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- Date: Fri, 10 Dec 93 16:11:10 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 V93 #1447
- To: Info-Hams
-
-
- Info-Hams Digest Fri, 10 Dec 93 Volume 93 : Issue 1447
-
- Today's Topics:
- 1.5 foot Microwave Dish *HELP*
- ARRL BOOK???WHERE???
- ENDEAVOUR
- FCC's "These Rules"
- ORBS$344.MISC.AMSAT
- PC HF FAX
- Receive broadcast FM on 2m mobile antenna?
- Scratchi, January, 1960
- Scratchi article
- WANTED GR MANUAL
- WinHams in Anaheim?
-
- 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: 7 Dec 1993 13:19:38 -0800
- From: news.sprintlink.net!news.world.net!cyberspace.com!cyberspace.com!not-for-mail@uunet.uu.net
- Subject: 1.5 foot Microwave Dish *HELP*
- To: info-hams@ucsd.edu
-
- Subject: 1.5 foot Microwave Dish *HELP*
- Newsgroups: rec.radio.amateur.misc
- Summary:
- Keywords:
-
-
- Recently I purchased a surplus aircraft microwave dish and would like to use
- it. The only problem is I have not been able to find very much information
- on feeding it. I do have 2 feed horns that go to it, but am afraid that
- I will have to adapt a gunplexer! Here is the information on the dish.
-
- 91892-1
- Reflector-Antenna
- 4.4 Ghz to 10.0 Ghz
- Made by
- Stoddart Aircraft Radio Co.,Inc.
- H9ollywood California
-
- 2-Feedhorns 4.4 to 7.3Ghz & 7.3 to 10 Ghz
-
-
- ------------------------------
-
- Date: 10 Dec 93 18:53:54 GMT
- From: ogicse!uwm.edu!wupost!wuecl.wustl.edu!cec2!jlw3@network.ucsd.edu
- Subject: ARRL BOOK???WHERE???
- To: info-hams@ucsd.edu
-
- Gary Coffman (gary@ke4zv.atl.ga.us) wrote:
- : that. First and foremost they have to dumb it down to the reading level
- : of current amateurs. It's currently at about an eighth grade reading
- : level. And second, the simple CW transmitter construction projects included
-
- Wait--I don't find the handbook (1991 ed) particularly easy reading--I'm
- definitely not at the eight grade level. OK, maybe just college, but
- even so, that handbook isn't really that simple to read if you aren't
- so experienced as to be an engineer or for that matter, an Advanced--
- Granted, things like electrical theory are um. . .abbreviated, but I think
- they are for people like me, who only have limited experience in
- electrical networks.
-
- : One of the better years for the Handbook is 1962. That's the edition to
- : which I refer most often. It uses bigger words and more complex sentence
- : structure, but it should be accessable to someone who was a tenth grader
- : in 1962, or to current college graduates. It includes more ambitious
-
- Are these current college graduated assumed to have graduated in a techincal
- field. i.e. What if the graduate is a graduate in the humanities or
- natural sciences??????
-
- IMHO that 2.25 inch thick manual is plenty to start with.
-
- --jesse (not yet a ham but working on it. . .)
-
- btw, no flame intended. . .
-
- ------------------------------
-
- Date: Wed, 8 Dec 1993 22:08:22 GMT
- From: news.Hawaii.Edu!uhunix3.uhcc.Hawaii.Edu!jherman@ames.arpa
- Subject: ENDEAVOUR
- To: info-hams@ucsd.edu
-
- In article <CHpvuo.FIt@pica.army.mil> mellis@ramcad.pica.army.mil (Mark Ellis) writes:
- >
- >In article (Graham Butler) writes:
- >
- >>From: Graham.Butler@f734.n153.z1.ship.net (Graham Butler)
- >>Newsgroups: rec.radio.amateur.misc
- >>Subject: ENDEAVOUR
- >>
- >>Does anybody know what frequency/frequencies the Endeavour shuttle-craft
- >>will be using on it's latest mission to repair the Hubble?
