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- Date: Tue, 25 Jan 94 19:43:33 PST
- From: Info-Hams Mailing List and Newsgroup <info-hams@ucsd.edu>
- Errors-To: Info-Hams-Errors@UCSD.Edu
- Reply-To: Info-Hams@UCSD.Edu
- Precedence: Bulk
- Subject: Info-Hams Digest V94 #75
- To: Info-Hams
-
-
- Info-Hams Digest Tue, 25 Jan 94 Volume 94 : Issue 75
-
- Today's Topics:
- Callbook Server
- CW filters and DSP-9 (4 msgs)
- Famous hams
- HDN Releases
- Internet Callbooks on line.
- SWR meters
- The DSP nobody mentioned
- What's the best Iambic paddle?
-
- Send Replies or notes for publication to: <Info-Hams@UCSD.Edu>
- Send subscription requests to: <Info-Hams-REQUEST@UCSD.Edu>
- Problems you can't solve otherwise to brian@ucsd.edu.
-
- Archives of past issues of the Info-Hams Digest are available
- (by FTP only) from UCSD.Edu in directory "mailarchives/info-hams".
-
- We trust that readers are intelligent enough to realize that all text
- herein consists of personal comments and does not represent the official
- policies or positions of any party. Your mileage may vary. So there.
- ----------------------------------------------------------------------
-
- Date: 25 Jan 94 22:01:58 GMT
- From: news-mail-gateway@ucsd.edu
- Subject: Callbook Server
- To: info-hams@ucsd.edu
-
- Willie Smith writes:
-
- >...Did the internet call book go away,...
-
- No, it hasn't vanished, it can still be reached by telnet at
-
- cc.buffalo.edu 2000
-
- (notice the word "callsign" is omitted from the address). 73
- --
- Shawn T. Conahan, Ph.D.
- N3CGT
- sconahan@ccantares.wcupa.edu
-
- ------------------------------
-
- Date: Tue, 25 Jan 1994 19:49:33 GMT
- From: agate!usenet.ins.cwru.edu!howland.reston.ans.net!cs.utexas.edu!sdd.hp.com!col.hp.com!srgenprp!alanb@network.ucsd.edu
- Subject: CW filters and DSP-9
- To: info-hams@ucsd.edu
-
- Kein{nen Paul (k23690@lehtori.cc.tut.fi) wrote:
-
- : ... I cascaded 175 Hz (-3 dB) wide
- : audio filters, three stages was still usable, but four stages sounded
- : horrible. The combined response for four stages is -12 dB at the 175 Hz
- : bandwidth or about 70 Hz for -3 dB.
-
- : The filter was used to monitor a distant VHF-beacon and thus most of the
- : time there was only noise in the passband causing this howling sound.
- : I am going to stagger tune each rection to a slightly diffrent frequency
- : to get the combined -3 dB bandwidth to 150 - 200 Hz and hope to get rid
- : of some of this howling.
-
- I think you would do better to cascade 3 stages of 300-400 Hz bandwidth
- (or 4 stages of slightly wider bandwidth.) That would give you the desired
- 150-200 Hz bandwidth with less ringing than if you stagger-tuned
- resonators with 175 Hz bandwidth.
-
- AL N1AL
-
- ------------------------------
-
- Date: Tue, 25 Jan 1994 20:31:07 GMT
- From: news.cerf.net!pagesat.net!olivea!sgigate.sgi.com!sgiblab!sdd.hp.com!col.hp.com!srgenprp!alanb@network.ucsd.edu
- Subject: CW filters and DSP-9
- To: info-hams@ucsd.edu
-
- William E Van Horne (wvanhorn@magnus.acs.ohio-state.edu) wrote:
-
- : I used crystal filters in old tube receivers for many years and always
- : thought that ringing was an inevitable result of narrow bandwidths. ...
- : I used to think that an effective bandwidth of some
- : 200-300 Hz. was about minimum and that less than that would cause so
- : much ringing that weak signals would be lost. ...
-
- : Can someone with a great deal more technical knowledge than I have
- : state just what is the minimum usable bandwidth for a 10-20 WPM CW
- : signal, and how much audible ringing is truly inescapable?
