++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 08:12:54 -0400 From: Charles Greene Subject: Re: [Elecraft] Superantennas MP-1 (Portable Antennas... really) At 08:31 PM 5/23/2001 -0400, Don Wilhelm wrote: >Steve, (longish response) > >In my experience with antennas - particularly dipoles - is that they do not >have to be resonant to do a good job of radiating a signal. Effeciency >decreases dramatically if the length is less than 1/8 wavelength, and the >radiation pattern will break into lobes if the length is more than 5/8 wave. >One of the nice lengths for 40 thru 10 meters is 44 feet or 88 feet for 80 >thru 20 meters (higher if you don't mind the extra lobes on the pattern). >See L. B. Cebiks website for more information www.cebik.com and look for >something like 'If I could have only one antenna'. Don, I wanted to ask the question because I haven't seen it discussed. How about an antenna with multiple 1/2 wave dipole wires all connected at the center? I have some small lightweight cable with 8 solid copper PVC insulated wires that I am considering using for a multiband dipole, fed with the #26 teflon insulated twisted pair and supported in the center inverted V fashion with my 33' telescoping fiberglass mast for portable use. I always had good luck with an OCF antenna but with a 4:1 current balun at the antenna and fed with coax and never had any problems with RF in the shack but it really just covers 80, 40, 20, and 10 well. 73, Chas, W1CG ++++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 13:18:04 -0400 From: "Babe" Subject: [Elecraft] Antenna Hello all, I am making an antenna to experiment with. It is basically a multiband dipole, (a few 1/2 wave dipoles sharing a common feed). I plan on putting the center about 45 ft. up the tower and put the ends in trees about 15 ft. off the ground. (an inverted vee). My question is this: Is there an order to follow in trimming the antennas to resonance ie.. do I do 80m,then 40m then 30m etc.. or do I do 12m then 17m then 30m etc. I thought I read somewhere to go from low bands to high bands (80..40..30..17..12) or does it really matter?? Thanks Larry WA2DGD K2 #1672 ++++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 13:18:04 -0400 From: "Babe" Subject: [Elecraft] Antenna Hello all, I am making an antenna to experiment with. It is basically a multiband dipole, (a few 1/2 wave dipoles sharing a common feed). I plan on putting the center about 45 ft. up the tower and put the ends in trees about 15 ft. off the ground. (an inverted vee). My question is this: Is there an order to follow in trimming the antennas to resonance ie.. do I do 80m,then 40m then 30m etc.. or do I do 12m then 17m then 30m etc. I thought I read somewhere to go from low bands to high bands (80..40..30..17..12) or does it really matter?? Thanks Larry WA2DGD K2 #1672 +++++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 13:18:04 -0400 From: "Babe" Subject: [Elecraft] Antenna Hello all, I am making an antenna to experiment with. It is basically a multiband dipole, (a few 1/2 wave dipoles sharing a common feed). I plan on putting the center about 45 ft. up the tower and put the ends in trees about 15 ft. off the ground. (an inverted vee). My question is this: Is there an order to follow in trimming the antennas to resonance ie.. do I do 80m,then 40m then 30m etc.. or do I do 12m then 17m then 30m etc. I thought I read somewhere to go from low bands to high bands (80..40..30..17..12) or does it really matter?? Thanks Larry WA2DGD K2 #1672 +++++++++++++++++++++++++ Date: Thu, 24 May 2001 09:49:52 -0700 From: Louis Hlousek Subject: Re: [Elecraft] Antenna <<>> Yes. The long ones have a significant effect on the shorter ones but the shorter ones have very little effect on the longer ones. If you plan on using the 40 meter dipole on 15 it'll have to be a little long for 40 to tune on 15. I tuned mine for best SWR on 15 and took whatever I got of 40 since the transmission line loss is significantly less at 40. I wound up with an SWR of 3:1 on 15m and 4:1 on 40. I have 40/20/10 m dipoles in parallel and with the KAT2 they work FB on all bands 40 thru 10m. They even work OK on 80 but the SWR is 15:1. Since I'm running at SWRs ranging from 1.1:1 to 15:1 I use foam/foil RG8 (Wireman) which is considerably lower loss than other choices of feedline. Lou W7DZN +++++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 16:17:11 -0400 From: "Babe" Subject: [Elecraft] Antennas - Thanks Thanks to all who responded to my antenna question.the general consensus is to trim the lower bands first. (80..40..30..etc). The basic antenna is stranded wire(7/22) for 80m dipole element, with all the other bands consisting of 3 lengths of 22ga teflon insulated wire for each dipole element, all bound together with various lengths of heat shrink tubing. I'm using a 1:1 balun in the center and will be fed with RG-213. Larry WA2DGD K2 #1672 +++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 15:40:39 -0400 From: "Steve Lawrence" Subject: Re: [Elecraft] Antenna Phil Wheeler wrote: > It definitely DOES matter. But I've forgotten the order (and not built > one myself). Excellent article in QST abt 10 yrs ago. In the following link, in a section under Multiband Dipoles, the recommended tuning sequence is from longest to shortest. There's other interesting stuff here too! http://www.arc.itb.ac.id/rf/arrlhbk/ch20/PracticalDipoleAntenna.htm 73, Steve aa8af +++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 15:48:10 -0500 From: "George, W5YR" Subject: Re: [Elecraft] Antennas - Thanks Larry, are these wires all jammed up close to one another or separated? I don't understand your comment atbout the heat shrink tubing. If the wires are NOT separated a fair amount, you can expect that "formula lengths" will probably be far removed from the "right" lengths. 