CobWeb Antenna

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sdu219

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Does anyone know anything about the CobWeb antenna that MFJ sells. I have bought one and the boom truck comes tomorrow to put it up on my 50 tower. I am totally miffed by this thing.
I have spent 13 hrs trying to tune it with a Comet SWR 500 Mark 2 meter and i am at my wits end. I am starting to think it was the stupidest thing I ever bought or I am just so stupid that I cant tune the dam thing. I have gone through 2 sets of wires ( bought new set from MFJ) and today I have put 8 hours into the thing.
I cant seem to see how this is going to work when I center it on the center of the 20, 17. 15, 12 and 10 meter bands the meter shows a spike right at the center but is crap on either side. My Pro 756-2 has built in tuner that can make it OK but what is the good if I use LDF4-50 to the antenna but signal is not getting out.
HELP I need an ELMER
 

prcguy

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I looked at the cobweb when shopping for a multiband directional antenna but went with a Hexbeam instead. I did not see many complaints about the cobweb and most comments are positive, which is unusual for an MFJ product. I would think people would be complaining if the antenna was as narrow as you are reporting.

Many if not most antennas will have different tuning when near the ground compared to on the tower. How far above the ground is the antenna when you are measuring it? What is the match at resonance compared to band edges?

On the other hand my Hexbeam from NA4RR went together in just 45min and 6ft off the ground the tuning was centered perfectly on every band 20 through 6m and it covers each band with less than a 1.5:1 match worst case at band edges. In fact there are no provisions for tuning or changing the wire lengths. When it went on the tower at about 35ft up the match did not change. I'm really happy.

The Hexbeam is a compact 2 element beam where the MFJ Cobweb appears to be a full size but folded up dipole on each band. I don't see any good reason it should not have a similar BW to the Hexbeam, which also uses a full size but bent up dipole as the driven element.
prcguy

Does anyone know anything about the CobWeb antenna that MFJ sells. I have bought one and the boom truck comes tomorrow to put it up on my 50 tower. I am totally miffed by this thing.
I have spent 13 hrs trying to tune it with a Comet SWR 500 Mark 2 meter and i am at my wits end. I am starting to think it was the stupidest thing I ever bought or I am just so stupid that I cant tune the dam thing. I have gone through 2 sets of wires ( bought new set from MFJ) and today I have put 8 hours into the thing.
I cant seem to see how this is going to work when I center it on the center of the 20, 17. 15, 12 and 10 meter bands the meter shows a spike right at the center but is crap on either side. My Pro 756-2 has built in tuner that can make it OK but what is the good if I use LDF4-50 to the antenna but signal is not getting out.
HELP I need an ELMER
 

mm

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oregon
How is it setup when you are measuring the vswr?

It should be > 1/4 wavelength above ground at 20 meters and at least 1/4 wavelength at 20 meters separated from any conductive objects when attempting to adjust the antenna.

you said it will be on your tower when the boom truck arrives so describe the mounting scheme in which you have issues?

I know several users who assembled their MFJ cob-webs per the instructions and didn't require any adjusting afterwards.
 

wb6uqa

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Cobb Web

Why not just buy a Hex Beam. Six bands, one feed line, and no tuning. The cobb is more like a dipole. Look at the Na4rr Hex.
 

sdu219

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Well I tuned it the best I could. Center of the bands. 15 feet in the air for tuning. Its now at 50 feet and I have not checked it as it has been a long day and I am done with radios and Antennas for today.
Despite it being in the center of the General class voice section on the ground (15 feet) it went up sharply. A skinny "V" not a "U".
I will see how it goes. I looked at the hexbeam maybe next year.
 
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