-
- For a single-resonator bandpass filter, I believe that the formula is
-
- TC = 1 / (PI*BW)
-
- Where TC is the time constant of the ringing (time it takes the tone to
- die off to .37 the initial value), PI = 3.14, and BW = 3 dB bandwidth of
- the filter. If you have a number of isolated, cascaded, identical
- resonators, then I think the above formula is still approximately correct,
- where BW is now the 3 dB bandwidth of the entire filter. Someone more
- knowledgable than I might want to post the exact formula.
-
- When all the resonators are tuned to the same frequency, the filter shape
- has a humped, or rounded response. You can think of a "flat-top" filter
- as being made of a number of narrow-band (high-Q) filters stagger-tuned
- across the passband. Since each filter has a much narrower bandwidth
- than the filter as a whole, flat-top filters have worse ringing than
- "round-top" filters.
-
- You can also make a flat-top filter by overcoupling resonators that
- are nominally tuned to the same frequency. Although it's not as easy
- to visualize, this method has exactly the same ringing problem as
- the stagger-tuned method.
-
- Bottom line: There is a tradeoff between having good pulse response
- (less ringing) with a round-top filter, versus having a flat passband and
- good ultimate rejection (but poorer pulse response).
-
- So to answer your question about minimum usable filter bandwidth:
- It depends on your desired keying speed (baud rate). 48 wpm Morse code
- results in 20 dots per second, or 0.025 seconds between dots (50%
- on/off ratio.) Let's assume the tone must die off to 5% (-26 dB) of
- its maximum value during this off time. That requires 3 time constants:
-
-
- TC = 3 / (PI*BW) ---> BW = 3 / (PI*TC)
-
- BW = 3 / (3.14*0.025) = 38 Hz
-
- For a flat-top filter, the bandwidth must be greater, as discussed above.
-
- Digital filters, whether implemented by a DSP or some other way, have a
- similar problem. If an IIR (infinite impulse response) filter is used,
- the analysis is exactly the same as with an analog filter. FIR (finite
- impulse response) filters have the advantage that the response decays
- exactly to zero at some point. (Whereas IIR and analog filters
- theoretically have an infinite "tail.") But even with an FIR
- filter, the ringing gets longer the narrower the bandwidth.
-
- AL N1AL
-
- ------------------------------
-
- Date: 25 Jan 1994 16:03:42 GMT
- From: news.cstar.andersen.com!news.acns.nwu.edu!casbah.acns.nwu.edu!rdewan@uunet.uu.net
- Subject: CW filters and DSP-9
- To: info-hams@ucsd.edu
-
- In article <CK5Jqz.2p9@srgenprp.sr.hp.com>, Alan Bloom <alanb@sr.hp.com> wrote:
- >Kein{nen Paul (k23690@lehtori.cc.tut.fi) wrote:
- >
- >
- >: Clark Savage Turner (turner@safety.ics.uci.edu) wrote:
- >
- >: > Most IF filters don't have much ring, though some, many audio filters
- >: > (except DSP I understand) can ring pretty badly.
- >
- >: What should the audio filter frequency (and phase response) look like
- >: to avoid ringing. A high-Q single stage bandpass sounds horrible, but
- >: how does a filter with flat passband (eg. Butterworth or elliptic)
- >: sound like or is it really required to use Bessel-response in order
- >: to get rid of the hollow sound produced by noise peaks.
- >
- >Another name for ringing is "pulse response" since CW dots and dashes
- >are really pulses of RF. The filter shape with best pulse response for
- >a given bandwidth is, I believe, Gaussian. This is closely approximated
- >by a series of cascaded single-resonator filters, all tuned to the same
-
- ... a few lines on filters and shape factors have been deleted for brevity ..
-
- >
- >Butterworth and Chebyshev filters have flatter passbands and better shape
- >factors, but at the expense of poorer pulse response (ringing).
-
- If we broaden the definition of ringing to allow for noisy signals, of
- the kind encountered on the low HF bands such as 80m, then there might
- be more than one source of ringing:
-
- 1. As Al described. Ringing that arises out of improper pulse
- response.