72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6 Fairview, TX 30 mi NE of Dallas in Collin county EM13qe Amateur Radio W5YR, in the 55th year and it just keeps getting better! Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437 ++++++++++++++++++++++++++++++++ Date: Sat, 26 May 2001 22:23:08 +0100 From: "Ed Taylor, G3SQX" Subject: [Elecraft] {Off topic} Multiple antennas with one feeder A couple of correspondents have asked about using several resonant dipoles on one coaxial feeder. I have tried this configuration many times, and can add the following (briefly, since it doesn't really relate to Elecraft stuff). It's extremely difficult to get more than three dipoles on one feeder to resonate successfully -- two is pretty easy, four will drive you mad. I've always found the 10m antenna is the hardest (haven't exactly worked out why -- but since it will be rather short, it may be that it is too much affected by the length of the others). In any event, centre support is usually best, since the weight of all the wire will cause lots of sagging otherwise. It's hard to get a 40m dipole to work on 15m. A 40m dipole will be fine on 15 when on its own, but the impedance is apparently too much changed by the other antennas to be effective on 15 when combined with other dipoles. The lowest frequency (longest) dipoles should be tuned first. They may need adjustment again when you have finished the higher frequencies, but it's not likely. The bandwidth (SWR below 2:1) of the lower frequency antennas may be increased a little because of the presence of the other antennas on the feeder. The system works MUCH better if the ends of each antenna on a feeder are separated -- my best configuration had three dipoles with each leg at about 60 degrees, like a sort of maypole. But even a metre or two spacing will help a lot. When the antennas are too close, the slightest sway in the wind will cause unacceptable fluctuation in SWR. Once you have got three resonant dipoles on one antenna, you will find that the SWR is below 3:1 on other (unplanned) bands. On some frequencies, additional dips towards 50 ohms may enable you to get WARC bands for "free," or at least, with your rig's internal ATU, at consequent fairly low feeder loss. If you use a choke balun, you will remove some of the unpredictables which result from feeder radiation (and the associated unknown "outside of the feeder" impedance). I generally use 10-12 turns of coax next to the feedpoint, but ferrite chokes are equally effective. The benefit of this sort of system are the very easy switching of antennas, and quick band changes. Each dipole will be close to optimum in performance, although the radiation patterns may not be easy to predict (usually not an issue -- they'll normally be more omni-directional). 73, Ed, G3SQX (K2 no.1941 still unassembled on bench -- waiting for long winter evenings, but announcement of 100w PA may change that!) ++++++++++++++++++++++++++++++++++++++ Date: Mon, 18 Jun 2001 15:26:19 -0500 From: "George, W5YR" Subject: Re: [Elecraft] K1 antenna(s) Steve, if you can stand the extra length, making the flat-top 88 ft instead of 66 ft might avoid a lot of tuning problems plus give you up to 3 db gain on 20 meters and allow the antenna to be used on 80 - 10! On 20 meters, your 40-meter dipole is going to present a very high Z to the feedline which depending upon its length, etc. could present a very awkward Z and voltage/current levels for the rig. And there is always the possibility with internal tuners of excessive voltage/current at the tuner terminals causing damage. I gave up on multi-band "resonant" antennas a long time ago . . . 72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6 Fairview, TX 30 mi NE of Dallas in Collin county EM13qe Amateur Radio W5YR, in the 55th year and it just keeps getting better! Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437 Steve Lawrence wrote: > > Bob, > I'm about to venture into the field with a ladder-line fed dipole, cut for > 7.150 mHz. Experiments seem to indicate that the K2 tuner (yes, I > understand you have a K1) will tune this setup on 40M and higher. The > antenna is simple, I guess I can hang it as an inverted-V or a traditional > horizontal dipole. +++++++++++++++++++++++++++++++++++ Date: Mon, 18 Jun 2001 14:26:54 -0700 From: "Ron D' Eau Claire" Subject: RE: [Elecraft] K1 antenna(s) Steve, AA8AF wrote: I'm about to venture into the field with a ladder-line fed > dipole, cut for > 7.150 mHz. Experiments seem to indicate that the K2 tuner (yes, I > understand you have a K1) will tune this setup on 40M and higher. The > antenna is simple, I guess I can hang it as an inverted-V or a > traditional > horizontal dipole. > > I am pretty much convinced that an antenna like this represents a lot of > pluses... Good points. Actually, the antenna will be quite efficient as long as it is at least 1/8 wavelength overall. That is, an antenna