2247	2008-10-14 21:19:27	rcbuckiii	I need L-C filter suggestions
Message	Date	From	Subject
I am putting together an upconverting receiver. I am going to have 3.5-4.0, 7.0-7.5, and 14.0 to 14.5 bands. I would like to use 45 MHz for the upconversion IF with a 500 KHz bandwidth. I will be using fixed frequencies for the 1st local oscillator which is why the wide bandwidth is required. I will subtract the desired frequency from the local oscillator. And I want to reject the LO+desired frequecy band. I want to place the bandpass filter right after the 1st mixer. Using AADE and Elsie gives strange values for the inductor and capacitor values, such as .5pf and 1.4 nH. Analyzing the filters with these values gives good results. However, if I try to change the values to something reasonable, the simulation shows very poor side slopes. Only 3 dBm difference between the 45 MHz CF and 49 MHz image for the 80 meter frequencies. If I change the upconversion IF to 75 MHz, I am able to come up with reasonable component values and a good response shape. However, that makes my 2nd coversion down to 9 MHz more difficult. Does anyone have any suggestions for a 45 MHz bandpass design using reasonable component values? And it would also be desirable not to have to go to a 12 order design. Or would it be better to try and combine a low pass filter with a high pass one to get the desired response? Ray AB7HE
2251	2008-10-15 07:20:55	timshoppa	Re: I need L-C filter suggestions

2252	2008-10-15 07:47:51	sm5glc	Re: I need L-C filter suggestions
What kind of specs are you shooting for on 45 MHz?? Just tested a quick 2 and 3 pole filter with the requested 1% BW. Using Qu of 200 on inductors and 500
2253	2008-10-15 12:24:06	Wes Hayward	Re: I need L-C filter suggestions
Ray, There are some third order bandpass filters at 40 and at 50 MHz on pages 6.85 and 6.88 of EMRFD. These were designed from first principals, but then run through TTC.exe that is on the EMRFD CD. The approach taken within that program is to tread the inductors as the beginning variable and to then calculate the capacitors needed to obtain a viable filter response. As with any filters, the results you get are vitally dependent up
2254	2008-10-15 18:50:38	wimmie262000	Re: I need L-C filter suggestions
Have you looked in EMRFD at page 3.14? The table seems to give acceptable values up to 50MHz. For an accurate value of the small coupling capacitor you could use the "trick" at the top of page 3.15. (or figure 3.24, but there the values are not quantified in detail) Joop
2256	2008-10-15 18:50:38	rcbuckiii	Re: I need L-C filter suggestions
Quote: "I personally don't like the challenges imposed by upconverging multiple-conversion receivers..." Tim, I'm not looking for excellent performance. Just something for general listening. My idea was to use a PLL to generate the 3 frequencies for the LO to upconvert to 45 MHz. Then I was going to mix a ~5MHz L-C VFO with a crystal oscillator for final down conversion. Just an idea I was playing with. I may end up having to use the PLL as a tunable 1st oscillator to avoid some of the issues you mention. That is the way the Yaseau FRG-7 that I have does it. Lasse, what tool did you use to model your design? I was using Qu of 200 for the inductors. AADE doesn't require Qu for caps. I guess they assume ideal parts. I'll go back and test the design with 220 nH inductors. If I can get > 10 dB difference between the desired 41.5 MHz signal and the 48.5 image signal I think that will be sufficient. Ray AB7HE
2257	2008-10-15 18:50:38	victorkoren	Re: I need L-C filter suggestions
I don't have any problem using the AADE filter designer to design a 3 pole BPF with practical component values. A step by step design: 1) file > new 2) design > coupled resonator > butterworth 3) cf=45M bw=600k order=3 >enter 4) Li=0.18u Qu=200 >enter 5) Zin=50 Zout=50 >enter 6) enter a neme for the filter >enter You get the filter schematic with values. All the inductors are 180 nHy, resonator capacitors are 62pF and 68pF and coupling capacitors are 6.4pF and 0.65pF. All components are practical Analysis of the filter shows a center frequency attenuation of 6.85dB 73's Victor - 4Z4ME
2259	2008-10-15 18:50:47	rcbuckiii	Re: I need L-C filter suggestions
Wes, Thanks for the information. As usual you come to the rescue. I will pull the CD out and run those filters through TTC. Then I can make the adjustments to center one of them on 45 MHz. In the paragraph at the bottom of 6.84 you say you measured 80-dB rejection of the unwanted signals. If I can obtain 40-dB I will be happy. Ray AB7HE
2260	2008-10-15 21:17:55	rcbuckiii	Re: I need L-C filter suggestions
Victor, Thanks for the great tip. I was selecting Design -> Butterworth -> Bandpass. The coupled resonator gives much better results. This is the same type of filter that Wes was referring to in his DTC and TTC examples. I had never tried that type of design in AADE. I changed the two .65pF caps to 1pF and re-analyzed the filter. This creates a very slight ripple in the passband but not enough to worry about. And the side slopes are more than ample for my application. Ray AB7HE --- In emrfd@yahoogroups.com, "victorkoren" wrotcoupled resonator e: > > I don't have any problem using the AADE filter designer to design a 3 > pole BPF with practical component values. > A step by step design: > 1) file > new > 2) design > coupled resonator > butterworth > 3) cf=45M bw=600k order=3 >enter > 4) Li=0.18u Qu=200 >enter > 5) Zin=50 Zout=50 >enter > 6) enter a neme for the filter >enter > You get the filter schematic with values. > All the inductors are 180 nHy, resonator capacitors are 62pF and 68pF > and coupling capacitors are 6.4pF and 0.65pF. > All components are practical > Analysis of the filter shows a center frequency attenuation of 6.85dB > > 73's > Victor - 4Z4ME > >
2261	2008-10-16 01:29:41	sm5glc	Re: I need L-C filter suggestions
I just uploaded some screengrabs (in photo folder) that shows how a 3-pole Chebychev filter would look like. Center f=45 MHz, BW=500kHz and 0.5 dB ripple. http://groups.yahoo.com/group/emrfd/photos/album/901884601/pic/list First plot shows an idealistic value of Q>10e5 Second plot shows how the filter turns out with QL=200 and QC=500, not an impossible feat. Third plot shows how the fitler looks like with pretty poor Q-values, QL=125 and QC=200. What you see is how important it is to have high-Q components when designing narrow band filters, in this case a BW of ~1%. If I had to do this, I would look into helical resonators, which should provide better Q's than those in second plot, but at the cost of size. BTW, program used is Gensys with filter module by Agilent /Lasse SM5GLC