MFJ can mess up a wet dream so don't get your hopes up too high.
You suggested that on Dec. 5, when I was just contemplating ordering the cobweb.
I should've listened.
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The Search for the Perfect Antenna . . .
- Thread starter Riverman
- Start date
You suggested that on Dec. 5, when I was just contemplating ordering the cobweb.
I should've listened.
I'll bite. Regarding the MFJ 259B Accuracy varies according to temperature, and calibration is a burden due to shipping two ways. The MFJ 226 doesn't count because it isn't even manufactured by MFJ and I highly recommend it over the older models. Calibration can be done at home, assuming you have the loads.
Glad I opted for my RigExpert analyzer.
I passed on the MFJ because of all the QC complaints concerning their antennas and other stuff. Then what did I do? I took a chance on one of their expensive magnetic loops.
Luckily, DX Engineering took it back, no questions asked, and refunded my money less a small re-stocking fee. And now, months later, I have a cobweb and a hacksaw that's begging to be put into service. Took a while, but I'm done with MFJ.
BJ radionut
Supporting Member and 6m addict
Riv71: Just MHO...Don't give up on the Cobweb just yet...now that you understand the tuning issues and a few "bugs" of the general design. I think you can work with it.
Tune it at 6 ft where your not running in/out to the rig. Set-up with the analyzer first time thru and then finish at same height with the rig for the final set-up. Get another spool of bare wire and restring it, and go from there. Then when you get it close, you can dab a little solder on the fastener points to hold it firm. I would think maybe even a bigger size washer to get little more "grip" at those points could be a option also. ( but that's just me)
I don't think I have EVER purchased a factory type antenna, that was a "Throw and Go" design.
I have always found things I did not like and made changes, whether hardware or just general specs...EVERY location and general install differs.
GL
All the Best
Gary
Tune it at 6 ft where your not running in/out to the rig. Set-up with the analyzer first time thru and then finish at same height with the rig for the final set-up. Get another spool of bare wire and restring it, and go from there. Then when you get it close, you can dab a little solder on the fastener points to hold it firm. I would think maybe even a bigger size washer to get little more "grip" at those points could be a option also. ( but that's just me)
I don't think I have EVER purchased a factory type antenna, that was a "Throw and Go" design.
I have always found things I did not like and made changes, whether hardware or just general specs...EVERY location and general install differs.
GL
All the Best
Gary
Have actually only used my hacksaw once, Gary. That was on a ProComm Patriot 12.
The cobweb is still lying in my yard. When the weather warms up, I'll likely give it another shot with different wire and a better tuning plan. If it turns out to be a good antenna I'll look like an idiot but that's okay. Won't be the first time.
Gary,
I know insulated wire will change the final length a little, but won't it come out in the wash during the tuning phase?
BJ radionut
Supporting Member and 6m addict
Couldn't stand looking at the cobweb lying in my backyard.
Carried it around to my garage, out it on a short tripod, and went to work (after a trip to Lowe's).
Stripped all the cheap wire off as well as the connections for 6 meters. Decided to go back with just 10, 15 and 20 meters. This will give more space between wires for less interaction (I think).
Cut wires to proper lengths and crimped/soldered on ring terminals.
Out to garage to attach the wires!
10 meters first.
Wait a minute. What the heck? Both legs are too short to reach the insulator. Re-measure the wires. Yep, each is 8'3" plus an extra 6". A total of 17'6". More than enough for a half-wave dipole at 28.4 MHz.
To reach the insulator and have a little left for trimming, each leg needs another foot of wire. A total of 19'6".
I've made 10 meter dipoles before and 17'6" was always too much wire. Now not even close to being enough. If anything, I thought this square dipole would be shorter than a standard flat dipole just as inverted vee's are.
Move on to 15 meters. Same thing. Won't reach the insulator.
Ends are just dangling in the wind. Each leg cut to 11' plus an extra 6". For. Total of 23'. Plenty for 21.325 MHz. But still need another 2'.
Stopped there. Hacksaw snging sweet music to my ears.
Carried it around to my garage, out it on a short tripod, and went to work (after a trip to Lowe's).
Stripped all the cheap wire off as well as the connections for 6 meters. Decided to go back with just 10, 15 and 20 meters. This will give more space between wires for less interaction (I think).