-
- 2. Progressive coloration of background white noise as the filter
- bandwidth is narrowed. Consider the following thought experiment:
- A white noise source that produces broadband output from 300Hz to 3KHz
- is fed into a fir filter. These filters have a flat phase response and
- with enough stages they have impressive shape factors. Lets say that the
- filter has a center frequency of 750Hz. As the filter is narrowed, a
- progressively pure 750Hz tone will emerge. This tone can also make
- copying a CW signal difficult.
-
- I suppose one could easily experiment by using the filter
- with signals with different Signal-to-Noise ratios.
-
- Rajiv
- aa9ch
- r-dewan@nwu.edu
-
- ------------------------------
-
- Date: 25 Jan 1994 12:58:43 +0200
- From: qualcomm.com!vixen.cso.uiuc.edu!howland.reston.ans.net!pipex!sunic!news.funet.fi!butler.cc.tut.fi!lehtori.cc.tut.fi!not-for-mail@network.ucsd.edu
- Subject: CW filters and DSP-9
- To: info-hams@ucsd.edu
-
- Alan Bloom (alanb@sr.hp.com) wrote:
-
- > Kein{nen Paul (k23690@lehtori.cc.tut.fi) wrote:
-
- [Deleted]
-
- > : What should the audio filter frequency (and phase response) look like
- > : to avoid ringing. A high-Q single stage bandpass sounds horrible, but
- > : how does a filter with flat passband (eg. Butterworth or elliptic)
- > : sound like or is it really required to use Bessel-response in order
- > : to get rid of the hollow sound produced by noise peaks.
-
- > Another name for ringing is "pulse response" since CW dots and dashes
- > are really pulses of RF. The filter shape with best pulse response for
- > a given bandwidth is, I believe, Gaussian.
-
- If the typical telegraph speeds would be 60 - 150 WPM, then the shape
- of typical CW-filters (250 - 700 Hz) would be very important. At typical
- CW-speeds (10-20 WPM) and rise and fall times (5-10 ms) the required
- bandwidth is about 100 Hz or below and thus the shape of a much wider
- (analogue) CW-filter doesn't radically alter the keyed waveform.
-
- I think that the reason for the howling sound in CW-filters is that
- in high-Q filters a noise pulse at (or close to) the center of the
- passband is causing an oscillation that slowly decays into the
- background noise. The higher the (loaded) Q is, the longer (more cycles)
- this decay takes.
-
- > This is closely approximated
- > by a series of cascaded single-resonator filters, all tuned to the same
- > frequency. Examples of a "resonator" would be an LC tuned circuit, a
- > quartz crystal, or a tuned cavity.
-
- Yes, this is true for connected resonators, but you have to control the
- connection between the resonators and the loaded-Q for each resonator to
- get the shape you want. You can get e.g. Butterworth and Chebyshev responses
- by manipulating these parameters.
-
- However, if cascade separate individual resonators (separated by amplifying
- stages or use many active filter stages) tuned to the same frequency,
- the responses of individual stages add together and the resulting response
- is similar to very high-Q single resonator. I cascaded 175 Hz (-3 dB) wide
- audio filters, three stages was still usable, but four stages sounded
- horrible. The combined response for four stages is -12 dB at the 175 Hz
- bandwidth or about 70 Hz for -3 dB.
-
- The filter was used to monitor a distant VHF-beacon and thus most of the
- time there was only noise in the passband causing this howling sound.
- I am going to stagger tune each rection to a slightly diffrent frequency
- to get the combined -3 dB bandwidth to 150 - 200 Hz and hope to get rid
- of some of this howling.
-
- Paul OH3LWR
-
-
- ------------------------------
-
- Date: 24 Jan 1994 13:10:20 GMT
- From: ucsnews!sol.ctr.columbia.edu!howland.reston.ans.net!darwin.sura.net!news-feed-1.peachnet.edu!concert!ecsgate!bruce.uncg.edu!mosier.uncg.edu!mosier@network.ucsd.edu
- Subject: Famous hams
- To: info-hams@ucsd.edu
-
- In article <2hmper$ppo@solaris.cc.vt.edu> benchoff@groupw.cns.vt.edu
- (Phil Benchoff) writes:
- >I know this has been discussed several times on this list. I am
- >looking for a list of famous hams.
