++++++++++++++++++ Date: Fri, 7 Sep 2001 08:59:25 -0100 From: "Julian, G4ILO" Subject: [Elecraft] Attic loop question My antenna is an attic wire loop, approx 6m x 5m, fed in the center of one 5m side by an SG-239 autocoupler. The amount of wire in the loop is approx a full wave at 20 metres. The loop seems to work fine on 20m and up, but performs poorly on 40m and below, although the SG-239 will match it, even on 160m! On 40m it works about as well as the 4 foot Miracle Whip on the back of my FT-817. I think this says more about the loop than it does the Miracle Whip... I am wondering if the reason is the loop has a high impedance on frequences where it is less than a full wave, and not much power is being transferred to/from the antenna. Are there any ways the loop could be made to work better on 40m, without worsening performance on the higher bands, bearing in mind the size which cannot be made larger? I am more interested in making inter-G contacts than trying to work DX. - -- Julian, G4ILO. (RSGB, ARRL, K2 #392) Homepage: http://www.qsl.net/g4ilo +++++++++++++++++++++++ Date: Fri, 7 Sep 2001 08:28:25 -0500 From: "benlightnd1" Subject: Fw: [Elecraft] Attic loop question Julian wrote: Are there any ways the loop could be made to work > better on 40m, without worsening performance on the higher bands, bearing > in mind the size which cannot be made larger? I am more interested in > making inter-G contacts than trying to work DX. Working with a loop myself right now Julian and seeing some of the same results. In testing this loop on all bands, I'm finding that the impedence runs from 20 to around 230 ohms. The biggest problem I am seeing it reactance. Even when I'm working against 50 ohms, I still have hight reactance. Trying different methods of matching but it looks like I will end up building a 4 to 1 balun to install at the feed point. This will match any of the feed conditions I am seeing and make this loop usable on any band with reasonable results. I know there are many folks here that will give you some good advise I will be watching in interest. I think a balun is what you need to help you get the most from your antenna. 73 and good luck: Keep us posted as to what you are doing and what effect it has: Jerry N0JRN K - 1 # 601 ++++++++++++++++++++ Date: Fri, 7 Sep 2001 07:19:52 -0700 (PDT) From: Jim Apple Subject: Re: Fw: [Elecraft] Attic loop question I would go with a 1:1 vs a 4:1. With a 1:1 the KAT does a great job from 80-10. A LDG Qrp has problems with it and the LDG AT11 is almost as capable as the KAT. ===== - - Jim Apple (WB1DOG) +++++++++++++++++++++++ Date: Fri, 07 Sep 2001 11:52:47 EDT From: N2EY at aol.com Subject: Re: [Elecraft] Attic loop question In a message dated Fri, 7 Sep 2001 4:03:11 AM Eastern Daylight Time, "Julian, G4ILO" writes: > My antenna is an attic wire loop, approx 6m x 5m, fed in the center of one > 5m side by an SG-239 autocoupler. The amount of wire in the loop is approx > a full wave at 20 metres. Consider downloading the demo version of EZNEC from W7EL's website and doing a bit of simulation. How high is the loop above ground? Where is the feedpoint - in the middle of a longer side, in the middle of a shorter side or at a corner? > > The loop seems to work fine on 20m and up, but performs poorly on 40m and > below, although the SG-239 will match it, even on 160m! That is a tribute to the matching ability of the SG-239. > On 40m it works > about as well as the 4 foot Miracle Whip on the back of my FT-817. I think > this says more about the loop than it does the Miracle Whip... > Exactly. There may be high loss in the SG-239 when matching the loop on 40 and below. If the SG-239 is a single-ended tuner feeding a balun, the balun losses may be very high when feeding the loop on 40 and below. > I am wondering if the reason is the loop has a high impedance on frequences > where it is less than a full wave, and not much power is being transferred > to/from the antenna. Maybe. On 40, the loop is only a half-wave of wire. In addition, it probably has lots of reactance that must be tuned out. >Are there any ways the loop could be made to work > better on 40m, without worsening performance on the higher bands, bearing > in mind the size which cannot be made larger? I am more interested in > making inter-G contacts than trying to work DX. > Try opening the loop at the point exactly opposite the feed, so that what you have is a bent-up dipole instead of a closed loop. A simple well-insulated switch at that point will permit you to compare performance. 