[minima] Re: Experimenting with the crystal filter
- From: Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Fri, 24 Jan 2014 01:34:46 -0800
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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