
and I measured the output
impedance to be 100
>>>>>>ohms. I simply measured
the output voltage in open
circuit (519 mV rms)
>>>>>>and the output current in
short circuit (5.1 mA).
This is as simple as
>>>>>>it gets but I think this
is correct.
>>>>>>
>>>>>>
>>>>>>A better way is to measure
the open circuit voltage
then apply a
>>>>>>resistive load to it and
adjust the resistance till
the voltage is one
>>>>>>half the open circuit
voltage. The load
resistance will be equal
to the
>>>>>>source impedance.
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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