298	2007-01-04 04:14:14	neomag_magneo	Bandpass filters with series resonators: a problem in the design
Message	Date	From	Subject
Hello group! Thanks for the advice concerning the H-mode mixer transformers! Another problem still bothers me: I have tried to reproduce the filter designs (triple tuned circuit, series resonators) as given for the Lichen transceiver in EMRFD. The MathCad sheet (or its equivalent in Excel spreadsheet) seems to fail when the numbers for 80 m TTC are plugged in, the bandwidth cannot be more than 500 kHz. When analyzing the very filter with GPLA or equivalent, it seems to work as expected, anyhow. Is there something wrong with the MathCad formulas, or have I missed something. All my efforts with parallel resonators have been quite succesful thus far (receicer preselectors and BPFs for transmitters), but now I am really stuck ! 73 de Heikki (OH2LZI)
300	2007-01-04 15:21:45	Wes Hayward	Re: Bandpass filters with series resonators: a problem in the design
Hello Heikki, et al, Many thanks for the comments regarding the MathCad sheet on my web site. There is no error, but there is a problem. For most readers who have not been chasing this issue, this is not directly about what is in EMRFD. Rather, it regards an extension on my web site having to do with the design of higher order filters using the EMRFD programs. That piece includes some MathCad sheets that show the equations for the design of double and triple tuned circuits that have series resonators. A problem shows up when you insert the filter parameters for a filter with center frequency of 3.75 MHz using 15 uH inductors with a Q of 50 and a filter bandwidth of 700 kHz. Dropping the bandwidth to 600 kHz produces a viable filter. I have updated the discussion on my web site. See http://users.easystreet.com/w7zoi/80bpf.html The problem comes about with wide bandwidth which sometimes produces a negative value inside a square root symbol. This then generates a complex capacitor value. The programs include k and q values for Butterworth filters. If Chebyshev k and q values are substituted, the complex valued capacitors are avoided. Chebyshev k and q data are available in Zverev's text, other texts, or are generated by a routine built into XLAD, the crystal filter program included with EMRFD. I analyzed the filters in Fig 6.135 of EMRFD and the values shown there are OK. Hope this helps. 73, Wes w7zoi
301	2007-01-05 03:50:57	neomag_magneo	Re: Bandpass filters with series resonators: a problem in the design
Hello Wes and others, First, my apologies for not referring to the W7ZOI-website where the Mathcad stuff can be found. Thanks for the clarifications, it seems that I just have encountered one of the inevitable limitations in current design methods. I agree with Wes that all the filters given Fig 6.135 of EMRFD should be OK, I have analyzed (with AADE Filter Design, freeware, highly recommended !!!) the 3.75 MHz version and also built one with results very similar to the simulated frequency response. This very filter, however, (with the component values given in the EMRFD table), cannot be an outcome of the Mathcad-procedure (for the reasons explained by Wes), and this is what made me doubt the whole method in the first place. When the bandwidth is reduced, a viable filter can be designed. The only problem lies in the Q-value (50) which is kinda low for toroids, at least. Furthermore, the whole design is highly dependent on this Q-value, which in my opinion, should be as high as possible. I have a feeling that the true problem is the high inductance value which could be reduced by a factor of two at least. The similar filter found in the Triad tranceiver (or its predecessor CDG 2000) has 8 uH inductors for the same bandwidth. Also switching into Tchebyshev-response (with 0.1 dB ripple) does the job, even with 15 uH inductors. I cannot quite understand the popularity of Butterworth, when better equal ripple filters are available with similar effort, the small ripple should be tolerable in most applications... In summary, the design methods do require some learning effort, and in that sense this short episode has been most educative for me, at least. From that viewpoint, I was actually lucky to get stuck with the single example not fully compliant with the design mathod given. A good starting point for an average design might be a reasonable inductor, following that rule I would not have encountered the problems with fitting some 55 turns on a T50-coil form to make the magic (!) 15 uH inductor, hihi. Finally I tried a 4th order series resonator filter design as proposed by Wes in the wed-article and got some nice results. After building quite a few parallel resonator filters with almost zero top coupling required, I will aplly this new (?) method for the receiver under construction. Best regards Heikki (OH2LZI) P.S. There is an active group and website in Scandinavia, the aim is an ssb-tranceiver utilizing currently available smd-components, DDS etc. The stuff can be found starting at: http://radio.thulesius.se/QROlle/ The language is variable, some English, too ! The transceiver is also available in kit form, as the trend seems to be these days. Personally, I am no real fan of any construction kits, but only wanted to inform the group of the activities on this side of the pond.