- >> Graham (VE7 BBZ)
-
- You might want to read r.r.scanner - the folks on there are quite excited
- about hearing these transmissions on their scanners; frequencies are being
- passed on there.
-
- Jeff NH6IL
-
- ------------------------------
-
- Date: 10 Dec 93 22:16:19 GMT
- From: news-mail-gateway@ucsd.edu
- Subject: FCC's "These Rules"
- To: info-hams@ucsd.edu
-
- A few comments have appeared recently dealing with the term "these rules"
- in context of FCC 97.403 and other applications.
-
- Answer appears to be best described in FCC 0.406:
- "0.406 (a) Format. The rules are set forth in the Code of Federal
- Regulations as Chapter I of Title 47. Chapter I is divided into parts
- numbered from 0-99. Each part, in turn, is divided into numbered
- sections....
- "In citing the Code of Federal Regulations, the citation, 47 CFR 5.1, for
- example, is to para. 5.1 (in Part 5) of Chapter I of Title 47 of the Code,
- and permits the exact location of that rule. No citation to other rule
- units (e.g., subpart or chapter) is needed."
-
- As I read this, "The Rules" includes everything in Chapter I of 47 CFR,
- and include ALL of the Parts. The rules governing amateur radio are in
- part 97 of "The Rules".
-
- Paul Marsh N0ZAU "still not proven guilty of anything" Omaha
- pmarsh@metro.mccneb.edu
-
- ------------------------------
-
- Date: 10 Dec 93 16:58:00 GMT
- From: news-mail-gateway@ucsd.edu
- Subject: ORBS$344.MISC.AMSAT
- To: info-hams@ucsd.edu
-
- SB KEPS @ AMSAT $ORBS-344.M
- Orbital Elements 344.MISC
-
- HR AMSAT ORBITAL ELEMENTS FOR MANNED AND MISCELLANEOUS SATELLITES
- FROM WA5QGD FORT WORTH,TX December 10, 1993
- BID: $ORBS-344.M
- TO ALL RADIO AMATEURS BT
-
- Satellite: MIR
- Catalog number: 16609
- Epoch time: 93343.56114036
- Element set: 20
- Inclination: 51.6180 deg
- RA of node: 58.4213 deg
- Eccentricity: 0.0005383
- Arg of perigee: 74.5508 deg
- Mean anomaly: 285.6216 deg
- Mean motion: 15.58960993 rev/day
- Decay rate: 1.0605e-04 rev/day^2
- Epoch rev: 44645
- Checksum: 291
-
- Satellite: HUBBLE
- Catalog number: 20580
- Epoch time: 93343.39583333
- Element set: 379
- Inclination: 28.4711 deg
- RA of node: 14.8965 deg
- Eccentricity: 0.0005601
- Arg of perigee: 267.3006 deg
- Mean anomaly: 145.0087 deg
- Mean motion: 14.90298067 rev/day
- Decay rate: 2.98e-06 rev/day^2
- Epoch rev: 105
- Checksum: 290
-
- Satellite: GRO
- Catalog number: 21225
- Epoch time: 93341.66776924
- Element set: 4
- Inclination: 28.4617 deg
- RA of node: 121.0915 deg
- Eccentricity: 0.0031871
- Arg of perigee: 286.3791 deg
- Mean anomaly: 73.2946 deg
- Mean motion: 15.46763151 rev/day
- Decay rate: 6.624e-05 rev/day^2
- Epoch rev: 2736
- Checksum: 300
-
- Satellite: UARS
- Catalog number: 21701
- Epoch time: 93342.65260819
- Element set: 418
- Inclination: 56.9828 deg
- RA of node: 202.5066 deg
- Eccentricity: 0.0005874
- Arg of perigee: 102.5209 deg
- Mean anomaly: 257.6002 deg
- Mean motion: 14.96251149 rev/day
- Decay rate: 3.629e-05 rev/day^2
- Epoch rev: 12240
- Checksum: 285
-
- Satellite: POSAT
- Catalog number: 22829
- Epoch time: 93341.80894716
- Element set: 208
- Inclination: 98.6692 deg
- RA of node: 54.3707 deg
- Eccentricity: 0.0010935
- Arg of perigee: 37.7065 deg
- Mean anomaly: 322.4792 deg
- Mean motion: 14.27988203 rev/day
- Decay rate: 9.1e-07 rev/day^2
- Epoch rev: 1038
- Checksum: 313
-
- /EX
-
- ------------------------------
-
- Date: Wed, 8 Dec 1993 12:43:27 GMT
- From: news.cerf.net!pagesat!olivea!spool.mu.edu!howland.reston.ans.net!pipex!uknet!doc.ic.ac.uk!syma!mpfb8@network.ucsd.edu
- Subject: PC HF FAX
- To: info-hams@ucsd.edu
-
- Does anyone have the details of the hardware interface for the PC HF
- Fascimile Program, V 5.0 please.