-
- Here's my list, gleaned from others:
-
- SOME FAMOUS HAMS...
-
- 9K2CS Prince Yousuf Al-Sabah
- 9M1 King of Malaya
- EA0JC Juan Carlos, King of Spain
- FO5GJ Marlon Brando aka Martin Brandeaux, actor
- G3TZH Tony Dolby, brother of "the" Dolby
- GB1MIR Helen Sharman, astronaut
- HS1A Bhumiphol Adulayadej, King of Thailand
- JY1 King Hussein of Jordan
- JY2 Queen of above
- K2ORS Jean Shepard, author
- K4LIB Arthur Godfrey, TV performer (SK)
- K6DUE Roy Neal, television reporter
- K7TA Clifford Stoll, author & scientist
- K7UGA Senator Barry Goldwater
- KB2GSD Walter Cronkite, newsman
- KC4OCA Gordon Barnes, weatherman
- KD6OY Garry Shandling, comedian
- LU1SM Carlos Saul Menem, President of Argentina
- N4KET David French, CNN newsman
- N4RH Ralph Haller, FCC Public Radio Bureau chief
- N6FUP Stu Cook, baseball player
- N6KGB Stewart Granger (born James Stewart), actor
- N6YOS Priscilla Presley, actress
- NK7U Joe Rudi, baseball player
- SU1VN/P Prince Talal of Saudi Arabia
- SV2ASP/A Monk Apollo
- U2MIR/UV3AM Musa Manarov, cosmonaut
- UA1LO Yuri Gagarin, cosmonaut (SK)
- VK2KB Sir Allan Fairhall, politician
- VU2RG Rajiv Gandhi, Prime Minister of India (SK)
- VU2SON Sonia Gandhi, XYL of VU2RG
- W0ORE Owen Garriot, astronaut
- W5LFL Tony England, astronaut
- W6EZV General Curtis LeMay (SK)
- W6QYI Cardinal Roger Mahony
- W6ZH Herbert Hoover Jr (ARRL President, son of HH) (SK)
- W8JK John Kraus (astronomer/electrical engineer/antenna guru)
- WA4CZD Chet Atkins, guitarist
- WA4SIR Ron Parise, astronaut
- WA7WYV Andy Griffith, actor
- WB4KCG Ronnie Milsap, singer
- WB6ACU Joe Walsh, singer
- WB6RER Andy Devine, actor (SK)
- OE3AH Anton Hapsburg, Pretender to throne of Austro-Hungarian Empire
- KZ3Y Prophet Elijah
- VR6TC Tom Christian, great (great-great ??) grandson of Fletcher
- Christian, from the original Bounty mutineers. He lives on Pitcairn Island.
-
- EVEN MORE FAMOUS HAMS...
-
- KA9FAT The Maytag repairman
- SW1SH Inventor of the intermittent windshield wipers
- V0LVO Famous car maker (and his true QTH!)
- Mc8HAM CEO of McDonald's
- PER0T A recent presidential candidate
- AX1GOP Another recent presidential candidate
- JA3NYC Owner of Empire State Building
- VE3WON Manager, Toronto Blue Jays
- A1PIG Madonna
- IM6GUN Matt Dillon (Gunsmoke)
- N3POP Orville Reddenbacker
- KA4CNN Ted Turner
- CU5YRS Mike Tyson
- CU8YRS Jim Bakker
- N5KKK David Duke
- G3BYE Princess Dianna
- N6ET Steven Spielberg
- W2TOP/10 David Letterman
-
-
- AND SOME SILENT KEYS...
-
- K1NG Elvis Presley
- K0MOO Merlin Perkins
- W6FLY Amelia Earhart
- P0LKA Lawrence Welk
- K0ZAP Nicolai Tesla
- C0ORS Adolph Coors
- W2UAW Jimmy Hoffa
- K2SNL John Balluchi
- W8CAR Henry Ford
- W4KFC Col. Sanders
-
-
- AND A FEW OTHER FAMOUS ONES HEARD ON THE AIR...
