RE: [Elecraft] here is how to get a feel for a roofing
Hi Brett, your questions are interesting but they requires many words to clarify them... I will try to give you simple answers and may be other friends will add replies. Message: 22 Date: Wed, 02 May 2007 11:38:44 -0400 From: Brett gazdzinski [EMAIL PROTECTED] Subject: RE: [Elecraft] here is how to get a feel for a roofing filter To: elecraft@mailman.qth.net Message-ID: [EMAIL PROTECTED] Content-Type: text/plain; charset=US-ASCII Is there no way to put dsp at/as the first filter? Yes, more or less. This is High Performance Software Defined Radio solution where you connect the ADC to the antenna, then a DSP is handling all the demodulation of signals, manage the filters and notches, once this works (software) is completed the voices or dit dah willa come out from an audio amplifier and on to the loudspeaker(s). K3 is on the hardware and software transmitter and receiver group. What are the limitations of the dsp, frequency, filter quality? Is there a problem getting dsp to work at say 455 khz? Putting the DSP (including ADC and DAC) at 455kHz is not a problem as the key is the ADC frequency limit. There will be not too much difference between havin the IF at 455kHz or 15kHz as the major work will be done by the software application. What would be the result of a real good variable filter at the 8.215 Mhz IF just after the mixer and NO dsp for filtering? (K2?) The result will be a K2 with a higher IF. DSP is a powerfull stage (including the software) to generate filters at audio level. No ringing with narrow filters and soft to straight attenuation skirt better than xtal filters. The 2nd IF of 15 khz is audio, is it not? NO. certainly if you have a good ear you can listen to something... It is an electrical Frequency like the ones used for submarine communications and other services. At what point does the audio spectrum end and RF begin? The RF (IF) ends inside the Analog to Digital Converter (ADC)... then you have digital signals handled by the DSP (and SW). The audio start at the output of the Digital to Analog Converter (DAC) I notice that the K3 info says the dsp is in the 2nd IF, but the 2nd IF is high pitched audio? Even if the 15kHz is a frequency that has an equivalent in the audio, it is a real IF and the conversion to this second IF is done by a second mixer converting from 8.250MHz to 15kHz, more or less like an SSB/CW demodulator. This modern stuff sure spins my head, the homebrew receiver is a single conversion to 455khz, no rf amp, good filter just after the mixer, wide IF chain, detector. It seems to work real well, and is basically the old tube table top radio (all American 5?) with a good filter, s meter, and a digital frequency readout. I know what you mean ... I am an analog chap and do not like a PC in my radioshack ... but I am fiddling with it, on and off to learn what SDR, Software Defined Radio con do ... today we can play with an analog mixer that converts from HF to audio...yes the stuff that comes out from the loudspeaker ... and then you have a BIG DSP ASSY ... the Audio Card (Stereo) a Big PC and a Software application that may make you crazy to look at the PC screen ... Soon all this type of SDR will become obsolete like a valve receiver because the receiver will be nearly 100% all digital ... the only analog stuff will be the antenna, the bandpass filters and the loudspeaker ... plus a BI and Powerfull PC. At this point you will have to change operating technique as you will be able to operate with several stations and your roofing filters will be your BandPass Filters ... our good friends at INRAD will retire and we will be able to buy second hand surplus xtal filters for a couple of dollars (I hope .. hi) I hope I was able to clarify at least partially your right questions BTW, if you can fidlle with a soldering iron and have a K2 I can send you a working front end mod (1st mixer replacement) that can improve it to an IP3 of +27dBm , from a +15dBm value, and the addition of a xtal homebrew roofing filter at 4.9xx MHz. 73 Gian I7SWX Brett N2DTS __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ 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] here is how to get a feel for a roofing
F.Y.I. I know of at least two experimental ANTENNA -- DSP designs that are out there being tested: HPSDR Mercury design http://hpsdr.org/mercury.html and Phil Covington N8VB's QuickSilver QS1R/QS1T design http://pcovington.blogspot.com/2006/12/qucksilver-qs1r-software-defined.html de ken n9vv Is there no way to put dsp at/as the first filter? Yes, more or less. This is High Performance Software Defined Radio solution where you connect the ADC to the antenna, then a DSP is handling all the demodulation of signals, manage the filters and notches, once this works (software) is completed the voices or dit dah willa come out from an audio amplifier and on to the loudspeaker(s). ___ 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] here is how to get a feel for a roofing