73 de Jim, N2EY ++++++++++++++++++++++++ Date: Fri, 7 Sep 2001 18:13:00 +0200 From: "Sverre Holm \(LA3ZA\)" Subject: Re: Fw: [Elecraft] Attic loop question I am using my own version of the Norcal BLT Z-match tuner to tune my 85 m horizontal loop. I don't have a KAT-2, but with this tuner as described on http://www.io.com/~n5fc/blt.htm I can tune the loop on all bands except 17 and 12 m. In order to tune it there also I had to add a switch with a series inductance of 1 uH in the input branch in series with C2. I wound that with 14 turns on a T50-2 toroid. According to my calculation, it is just below core saturation at a power level of 5-10 W, but I will probably change it to 2 stacked T50-2 cores. The frontpanel layout of the tuner can be found on http://www.qsl.net/la3za/div/BLT-match.pdf . It has been generated from the file http://www.qsl.net/la3za/div/BLT-match.txt using the program of WB8RCR at http://hfradio.org/wb8rcr/downloads/Panel-1.9.W32.zip . BTW, I would recommend this program for any homebrewer who wants to improve his panel layouts. I print mine in reverse on overhead foils and glue them to the panel. Best regards Sverre ____________________________________ 73 de LA3ZA http://www.qsl.net/la3za ++++++++++++++++++++++= Date: Fri, 7 Sep 2001 11:36:06 -0700 (PDT) From: Jim Apple Subject: Re: Fw: [Elecraft] Attic loop question I should have mentioned that my loop is feed with 450 ohm ladder line into the shack, then a 1:1 and a short coax jumper to the KAT. ===== - - Jim Apple (WB1DOG) +++++++++++++++++++++ Date: Sat, 08 Sep 2001 01:44:38 +0000 From: brendan Minish Subject: RE: [Elecraft] Attic loop question At 21:16 07/09/2001 -0100, Julian, G4ILO wrote: >Thanks for all the suggestions regarding improving the performance of my >loop on 40m. > Then Bob, N6WG, >suggested inserting a 40m trap at that point. This seems like a cool idea, >and would eliminate the need for any manual switching. Unless anyone thinks >of a snag, I'm going to give that a try. Not a snag but being able to break it in the middle (I.e turn it into a folded dipole ) will give you an alternative antenna pattern on 20m and up (especially on 15m (2x 3/4 wavelengths )), Allow you to have some chance of putting out a signal on 80m (although will never work DX ) and should provide better results on 30m than a 20m loop Designing the trap may also be a little tricky, I would try the switch first (mercury float switch and a Piece of string for remote control ?) and if you find the loop is always better than the doublet configuration on all bands except 40m try a trap. ++++++++++++++++++++++ Date: Tue, 19 Mar 2002 21:56:10 -0500 From: Haines Brown To: gw3pdw at telco4u.net Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] 20M Micro-loop antenna Reply-To: brownh at hartford-hwp.com Derek, The URL of the article you seek on 20 meter miniloop is: http://www.natradioco.com/rdey/ant20m2.htm Haines Brown KB1GRM +++++++++++++++++++++++ Date: Wed, 20 Mar 2002 05:27:15 -0700 From: Tim and Nancy Logan Reply-To: cyr999 at extremezone.com To: Elecraft Subject: [Elecraft] Horiz. loop & counterpoise Hi folks - I've run a horizontal loop for the last year and a half. It's about 270 feet (give or take) of wire connected to about 25' ladder line; then a 4:1 balun; and then a 9' piece of coax to an Alpha Delta antenna selector. This "stealth" antenna works beautifully and allows me to talk all over the world. I have a set counterpoise wires connected directly to the LDG-11 tuner which is connected to my "big rig" - an ICOM 756 PRO. I've always thought the only reason for this in a loop situation is for RFI. The K1 and K2 don't create RFI because of the low power - so I never really gave the counterpoise a second thought with the QRP rigs. Did I miss a beat here? Is there another reason (other than RFI) that I might want the counterpoise connected to the K1 and K2 when using a horizontal loop? I must admit, the K1 has to wrestle a bit more with the loop. Maybe I should connect the counterpoise to the ground on the Alpha Delta antenna selector instead. Any thoughts would be appreciated. 73/Tim +++++++++++++++++++++++