-
- RG8U
- R2D2
-
- steve
- mosier@fagan.uncg.edu
-
- ------------------------------
-
- Date: Sun, 23 Jan 1994 11:06:10
- From: unix.sri.com!headwall.Stanford.EDU!agate!howland.reston.ans.net!usenet.ins.cwru.edu!eff!news.kei.com!news.oc.com!utacfd.uta.edu!rwsys!ocitor!FredGate@hplabs.hp.com
- Subject: HDN Releases
- To: info-hams@ucsd.edu
-
- The following files were processed Sunday 1-23-94:
-
-
- HAMPACK [ HAM: Packet Communications programs ]
- ----------------------------------------------------------------------
- APRS310.ZIP ( 652564 bytes) Automatic Packet Reporting System
-
-
- ----------------------------------------------------------------------
- 652564 bytes in 1 file(s)
-
-
- Total of 652564 bytes in 1 file(s)
-
- Files are available via Anonymous-FTP from ftp.fidonet.org
- IP NET address 140.98.2.1 for seven days. They are mirrored
- to ftp.halcycon.com and are available for 60-90 days.
-
- Directories are:
- pub/fidonet/ham/hamnews (Bulletins)
- /hamant (Antennas)
- /hamsat (Sat. prg/Amsat Bulletins)
- /hampack (Packet)
- /hamelec (Formulas)
- /hamtrain (Training Material)
- /hamlog (Logging Programs)
- /hamcomm (APLink/JvFax/Rtty/etc)
- /hammods (Equip modification)
- /hamswl (SWBC Skeds/Frequencies)
- /hamscan (Scanner Frequencies)
- /hamutil (Operating aids/utils)
- /hamsrc (Source code to programs)
- /hamdemo (Demos of new ham software)
- /hamnos (TCP/IP and NOS related software)
-
- Files may be downloaded via land-line at (214) 226-1181 or (214) 226-1182.
- 1.2 to 16.8K, 23 hours a day .
-
- When ask for Full Name, enter: Guest;guest <return>
-
- lee - wa5eha
- Ham Distribution Net
-
-
- * Origin: Ham Distribution Net Coordinator / Node 1 (1:124/7009)
-
- ------------------------------
-
- Date: 26 Jan 94 00:06:41 GMT
- From: news-mail-gateway@ucsd.edu
- Subject: Internet Callbooks on line.
- To: info-hams@ucsd.edu
-
- Hello everyone:
-
- There is an Internet accessible call sign server sponsored
- by the Rhode Island 2x2 Amateur Repeater Association, in the
- Anomaly Amateur Radio Server:
-
- telnet ns.risc.net (155.212.2.2) login:hamradio
- (BuckMaster and Buffalo Callbooks on line)
-
- 73 & DX de XE1RGL.
-
- ------------------------------
-
- Date: 24 Jan 94 22:42:28 GMT
- From: sdd.hp.com!hpscit.sc.hp.com!cupnews0.cup.hp.com!jholly@hplabs.hp.com
- Subject: SWR meters
- To: info-hams@ucsd.edu
-
- Steve Bunis SE Southwest Chicago (doc@webrider.central.sun.com) wrote:
- : Greetings -
-
- : I'm curious as to my options on getting an SWR meter. I've
- : naturally heard much about the Bird meter, but that's a pretty
- : expensive choice.
-
- I would not exactly call the Bird meter a SWR meter, although one can
- obtain the SWR from the readings. The Bird meter is an in-line wattmeter.
- reads the power to and fro, and with this information and a little work
- with the bamboo sticks one can come up with the SWR.
-
- If you want something that is approxiamate, and will give you readings
- in SWR, why not buy one of the cheapo RS swr meters? Or one of the
- other cheapo swr meters handled by HRO, AES and the like? They generally
- are quite satisfactory. Now on the other hand if you want to know your
- power out....