- The audio from the HF RX is fed into the serial port but I believe there
- are
- more than one line used and I do not have the information.
- Any help or advice would be appreciated.
- TNX and 73, Peter.
-
- ------------------------------
-
- Date: 10 Dec 93 15:42:57 GMT
- From: ogicse!emory!kd4nc!ke4zv!gary@network.ucsd.edu
- Subject: Receive broadcast FM on 2m mobile antenna?
- To: info-hams@ucsd.edu
-
- In article <CHsMuy.DJH@boi.hp.com> riyadth@boi.hp.com (Riyadth Al-Kazily) writes:
- > I remember seeing combination CB/AM/FM antennas advertised in the
- >past, with some kind of isolator to prevent the CB from overloading the
- >AM/FM receiver. Is there any similar product for Amateur Radio use?
- >Otherwise, I guess I'll just buy a magnetic mount antenna for amateur
- >use -- but it sure would be nice to have a more permanent solution.
-
- Antenna Specialists carries just what you want in their *police*
- catalog. It's a "stealth" antenna for undercover work. They have
- models that exactly emulate the appearance of ordinary auto radio
- antennas for that vehicle model while actually being high band VHF
- antennas, and they still work for AM and FM reception too. They
- include the duplexer. Any AS dealer who supplies police agencies
- can order you one for your car. Installation can be a little
- tricky.
-
- Note, a center of roof mount will still work better than the cowl
- mount, but this is better than on-glass or magmount expedients.
-
- Gary
- --
- Gary Coffman KE4ZV | I kill you, | gatech!wa4mei!ke4zv!gary
- Destructive Testing Systems | You kill me, | uunet!rsiatl!ke4zv!gary
- 534 Shannon Way | We're the Manson Family | emory!kd4nc!ke4zv!gary
- Lawrenceville, GA 30244 | -sorry Barney |
-
- ------------------------------
-
- Date: Thu, 9 Dec 93 19:27:24 GMT
- From: mnemosyne.cs.du.edu!nyx10!lkollar@uunet.uu.net
- Subject: Scratchi, January, 1960
- To: info-hams@ucsd.edu
-
- >I'm not old enough to have read the "Scratchi" column in CQ when it first
- >came out, but I have seen plenty of back issues, so it never occurred to me
- >that people wouldn't realize that Scratchi was Japanese.
-
- I never saw the originals, either... but from the name & accent portrayal,
- I'd have guessed Scratchi was Pakistani or from that region.
-
- Judging, however, from the market share of American amateur radio, I'd say
- Scratchi had the last laugh.
-
-
- The article was interesting, though -- the prospective students seemed to
- be ridiculing the non-cutting-edge nature of Scratchi's equipment. And I
- thought that 1960's technology was pretty good in 1960! :-)
-
-
- Hoping to see more Scratchi articles, I am --
- --
- Larry Kollar, KC4WZK | I like CW, but that doesn't mean I think every ham
- lkollar@nyx.cs.du.edu | should have to learn it.
- "On the Internet, nobody knows you're a dog."