Additional comments on using an A/D at the front end of a radio. High Speed A/Ds that can handle the wide dynamic range of radio signals are still an art form. Any A/D suffers from the need to have filtering in front of it to avoid a malady known as aliasing. In A/D theory, without band limiting the signals into the A/D, it might try to convert signals out of the band you want, as well as the in band components. You could have the unwanted freqeuncies be the same spacing from the converter clock frequency, as the desired signals, and then they fold into the band of desired signals, but would be like noise or interference. The clocking of the A/D conversion, (the switching speed) must be at least twice your highest desired frequency, and preferably four times the highest in band frequency. The clock must be stable, and not have jitter. For a 30 MHz radio, you might then need a clock of 120 MHz. This has the aircraft band among others, below the clock frequency, and there is the FM broadcast band, as well as low band public safety communications. In other words, a lot of undesired signals that could fold into the desired HF bands when using an A/D. For this reason, as an Anti-aliasing filter we DO put a high quality filter in front of precision A/D converters, to limit the signals to those of interest to us as an HF radio. Thus, the need for a roofing filter is not restricted to just an analog radio, but enters in for direct digital conversion as well. If you Google search for Analog to Digital Conversion you will get many white papers and tutorials on all the faults of A/D processes. That is why they are not common in radios yet at front end RF frequencies. You need many bits to handle a radio's dynamic range, or you need programmable gain amplifiers to keep the incoming signal up at the optimum amplitude for the range of the A/D system. -Stuart K5KVH ___ 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
[Elecraft] here is how to get a feel for a roofing filter
Hi all: I knew this would be a tough one for many (most). Try this on for size Imagine that you walk into a very large office space (the band), filled with desks and a hundred people working at those desks. You sit down at a desk in the middle of the room. At first, nobody is talking (everyone is tuning the band). You sit down at a desk in the middle of the room and you strike up a conversation with the person next to you (one qso on the band). You can easily hear them. Now assume that five other deskmates (hams) within the room (band) also start talking and that they are randomly distributed about the room (the band). Your conversation will likely continue without issue. But maybe, ONE of the other conversations if taking place only 5 desks (kc) away form yours. It's a bit annoying. What to do? Well, you would ask your conversation-mate to talk louder (run more power), move to another desk (qsy), or you could put up some walls around the four desks adjacent to you (make a big cubicle). This helps to shut out some of the adjacent conversation (you narrow a conventional IF filter). If another conversation strikes up only 3 desks away from you, you might compensate by making the cubicle even smaller - say around just your two desks (narrow the conventional IF filter even more). Now assume that everyone in the room is communicating verbally with another person. A few people are whispering to each other (qrpers), some are at normal conversation levels, many are shouting (KW), and some are screaming at the top of their lungs (you know who they are). You have already build the smallest cubicle possible, but the other 99 conversations are still audible. You can not actually understand the other conversations, but the noise (IMD) is clearly there and making it hard or impossible for you to hear the person you are talking with. What to do? One solution is to make a smaller room with the big room (add a roofing filter). You might build a sound-insulated, concrete room that is one-tenth of the original size, but housed within the big room. This must mean that there are fewer other conversations within ear-shot because there are fewer desks in the new sub-room. So...lets suppose that you now have your smaller room built within the larger room. You now discover that there are NO other conversations that are so loud that you can hear them. In fact, it is so quiet now, that you can even take down your cubicle walls (open up - widen - the conventional IF filter) and still hear your own conversation without any other noise (IMD). [By the way, noise here = IMD squeaks, pops, bleeps, boops, etc., not static crashes or ignition noise, etc] Let's go back to the beginning. If you are having your solitary conversation in the original GIANT room and then build a walled-off section (sub-room), you WON'T notice any difference because it was quiet to start with and making your private room (smaller part of the big room) had no impact. It is still just as quiet after the new walls are put up. In other words, you can NOT hear the difference that a roofing filter makes unless there are lots of other LOUD signals within the first (typically broad) IF. I can guarantee you that Wayne and Eric will get complaints that the roofing doesn't work because folks just don't understand it's purpose. They will say (and I'll take bets on this), I don't hear any difference whether I use the wide or narrow roofing filter. And they'll be correct. Hope this analogy makes some sense for you. de Doug KR2Q ___ 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] here is how to get a feel for a roofing filter
