Re: [Elecraft] OT: Need Antenna Tuning Help
Below... > On Thursday, Mar 8, 2012, at Thursday, 12:14 PM, Gary Hinson wrote: > > > ... and thank YOU Jim for your encouraging words. I do have the space > for > > several quadrillion radials but not the energy to cut them all into the > > ground below sheep/cattle/deer foot level. So I'm waiting for the > postman > > to deliver some cores from Amidon, and I'll give an FCP a go. > > > > One thing is not v clear on W0UCE's site is the antenna: he shows an > > inverted L coupled directly in - it looks v simple but my inv-L will be > > different so aside from trimming the length and maybe configuration of > the > > L, are there any other tricks to achieving system resonance?I have > tall > > fir trees to hang the antenna from, so mine will be close to a quarter > wave > > vertical I hope. > > > > 73 > > Gary ZL2iFB www.G4iFB.com Hopefully a short simple addition to the discussion. Jim is using the 80m version of the "simple" arrangement: FCP plus required isolation transformer (IsoT) plus quarter-wave-ish radiator that is pruned to center the best impedance range at the desired operating frequency, and has the mechanical simplicity of a balun in the middle of an inverted vee. The FCP, being 5/16 on its only band (not multiband) is quite capacitively reactive. The IsoT has quite a bit of leftover inductive reactance on its band. The parts in the IsoT were chosen for efficiency, and in addition, under the antenna load, to have an inductive reactance that is close to the FCP, with the opposite sign. The turns count on both the 160 and 80m versions are specifically picked to allow you to put up a close-to-quarter-wave radiator that can be pruned to a zero reactance and an R in the 50-ish range as seen ON THE SHACK SIDE of the IsoT. Most are putting up inverted L's as radiators, for residential-plot-specific reasons, where trees are, etc. But you can put up any radiator you want. The different X and R curves for various "typical" 1/4 wave inverted L's and other radiators mean that sometimes you may have to start adding things to the IsoT to tune R and X. This gets into understanding tuning networks. There are some remarkably useful complex configurations using IsoT's and FCP's, but you won't work them just reading SWR, and you'll need to be looking at them as complex LCR networks. If you put the behavior of the IsoT under load into a model, you have to use an LC network plus a transformer widget to describe it. So in truth the antenna per se -- the 1/4-wave-ish radiator over the FCP -- is NOT a resonant antenna. You are using a required isolation device with INDUCTIVE non-resonant network characteristics that have been picked to be the opposite of typical L-wire/FCP CAPACITIVE non-resonant characteristics. For many, just pruning the L gets it close enough. Others have lengthened the L to make it inductive and put a transmitting cap in series. The details are at http://www.w0uce.net/K2AVantennas.html 73, Guy. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
On Thu, 8 Mar 2012, Tony Estep wrote: > On Thu, Mar 8, 2012 at 10:54 AM, WILLIS COOKE wrote: >> I wouldn't have mentioned it Jim, except Tony's funny comment muddied the >> water... > === > Yeah, there's always some smart-aleck to confuse the issue. But > seriously, I don't see why MFJ couldn't put a minus sign or something > on the display. My cheapo Autek gadget (<$100 on ebay) tells you > series and parallel reactance with sign, equivalent C, equivalent L, > phase angle, and some other stuff as well as SWR. I'm not an > MFJ-basher; I have been happy with all the MFJ stuff I have. But in > this case IMHO they left out some worthwhile functionality. Look at the different analyzer comparisons and you'll notice that a lot of them do NOT have the sign of the reactance. My buddy bought the Autek back in the day because of that reason and it was several hundred dollars. I just bought a Rig Expert for the same sort of reasons. -- Hisashi T Fujinaka - ht...@twofifty.com BSEE(6/86) + BSChem(3/95) + BAEnglish(8/95) + MSCS(8/03) + $2.50 = latte __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
Gary, My L wire started out from the formula L (ft) = 234 / f (mHz). Wasn't quite long enough and wound up adding a couple feet to it. But first, we had to get to a zero reactance spot, and that meant (for my installation) adding two feet to the total wire length of the FCP, as compared to what was on the W0UCE web page. That "may" have been because my FCP is only five feet off the ground, as opposed to the recommended eight feet. You didn't say if you were making one for 80 or 160 meters. Mine was for 80, so your figures may be different. When we lengthened my L, we also added the length to the FCP. But - and I highly recommend this - make a graph of your antenna's X, R, and SWR readings before doing any pruning / tuning, after installing the FCP. My graph showed exactly where the whole thing reached zero reactance, and it was a matter of bringing it down a few kHz from there. It also showed that I had another 80 meter antenna on my property that was being coupled to the inverted L, screwing up the entire thing! I eliminated THAT problem, and everything with the FCP and inverted L fell into place! It is my understanding that the vertical part of an inverted L is the most important, and the more of it in the up and down plane, the better. Good luck, and let us know how it works out for you. 73, Jim / W6JHB On Thursday, Mar 8, 2012, at Thursday, 12:14 PM, Gary Hinson wrote: > ... and thank YOU Jim for your encouraging words. I do have the space for > several quadrillion radials but not the energy to cut them all into the > ground below sheep/cattle/deer foot level. So I'm waiting for the postman > to deliver some cores from Amidon, and I'll give an FCP a go. > > One thing is not v clear on W0UCE's site is the antenna: he shows an > inverted L coupled directly in - it looks v simple but my inv-L will be > different so aside from trimming the length and maybe configuration of the > L, are there any other tricks to achieving system resonance?I have tall > fir trees to hang the antenna from, so mine will be close to a quarter wave > vertical I hope. > > 73 > Gary ZL2iFB www.G4iFB.com > > PS Please don't feel compelled to respond - I'm going to enjoy > experimenting with it in any case! > > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