-
- ------------------------------
-
- Date: Thu, 9 Dec 1993 19:34:55 GMT
- From: walter!speech!dk@uunet.uu.net
- Subject: Scratchi article
- To: info-hams@ucsd.edu
-
- I've glanced at old Scratchi articles from time to time over the
- years and have always been confused as to what was being satirized.
- So I have to agree with those who are surprised at how offensive
- Greg found the posted article. What I can't agree with is the
- nature of the attacks on him. A simple, "Gee Greg, I didn't find
- the article racist - what in particular are you referring to?"
- would have sufficed. Greg had the courage to speak up and say,
- "this sort of thing may be unnecessarily hurtful to a particular
- group; let's be careful." I applaud him for that.
-
- Dan Kahn, K1DK
-
- ------------------------------
-
- Date: Tue, 7 Dec 1993 23:06:01 GMT
- From: sdd.hp.com!vixen.cso.uiuc.edu!howland.reston.ans.net!spool.mu.edu!olivea!news.bu.edu!att!att-out!cbfsb!cbnewsb.cb.att.com!wb2qoq@network.ucsd.edu
- Subject: WANTED GR MANUAL
- To: info-hams@ucsd.edu
-
- Wanted: Manual for General Radio model 1650A Impedance Bridge. Will pay for
- manual or good photocopy.
- Bob Barns, KB2IKC, (908)464-6785 Berkeley Heights, N.J. or reply via e-mail
- to Rick WB2QOQ at rja\@whamt.att.com. tnx.
-
- ------------------------------
-
- Date: Fri, 10 Dec 1993 08:48:48 GMT
- From: netcomsv!netcom.com!tcj@decwrl.dec.com
- Subject: WinHams in Anaheim?
- To: info-hams@ucsd.edu
-
- Are there any fellow amateur radio operators attending the Microsoft Win32
- Developer's Conference in Anaheim next week? If so, has a BOF frequency
- been selected? If not, might I propose 146.55?
-
- Todd, KB6JXT
-
- ------------------------------
-
- Date: 10 Dec 93 17:59:13 GMT
- From: butch!rapnet!news@uunet.uu.net
- To: info-hams@ucsd.edu
-
- References <gregCHrsuv.3Jt@netcom.com>, <jchappel.80.755465269@sanders.lockheed.com>, <gregCHtM06.AzD@netcom.com>
- Subject : Re: Scratchi, January, 1960
-
- In article <gregCHtM06.AzD@netcom.com> greg@netcom.com (Greg Bullough) writes:
- >Newsgroups: rec.radio.amateur.misc
- >Path: rapnet!butch!netcomsv!netcom.com!greg
- >From: greg@netcom.com (Greg Bullough)
- >Subject: Re: Scratchi, January, 1960
- >Message-ID: <gregCHtM06.AzD@netcom.com>
- >Organization: Netcom Online Communications Services (408-241-9760 login: guest)
- >References: <jchappel.79.755364937@sanders.lockheed.com> <gregCHrsuv.3Jt@netcom.com> <jchappel.80.755465269@sanders.lockheed.com>
- >Distribution: usa
- >Date: Fri, 10 Dec 1993 13:12:06 GMT
- >Lines: 110
-
- >In article <jchappel.80.755465269@sanders.lockheed.com> jchappel@sanders.lockheed.com (Joel Chappell) writes:
- >>
- >>Greg - This is so typical of liberal behavior. Yes it was the best without
- >>really flaming yer butt....
-
- >Well, gawwwlleeee. My butt's hottern' a leaky ol' still. What is this,
- >the 'Hampshire Hillbillies?
-
- You prove my point exactly Greg...you are guilty of what you accuse the rest
- of us of being. Golleee, maybe I'll get my first pair of shoes for
- Christmas so's I can go out and work on the antenna in the snow.
-
- >> Now when faced with the truthful part that I
- >>wrote, and that is; this is a bit of amateur radio history and was
- >>written more than 30 years ago (as pointed out to you by others), you jump
- >>to another smart remark and try to raise color as an issue.
