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80 Meter End Fed Eire
I have just put up an 80 Meter End Fed Flexweave wire. Its about 63 feet
long and fed direct with 50 Ohm coax at the far end of the garden. The shield is connected straight down to a ground earth stake at this point and it is tuned for 3.700 MHz. It receives better than any thing I have used so far, but it is very death on 40 meters. Almost unusable. Is there a reason for this? The antenna is only up at 20 feet and my old G5RV is only 6 feet off the ground at the moment and receives far better on 40 meters than the End Fed wire. 73 Andy |
80 Meter End Fed Eire
"Andy" wrote in message ... I have just put up an 80 Meter End Fed Flexweave wire. Its about 63 feet long and fed direct with 50 Ohm coax at the far end of the garden. The shield is connected straight down to a ground earth stake at this point and it is tuned for 3.700 MHz. It receives better than any thing I have used so far, but it is very death on 40 meters. Almost unusable. Is there a reason for this? The antenna is only up at 20 feet and my old G5RV is only 6 feet off the ground at the moment and receives far better on 40 meters than the End Fed wire. 73 Andy Yes there is- it's a half wave long on 40M which implies voltage feed and a VSWR in the 60--80:1 range. Dale W4OP |
80 Meter End Fed Eire
In message K3X2k.2824$lE3.246@trnddc05, Dale Parfitt
writes "Andy" wrote in message ... I have just put up an 80 Meter End Fed Flexweave wire. Its about 63 feet long and fed direct with 50 Ohm coax at the far end of the garden. The shield is connected straight down to a ground earth stake at this point and it is tuned for 3.700 MHz. It receives better than any thing I have used so far, but it is very death on 40 meters. Almost unusable. Is there a reason for this? The antenna is only up at 20 feet and my old G5RV is only 6 feet off the ground at the moment and receives far better on 40 meters than the End Fed wire. 73 Andy Yes there is- it's a half wave long on 40M which implies voltage feed and a VSWR in the 60--80:1 range. Dale W4OP The question is, what are the consequences of having such a high SWR? It all depends on how much attenuation the coax has. If the coax was lossless, there would be no signal loss, regardless of the SWR. For many years, I have been an advocate of this 'far-end feed' type of antenna. Its great advantage is that it greatly reduces the amount of local interference it receives (and creates). Also, all the essential RF grounding is at the far end. You don't need an RF ground in the shack. The shack is RF-dead. Ideally, you would use a tuning/matching unit at the antenna feedpoint but, provided your coax has adequately low loss, you can get away with having the tuning unit at the shack end of the coax. It's surprising how well this works - especially on the lower frequency amateur bands. For reception only, it might be worth while considering fitting a matching transformer at the antenna feedpoint. These typically have an impedance ratio of 9:1. The essential purpose is to prevent extremes of impedance mismatch between the antenna and the coax. Below, I have appended some information from 'RHF', one of the contributors to the rec.radio.shortwave newsgroup. Note that these devices are NOT baluns! My present antenna is about twice the size of that described. It's about 120 foot inverted-L, at around 25 feet. The coax length is about 90 foot. I can tune it up from 160 to 10m. It certainly seems lively enough up to 20m. As I said, you do need really good low-loss coax. CATV trunk cable is pretty good, if you can lay your hands on some. Don't worry about it being 75 ohms. Depending on frequency, you are going to get quite a variety of weird impedances at the shack end of the coax. What you get will be whatever the feed impedance of the antenna is, but transformed by the length of the coax, and influenced by its attenuation. In the example of the Flexweave wire, the antenna is around a halfwave long, so the impedance is very high. However, the coax will be (guessing) 40 foot long, which, allowing for a velocity factor of 0.6, will also be a halfwave at 40m. The impedance at the shack end will therefore be very high, which may not suit the receiver. You will certainly need a matching unit to transmit. Finally, having used the 'tuner-in-the-shack' method for around 30 years, in my old age I am considering investing in one of the automatic remote tuning units (such as the SG-230). However, one slight disadvantage is that, in order to work, they need to be fed with RF, so are not suitable for SWL-use only. ------------------------------------------------------------------------- ------------ From 'RHF' in rec.radio.shortwave (29 March 2008) Some people as a result of the coining of the Word "Balun" [Bal-Un] for Balanced-to-Unbalance Matching Transformer : Also like to use the Word "Unun" [Un-Un] for the Unbalance- to-Unbalanced Matching Transformer. "Balun" a specific Contraction becoming an inclusive Buzz Word relegated to commonly misused technical Jargon. http://en.wikipedia.org/wiki/Balun Most of these Matching Transformers used between Single Wire Antenna Elements and Coax Cable are 'not' Baluns but Ununs since the Match-up an Unbalanced Antenna Element with an Unbalanced Coax Calbe feed-in-line. Many Manufactures have come-up with Trade Marked Names for these Products like : * Magnetic Longwire Balun (MLB) -by- RF Systems http://www.rf-systems.nl/pdf/mlbm.pdf * Magnetic Longwire Balun(MLB-1) -by- Palomar Enginers http://www.palomar-engineers.com/MLB-1/mlb-1.html * Long Wire Antenna Adapter (LWA) LWA-0130 -by- WinRadio http://www.winradio.com/home/lwa.htm * Longwire Balun 9:1 Transformer -by- LowBander http://cgi.ebay.com/_W0QQitemZ180227972387 * Universal Magnetic Balun (UMB) -by- Wellbrook http://www.wellbrook.uk.com/longwire.html + UMB and Antenna Feed-in-Line Isolation http://www.wellbrook.uk.com/UMB.html * Longwire Impedance Matcher (LIM) http://www.angelfire.com/mb/amandx/lim.html http://www.shortwavestore.com/pdf/lo...ce-matcher.pdf READ - Magnetic Longwire Balun - Not Really a Balun http://www.hard-core-dx.com/nordicdx...d/magbal2.html From : John Doty ) Date : August 24, 1995 Original Source : UseNet's Rec.Radio.Shortwave READ - Magnetic Longwire Balun - A Con or Not ? http://www.hard-core-dx.com/nordicdx...d/magbal1.html -hosted by- Hard Core DX .Com READ - The Verdict {One Man's Opinion} : The Magnetic Longwire Balun Is Too Expensive http://www.hard-core-dx.com/nordicdx.../magbalun.html -by- Alan Johnson READ - About the MLB "Magnetic Longwire Balun" - How To ! http://users.belgacom.net/hamradio/s...ire%20Balun_ML B.htm -by- Guy Roels [ON6MU] |
80 Meter End Fed Eire
Hi Dale,
Does this only apply to 1/2 wave long end feds only? Does this apply to any frequency? The maximum space here is only 66 feet at best. What options am I left with that would work for 80-40 meters? I have a question about traps. I read yesterday that traps should not be tuned to resonance of the wanted frequency. If I constructed a homebrew trap for say 7.1 MHz. How far away from this frequency should I tune the trap? Should it be tuned higher or lower? I did search the internet, but I could not find any info on whether its best to setup the trap higher or lower than the wanted frequency and by how much. Andy "Dale Parfitt" wrote in message news:K3X2k.2824$lE3.246@trnddc05... "Andy" wrote in message ... I have just put up an 80 Meter End Fed Flexweave wire. Its about 63 feet long and fed direct with 50 Ohm coax at the far end of the garden. The shield is connected straight down to a ground earth stake at this point and it is tuned for 3.700 MHz. It receives better than any thing I have used so far, but it is very death on 40 meters. Almost unusable. Is there a reason for this? The antenna is only up at 20 feet and my old G5RV is only 6 feet off the ground at the moment and receives far better on 40 meters than the End Fed wire. 73 Andy Yes there is- it's a half wave long on 40M which implies voltage feed and a VSWR in the 60--80:1 range. Dale W4OP |
80 Meter End Fed Eire
Ian Jackson wrote:
The question is, what are the consequences of having such a high SWR? It all depends on how much attenuation the coax has. If the coax was lossless, there would be no signal loss, regardless of the SWR. True, but the value of Z0 of the transmission line has a large effect. Let's say we are feeding one of those 5000 ohm antennas. The SWR on 50 ohm coax would be 100:1. The SWR on 450 ohm ladder-line would be 11:1. Even if the coax had the same matched-line loss as the ladder-line, it would still be much lossier than the ladder-line - and much more expensive. -- 73, Cecil http://www.w5dxp.com |
80 Meter End Fed Eire
Andy wrote:
I have a question about traps. I read yesterday that traps should not be tuned to resonance of the wanted frequency. If I constructed a homebrew trap for say 7.1 MHz. How far away from this frequency should I tune the trap? Should it be tuned higher or lower? Tune it for lower than the operating frequency to minimize trap losses. The point to shoot for is the maximum inductive reactance point which is at a lower frequency than the parallel resonant resistance point. How much lower depends upon the Q of the trap. -- 73, Cecil http://www.w5dxp.com |
80 Meter End Fed Eire
I have nothing here to measure the Q of the trap.