I think you will find the original designer was Tom Rauch W8JI. 73, Don W3FPR On 3/8/2012 2:15 PM, Ian Wilson wrote: > So I think that the original designer made a reasonable tradeoff. I wonder > who that was - the design was purchased by MFJ from Vectronics, I think). > > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
Tony, There is more to it than just putting a + or - sign on the display. The instrument must have adequate measurements starting at the front end reflectometer to determine the sign of the reactance. The MFJ does not have that. If there were a microprocessor in the instrument, and it had the capability of electrically varying the frequency, it could move the frequency up or down to determine the sign. The MFJ259 manual tells you how to determine the sign by moving the frequency up or down while watching the reactance. 73, Don W3FPR On 3/8/2012 1:51 PM, Tony Estep wrote: > But seriously, I don't see why MFJ couldn't put a minus sign or > something on the display. My cheapo Autek gadget (<$100 on ebay) tells > you series and parallel reactance with sign, equivalent C, equivalent > L, phase angle, and some other stuff as well as SWR. I'm not an > MFJ-basher; I have been happy with all the MFJ stuff I have. But in > this case IMHO they left out some worthwhile functionality. Tony KT0NY __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
The basic bridge in the MFJ - and lots of other impedance analyzers - is insensitive to the sign of the reactive impedance. You can figure it out by making a "small" change in frequency and seeing whether the reactance increases or decreases. However, this takes additional software in the uP, increases the measurement time, and guessing how large a small step you can get away with is not trivial. So I think that the original designer made a reasonable tradeoff. I wonder who that was - the design was purchased by MFJ from Vectronics, I think). 73, ian K3IMW On Thu, Mar 8, 2012 at 6:51 PM, Tony Estep wrote: > On Thu, Mar 8, 2012 at 10:54 AM, WILLIS COOKE wrote: > > I wouldn't have mentioned it Jim, except Tony's funny comment muddied > the water... > === > Yeah, there's always some smart-aleck to confuse the issue. But > seriously, I don't see why MFJ couldn't put a minus sign or something > on the display. My cheapo Autek gadget (<$100 on ebay) tells you > series and parallel reactance with sign, equivalent C, equivalent L, > phase angle, and some other stuff as well as SWR. I'm not an > MFJ-basher; I have been happy with all the MFJ stuff I have. But in > this case IMHO they left out some worthwhile functionality. > > Tony KT0NY > > > -- > http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352 > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
On Thu, Mar 8, 2012 at 10:54 AM, WILLIS COOKE wrote: > I wouldn't have mentioned it Jim, except Tony's funny comment muddied the > water... === Yeah, there's always some smart-aleck to confuse the issue. But seriously, I don't see why MFJ couldn't put a minus sign or something on the display. My cheapo Autek gadget (<$100 on ebay) tells you series and parallel reactance with sign, equivalent C, equivalent L, phase angle, and some other stuff as well as SWR. I'm not an MFJ-basher; I have been happy with all the MFJ stuff I have. But in this case IMHO they left out some worthwhile functionality. Tony KT0NY -- http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
The feed point is at exactly the same elevation as the FCP - just around five feet off the ground. The FCP should have been eight feet high, but that would put it in the neighbor's cross-hairs and we live in a CC&R / HOA area, so stealth is best for me. The isolation transformer unit is loosely strapped (in it's box, of course) to the side of a redwood tree, about three feet horizontally from the FCP, which is a few inches off of the wooden property line fence. When I built the FCP, I left several feet of extra #12 AWG copper wire at the bottom end for connection to the FCP. It is that wire that runs over to one binding post on the isolation transformer. The other binding post connects to the vertical part of the Inverted L, which runs up through the limbs of the tree, approximately 31 feet, and then around 40 feet or so horizontal across the back yard. It is not perfectly horizontal - comes down on a slight angle. The antenna wire I used is #13 AWG "Silky Coat" from The Wire man. The transformer is a true isolation transformer - 15 bifilar turns of #14 AWG Polyimide Insulated Wire with teflon sleeving, wound on an AmidonT300A-2 powdered iron toroid. All part numbers, pictures, and a complete description can be found at: http://www.w0uce.net/K2AVantennas.html This is really cool for me, as I'm waiting for that elusive KAT500, but I can now freely roam around the CW part of 80 meters and the KPA500 happily follows me! Jim / W6JHB On Thursday, Mar 8, 2012, at Thursday, 8:34 AM, WILLIS COOKE wrote: > Congratulations Jim! I have been watching this thread with interest to see > how it worked out. I would like to know a bit more. Is your feed point at > the same elevation as your counterpoise, or at ground level? If at ground > level, describe your transition to five feet for the counterpoise. What do > you use for a support and how high is your transition to horizontal? Is your > transformer a true isolation transformer with two windings and DC isolation > or an UnUn wound transformer? Is your powdered iron core a rod or toroid? > What is the Amidon model number? > > Again, congratulations! I love this kind of dialog! 73! > Willis 'Cookie' Cooke > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