REALLY nicely done, Doug. An excellent analogy. And I would wager heavily on the correctness of your prediction. ;-) Bill / W5WVO DOUGLAS ZWIEBEL wrote: Hi all: I knew this would be a tough one for many (most). Try this on for size Imagine that you walk into a very large office space (the band), filled with desks and a hundred people working at those desks. You sit down at a desk in the middle of the room. At first, nobody is talking (everyone is tuning the band). You sit down at a desk in the middle of the room and you strike up a conversation with the person next to you (one qso on the band). You can easily hear them. Now assume that five other deskmates (hams) within the room (band) also start talking and that they are randomly distributed about the room (the band). Your conversation will likely continue without issue. But maybe, ONE of the other conversations if taking place only 5 desks (kc) away form yours. It's a bit annoying. What to do? Well, you would ask your conversation-mate to talk louder (run more power), move to another desk (qsy), or you could put up some walls around the four desks adjacent to you (make a big cubicle). This helps to shut out some of the adjacent conversation (you narrow a conventional IF filter). If another conversation strikes up only 3 desks away from you, you might compensate by making the cubicle even smaller - say around just your two desks (narrow the conventional IF filter even more). Now assume that everyone in the room is communicating verbally with another person. A few people are whispering to each other (qrpers), some are at normal conversation levels, many are shouting (KW), and some are screaming at the top of their lungs (you know who they are). You have already build the smallest cubicle possible, but the other 99 conversations are still audible. You can not actually understand the other conversations, but the noise (IMD) is clearly there and making it hard or impossible for you to hear the person you are talking with. What to do? One solution is to make a smaller room with the big room (add a roofing filter). You might build a sound-insulated, concrete room that is one-tenth of the original size, but housed within the big room. This must mean that there are fewer other conversations within ear-shot because there are fewer desks in the new sub-room. So...lets suppose that you now have your smaller room built within the larger room. You now discover that there are NO other conversations that are so loud that you can hear them. In fact, it is so quiet now, that you can even take down your cubicle walls (open up - widen - the conventional IF filter) and still hear your own conversation without any other noise (IMD). [By the way, noise here = IMD squeaks, pops, bleeps, boops, etc., not static crashes or ignition noise, etc] Let's go back to the beginning. If you are having your solitary conversation in the original GIANT room and then build a walled-off section (sub-room), you WON'T notice any difference because it was quiet to start with and making your private room (smaller part of the big room) had no impact. It is still just as quiet after the new walls are put up. In other words, you can NOT hear the difference that a roofing filter makes unless there are lots of other LOUD signals within the first (typically broad) IF. I can guarantee you that Wayne and Eric will get complaints that the roofing doesn't work because folks just don't understand it's purpose. They will say (and I'll take bets on this), I don't hear any difference whether I use the wide or narrow roofing filter. And they'll be correct. Hope this analogy makes some sense for you. de Doug KR2Q ___ 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 ___ 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] here is how to get a feel for a roofing filter
The confusion here may be primarily one of semantics. The K3's main narrow IF filters -are- the first filters seen after the first mixer, just like those in the K2. Our first IF at 8.215 MHz acts as our primary narrow IF filter stage and can also be considered our roofing filter stage, since it is followed by the DSP IF and its additional filtering. We had so many questions about what our 'roofing' filters were on the K2 and K3, that we decided to refer to the 8.215 MHz narrow filters as roofing filters. Since they are the first IF filter this is also technically correct. :-) In our case, since the roofing filters ARE the main, narrow, IF filters (just like the 4.915 1st IF filter is in the K2), dynamic range is measured for signals OUTSIDE the filter b/w, not inside. The K3's 1st IF (8.215 MHz) can easily use a crystal filter down to 200 Hz. Higher frequency first IF stages in other radios are limited to about 3 kHz minimum and typically use filters in the 5 kHz to 10 kHz width range. They only have one filter at their 1st IF (their roofing filter) so it has to be at least wide enough to handle SSB. Plus it is very difficult to make a filter narrower than 3 kHz economically at an IF of 40-70 MHz. On traditional up-converting IF radios with wide (=3 kHz) roofing filters at their first IF (40 MHz to 70 MHz) the interfering signal can easily be inside their first roofing filter but outside their next stage narrow (500 Hz etc) IF filters. This causes havoc with the stages between their roofing filter and their narrower IF filters. (The ARRL test sweeps to 1 kHz away with a 500 Hz main IF filter.) 73, Eric WA6HHQ Elecraft ___ 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] here is how to get a feel for a roofing filter
Hello Brett! Is there no way to put dsp at/as the first filter? What are the limitations of the dsp, frequency, filter quality? Is there a problem getting dsp to work at say 455 khz? To answer these questions would take a textbook! Or at least a very long essay. The short version is: there are many ways to design a radio, and to partition the analog and digital circuitry. We chose a design architecture that provides world-class performance at a realistic cost. What would be the result of a real good variable filter at the 8.215 Mhz IF just after the mixer and NO dsp for filtering? (K2?) It would be a K2 without the KDSP2 :-) The 2nd IF of 15 khz is audio, is it not? The use of a final IF in the 12 kHz to 40 kHz range is used by virtually every manufacturer of DSP-equipped radios. There are solid technical and economic reasons for this. 73, Lyle KK7P ___ 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