-
- 73, Jim, WA6SDM
- jholly@cup.hp.com
-
- ------------------------------
-
- Date: 25 Jan 1994 21:51:16 GMT
- From: agate!howland.reston.ans.net!europa.eng.gtefsd.com!news.umbc.edu!eff!news.kei.com!yeshua.marcam.com!zip.eecs.umich.edu!news2.cis.umn.edu!gaia.ucs.orst.edu!news.uoregon.edu!@network.
- Subject: The DSP nobody mentioned
- To: info-hams@ucsd.edu
-
- While a guest at the Willamette Valley DX Association meeting a few months
- ago, they had a demonstartion of a DSP filter which completely blew
- everyone away.
-
- The main difference between the particlar unit they demonstrated and all
- the other units we've heard about here on the net is that fact that the
- filtration is all software configurable.
-
- In addition to running the library of filters already included with the
- unit, you can design your own by using your PC. From what I understand of
- how it works, the computer samples the audio that you are analyizing. Then,
- this audio is displayed graphically. By highlighting the "peaks" of the
- display and drawing "cut-off" lines at the noise, you can build your own
- library of filters for various operating situations.
-
- Thus, it is possible to construct a filter for the specific characteristics
- of an individual voice (great for those skeds on crowded bands, eh?).
-
- At the meeting, a demonstration of how the filter can be used to help pull
- out extremely weak signals from atmospheric noise was also performed. In
- this instance they used a sample of a moonbounce CW signal. Without the
- filter, one would be hard pressed to even imagine the existence of a
- signal. With it, you could copy very distinctly. Don't get me wrong, it was
- still extremely weak, but you could copy it.
-
- Everyone was impressed, to say the least. Especially when they found that
- the cost was only in the $330 range. Apparently these things sold out at
- Dayton last year and the backlog on orders was phenomenal.
-
- A friend of mine, Steve, AI7W, bought one recently and here's a short
- description from him:
-
- My DSP's model is the DSP-120, it's made by Digital Interactive
- Signal Corp.. It has 8 programable filter memories and connects to
- the parallel interface of a P.C. (386 with VGA or better). It provides
- a real time audio spectrum display and a digital recording feature
- as well as providing a number of ways to custom design filters. Sets
- of 8 filter designs can be stored as files on the P.C. making it
- possible to have an almost unlimited number of filters.
-
- If you're interested in DSP, this is definitely wirth looking into.
-
- ------------------------------
-
- Date: 21 Jan 94 14:51:06 GMT
- From: noc.near.net!news.delphi.com!BIX.com!hamilton@uunet.uu.net
- Subject: What's the best Iambic paddle?
- To: info-hams@ucsd.edu
-
- It looks like the Bencher BY-x and Vibroplex Iambic models may be the
- largest sellers, but I happened to see a really intriguing iambic key
- by Schurr. It's made in Germany out of solid brass with a plexiglass
- cover. The detailing is superb to look at: everything looks hand-
- machined and fit together with precision. Then again, maybe it
- _should_ look pretty good at $150, compared to $90 or $100 for the
- Bencher and Vibroplex keys.
-
- What makes for a good key? I presume this is a matter of personal
- taste, but okay, how _do_ personal tastes run? Any advice (short of
- buying them all and trying them myself :-) on deciding which I'd
- like best?
-
- ------------------------------
-
- Date: 25 Jan 1994 18:18:20 GMT
- From: agate!howland.reston.ans.net!cs.utexas.edu!swrinde!sdd.hp.com!vixen.cso.uiuc.edu!ux2.cso.uiuc.edu!ignacy@network.ucsd.edu
- To: info-hams@ucsd.edu
-
- References <CK5Jqz.2p9@srgenprp.sr.hp.com>, <2i2u13$oud@cc.tut.fi>, <2i38ta$ki6@charm.magnus.acs.ohio-state.edu>
- Subject : Re: CW filters and DSP-9
-
- wvanhorn@magnus.acs.ohio-state.edu (William E Van Horne) writes:
-
- >Kein{nen Paul wrote:
- ..............................
-
- >Can someone with a great deal more technical knowledge than I have
- >state just what is the minimum usable bandwidth for a 10-20 WPM CW
- >signal, and how much audible ringing is truly inescapable?