I wouldn't have mentioned it Jim, except Tony's funny comment muddied the water some. I like humor, but I also don't want anyone to be confused by humorous dialog. I am sure Tony knows how the analyzer works. In your case, there were enough confusing factors to leave some doubt about the polarity that was not resolved without a lot of thought and experimentation. It usually is not that difficult to reason the polarity of the reactance. Willis 'Cookie' Cooke K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart From: Jim Bennett To: Elecraft Reflector Sent: Thursday, March 8, 2012 10:44 AM Subject: Re: [Elecraft] OT: Need Antenna Tuning Help I stand corrected. I should have said that it simply shows numbers and it is up to the user to figure out the correct polarity. Thanks for the input. > I think the original statement was incorrect. The MFJ-259B does show > reactance, both positive and negative, but it does not show polarity, so you > have to experiment a little or add some knowledge to find out the polarity of > the reactance. That is one of the reasons that the MFJ-259B is not the best > antenna analyzer on the market, just a cost effective, but inexpensive > antenna analyzer. My German professor when asked to explain how the science > students with only 8 hours of German aced the senior German students on a > major test "Man muss hab kopf!" which translates to "One must have a head" or > better "One needs a brain!" > > Willis 'Cookie' Cooke > K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart > > > ____ > From: Tony Estep > To: elecraft@mailman.qth.net > Sent: Thursday, March 8, 2012 9:07 AM > Subject: Re: [Elecraft] OT: Need Antenna Tuning Help > > On Thu, Mar 8, 2012 at 2:19 AM, Jim Bennett wrote: >> ... the MFJ-259B does NOT show minus reactance > === > Gee whiz! That's pretty lame. As my favorite soccer announcer says > when a guy misses from short range, "Me pongo las manos en la cabeza." > > Tony KT0NY > > > -- > http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352 > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
I stand corrected. I should have said that it simply shows numbers and it is up to the user to figure out the correct polarity. Thanks for the input. > I think the original statement was incorrect. The MFJ-259B does show > reactance, both positive and negative, but it does not show polarity, so you > have to experiment a little or add some knowledge to find out the polarity of > the reactance. That is one of the reasons that the MFJ-259B is not the best > antenna analyzer on the market, just a cost effective, but inexpensive > antenna analyzer. My German professor when asked to explain how the science > students with only 8 hours of German aced the senior German students on a > major test "Man muss hab kopf!" which translates to "One must have a head" or > better "One needs a brain!" > > Willis 'Cookie' Cooke > K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart > > > > From: Tony Estep > To: elecraft@mailman.qth.net > Sent: Thursday, March 8, 2012 9:07 AM > Subject: Re: [Elecraft] OT: Need Antenna Tuning Help > > On Thu, Mar 8, 2012 at 2:19 AM, Jim Bennett wrote: >> ... the MFJ-259B does NOT show minus reactance > === > Gee whiz! That's pretty lame. As my favorite soccer announcer says > when a guy misses from short range, "Me pongo las manos en la cabeza." > > Tony KT0NY > > > -- > http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352 > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
Congratulations Jim! I have been watching this thread with interest to see how it worked out. I would like to know a bit more. Is your feed point at the same elevation as your counterpoise, or at ground level? If at ground level, describe your transition to five feet for the counterpoise. What do you use for a support and how high is your transition to horizontal? Is your transformer a true isolation transformer with two windings and DC isolation or an UnUn wound transformer? Is your powdered iron core a rod or toroid? What is the Amidon model number? Again, congratulations! I love this kind of dialog! 73! Willis 'Cookie' Cooke K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart From: Jim Bennett To: elecraft@mailman.qth.net Sent: Thursday, March 8, 2012 2:19 AM Subject: Re: [Elecraft] OT: Need Antenna Tuning Help Folks - back on the 28th of Feb I started this thread, looking for assistance getting the K2AV Folded CounterPoise (FCP) to work on my 80 meter Inverted L antenna. Got several good suggestions and wound up having a long series of off-line email exchanges with Guy, K2AV. With his help, we got the thing working perfectly. I now have an antenna that has a 100 kHz wide segment of the band with zero reactance, and an SWR that is 1.5:1 or below for 125 kHz. I learned quite a bit about antenna tuning, and the fact that the MFJ-259B does NOT show minus reactance. When I put the Resistance ( R ) and Reactance ( X ) figures on a graph - they were quite whacky. Turns out that there were several negative values that I'd "assumed" as being positive. Once adjusted, the chart looked reasonable. I also had another antenna on the property, resonant on 80 meters, that was messing up the works. With Guy's guidance, I adjusted dimensions of the FCP and the Inverted L radiator and bingo - it works great! I opted to build my own isolation transformer, saving a couple bucks. The FCP is mounted about five inches out from a property line wooden fence, about five feet off the ground. I used schedule 40 PVC pipe for the FCP wire supports. The PVC and enclosure for the isolation transformer were purchased at a local Ace Hardware. The powdered iron core and teflon wire insulation came from Amidon and the wire for the FCP and isolation transformer came from The Wireman. The W0UCE web site has detailed information, including parts information. If you don't have room for a bazillion radials on 80 or 160 meters, by all means look into using an FCP with your Inverted L. Many thanks to K2AV for his gracious help and his putting up with my lack of technical knowledge! __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