-
- >Color *IS* the issue, you ignoramus. Look up 'race' in the dictionary.
-
- uh uh uhhh.... your doing it again Greg
-
-
- >Use the call-sign server. I did, and found I've been an active ham
- >longer than it suggests you have. You can find the same information,
- >at least if you can read the FAQs well enough to glean it. By the
- >way, how is your ad hominem argument relevant?
-
- Greg the data base just records from my last 610...I was pounding brass on
- 80 CW many years before you were born. I've got kids your age with better
- education.
-
-
- >>What do you know about the person who originally wrote the Scratchi
- >>letters? What do you know about his motives? How many other Scratchi
- >>letters have you read?
-
- >I'd invite you over to see my collection of old ham literature (I've been
- >one of those wierd collectors of the stuff since before it was popular.
- >Used to pick up QSTs at the local thrift stores.)
-
- But Greg...you didn't answer the question....who wrote Scratchi?
- What was his main motive in writing the Scratchi column? If you had all of
- these (and they were not in QST btw) you should have some idea of what the
- purpose was, what the ongoing theme was on a monthly basis.
-
- >> The answer is nothing, not much, zero..zip.
-
- >While you're looking up 'race,' look up prejudice. Your refusal to read
- >what's written, to label everything and move on, to answer your own questions
- >before hearing the answer demonstrates an inclination towards prejudice.
- >One wonders how you've managed to have any success as an engineer. Then
- >again, it is defense...
-
- Your making assumptions again..but you should be so successful!
-
- -=Joel=-
- ===
- |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
- | Joel B. Chappell - KC1SG Lockheed Sanders |
- | Principal Engineer Nashua, NH 03061 |
- | |
- | -= Standard Disclaimer: All opinions are mine. =- |
- | |
- | jchappel@rapnet.sanders.lockheed.com |
- | Fido: 1:132/204.1 |
- | |
- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
- ------------------------------
-
- Date: Thu, 9 Dec 93 19:27:56 GMT
- From: butch!rapnet!news@uunet.uu.net
- To: info-hams@ucsd.edu
-
- References <gregCHo43F.9o4@netcom.com>, <jchappel.79.755364937@sanders.lockheed.com>, <gregCHrsuv.3Jt@netcom.com>
- Subject : Re: Scratchi, January, 1960
-
- In article <gregCHrsuv.3Jt@netcom.com> greg@netcom.com (Greg Bullough) writes:
- >Newsgroups: rec.radio.amateur.misc
- >Path: rapnet!butch!uunet!tadpole.com!news.dell.com!swrinde!elroy.jpl.nasa.gov!decwrl!netcomsv!netcom.com!greg
- >From: greg@netcom.com (Greg Bullough)
- >Subject: Re: Scratchi, January, 1960
- >Message-ID: <gregCHrsuv.3Jt@netcom.com>
- >Organization: Netcom Online Communications Services (408-241-9760 login: guest)
- >References: <mac.755206284@depot.cis.ksu.edu.cis.ksu.edu> <gregCHo43F.9o4@netcom.com> <jchappel.79.755364937@sanders.lockheed.com>
- >Distribution: usa
- >Date: Thu, 9 Dec 1993 13:44:54 GMT
- >Lines: 16
-
- >In article <jchappel.79.755364937@sanders.lockheed.com> jchappel@sanders.lockheed.com (Joel Chappell) writes:
- >>
- >>Greg - You must not have been dry behind the ears the first time that
- >>Scratchi letter was published (I cleaned up my first thought). I rather
- >>enjoyed the nostalga of rereading Scratchi and I'll not allow your liberal
- >>attitude to ruin that. Go rain on someone elses parade. Take your
- >>politically correct narrow nose and poke it up the Clinton's backside
- >>instead of sticking it into a part of Amateur Radio history and trying to
- >>make it into something it is not!
-
- >Is that the best you can do?
-
- >Bet y'all miss them minstrel shows, too.