Cut wires to proper lengths and crimped/soldered on ring terminals.
Out to garage to attach the wires!
10 meters first.
Wait a minute. What the heck?
Both legs are too short to reach the insulator. Re-measure the wires. Yep, each is 8'3" plus an extra 6". A total of 17'6". More than enough for a half-wave dipole at 28.4 MHz.To reach the insulator and have a little left for trimming, each leg needs another foot of wire. A total of 19'6".
I've made 10 meter dipoles before and 17'6" was always too much wire. Now not even close to being enough. If anything, I thought this square dipole would be shorter than a standard flat dipole just as inverted vee's are.
Move on to 15 meters. Same thing. Won't reach the insulator.
Ends are just dangling in the wind. Each leg cut to 11' plus an extra 6". For. Total of 23'. Plenty for 21.325 MHz. But still need another 2'.
Stopped there. Hacksaw snging sweet music to my ears.
Well that sucks. Unfortunately the "measure twice, cut once" rule still gets us every now and then. I'm sure you can find a use for 17' of wire somewhere.
What was the reason for replacing the wire? I know it was "cheap" but was there something wrong with it?
What was the reason for replacing the wire? I know it was "cheap" but was there something wrong with it?
Measured 3 times before cutting. Had them at the lengths I wanted. Have never seen a 10 meter dipole that needed 19' of wire.
The original wire was already frayed in a number of places. Was worried it would worsen in the wind. Decided to replace rather than solder. And wanted a fresh start.
Well, this is a mystery to me. There's just no way to restring this using reasonable half wave dipole lengths for the different bands. The original wires are at the bottom of the trash and I won't be fishing them out to measure them. Maybe this design requires the lengths to be what I consider excessively long. I don't know. But I know this. I'm not buying more wire or spending the time to solder extra pieces to what I have.
Had a friend of mine look at it and he just scratched his head and said, well, I can't repeat what he said here.
End of story. Well, this one. Another antenna adventure awaits. Someday.
Had a friend of mine look at it and he just scratched his head and said, well, I can't repeat what he said here.
End of story. Well, this one. Another antenna adventure awaits. Someday.
BJ radionut
Supporting Member and 6m addict
Riv71: Not really surprised these lengths are not "perfect" for the formulas.
A true electrical Half wave length at 28.0 is very near 17 ft. long.
Then you have to adjust lengths due to the "combined" impedance of All the loops together are equal to 12.5 Ohms at feedpoint. Thus the usage of the 4:1 matching transformer to bring the whole 5 band array up to 50 Ohms.
The wires do interact, thus lets say 20 meters: that loop is not the only wire(s) radiating.
There will be radiation on the other wires, it may be very low but again that is part of the total impedance of the whole array. The 20m loop measured at the feedpoint will not be a "True" 50 Ohms. I am speculating more like 72 Ohms which is the true impedance of a Horizontal 1/2 wave dipole.
To me, this would account somewhat for the difference in length of the wires.
Another consideration is the place where the array is tuned. Not everyone will want this to tune in the "Middle" of the phone band. Thus the construction will have to account for operation and tuning for the low ends of the CW sections also. Therefore a "compromise" must occur in where the whole array will be resonate to accomplish both.
My penny's worth.
All the Best
Gary
A true electrical Half wave length at 28.0 is very near 17 ft. long.
Then you have to adjust lengths due to the "combined" impedance of All the loops together are equal to 12.5 Ohms at feedpoint. Thus the usage of the 4:1 matching transformer to bring the whole 5 band array up to 50 Ohms.
The wires do interact, thus lets say 20 meters: that loop is not the only wire(s) radiating.
There will be radiation on the other wires, it may be very low but again that is part of the total impedance of the whole array. The 20m loop measured at the feedpoint will not be a "True" 50 Ohms. I am speculating more like 72 Ohms which is the true impedance of a Horizontal 1/2 wave dipole.
To me, this would account somewhat for the difference in length of the wires.
Another consideration is the place where the array is tuned. Not everyone will want this to tune in the "Middle" of the phone band. Thus the construction will have to account for operation and tuning for the low ends of the CW sections also. Therefore a "compromise" must occur in where the whole array will be resonate to accomplish both.
My penny's worth.
All the Best
Gary