I think the original statement was incorrect. The MFJ-259B does show reactance, both positive and negative, but it does not show polarity, so you have to experiment a little or add some knowledge to find out the polarity of the reactance. That is one of the reasons that the MFJ-259B is not the best antenna analyzer on the market, just a cost effective, but inexpensive antenna analyzer. My German professor when asked to explain how the science students with only 8 hours of German aced the senior German students on a major test "Man muss hab kopf!" which translates to "One must have a head" or better "One needs a brain!" Willis 'Cookie' Cooke K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart From: Tony Estep To: elecraft@mailman.qth.net Sent: Thursday, March 8, 2012 9:07 AM Subject: Re: [Elecraft] OT: Need Antenna Tuning Help On Thu, Mar 8, 2012 at 2:19 AM, Jim Bennett wrote: >... the MFJ-259B does NOT show minus reactance === Gee whiz! That's pretty lame. As my favorite soccer announcer says when a guy misses from short range, "Me pongo las manos en la cabeza." Tony KT0NY -- http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
On Thu, Mar 8, 2012 at 2:19 AM, Jim Bennett wrote: >... the MFJ-259B does NOT show minus reactance === Gee whiz! That's pretty lame. As my favorite soccer announcer says when a guy misses from short range, "Me pongo las manos en la cabeza." Tony KT0NY -- http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
Folks - back on the 28th of Feb I started this thread, looking for assistance getting the K2AV Folded CounterPoise (FCP) to work on my 80 meter Inverted L antenna. Got several good suggestions and wound up having a long series of off-line email exchanges with Guy, K2AV. With his help, we got the thing working perfectly. I now have an antenna that has a 100 kHz wide segment of the band with zero reactance, and an SWR that is 1.5:1 or below for 125 kHz. I learned quite a bit about antenna tuning, and the fact that the MFJ-259B does NOT show minus reactance. When I put the Resistance ( R ) and Reactance ( X ) figures on a graph - they were quite whacky. Turns out that there were several negative values that I'd "assumed" as being positive. Once adjusted, the chart looked reasonable. I also had another antenna on the property, resonant on 80 meters, that was messing up the works. With Guy's guidance, I adjusted dimensions of the FCP and the Inverted L radiator and bingo - it works great! I opted to build my own isolation transformer, saving a couple bucks. The FCP is mounted about five inches out from a property line wooden fence, about five feet off the ground. I used schedule 40 PVC pipe for the FCP wire supports. The PVC and enclosure for the isolation transformer were purchased at a local Ace Hardware. The powdered iron core and teflon wire insulation came from Amidon and the wire for the FCP and isolation transformer came from The Wireman. The W0UCE web site has detailed information, including parts information. If you don't have room for a bazillion radials on 80 or 160 meters, by all means look into using an FCP with your Inverted L. Many thanks to K2AV for his gracious help and his putting up with my lack of technical knowledge! __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
The original poster and I have a significant thread going off reflector, and have been dealing with the tuning issues. A quarter-wave-ish wire over an FCP and an isolation transformer is a complex, dual tuned impedance. It sometimes does NOT prune simple like a dipole. We don't have a lot of experience with the 80 meter version yet, but are making some adjustments based on Jim's experience. We will post on the W0UCE web page when we have it nailed down. 73, Guy. On Thu, Mar 1, 2012 at 12:11 PM, briana wrote: > I think you have to identify which of the two resonances is due to the > antenna and not due to the antenna + feedline. Elevated radials that > exhibit resonances of their own can also be confounding. > > The multiple resonance may be due to a fortunate length of coax that > presents a 50 ohm at the shack end. > You can identify which resonance is due to the antenna by attaching a > short length of coax at the antenna feed and find the resonance with > your antenna analyzer. > > Then you will know if you have to add or subtract wire. > > The fact that SWR "goes up" when you keep adding wires (@ complex part > =0) only means that the impedance at resonance is changing. > > At resonance (complex part=0) different antennas have different values of Z > > Inverted L's and verticals have Z's of 30 to 35 ohms at resonance with a > really good ground system. That isn't > an SWR of 1:1.A yagi may have a Z of 15 ohms-- hence a big SWR. > > Once you have the antenna resonant where you want, then you have to deal > with the mismatch. A simple L network at the base of the antenna will > take care of the mismatch. 