Date: Mon, 25 Jul 94 04:30:17 PDT From: Ham-Ant Mailing List and Newsgroup Errors-To: Ham-Ant-Errors@UCSD.Edu Reply-To: Ham-Ant@UCSD.Edu Precedence: Bulk Subject: Ham-Ant Digest V94 #238 To: Ham-Ant Ham-Ant Digest Mon, 25 Jul 94 Volume 94 : Issue 238 Today's Topics: ??Loop or dipole ..BEST?? DDRR antenna for Radio Astronomy Feed lines and AC power How to match 2-meter 1/2 wave Jupiter decametric emission info Log Periodics ? mfj 1796 Send Replies or notes for publication to: Send subscription requests to: Problems you can't solve otherwise to brian@ucsd.edu. Archives of past issues of the Ham-Ant Digest are available (by FTP only) from UCSD.Edu in directory "mailarchives/ham-ant". 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: Mon, 25 Jul 1994 03:44:06 GMT From: ihnp4.ucsd.edu!library.ucla.edu!news.ucdavis.edu!chip.ucdavis.edu!szhall@network.ucsd.edu Subject: ??Loop or dipole ..BEST?? To: ham-ant@ucsd.edu I am interested in someone's comment on the following..Right now I have a dipole about 15 feet off the ground and I considering in making a hortizonal loop around the lot of my house 15 feet off the ground..Would the loop be that much better?? It has to be a hortizonal loop I can't put up a vertical loop. I almost forgot this for HF 10-40 meters...thanks for reading this...73es..Jeff ------------------------------ Date: Sun, 24 Jul 1994 23:04:33 GMT From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!agate!dog.ee.lbl.gov!newshub.nosc.mil!news!aburto@network.ucsd.edu Subject: DDRR antenna for Radio Astronomy To: ham-ant@ucsd.edu ------- In article <32964@uswnvg.uswnvg.com> tconboy@uswnvg.com (Terry A. Conboy) writes: >Just take all the dimensions and multiply them by (21.6/25.2)=0.857 >To be exact, this should include the diameter of the tubing, but you >probably can get away with using the same tubing as the original. Thanks, and thanks to all the others that sent email too. Appreciate your help. Didn't know about the tubing diameter relationship. I'm new at this. Actually I got a slightly bigger piece of copper tubing (3/8 inch vice 1/4 inch). It just 'seemed' more copper would be better but I really didn't know. Also I just assumed 14 wavelength at 25.2 MHz to get the copper tubing length (117 inches), but I read in the ARRL Antenna Book that the actual frequency (from empirical experience) will be at least 5% less due to stray capacitance. So I made the tubing length 111 inches instead. I built the antenna already out of 3/8" soft copper tubing, 1+1/4" PVC pipe, and fine mesh screen wire. It looks good. I'm not sure it really works :-), but I leaned the antenna over last night so it would look at Jupiter and listened to noise for several hours. I got excited once when the noise level went up 5 dB, but when I switched to WFM I heard voice. Other than that I heard nothing. I'm building a crude mount for it with axis aligned East-West so I can rotate the 'beam' up and down to (ahem) 'lock' on to Jupiter :-). Oh well, it is fun and it cost only $70 to build with coax cable and connectors and all. >Actually, I am surprised that they are using this antenna for radio >astronomy. It functions as a very short vertical antenna with a >capacity hat, so it radiates best at the horizon and minimally straight >up. In general, vertically polarized antennas are great for receiving >man-made noise, which could obscure the emissions you want to hear. But >maybe I don't fully understand the application... I'm glad you raised this point as I'm wondering too. I'm new at this and I don't really (exactly) know what I'm doing. In the Radio Astronomy Journal article the antenna was referred to as a "DDRR Loop Antenna". However when I looked up DDRR antennas in the ARRL Antenna Book and in magazine articles in QST and Electronics I found that the DDRR was similar to but in detail really different from the antenna I was trying to build. >It could be that your design is not the classic DDRR. It could be the >classic "halo" antenna (which is a horizontally polarized half >wavelength bent