On Thu, 19 Nov 2009 06:05:20 -0600, "amdx" wrote:

I have found the need to work for a living, gets in the way of a lot of
fun!

5 hours on the phone on a slow motion conference call this morning.
Absolutely nothing useful accomplished. Such online meetings should
be banned, taxed, or both as a threat to national productivity.

I took the coax loose on the MFJ-1800 and and removed the toroids, I found
the letters found M1Z/111-RG and then the insulation ended. Argh!
Oh, I have a second antenna, so I took that one apart, Eureka! RGS-303
http://wireandcable.thermaxcdt.com/i...d-70-?&seo=110
50 ohm coax. PTFE center insulator, FEP jacket.
Mike

Thanks. 50 ohm coax does not make it a matching section to a 200 ohm
folded dipole. However, the ferrite beads are a good way to simply
block the reflected power from the folded dipole so that it looks like
it's matched. In any case, that reflected power is lost (converted to
heat) in the ferrite beads. So much for efficiency. When I change
the characteristic impedance of the model from 200 ohms to 50 ohms,
the VSWR climbs to 5.5:1. Yech. (Note that the radiation efficiency
is 75% with or without the mismatch).

I suppose the antenna could be made to function by replacing the coax
section with a real 1/4 wave 4:1 balun, but I'll leave that to MFJ to
figure out.

If you need some more entertainment value, it would be interesting to
actually measure the gain of the antenna. Find a known good reputable
antenna with similar gain. A panel or patch will work. Find a signal
source that isn't infested with reflections (including ground
reflections), Fresnel Zone issues, and is fairly stable (i.e. doesn't
physically move). Use Netstumbler, WirelessMon, or Kismet to compare
the signal strengths. For additional accuracy, use a step attenuator
to adjust the signal levels to a common reference level. Better yet,
use a spectrum analyzer.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558