500 watts doesn't require monster components. > > 73 de Brian/K3KO > > On 2/28/2012 7:20 PM, Don Wilhelm wrote: > > Jim, > > > > I did a little chatting with Guy K2AV when he was starting to work on > > that project (W0UCE lives only a few miles from me), and I recall that > > changing the height above ground changed the behavior. > > So if you do not have the lowest wire 8 feet above the ground, it will > > not be tuned properly. > > Maybe Guy will comment, he frequently posts on this reflector. > > > > 73, > > Don W3FPR > > > > On 2/28/2012 5:22 PM, Jim Bennett wrote: > > > >> I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 > meters is my biggest hurdle. I put up an 80 meter Inverted L several months > ago - prior to getting the KPA500. The vertical part of the antenna is 40 > feet in length. I had been using two radials, about 14 inches above ground > - small lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3 > and the internal tuner. I had done some pruning of the radials to get it > resonant on 3.550. The K3 tuner took care of the rest. Well, along came the > KPA500 and as yet, no KAT500. So I started looking at the antenna to see > what I could do. I opted to replace the two single radial wires with a K2AV > Folded CounterPoise (FCP). Not sure if this was a mistake or not. > Everything I've read said that the FCP approach on 80 / 160 meter Inverted > L antennas would result in a greatly improved signal. What has happened is > that I cannot for the life of me get this thing resonant around 3.520. And > yes, I did build the isolation t > r > >> > > an > > > >>sformer, per the instructions. > >> > >> Here is what is happening and I am certainly perplexed. I'm using an > MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls. > Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second > null is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna > resonant at 3.520 or so, I started adjusting the length of the antenna. > Adding wire to it makes the two "nulls" go down in frequency, as I would > expect. If I instead shorten the antenna wire, the "resonant frequencies" > both go up. However, there comes a point with both approaches where the > change of frequency stops, but the SWR goes up. > >> > >> As you can guess, I am NOT an antenna expert. Why do I get two > different resonant frequencies, separated by only 200 KHz? > >> > >> I've spent the better part of two days futzing around with this thing > and am about at my wit's end. I don't necessarily want to toss the entire > FCP assembly in the trash, and go back to the two radials, but this is not > going as I'd hoped! If someone on this list who has a good handle on wire > antenna tuning can give me some pointers and/or hints, off the list, I'd > certainly appreciate it. :-) > >> > >> > > __ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:Elecraft@mailman.qth.net > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > > > > > - > > No virus found in this message. > > Checked by AVG - www.avg.com > > Version: 10.0.1424 / Virus
Re: [Elecraft] OT: Need Antenna Tuning Help
I think you have to identify which of the two resonances is due to the antenna and not due to the antenna + feedline. Elevated radials that exhibit resonances of their own can also be confounding. The multiple resonance may be due to a fortunate length of coax that presents a 50 ohm at the shack end. You can identify which resonance is due to the antenna by attaching a short length of coax at the antenna feed and find the resonance with your antenna analyzer. Then you will know if you have to add or subtract wire. The fact that SWR "goes up" when you keep adding wires (@ complex part =0) only means that the impedance at resonance is changing. At resonance (complex part=0) different antennas have different values of Z Inverted L's and verticals have Z's of 30 to 35 ohms at resonance with a really good ground system. That isn't an SWR of 1:1.A yagi may have a Z of 15 ohms-- hence a big SWR. Once you have the antenna resonant where you want, then you have to deal with the mismatch. A simple L network at the base of the antenna will take care of the mismatch. 500 watts doesn't require monster components. 73 de Brian/K3KO On 2/28/2012 7:20 PM, Don Wilhelm wrote: > Jim, > > I did a little chatting with Guy K2AV when he was starting to work on > that project (W0UCE lives only a few miles from me), and I recall that > changing the height above ground changed the behavior. > So if you do not have the lowest wire 8 feet above the ground, it will > not be tuned properly. > Maybe Guy will comment, he frequently posts on this reflector. > > 73, > Don W3FPR > > On 2/28/2012 5:22 PM, Jim Bennett wrote: > >> I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters >> is my biggest hurdle. I put up an 80 meter Inverted L several months ago - >> prior to getting the KPA500. The vertical part of the antenna is 40 feet in >> length. I had been using two radials, about 14 inches above ground - small >> lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the >> internal tuner. I had done some pruning of the radials to get it resonant on >> 3.550. The K3 tuner took care of the rest. Well, along came the KPA500 and >> as yet, no KAT500. So I started looking at the antenna to see what I could >> do. I opted to replace the two single radial wires with a K2AV Folded >> CounterPoise (FCP). Not sure if this was a mistake or not. Everything I've >> read said that the FCP approach on 80 / 160 meter Inverted L antennas would >> result in a greatly improved signal. What has happened is that I cannot for >> the life of me get this thing resonant around 3.520. And yes, I did build >> the isolation t r >> > an > >>sformer, per the instructions. >> >> Here is what is happening and I am