into a loop with the ends *almost* touching) mounted >above a ground plane to give it about 3 dB gain straight up. I would >expect that to work great in your application. > I'm probably building the classic "halo" antenna, but if it is 1/2 wavelength then what I built might be wrong for 25.2 MHz or so? Basically I have a 111" long and 3/8" diameter soft copper tube bent into a circle with about a 2" gap. This is held about 6" above a 60" by 60" ground plane made of screen wire mesh. The coax cable (RGU-58) has center conductor attached near to one end of the copper tube and the coax shield is attached to the ground plane. Thats it in a nutshell. Al Aburto ------- ------------------------------ Date: 24 Jul 1994 14:06:56 GMT From: ihnp4.ucsd.edu!swrinde!hopper.acm.org!ACM.ORG!SMITHSON@network.ucsd.edu Subject: Feed lines and AC power To: ham-ant@ucsd.edu Greetings! I'm getting ready to dig a deep trench from my house to my barn (120') to get water and power out there. The barn is in the middle of a large pasture, and is also very close to where I plan to put a tower some day. My question is this. Would there be any problem in running some coax out to the barn in the same trench? The water and power will be enclosed in 4" PVC pipe and come in through the basement wall. I was thinking of putting in another pipe and running coax, etc. through it. Any thoughts? Thanks! -Brian n8wrl smithson@acm.org ------------------------------ Date: Sun, 24 Jul 1994 16:11:29 GMT From: news.Hawaii.Edu!kahuna!jeffrey@ames.arpa Subject: How to match 2-meter 1/2 wave To: ham-ant@ucsd.edu jdc3538@ultb.isc.rit.edu (J.D. Cronin) writes: > > How does one match a 1/2 wave antenna to 50 ohms? If you lengthen it a bit so that it's 5/8 wave then you can match it easily - see the ARRL Handbook for details about making 5\8 wave verticals for 17, 12, 2, and 1 1/4 meter bands; in particular, page 33-30 in the 1991 edition gives details for the 2M antenna. NH6IL jeffrey@math.hawaii.edu ------------------------------ Date: Sat, 23 Jul 1994 03:08:26 GMT From: ihnp4.ucsd.edu!usc!nic-nac.CSU.net!charnel.ecst.csuchico.edu!yeshua.marcam.com!hookup!reptiles.org!geac!torsqnt!problem!vigard!mdf@network.ucsd.edu Subject: Jupiter decametric emission info To: ham-ant@ucsd.edu pharden@Mr-Hyde.aoc.nrao.edu (Paul Harden) writes: >Here is some basic information regarding Jovian decametric emissions to >help answer some of the questions thus far raised on the net. excellent post! > If the signal comes from space, it will > strike each antenna about the same time; if it comes from earth, the > signal will slide across the antennas one-at-a-time. Thus, only > coherent signals (those arrive about the same time) are processed as > coming from space. what is the general configuration of these arrays? and i don't see what is preventing a on-earth signal from arriving at the array in a manner similar to what is expected for an off-earth signal. does this means that the arrays are absolutely mindbogglingly gigantic, or most of the terrestrial noise one receives has a source fairly close to the array? or some other reason? -- Matthew Francey mdf@vigard.mef.org ve3rqx@io.org "live before you die" GPS(NAD27): N43o34.210' W079o34.563' +0093m ------------------------------ Date: Sun, 24 Jul 1994 19:06:41 +0000 From: ihnp4.ucsd.edu!swrinde!pipex!demon!plains.demon.co.uk!Nick@network.ucsd.edu Subject: Log Periodics ? To: ham-ant@ucsd.edu HI, Does anybody know where I can find a program for a PC that will allow me to design a log-periodic ? I have a very old textbook with graphs and formulae, surely these days there must be something that does it by computer ! Thanks, Nick G4IRX ========================================== | Nick Button, Nottingham, England | | Internet:- nick@plains.demon.co.uk. | ========================================== ------------------------------ Date: Mon, 18 Jul 1994 19:23:43 GMT From: pa.dec.com!datum.nyo.dec.com!doublj.njo.dec.com!jeff@decwrl.dec.com Subject: mfj 1796 To: ham-ant@ucsd.edu In article greg@netcom.com (Greg