cut for 40 will work well on 80 meters as well with only a small loss in efficiency. The usual problem with a horizontal antenna on the lower bands is height above ground. You want it 1/2 wavelength up if you can get it, and at the very least 1/4 wave high for it to put out much of a signal except straight up. That's a bit over 30 feet on 40 - pretty easy to arrange most places - but it's 60 feet on 80! If you are hanging it 'inverted vee' style, the effective height is about 80% of the peak height at the center, so the center needs to be proportionately higher. The issue with the balanced feed is converting the K2 or K1 tuner output to balanced feed. Most ops use a balun, which works as long as the feedpoint impedance isn't too awfully high or low. The balun quits working at extreme impedance's, and can act as a great dummy load at times, letting the rig tune up nicely but not putting out much of a signal. Probably the easiest way to alter the impedance at the feedpoint is to change the length of the feedline if needed. For only two bands, as the original question posed, a dual dipole (one feedline with two dipoles connected to the feedline each cut to 1/2 wavelength) can work very well. They are trickier than most realize to cut so you have a very low (less than 2:1 SWR) on both bands, but the ATU in the K1 or K2 will take care of the SWR on the feedline so it's not an issue. Just cut them to 'textbook' length (468/f(MHz)). If one uses good feedline (no RG-174 miniature coax!) the dual dipoles won't create a high enough feeder SWR to cause significant losses. RG-58 for a reasonably short run or larger lower loss coax for longer runs is easier to deal with than the open wire line for most ops, and it does not require a balun. Ron AC7AC K2 # 1289 ++++++++++++++++++++++++++++++++++++++ Date: Sun, 7 Oct 2001 09:33:14 -0400 From: "Steve and Anne Ray" To: Cc: Subject: [108221] Re: Antenna ?? A bit long. Message-ID: <003301c14f34$a110a1c0$d2cc5c0c at home> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit I agree with the group that the only way to go is ladder line and cutting the antenna either for 80 Meters (120 or feet) or 40 meters (65 or so feet). I presently use a 125 foot dipole fed with ladder line on 80 thru 10 meters. To provide some overall background all my antennas are no higher then 32 feet ( tower is 32 feet high). The following refers to how well I receive signals and therefore I presume the transmitted radiation pattern also applies. I can match the 80 meter dipole on all bands 80-10 meters, but it just does not cut it on receiving on 30, 17, 15 and 12 meters, compared to my dedicated coax fed dipoles for these bands. I found out that while it works great on 80, 40, 20, and 10 it leaves a lot to be desired on 30, 17, 15 and 12 meters. My coax fed dipoles for these bands worked a lot better. I have now up a dipole cut for 30 meters fed with ladder line and it works great on 30 and 15 meters (1/2 wavelength on 30 meters and 1 wavelength on 15 meters. I then took the advice of W4RNL and put up a 1/2 wavelength for 17 meters and it works great also on 12 meters. Remember I can match any antenna, fed with ladder line, my concern is how well it receives and therefore gets out. My simple experiments on comparing antennas was just based upon strongest received signal when switching between the various dipoles. In QSOs switching between antennas gave consistently identical reports, the antenna I received the signal strongest on was also the strongest transmitting antenna (hey this reciprocity stuff really applies Hi Hi) I gave up on the coax fed fan dipoles, years ago, while they work, they can be fun (work) to get working due to interaction. Just as a side note, I tie the ladder line feedline of the 80 meter together connect it to the antenna tuner as a long wire, and run a 50 foot counter poise across the yard to my 120 foot chain link fence and have worked QRP 160 meters during the 160 meter contest. Worked up and down the East Coast, Canada and the mid west. This antenna is only at 32 feet. Recommend you visit W4RNL site http://www.cebik.com/radio.html it is a wealth of info on antennas. 72, Steve Ray K4JPN ex K1VKW HW-101, HW-8, Elecraft K2 1422 HeathKit fan EM82fp +++++++++++++ Date: Sun, 7 Oct 2001 12:13:16 -0600 From: William R Colbert To: qrp-l at lehigh.edu Subject: [108236] Re: Antenna ?? Message-ID: <20011007.121318.-367355.1.w5xe at juno.com> MIME-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit I notice some naysayers about the proposed fan dipole, and perhaps they have not used such an antenna. I had used one at one time or another with excellent results. Coax fed, and with the flattop set for 80 and the fans for the higher bands. The best was a commercial trap fan dipole made by Hy-gain and it worked extremely well with my qrp in the early 1960's, strung as a sloper from the roof of the barracks in Germany to a short tree. Home made versions without the traps worked equally well. I would say go for it, and there are numerous writings in the antenna publications, particularly some years ago, so they have been around a long time, successfully. 73 Ray "The more I see of the representatives of the people, the more I admire my dogs." letter from Count d'Orsay Ray Colbert, W5XE, OOTC#3618, SOWP#1064M NARTE-NCT2R FP# 111, SOC#78,ARCI 5784, El Paso,(FAR WEST)TEXAS ++++++++++++++