certainly perplexed. I'm using an >> MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls. >> Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null >> is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at >> 3.520 or so, I started adjusting the length of the antenna. Adding wire to >> it makes the two "nulls" go down in frequency, as I would expect. If I >> instead shorten the antenna wire, the "resonant frequencies" both go up. >> However, there comes a point with both approaches where the change of >> frequency stops, but the SWR goes up. >> >> As you can guess, I am NOT an antenna expert. Why do I get two different >> resonant frequencies, separated by only 200 KHz? >> >> I've spent the better part of two days futzing around with this thing and am >> about at my wit's end. I don't necessarily want to toss the entire FCP >> assembly in the trash, and go back to the two radials, but this is not going >> as I'd hoped! If someone on this list who has a good handle on wire antenna >> tuning can give me some pointers and/or hints, off the list, I'd certainly >> appreciate it. :-) >> >> > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > > - > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1424 / Virus Database: 2113/4837 - Release Date: 02/28/12 > > > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
Guess FCP as a concept has hit the big time if it's being bandied on Elecraft reflector. :>) We do not have much feedback from 80 meter use at all. It's been 99.9% about 160 meters where the huge space crunch hurts the worst. You DO need to do all the measuring at the output of the isolation transformer. Otherwise the coax can completely screw up the clues you need to prune the thing. I'll wait to hear what you measure at the IsoT. The only way you can correctly measure at the shack end of the coax is if you are using an AIM 4170 and have run a remote calibration to the end of the coax. There are some other analyzing devices that can do the remote measure thing besides the AIM. The program that runs with the analyzer keeps the calibration data for that specific piece of coax and then uses a mathematical transformation to adjust out the effects of the coax. Cannot do that with the MFJ analyzers. On another issue, it was not clear from your post, but understand that a +/- 33 foot FCP is a 160 meter device only and the isolation transformer for that is 20 bifilar turns, and you will need something in the order of magnitude of 125 feet in the "L" to resonate. For 80 meters ONLY, the FCP is +/- 16 feet, and the isolation transformer is 15 bifilar turns to work with something in the order of 60-65 feet. You can use the 20 turn, but electrically it has a lot more leftover inductance, and most likely runs with shorter L's for the "simple" configuration. If you were doing that, you would be the first "guinea pig" on how to use the 160 IsoT on 80 meters. Nobody has figured out how to do a dual band FCP, nor can you just put them in parallel. You might get an impedance dip, but the field cancelling effect that makes an FCP work is simply absent off-band, and the ground loss is back. The "simple" configuration is the FCP, the isolation transformer and something approximately a quarterwave L, whose length gets adjusted to bring the zero reactance crossing point where you want it. If you want to get into the theory, there are more complex applications, like how to do a 4 square with FCPs, while not using any radials. We are talking here about the "simple" configuration. The actual value of the resistance at zero reactance a given person gets depends on the specifics of the "L" that you have up. If you get the zero reactance point right, significantly off-50 R values can be dealt with using a series matching transformer of 50 ohm then 75 ohm, then 50 ohm coax rest of the way, calculated by a little free program called SMC.EXE. Most often the basic shape of the L is dictated by available trees, staying hidden, or..., very specific to the individual. So we don't publish "ideal" dimensions for the L. The double dip is possible, but explaining why without a slide show of EZNEC graphs ain't possible for us normal mortals. Or it could just be an effect of your specifics and the length of your coax. I would like to know the specific dimensions of your L. If you are getting 50 +j1 at 3654, then the current wisdom is you need to add length to force it down. But we don't have 80 meter information on how far down you can force it before the FCP starts to "argue with you" and won't move any more. Moving it from 3654 to 3535 is adding something like 4 and a half feet. My current 160 meter antenna, up 90 out 105 over a 160 FCP, has a "sort of half-way decent" spot down around 1700, but it's nowhere close to adjustable to 50 +j0. It's also lossy, as the FCP has flipped out of its cancellation mode. This leads me to believe the upper dip is the one you want to manage. For the extended audience here, the concept is on W0UCE's web page at http://www.w0uce.net/K2AVantennas.html Sorry about the OT. We don't have an "FCP reflector". Reflector discussion has been entirely on TopBand. 73, Guy K2AV. On Tue, Feb 28, 2012 at 6:51 PM, Jim Bennett wrote: > Well, crud - my fat fingers messed up the original post. That reading at > 3.654 should have been R=50, X=1, SWR=1.0. I'll take the MFJ out to the > antenna base and see what I get. > > On Tuesday, Feb 28, 2012, at Tuesday, 3:43 PM, Fred Jensen wrote: > > > On 2/28/2012 2:22 PM, Jim Bennett wrote: > > > >> > >> I get TWO SWR > >> nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. > >> The second null is at 3.654, R=0, X=1, SWR=1.0. > > > > You have something seriously wrong, 0+j1 ohms is a short circuit, or > > extremely close to one. I'm sure the SWR reading at that point is > > bogus, the MFJ was not designed to operate into a short circuit. In > > fact, the apparent "short circuit" could be bogus, I've gotten some very > > improbable results a few times with my MFJ. > > > > I'd suggest: > > > > 1. Take your MFJ259 out to the feedpoint of the antenna and see what > > you get. > > > > 2. Put a dummy load at the antenna end of your coax run and measure the > > impedance at the shack end. It should be 50+j0 ohms everywhere
