advice with homebrew traps - elmers Forum at eHam.net

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advice with homebrew traps	Reply
by M0JHA on August 22, 2007	Mail this to a friend!
hello, im thinking of putting together a trap dipole for 40-10.. i copied a design from the arrl antenna book. i made a single 10m trap to see how i went on. testing for the resonant frequency with a mfj 259b and a loop of wire around 3"diameter connected from center of pl to eart post.. ( told this was one way of doing it???) i wanted resonance at around 28.500. the mfj peak z read 444 at 28.445mhz the z stayed the same till the frequency reached 28.485mhz then dropped right off. does this sound right?? and if so does this mean i will only have a bandwidth of some 40 khz?? and just one more question .. do both traps need to be identical in resonant frequency or is there room for slight differances? thanks in advance billy uk

RE: advice with homebrew traps	Reply
by N6AJR on August 22, 2007	Mail this to a friend!
try one of these starter Bye the way, none of this is mine, Its just stuff I pulled from here and there. thanks to all the folks with the great sites. this is My take on the multi-band, single feed wire dipole ( but fan dipole is easier to type. a true fan dipole is also called similar to a cage dipole and has 3 or 4 wires of different lengths on the same band , like a 64 foot , 66 foot and 68 foot double leg wires on the same feed to give wider bandwidth, but bottom line, they are cheap, easy to build, and they work.. http://www.ku4ay.net/dipole.html http://www.qsl.net/kd7rem/antdipole.htm http://www.hamuniverse.com/multidipole.html http://www.angelfire.com/nb/ni4l/ni4ldipole.html http://www.arrl.org/tis/info/pdf/9611073.pdf http://www.geocities.com/n2uhc/2banddipole.html http://www.qsl.net/na4it/fandipole.html by N3JBH on October 12, 2006 FAN DIPOLE OR MULTIPLE BAND DIPOLE SPECS: (Each leg is shown in length so you will need two legs.) 10 METERS = 8'4" 12 METERS = 9'5" 15 METERS = 11'1" 17 METERS = 12'10" 20 METERS = 16'8" 30 METERS = 23'2" 40 METERS = 32'9" 60 METERS = 43'7" 75 METERS = 60'9" 80 METERS = 65'6" 160 METERS = 123'5" 137 KHZ = 1708'1"

RE: advice with homebrew traps	Reply
by W8JI on August 22, 2007	Mail this to a friend!
Traps are a great way to go. I'm considering making my 160 dipole into a trap antenna. The MFJ antenna analyzer is a pretty poor way to measure a trap or any high Q resonant circuit. You really can't tell much other than the approximate frequency of resonance. You certainly cannot get any idea about Q. Fortunately the exact frequency doesn't matter as much as we might think. Anything from 27.5 to 29 MHz would work as a ten meter trap on the low end of the band. The traps should be reasonably close to the same frequency, but it isn't necessary they be exact. 73 Tom

RE: advice with homebrew traps	Reply
by N3OX on August 22, 2007	Mail this to a friend!
"Fortunately the exact frequency doesn't matter as much as we might think. Anything from 27.5 to 29 MHz would work as a ten meter trap on the low end of the band. " I threw some together out of copper flashing, teflon tape, and copper wire, measured 'em with my MFJ-259 at about 28.400 and stuck them in my 15m dipole and strung it back up. I used the "dip meter" plug in coils that came as part of the accessory pack (which I probably wouldn't have bought on my own but it was a christmas gift many years ago) Worked like a charm. I did the same thing with copper wire coil and coax cable capacitor traps on a 10/15 rotatable dipole some years ago. Again, no problem. I like traps too. They get a bad rap, mostly from people trying to sell non-trap antennas, but I'd personally pick a trap dipole over a fan dipole any day. They're just easier to tune. Dan

RE: advice with homebrew traps	Reply
by M0JHA on August 23, 2007	Mail this to a friend!
thanks guys.. iv tried the fan dipole as i quite like that idea . couldnt get it to tune . all the elements were interacting as i didnt have enough room to fan them out with eniough space between elements. my problem is i can only get inverted v into my garden with max leg length just ok for 40m dipole.. tried a ground mounted vert which worked nice but dont like the idea of buried radials as from what iv read there a pretty poor way to install radials?? i also have 4 ankle biters that run riot in the garden and here in the uk we dont have large gardens.. and it would simply get broken in some way.. billy

RE: advice with homebrew traps	Reply
by WA3SKN on August 23, 2007	Mail this to a friend!
Consider taking that 40 meter "inverted V" and feeding it with 450 ohm open-wire line and a manual antenna tuner. Multi-band with a single antenna tuned at the rig! And, not that expensive to do! -Mike.

RE: advice with homebrew traps	Reply
by M0JHA on August 23, 2007	Mail this to a friend!
cheers mike, i dont know if its just me but iv tried the ladder line and tuner approach and it doesnt seem to work great for me.. i used the said antenna with ladderline resonant on 40m. no problem... when i come off resonance and use a tuner the rx seems down a couple of s points so i presume its the same tx as i will have trouble with contacts..( i only run 5w max also) .. if im using a resonant antenna the radio comes alive with a big differance to that when using a tuner and a non resonant antenna, so i want something thats going to be resonant on the bands of choice.. i could be wrong, i was told the only advantage to a resonant antenna is it can be fed with coax.. not convinced thats all though.. billy

RE: advice with homebrew traps	Reply
by WA3SKN on August 23, 2007	Mail this to a friend!
Billy... It shouldn't be that low. What type of ground do you have to the antenna tuner? (And I used an Argonaut 509 for 14 years-adjusted to 900 milliwatts output, so I know what 5 watts can do!) -Mike.

RE: advice with homebrew traps	Reply
by M0JHA on August 23, 2007	Mail this to a friend!
hello mike.. i have a braided lead(1/2"dia)from rig to atu(8" length). around 2 foot in length going from tuner to copper pipe (bus i think you call them) under my bench.. from this i have same type of wire leading outside (around 6 foot piece) to a ground rod and from the ground rod id say roughly 15/20 long wires running under my lawn.. at least 10-15 foot long... the best way i can describe what i hear is the radio being deaf?? but with a resonant ant its really noticable that theres a differance.. this is on my 817 but had the same thing with my icom 718 also.. this is the reason iv kept away from using a tuner if i could.. cheers billy

RE: advice with homebrew traps	Reply
by WA3SKN on August 23, 2007	Mail this to a friend!
That ground sounds OK! You might have a tuner problem. Have you tried just connecting each 450 ohm lead to the tip side of your antenna jack... RECEIVE only, and listen? Now, DON'T TRAMSMIT! -Mike.

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