-
- Greg - This is so typical of liberal behavior. Yes it was the best without
- really flaming yer butt....Now when faced with the truthful part that I
- wrote, and that is; this is a bit of amateur radio history and was
- written more than 30 years ago (as pointed out to you by others), you jump
- to another smart remark and try to raise color as an issue. Typical liberal
- way to squirm away from the truth. I doubt that Myron had any other motive
- other than to replay a bit of that history for us. What do you really know
- about amateur radio Greg? Do you have a ticket? I have not seen your
- callsign here. What do you know about life in the USA 40 to 50 years ago?
- What do you know about the person who originally wrote the Scratchi
- letters? What do you know about his motives? How many other Scratchi
- letters have you read? The answer is nothing, not much, zero..zip. No, you
- just jumped in with your new age PC crap and raised a lot of issues without
- doing the research. Too many folks use this political correctness to white
- wash the truth Greg....and that's what I object to. And they use it to
- rewrite history books and change our social values. Now in typical liberal
- fashion you have me stereo-typed as some sort of bigot. Why I might even be
- black for all you know, or a member of some ethnic group....but you're so
- cocked sure about what I found funny about Scratchi..and it can't be good.
- Well Greg..you have no idea what I believe, what I know, what I've done..how
- well I do it...but you're guilty of what you accuse the rest of doing. Now
- you can go back to your cage and clean the egg off your face.
-
- -=Joel=-
- ===
- |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
- | Joel B. Chappell - KC1SG Lockheed Sanders |
- | Principal Engineer Nashua, NH 03061 |
- | |
- | -= Standard Disclaimer: All opinions are mine. =- |
- | |
- | jchappel@rapnet.sanders.lockheed.com |
- | Fido: 1:132/204.1 |
- | |
- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
- ------------------------------
-
- Date: Thu, 9 Dec 1993 16:21:28 GMT
- From: pravda.sdsc.edu!usc!howland.reston.ans.net!europa.eng.gtefsd.com!emory!rsiatl!ke4zv!gary@network.ucsd.edu
- To: info-hams@ucsd.edu
-
- References <1993Dec6.162309.23130@cirrus.com>, <1993Dec7.234425.4647@ke4zv.atl.ga.us>, <1993Dec8.184205.20082@ll.mit.edu>
- Reply-To : gary@ke4zv.atl.ga.us (Gary Coffman)
- Subject : Re: hypochondriac scared of cancer!
-
- I'm posting this in hopes it shows how thinking about these types of
- problems is done, and how you can sometimes get the right answers for
- the wrong reasons. The textbooks always make it look too easy. :-)
-
- In article <1993Dec8.184205.20082@ll.mit.edu> wjc@ll.mit.edu (Bill Chiarchiaro) writes:
- >In article <1993Dec7.234425.4647@ke4zv.atl.ga.us>, gary@ke4zv.atl.ga.us (Gary Coffman) writes:
- >|> ...stuff deleted...
- >|>Note that the *tower* is 70 feet tall according to our poster, but
- >|>that's not the length of the *antenna*. I'm assuming a single bay
- >|>for simplicity of calculation. That's a halfwave dipole. Now the field
- >|>strength will be maximum across a sphere with a diameter of a halfwave
- >|>that just encompasses the element because there's a 180 degree phase
- >|>shift across a halfwave and that gives maximum voltage. That also happened
- >|>to be 1 meter in my simplified calculation, but turned into 1.44 meters
- >|>in the more accurate calculation. Since field strength falls off with
- >|>the inverse of the distance, and since we know the voltage at 1.44 meters,
- >|>it's simple to find the voltage at 30.46 meters. Now the power density is
- >|>P=E^2/R. Since R for free space is 377 ohms, we have 34.92^2/377=3.23 W/m^2.
- >|>Now divide that by 100,000 to get 0.0323 milliwatts/cm^2. I slipped a decimal
- >|>there before when calculating a power ratio directly. The power density is
- >|>well below the OSHA and ANSI limits.