Re: [Elecraft] OT: Need Antenna Tuning Help
Jim, I did a little chatting with Guy K2AV when he was starting to work on that project (W0UCE lives only a few miles from me), and I recall that changing the height above ground changed the behavior. So if you do not have the lowest wire 8 feet above the ground, it will not be tuned properly. Maybe Guy will comment, he frequently posts on this reflector. 73, Don W3FPR On 2/28/2012 5:22 PM, Jim Bennett wrote: > I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters is > my biggest hurdle. I put up an 80 meter Inverted L several months ago - prior > to getting the KPA500. The vertical part of the antenna is 40 feet in length. > I had been using two radials, about 14 inches above ground - small lot, > CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the internal > tuner. I had done some pruning of the radials to get it resonant on 3.550. > The K3 tuner took care of the rest. Well, along came the KPA500 and as yet, > no KAT500. So I started looking at the antenna to see what I could do. I > opted to replace the two single radial wires with a K2AV Folded CounterPoise > (FCP). Not sure if this was a mistake or not. Everything I've read said that > the FCP approach on 80 / 160 meter Inverted L antennas would result in a > greatly improved signal. What has happened is that I cannot for the life of > me get this thing resonant around 3.520. And yes, I did build the isolation tr an > sformer, per the instructions. > > Here is what is happening and I am certainly perplexed. I'm using an MFJ-259B > meter, at the shack end, to take my readings. I get TWO SWR nulls. Yes, two. > One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null is at > 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at 3.520 > or so, I started adjusting the length of the antenna. Adding wire to it makes > the two "nulls" go down in frequency, as I would expect. If I instead shorten > the antenna wire, the "resonant frequencies" both go up. However, there comes > a point with both approaches where the change of frequency stops, but the SWR > goes up. > > As you can guess, I am NOT an antenna expert. Why do I get two different > resonant frequencies, separated by only 200 KHz? > > I've spent the better part of two days futzing around with this thing and am > about at my wit's end. I don't necessarily want to toss the entire FCP > assembly in the trash, and go back to the two radials, but this is not going > as I'd hoped! If someone on this list who has a good handle on wire antenna > tuning can give me some pointers and/or hints, off the list, I'd certainly > appreciate it. :-) > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
Well, crud - my fat fingers messed up the original post. That reading at 3.654 should have been R=50, X=1, SWR=1.0. I'll take the MFJ out to the antenna base and see what I get. On Tuesday, Feb 28, 2012, at Tuesday, 3:43 PM, Fred Jensen wrote: > On 2/28/2012 2:22 PM, Jim Bennett wrote: > >> >> I get TWO SWR >> nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. >> The second null is at 3.654, R=0, X=1, SWR=1.0. > > You have something seriously wrong, 0+j1 ohms is a short circuit, or > extremely close to one. I'm sure the SWR reading at that point is > bogus, the MFJ was not designed to operate into a short circuit. In > fact, the apparent "short circuit" could be bogus, I've gotten some very > improbable results a few times with my MFJ. > > I'd suggest: > > 1. Take your MFJ259 out to the feedpoint of the antenna and see what > you get. > > 2. Put a dummy load at the antenna end of your coax run and measure the > impedance at the shack end. It should be 50+j0 ohms everywhere [within > reason] > > 3. Check the SWR with your K3 with the tuner in bypass at 3501 and up > the band a few places and draw a graph of the readings. Keep the power > down, you can't really hurt the K3, it'll quit making RF if it gets > really annoyed. If the null at 3461 is really the resonant point of > your antenna, you should see the SWR climbing rapidly as you go up the band. > > When really weird things happen in conflict with known physics, it's > almost always a simple error in the system or measurement configuration. > I'd look carefully at the wiring. Let us all know what you find, I'd > like to write it into my notebook for future ref. > > 73, > > Fred K6DGW > - Northern California Contest Club > - CU in the 2012 Cal QSO Party 6-7 Oct 2012 > - www.cqp.org > > > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
On 2/28/2012 2:22 PM, Jim Bennett wrote: > > I get TWO SWR > nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. > The second null is at 3.654, R=0, X=1, SWR=1.0. You have something seriously wrong, 0+j1 ohms is a short circuit, or extremely close to one. I'm sure the SWR reading at that point is bogus, the MFJ was not designed to operate into a short circuit. In fact, the apparent "short circuit" could be bogus, I've gotten some very improbable results a few times with my MFJ. I'd suggest: 1. Take your MFJ259 out to the feedpoint of the antenna and see what you get. 2. Put a dummy load at the antenna end of your coax run and measure the impedance at the shack end. It should be 50+j0 ohms everywhere [within reason] 3. Check the SWR with your K3 with the tuner in bypass at 3501 and up the band a few places and draw a graph of the readings. Keep the power down, you can't really hurt the K3, it'll quit making RF if it gets really annoyed. If the null at 3461 is really the resonant point of your antenna, you should see the SWR climbing rapidly as you go up the band. When really weird things happen in conflict with known physics, it's almost always a simple error in the system or measurement configuration. I'd look carefully at the wiring. Let us all know what you find, I'd like to write it into my notebook for future ref. 73, Fred K6DGW - Northern California Contest Club - CU in the 2012 Cal QSO Party 6-7 Oct 2012 - www.cqp.org __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] OT: Need Antenna Tuning Help