Is there another way of working out the correct frequency needed for the trap? The traps are made from RG58 C/U. I think these are a low Q but I'm not sure. Andy "Cecil Moore" wrote in message ... Andy wrote: I have a question about traps. I read yesterday that traps should not be tuned to resonance of the wanted frequency. If I constructed a homebrew trap for say 7.1 MHz. How far away from this frequency should I tune the trap? Should it be tuned higher or lower? Tune it for lower than the operating frequency to minimize trap losses. The point to shoot for is the maximum inductive reactance point which is at a lower frequency than the parallel resonant resistance point. How much lower depends upon the Q of the trap. -- 73, Cecil http://www.w5dxp.com |
80 Meter End Fed Eire
In message , Cecil Moore
writes Ian Jackson wrote: The question is, what are the consequences of having such a high SWR? It all depends on how much attenuation the coax has. If the coax was lossless, there would be no signal loss, regardless of the SWR. True, but the value of Z0 of the transmission line has a large effect. Let's say we are feeding one of those 5000 ohm antennas. The SWR on 50 ohm coax would be 100:1. The SWR on 450 ohm ladder-line would be 11:1. Even if the coax had the same matched-line loss as the ladder-line, it would still be much lossier than the ladder-line - and much more expensive. I think that the secret is to make sure that antenna is not exact multiples of a halfwave. This prevents the SWR being absolutely sky-high - say, 'only' 20:1, worst case. The proviso is certainly that the coax should be as lossless as possible. I'm happy to lose 3 or 4dB in the interests of simplicity and good EMC. It's mainly 160/80/40 which I'm interested in. There's just a load of foreigners on the higher bands! Some time ago, I did some (more) Smith Chart guestimation with the object of trying to find which 'magic' inverted-L antenna lengths would present 'reasonable' impedances on all (or most) of the amateur bands up to 30Mhz. [Many years ago, I reckoned that around 185 feet was a good length.] However, my recent efforts ended in dismal failure. In the meantime, I will continue in complete ignorance, and use my antenna as it is, accidentally having the occasional QSO and causing no obvious interference problems. But, after all these years, I might treat myself to an automatic tuner for the far end of the coax. -- Ian |
80 Meter End Fed Eire
Andy wrote:
I have nothing here to measure the Q of the trap. Is there another way of working out the correct frequency needed for the trap? Sorry, I would just be guessing. I made my 40m traps resonant on 7.4 MHz and they worked well over the 40m band. But I never made any measurements or A/B comparisons. The traps are made from RG58 C/U. I think these are a low Q but I'm not sure. The following web page might be of interest: http://www.seed-solutions.com/gregor...n/CoaxTrap.htm -- 73, Cecil http://www.w5dxp.com |
80 Meter End Fed Eire
I've given up on this idea for now. I just can't get any ground wires above
or below ground here at present and the couple of earth rods that I have sunk in just doesn't do the job. 73 Andy "Cecil Moore" wrote in message ... Andy wrote: I have nothing here to measure the Q of the trap. Is there another way of working out the correct frequency needed for the trap? Sorry, I would just be guessing. I made my 40m traps resonant on 7.4 MHz and they worked well over the 40m band. But I never made any measurements or A/B comparisons. The traps are made from RG58 C/U. I think these are a low Q but I'm not sure. The following web page might be of interest: http://www.seed-solutions.com/gregor...n/CoaxTrap.htm -- 73, Cecil http://www.w5dxp.com |
80 Meter End Fed Eire
Andy,
You have learned something though. Those 'ground/earth' rods aren't all they are cracked up to be, not exactly the 'best' choice in every case (especially for lower frequencies). Not much consolation, huh? Oh well, that's the way it goes... - 'Doc |
80 Meter End Fed Eire
Hi Doc,
