RE: [Elecraft] Noise gen / Spectrogram--who invented?
Steve, GU3MBS: I recall using Rhode & Schwarz test-sets for filter alignment, also Tektronix tracking-generator and spectrum analyzer combos. Further back I recall similar devices called wobbulators used for IFs. - when was the technique of using wideband noise followed by audio or video spectrum analysis first described? - ditto, for amateur radio applications? --- I can't cite the earliest documentation, but I know that filter-analysis using broad-band noise and a spectrum analyzer combo was well known half a century ago. In '62 I designed a production test station for Lenkurt Electric using that process to align microwave filters. The difference is that those set-ups covered a good-sized workbench and would have cost us over $50,000 in today's money. The power of the PC coupled with some clever code that we can buy for almost "pocket change" has made techniques that were barely affordable to a large corporation back then almost a basic part of any Ham workshop today. The biggest short-coming of Spectrogram is the PC, too. That's what limits the usable dynamic range of the measurements to about 60 dB. It still takes better gear to do real stop-band attenuation measurements. The real advantage of Spectrogram is the visual display that is easily interpreted. It's "intuitive" by someone with a minimal understanding of what's going on. That's exactly why we spent the money on the system I built in the 60's. It needed to be operated correctly by factory alignment techs with the least chance of error and minimal 'training'. The same is true today when someone wants to set up their K2 filters. For more exacting measurements over a larger dynamic range, I still rely on a combination of either a tunable signal generator and sensitive broad-band RF voltmeter or a wide-band noise source and a tunable RF voltmeter. Indeed, when I build a filter for a project that falls within the K2's tuning range, the K2 itself makes a great tunable RF voltmeter for such a setup. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Noise gen / Spectrogram--who invented?
Good Evening Steve, I cannot remember reading anything about the use of a noise generator for "tuning" filters, but back in the early '50s we used to use a noise generator plus spectrum analyser to align 30MHz IF strips used in radar receivers. Also during the design of filters etc. We simply cranked up the noise generator that was used for noise figure measurements, and the technique was very useful also when designing antenna systems. But I have no idea from whence the concept came. But KM4DT and Tom ARE to be applauded for letting us know about Spectrogram in this day of the PC, which as I see it gives us all a low (zero) cost LF spectrum analyser. The mind boggles at the number of possible applications! 73, Geoff GM4ESD - Original Message - From: "Steven Gibbs" <[EMAIL PROTECTED]> To: Sent: Sunday, January 16, 2005 4:35 PM Subject: Re: [Elecraft] Noise gen / Spectrogram--who invented? > Tom Hammond wrote: > > I was NOT the one to find and > > suggest the use of Spectrogram... > > > In September of 1999, Alan Childress, KM4DT, first brought our > > attention to the freeware program Spectrogram, and he first > > mentioned its use in aligning the K2's CW filters. Because it > > was such a radical concept, > > Yes, thanks Tom for setting out the facts, and our thanks to KM4DT. > > Do Elecraft listers know of earlier mention of this technique in > the amateur or professional literature? > > If not, then KM4DT deserves an even BIGGER accolade. In any case, > many will acknowledge that making filter & BFO adjustent so > straightforward has contributed greatly to the K2's success. > > 73, Steve GU3MBS. > ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Noise gen / Spectrogram--who invented?
