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. >>> >>> >> >> > >