If there is no reactance, then yes this would be true. But it's not
likely to be either one of those (16.6 or 150 ohms). Go back to the
definitions of SWR. You most likely have some reactance in the antenna,
which means you are not at the resonant point.
When you use the MFJ, one bad thing that can happen is that long
antennas like this tend to pick up local broadcast stations and this
will mess up the MFJ. You can get some really misleading measurements.
Also if you do the measurements from inside the shack using a long coax,
you can get most anything if you have a badly mismatched antenna and
feedline. If you get desperate enough, I guess you could take your rig
to the base of the L.
I don't think your 80M inverted vee will effect the 160M L too much. The
40 meter verticals shouldn't effect it either. If you have a big tower
close by, that could do it.
An inverted L, like the one you built, with a good ground should be
around 35 to 45 ohms. That said, if everything was OK, you should have
measured low SWR at your rig even with a long coax.
My best guess is that you tuned it with the MFJ and got the wrong length
due to a misleading measurement on the MFJ (RF pickup by the antenna).
Tom Osborne wrote:
>>As you measured, you can have a 3:1 SWR and read 40 ohms on the meter.
>>This says that the equivalent impedance of the circuit being measured is
>>40 ohms. It doesn't tell you anything about the actual resistance or
>>reactance of the load. The SWR is defined in term of reflection
>>coefficients, not in terms of resistance ratios, or in terms of
>>equivalent impedance ratios. In your case, you have a circuit with high
>>reflection coefficients (caused by high reactance).
>OK, now were getting somewhere. I'm really not too concerned if the meter
>is a good one or not. The swr in the shack meter agrees with what the
>Without all the meter readings etc, if I did have a SWR of 3:1 with a 50 ohm
>cable, that would mean the impedance at the feedpoint could be 16.6 ohms or
>it would be 150 ohms. I can't figure why it would be clear down to 16.6 as
>I know the radials are in good shape. I trimmed all the ends and
>re-soldered them so they would be fresh. Would the presence of the 80 meter
>dipole about 6-8 feet away from the point where the antenna goes from
>horizontal to vertical mess it up that bad.
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
>questions and ask for Sherman, W2FLA.
>TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list