On Sun, 16 Jan 2005 14:27:51 +, Steven Gibbs wrote: >I recall using Rhode & Schwarz test-sets for filter >alignment, also Tektronix tracking-generator and >spectrum analyzer combos. Further back I recall >similar devices called wobbulators used for IFs. > >- when was the technique of using wideband noise > followed by audio or video spectrum analysis first > described? > >- ditto, for amateur radio applications? For roughly 35 years, pink noise and real time analyers have been used to evaluate the amplitude response of audio systems and and equipment, adjust system equaliztion for a desired response. In the late 60's, the late Dick Heyser developed and patented a powerful analysis technique the he called "Time Delay Spectrometry," whereby a generator and narrowband detector were swept at the same rate, but with time offset that could be set by the user. This allowed coherent measurement of two-port systems -- that is, magnitude and phase -- and it also allowed the direct sound of a loudspeaker to be separated from reverberation in a room. Heyser demonstrated the technique to the pro audio community using a collection of HP and GR gear that filled a van. It took about ten years before Bruel and Kjaer built a dedicated product to do it. Crown Int'l introduced a dedicated product in 1982. Although it wasn't widely known, that box included FFT capability, and many of us, including myself, used the FFT capability for various functions. About that time, a number of folks began using single channel and dual channel FFT analyzers to to analyze and tune sound systems. With the single ended technique, the source was usually pink noise and you got only an amplitude response. With dual channel analysis, one could compare any excitation signal (including program material) with the output. These two forms now dominate the landscape in pro audio. A program called Smaart, at least some of which was written by a programmer who had been associated with the Crown box, was introduced at least ten years ago. It runs on any Windoze box, and uses the sound card for I/O. It is QUITE widely used to tune live systems. Nearly 25 years ago, I used my portable real time analyzer to determine the response of systems where I had access to both input and output. The analyer could store and display two measurements, and I subtracted them point by point to get the system response. I did this with the telco links between the Chicago FM Club's 146.76 repeater and two remote receivers in the late-70's -- the input was my radio listening to a station on the input, the output was the same radio listening to the repeater output. We then adjusted an equalizer at the repeater site to optimize (or at least improve) system response. I also used the technique professionally to analyze the response of the duplication systems used for TV spots. There are now dozens (hundreds?) of FFT programs written to run on PC's, and for use in many disciplines. Spectrogram was written to facilitate the analysis of bird calls! A very powerful new one called EASERA, for which I have been a beta tester, was written by some good friends in Berlin. It is primarily a tool for acoustic testing, but from a single log sine sweep, it can quickly computer and display harmonic distortion vs. frequency, BY HARMONIC ORDER! Jim Brown K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Noise gen / Spectrogram--who invented?
Tom Hammond wrote: I was NOT the one to find and suggest the use of Spectrogram... In September of 1999, Alan Childress, KM4DT, first brought our attention to the freeware program Spectrogram, and he first mentioned its use in aligning the K2's CW filters. Because it was such a radical concept, Yes, thanks Tom for setting out the facts, and our thanks to KM4DT. Do Elecraft listers know of earlier mention of this technique in the amateur or professional literature? If not, then KM4DT deserves an even BIGGER accolade. In any case, many will acknowledge that making filter & BFO adjustent so straightforward has contributed greatly to the K2's success. 73, Steve GU3MBS. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Noise gen / Spectrogram--who invented?
I know we must all thank N0SS for suggesting this tecnique using the Spectrogram program for K2 filter & BFO setting, and also for providing a circuit and pcb for a suitable noise generator. -- A LOT better than the other methods I mentioned above. I may have come up with using the noise generator as a signal source (truthfully, I don't recall any more), but I was NOT the one to find and suggest the use of Spectrogram... wish I had though... heheheh! In fact, here are a couple opening paragraphs from my docs... trying to give credits where it's really due... In September of 1999, Alan Childress, KM4DT, first brought our attention to the freeware program Spectrogram, and he first mentioned its use in aligning the K2's CW filters. Because it was such a radical concept, I think his comments tended to fall on deaf ears. Later, both W3GDZ and I wrote instructions for using Spectrogram (http://www.visualizationsoftware.com/gram.html1), to align the Elecraft K2's CW filters. Subsequent to both of those sets of instructions, Don Wilhelm, W3FPR, posted a fine description of the procedures he'd used to align his K2 for SSB reception, using Spectrogram. Again, it fell thru the cracks of the reflector and was lost. I doubt that many K2 owners picked up on it, and that's too bad. So, in response to several more recent requests, and in order to not have to re-write an individual paper for each future response to the subject, I am going to attempt to use Don's basic procedure and then set down some simple steps for basic alignment of the K2's SSB filters using Spectrogram. (I hope I can do justice to Don's initial efforts). 73, Tom ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