Jim: You need to pay attention to your numbers. "R=0, X=1, SWR=1.0" is a short circuit with a short piece of wire. While it is possible to have multiple resonances and multiple nulls this not the case here. You have a major problem. Perhaps something is breaking down or perhaps you have made a construction error. Recheck everything. Use a simple ohm meter to check for shorts and continuity. If that doesn't find your problem prove your transmission line by putting a 50 ohm dummy load at end of your coax (antenna end) and check with your MFJ259. It should say 50 j0. If it does inspect your antenna carefully. Make sure your insulators insulate. Whatever you do don't hook up the KPA500 until you fix this problem. Let us know how you come out. 73 Fred, AE6QL -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Jim Bennett Sent: Tuesday, February 28, 2012 2:23 PM To: Elecraft@mailman.qth.net Subject: [Elecraft] OT: Need Antenna Tuning Help I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters is my biggest hurdle. I put up an 80 meter Inverted L several months ago - prior to getting the KPA500. The vertical part of the antenna is 40 feet in length. I had been using two radials, about 14 inches above ground - small lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the internal tuner. I had done some pruning of the radials to get it resonant on 3.550. The K3 tuner took care of the rest. Well, along came the KPA500 and as yet, no KAT500. So I started looking at the antenna to see what I could do. I opted to replace the two single radial wires with a K2AV Folded CounterPoise (FCP). Not sure if this was a mistake or not. Everything I've read said that the FCP approach on 80 / 160 meter Inverted L antennas would result in a greatly improved signal. What has happened is that I cannot for the life of me get this thing resonant around 3.520. And yes, I did build the isolation tran sformer, per the instructions. Here is what is happening and I am certainly perplexed. I'm using an MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at 3.520 or so, I started adjusting the length of the antenna. Adding wire to it makes the two "nulls" go down in frequency, as I would expect. If I instead shorten the antenna wire, the "resonant frequencies" both go up. However, there comes a point with both approaches where the change of frequency stops, but the SWR goes up. As you can guess, I am NOT an antenna expert. Why do I get two different resonant frequencies, separated by only 200 KHz? I've spent the better part of two days futzing around with this thing and am about at my wit's end. I don't necessarily want to toss the entire FCP assembly in the trash, and go back to the two radials, but this is not going as I'd hoped! If someone on this list who has a good handle on wire antenna tuning can give me some pointers and/or hints, off the list, I'd certainly appreciate it. :-) Regards, Jim / W6JHB __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
[Elecraft] OT: Need Antenna Tuning Help
I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters is my biggest hurdle. I put up an 80 meter Inverted L several months ago - prior to getting the KPA500. The vertical part of the antenna is 40 feet in length. I had been using two radials, about 14 inches above ground - small lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the internal tuner. I had done some pruning of the radials to get it resonant on 3.550. The K3 tuner took care of the rest. Well, along came the KPA500 and as yet, no KAT500. So I started looking at the antenna to see what I could do. I opted to replace the two single radial wires with a K2AV Folded CounterPoise (FCP). Not sure if this was a mistake or not. Everything I've read said that the FCP approach on 80 / 160 meter Inverted L antennas would result in a greatly improved signal. What has happened is that I cannot for the life of me get this thing resonant around 3.520. And yes, I did build the isolation tran sformer, per the instructions. Here is what is happening and I am certainly perplexed. I'm using an MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at 3.520 or so, I started adjusting the length of the antenna. Adding wire to it makes the two "nulls" go down in frequency, as I would expect. If I instead shorten the antenna wire, the "resonant frequencies" both go up. However, there comes a point with both approaches where the change of frequency stops, but the SWR goes up. As you can guess, I am NOT an antenna expert. Why do I get two different resonant frequencies, separated by only 200 KHz? I've spent the better part of two days futzing around with this thing and am about at my wit's end. I don't necessarily want to toss the entire FCP assembly in the trash, and go back to the two radials, but this is not going as I'd hoped! If someone on this list who has a good handle on wire antenna tuning can give me some pointers and/or hints, off the list, I'd certainly appreciate it. :-) Regards, Jim / W6JHB __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