-
- >73, Van - W8UOF
-
- I assume that G is an average-size letter in Morse and the
- transmission is at 120 wpm (2 characters/s). G's sound is:
-
- 111011101000
-
- where 1 corresponds to key on, and the last 3 pauses are character delmiters.
- Assuming that a single sinusoid cycle has 2 items (00, 10, 01 or 00),
- G has 6 transitions or cycles or Hz.
- So the minimum bandwith at 120 wpm would be
- 2 characters/s * 6 cycles/character =12 Hz.
- Multiple by 2-3 so that dots and dahs are flatter and (probably) by 2 if
- you want to copy the other sideband.
-
- The bandwith at 120 wpm is in the range of 24-72Hz, assuming no drift,
- no off-tuning and well shaped signals.
-
- Ignacy Misztal, NO9E
- University of Illinois
- ignacy@uiuc.edu
-
- ------------------------------
-
- Date: 25 Jan 1994 14:04:26 GMT
- From: pacbell.com!uop!lll-winken.llnl.gov!uwm.edu!vixen.cso.uiuc.edu!howland.reston.ans.net!usenet.ins.cwru.edu!magnus.acs.ohio-state.edu!wvanhorn@network.ucsd.edu
- To: info-hams@ucsd.edu
-
- References <2hrk3q$4m9@cc.tut.fi>, <CK5Jqz.2p9@srgenprp.sr.hp.com>, <2i2u13$oud@cc.tut.fi>d
- Subject : Re: CW filters and DSP-9
-
- Kein{nen Paul wrote:
-
- >If the typical telegraph speeds would be 60 - 150 WPM, then the shape
- >of typical CW-filters (250 - 700 Hz) would be very important. At typical
- >CW-speeds (10-20 WPM) and rise and fall times (5-10 ms) the required
- >bandwidth is about 100 Hz or below and thus the shape of a much wider
- >(analogue) CW-filter doesn't radically alter the keyed waveform.
-
- >I think that the reason for the howling sound in CW-filters is that
- >in high-Q filters a noise pulse at (or close to) the center of the
- >passband is causing an oscillation that slowly decays into the
- >background noise. The higher the (loaded) Q is, the longer (more cycles)
- >this decay takes.
-
- I used crystal filters in old tube receivers for many years and always
- thought that ringing was an inevitable result of narrow bandwidths. In
- fact, I though that basic information theory (Turing, Naiquist, et al.)
- dictated it. I used to think that an effective bandwidth of some
- 200-300 Hz. was about minimum and that less than that would cause so
- much ringing that weak signals would be lost. Then modern 250 Hz.
- CW filters made me realize that as little as 100 Hz. may be OK.
-
- A few months ago I built a kit of W9GR's DSP unit, described in QST
- September, 1992. One of the modes it provides is a CW filter with 30
- Hz. bandwidth. (Yes, I said 30 Hz!) It has a center frequency of 750
- Hz. and is very effective in copying CW. To my ears, it does very
- little ringing, yet is usable with quite high-speed CW.
-
- Now I doubt that the basic physical laws have been "repealed". One
- can question whether the passband is really as narrow as 30 Hz. I
- have not analyzed it on laboratory-grade instrumentation, but I have
- made a rough measure of bandwidth. Using my Kenwood TS940, I tuned
- in the carrier of a local broadcast station. With the transceiver in
- CW mode, I offset the tuning to get a 750 Hz. beat note, then tuned up
- and down, noting the frequency on the digital counter. I can verify
- that the 6 dB. bandwidth is something like 30 Hz. - certainly less than
- 50.
-
- Can someone with a great deal more technical knowledge than I have
- state just what is the minimum usable bandwidth for a 10-20 WPM CW
- signal, and how much audible ringing is truly inescapable?
-
- 73, Van - W8UOF
- * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
- * It ain't wot you don't know 't gets you into trouble. *
- * It's wot you know 't ain't true. - "Mr. Dooley" *
- * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
- wvanhorn@magnus.acs.ohio-state.edu
-
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-
- End of Info-Hams Digest V94 #75
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