Bullough) writes: >In article dmartin@dlink.uucp (Dave Martin) writes: >>NEED ALL THE INFO I CAN FIND AS I CANNOT HAVE MORE THAN 1 ANTENNAE.... >>PLEASE RESOPND QUICKLY!!!!!!! >>THANK YOU FOR READING THIS. > >This seems the ideal antenna for areas with antenna restrictions. As >nobody on the net seems to have thus far succeeded in obtaining this >product, which has been announced and advertised for several months, >it ranks as one of the least visible antennas yet devised. > >Recommendation: consider a product which exists! (one of the GAP verticals >includes VHF and 80m coverage, at the expense of WARC bands). > I had also considered this antenna - I placed my order and after checking in with mfj more than a dozen times over 4 months, cancelled my order! Very frustrating todo business this way - I was repeatly told "give it another week" - I really wanted to get on the air! I ended up getting an R7 and have been extremely pleased with this antenna (except for the very limited bandwidth on 40m) - I also use a transmatch with the R7 and have had many fine QSO's on 80m (not high power). I recently ran a contest using an amp and pushing 800watts pep for more than 24 straight hours - no problem (except rfi/tvi, but that is another post :-) Good luck! -jj - n2mzh ------------------------------ Date: Sun, 24 Jul 1994 20:47:49 GMT From: rit!isc-newsserver!ultb!jdc3538@cs.rochester.edu To: ham-ant@ucsd.edu References <1994Jul23.020711.2434@ultb.isc.rit.edu>, , Subject : Re: How to match 2-meter 1/2 wave In article jeffrey@kahuna.tmc.edu (Jeffrey Herman) writes: >jdc3538@ultb.isc.rit.edu (J.D. Cronin) writes: >> >> How does one match a 1/2 wave antenna to 50 ohms? > >If you lengthen it a bit so that it's 5/8 wave then you can match >it easily - see the ARRL Handbook for details about making 5\8 >wave verticals for 17, 12, 2, and 1 1/4 meter bands; in particular, >page 33-30 in the 1991 edition gives details for the 2M antenna. > >NH6IL jeffrey@math.hawaii.edu > I've seen the 5/8's wave articles in the Handbook and he Antenna Book. A 1/4 wave ground plane is recommended, which is difficult on a HT. J-poles don't need a ground plane to work, but they match a 1/2 wave with a 1/4 wave section. I built a j-pole for 440 on a BNC connector and it works great. The same antenna would be a bit cumbersome on 2-meters, hence the desire to match a 1/2 wave without a 1/4 wave stub. 73...Jim N2VNO ------------------------------ Date: Tue, 19 Jul 1994 12:11:34 GMT From: pa.dec.com!datum.nyo.dec.com!doublj.njo.dec.com!jeff@decwrl.dec.com To: ham-ant@ucsd.edu References , , <30f3n9$52c@jabba.cybernetics.net>wrl Subject : Re: mfj 1796...MFJ's attitude In article <30f3n9$52c@jabba.cybernetics.net> ab4el@jabba.cybernetics.net (Stephen Modena) writes: > >I love it...use it regularly...works fine...but MFJ works with the >lowest possible quality assembly plants in Asia. > I have heard that MFJ uses piece workers, local or otherwise, to make their products! Wonder where the truth lies? It would seem to be plausable due to the random quality of their product line. I have purchased many MFJ products and this reflects my experiance. If you saw my previous post, I echo the attitude issues as why I prefer not todo business with MFJ... 73, -jj - n2mzh ------------------------------ Date: Sun, 24 Jul 1994 12:02:53 GMT From: pa.dec.com!datum.nyo.dec.com!doublj.njo.dec.com!jeff@decwrl.dec.com To: ham-ant@ucsd.edu References , , <30s5c3$rfr@apple.com>u Subject : Re: mfj 1796 In article <30s5c3$rfr@apple.com> kchen@apple.com (Kok Chen) writes: > >Would be kinda difficult to load this antenna, I imagine. Being an >imaginary antenna, it obviously has an impedance of z = i50 ohms. > I heard from a very reliable source yesterday (has had the mfj1796 on order for 22months now!), that they have not even shipped ONE of these and that they are still awaiting hardware to complete this critters... the above comment is too accurate! n2mzh -jj ------------------------------ End of Ham-Ant Digest V94 #238 ******************************