-
- Urp. I slipped the decimal *again*. To convert from W/m^2 to mW/cm^2
- you have to multiply by 1,000 to get the power into milliwatts and
- divide by *10,000* to get the area into square centimeters. That's
- the same as dividing by 10 so the corrected answer becomes 0.323 mW/cm^2.
-
- > Something's still wrong here. The claim that the field strength
- >half a wavelength from the transmitting antenna is equal to the square
- >root of the product of the transmitted power and the impedance of free
- >space looks like a rule of thumb with which I'm not familiar. In any
- >event, I claim that the resulting field strength figure at 100 feet is
- >off by a factor of 3.55 (I don't know if this is close enough to pi to
- >be suspicious).
- >
- > I calculate the field strength as follows (making the same isotropic
- >antenna assumption as did Gary):
-
- Note I didn't make the assumption that the antenna was isotropic.
- I assumed it to be a dipole oriented perpendicular to the line of
- sight to the window. A purpose of an antenna is to act as an impedance
- matching device between the transmission line impedance and that of free
- space. Since we know that the maximum voltage will appear across points
- separated by 1/2 wave, and if we assume the antenna is perfect, then using
- E=sqrt(Po*Rfree) should give us the voltage across a 1/2 wave of free
- space in the plane perpendicular to our line of sight to the window,
- *at the antenna*. I just realized I'm basically ignoring the fall off of
- field strength in the first 1.44 meters. That's where the difference lies,
- I can't do that. The number I got is the field strength at the dipole
- *tips*. Double aaarrrgh!
-
- > Radiated Power = 3,000 watts
- >
- > Surface Area of
- > 100-foot-radius
- > sphere centered
- > on antenna = 125,664 ft^2
- > = 11,675 m^2
- >
- > Power Flux = Power / Area = 0.2570 W/m^2
- > = 2.570 mW/cm^2
-
- 0.0257 mW/cm^2, you slipped the decimal too. :-)
-
- > Electric Field Strength = sqrt(Power Flux * Free-Space Impdnc)
- > = sqrt(0.2570 W/m^2 * 377 ohms)
- > = 9.84 V/m rms
- >
- > Note also that to convert from W/m^2 to mW/cm^2 you need to multiply
- >by 10.
-
- Divide by 10. I don't see anything wrong with your approach, aside from
- the slipped decimals. Our answers differ by about an order of magnitude.
- That's because I screwed up assuming the field at the dipole was the
- same as the field a bit over 1/2 wave away. It isn't. Just for grins,
- let's do it another way and see how the answer falls out. Let's assume
- the isotropic radiator to attempt to get the same answer. So 1 meter from
- the radiator we have a sphere of 4*pi*R^2 or 12.57 square meters surface
- area. That gives a power density of 3000/12.57 or 238.66 W/m^2 for a field
- strength of sqrt(238.66*377) or 299.96 V/m. Now divde by 30.46 to get the
- field strength at the window of 9.85 V/m. And that gives a power density at
- the window of 0.257 W/m^2. Dividing by 10 we get 0.0257 mW/cm^2.
-
- Ah, convergence. We're singing from the same songbook now.
-
- Now isotropic radiators aren't real. If we assume a cylindrical pattern
- from a dipole perpendicular to our window with no end effects, (simplifying
- again), our field strength 1 meter from the antenna becomes 353.56 V/m. And
- that puts the field strength at the window at 11.61 V/m. the power density
- becomes 0.0358 mW/cm^2 which is almost the same as the number I stumbled
- into in my original post thanks to errors of assumption and slipped decimals.
- No credit for correct answers arrived at by incorrect methods. :-(
-
- Gary
- --
- Gary Coffman KE4ZV | I kill you, | gatech!wa4mei!ke4zv!gary
- Destructive Testing Systems | You kill me, | uunet!rsiatl!ke4zv!gary
- 534 Shannon Way | We're the Manson Family | emory!kd4nc!ke4zv!gary
- Lawrenceville, GA 30244 | -sorry Barney |
-
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-
- End of Info-Hams Digest V93 #1447
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