302	2007-01-05 12:38:18	Wes Hayward	Re: Bandpass filters with series resonators: a problem in the design
Hi Heikki (and the group), One of the fun and exciting things about filters is that as we get deeper into any part of it, we start to see more and more about the complexities. As the risk of making things even more complex, I expanded the triple tuned circuit part of my web page to include some Chebyshev filter designs. That turned out to be most interesting. By allowing a passband ripple of 1 dB, it was possible to extend the bandwidth of the filter we have been considering to 1.34 MHz. I put the details on my web page, and included some plots of S21 and S11 for a filter with very high Q inductors. The only change of significance when a low Q=50 inductor is used is increased passband loss. You are correct -- we do always want to go for Q values as high as we can get. But this brings problems. The high Q elements are often larger than we would want. They can become expensive. I picked a Q of 50 for these 15 uH inductors because it is possible to purchase inexpensive RF chokes with this L value that have this Q. When we use them in a wide band filter, the loss is not an issue. I'm not sure that it is valid to call the CDG-2000 a predecessor to the Triad transceiver. G3SBI, W4ZCB, and W7AAX were working on the the Triad as early as 1995, if not before. It has been kicking around for a long time, much of it the result of the early H-Mode Mixer work of Colin, G3SBI. I don't recall when the CDG-2000 made it into print. I think that it generally followed from the front end work of the Triad. W4ZCB may be able to shed light on this. The CDG-2000 includes a lot of other details, especially in the DSP area. The later variation is the STAR. While I have not kept up on it, this design has become very popular. I believe it also uses the same G3SBI front end topology. Many thanks for the link to the Finish transceiver. That should be an interesting one to investigate. 73, Wes w7zoi
304	2007-01-06 06:50:52	w4zcb77	Re: Bandpass filters with series resonators: a problem in the design
> By allowing a passband ripple of 1 dB, it was possible to extend the > bandwidth of the filter we have been considering to 1.34 MHz. > > I put the details on my web page, and included some plots of S21 and > S11 for a filter with very high Q inductors. The only change of > significance when a low Q=50 inductor is used is increased passband > loss. Wes, I always attributed Chebychev "ripple" with return loss. (ie, 0.044 dB specified ripple will yield a 20 dB S11) I haven't been following the thread sufficiently closely to understand where you're going with this, wouldn't another topology be prefered for the goals? > > > I'm not sure that it is valid to call the CDG-2000 a predecessor to > the Triad transceiver. G3SBI, W4ZCB, and W7AAX were working on the > the Triad as early as 1995, if not before. It has been kicking > around for a long time, much of it the result of the early H-Mode > Mixer work of Colin, G3SBI. I don't recall when the CDG-2000 made > it into print. I think that it generally followed from the front > end work of the Triad. W4ZCB may be able to shed light on this. > 73, Wes > w7zoi > Well, It all started with Makhinsons HDR in the fall of 1990 Communications Quarterly. (I miss that almost as much as I miss Skip Tenney's "Ham Radio".) That started Colin G3SBI to thinking (He's a great outside the box thinker!) and he shortly removed the signal path from the LO path with his "H" mode mixer. Initially performed with the SD-5000 from Siliconix, it blossomed with the advent of the quad buss switches as in the FST 3125/6 series. (And is now progressing very interestingly with the FSAV 332 series and his new fundamental frequency squarer.) If we wait just a bit more patiently, technology is going to solve all our problems, but my personal definition of Hell is to have the perfect radio and no interesting hams with which to have an intelligent QSO. I still have a shop SD-5000 receiver, Ip3 measured >+50 dBm, and no, I didn't measure that, Colin did with the Queens finest test equipment. My capabilities poop out in the vicinity of +40 and even that somewhat depends on which cheek I hold my tongue in. Bill and I communicated with Colin as early as 1993, and I met him first time on a visit to Manchester in 1996 when Alice and I travelled to the UK celebrating our 50th anniversary. We trekked to Darsbury Labs where he measured my first efforts. The CDG 2000 was an effort spearheaded by George Fare, G3OGQ and a superb homebrewer despite a career in a totally different discipline than electronics, and Dave did a magnificent job on the software and controller for the transceiver. A three handed effort, not bad for a product that transcends most of todays commercial efforts with staffs of hundreds, but then, they didn't have to bring out a new radio every 30 minutes.. The radio was published in RadCom, the RSGB's equivalent of QST in a 3 part series in October, Nov and Dec of 2003. I know that Dave has done some work on a DSP package for the radio, but am not aware of anything published on that addition. The PicaStar, G3XJP's magnificent project spanned some 20 issues of RadCom, starting with the first in June of 2003. By that time, 8 of us in the Beta group had finished 8 beautiful DSP transceivers and were enjoying a truly unique experience. A radio that kept being reborn with every new issue of Peters software. I've had something like 20-25 new radios in the last 4 years despite my trusty dusty old Signal One serving me rather faithfully for over the previous 20. (Those 20 issues of RadCom would have had me turn in my life membership in QST if it had only been printed on heavier paper and in standard US sized magazines so it would fit my bookcase.) The Picastar Yahoo group is now nearing 1000 members and the radio transceiver is being built in many countries. The Ukraine has several, a large group of students in Syria are building them as a part of their head of department in the EE school of Engineerings efforts. There are presently two operational in the US and only one in Canada, but the list of European constructors is a very large number indeed. Peter is presently working diligently on a STAR II, second generation DSP radio, using the original hardware as a vehicle, there's a whole new paradigm around the corner. > > Regards to the group W4ZCB