Yep I guess I've learned that earth rods on there own are a no-go for end-fed wires at those frequencies. I shell know better next time. 73 Andy wrote in message ... Andy, You have learned something though. Those 'ground/earth' rods aren't all they are cracked up to be, not exactly the 'best' choice in every case (especially for lower frequencies). Not much consolation, huh? Oh well, that's the way it goes... - 'Doc |
80 Meter End Fed Eire
In message , Andy
writes wrote in message ... Andy, You have learned something though. Those 'ground/earth' rods aren't all they are cracked up to be, not exactly the 'best' choice in every case (especially for lower frequencies). Not much consolation, huh? Oh well, that's the way it goes... - 'Doc Hi Doc, Yep I guess I've learned that earth rods on there own are a no-go for end-fed wires at those frequencies. I shell know better next time. 73 Andy This does sound rather defeatist. While ground rods alone may not be the 'ultimate', surely they are usually be adequate for listening-only purposes? -- Ian |
80 Meter End Fed Eire
Ian,
They probably are adequate for 'just listening'. In a lot of cases, not using a ground works just fine too. Just depends on the circumstances. Receivers just don't seem to be very 'picky' like transmitters are. Since the 'ground' can sort of affect where you hear things from, that's one of those 'things' to consider too. There are very few 'perfect' antennas or installations, almost all of them are a compromise in some way. The idea is to make the best of what you got (Ooooo, is that a can of worms!:)). And the mostest important thingy is to have fun at it. - 'Doc |
80 Meter End Fed Eire
I'm having loads of fun since I started.
I recently purchased an RigExpert AA-200 Antenna Anal;yser from Radio World. Here's the link if anyone wants a read. http://www.radioworld.co.uk/~radio/c...a4a96691a21039 Trouble now is I can't put the AA-200 down with out thinking of some thing else to try out. I'm getting addicted. 73 Andy wrote in message ... Ian, They probably are adequate for 'just listening'. In a lot of cases, not using a ground works just fine too. Just depends on the circumstances. Receivers just don't seem to be very 'picky' like transmitters are. Since the 'ground' can sort of affect where you hear things from, that's one of those 'things' to consider too. There are very few 'perfect' antennas or installations, almost all of them are a compromise in some way. The idea is to make the best of what you got (Ooooo, is that a can of worms!:)). And the mostest important thingy is to have fun at it. - 'Doc |
80 Meter End Fed Eire
Andy wrote:
I'm having loads of fun since I started. I recently purchased an RigExpert AA-200 Antenna Anal;yser from Radio World. Here's the link if anyone wants a read. http://www.radioworld.co.uk/~radio/c...a4a96691a21039 Trouble now is I can't put the AA-200 down with out thinking of some thing else to try out. I'm getting addicted. 73 Andy Andy, I see that it has a USB interface and CD, is this purely Windows based and is a computer actually necessary? 73, Charlie -- M0WYM www.radiowymsey.org Wymsey - Ten years Old! www.wymsey.co.uk |
80 Meter End Fed Eire
Charlie,
Yes the software is Windows only, on my CD. No you don't need to connect it to the computer to use it, but you can do if you want to. 73 Andy "M0WYM" wrote in message ... Andy wrote: I'm having loads of fun since I started. I recently purchased an RigExpert AA-200 Antenna Anal;yser from Radio World. Here's the link if anyone wants a read. http://www.radioworld.co.uk/~radio/c...a4a96691a21039 Trouble now is I can't put the AA-200 down with out thinking of some thing else to try out. I'm getting addicted. 73 Andy Andy, I see that it has a USB interface and CD, is this purely Windows based and is a computer actually necessary? 73, Charlie -- M0WYM www.radiowymsey.org Wymsey - Ten years Old! www.wymsey.co.uk |
80 Meter End Fed Eire
Andy wrote:
Charlie, Yes the software is Windows only, on my CD. No you don't need to connect it to the computer to use it, but you can do if you want to. 73 Andy Andy, That's what I suspected. Thanks, Charlie. -- M0WYM www.radiowymsey.org Wymsey - Ten years Old! www.wymsey.co.uk |
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