Dear Topbanders:
Joe, W1JR wrote about the MA160V as follows:
----- Original Message -----
From: "by way of Bill Tippett<btippett@alum.mit.edu>"
<topband-bounces@contesting.com>
To: <topband@contesting.com>
Sent: Wednesday, May 10, 2006 6:30 AM
Subject: Re: Topband: MA160V - Performance?
> Date: Tue, 09 May 2006 20:46:17 -0400
> From: "Joe Reisert, W1JR" <W1JR@arrl.net>
> Subject: Fwd: Re: Topband: MA160V - Performance?
>
>
>>Hi Javier,
>>
>>The MAV160 performs quite well for its size. I tested one here (see
>>below) and it was sometime nearly equal to or only a few dB down
>>from my normal loaded tower.
>>
>>However, Cushcraft in their original assembly manual only recommends
>>8 radials (per the MAV8040 manual. 4 by 65 feet and 4 by 35 feet)
>>with the 400 feet of #18 AWG wire they provide. Some have tried this
>>and the antenna seems to work OK and has a good VSWR. Others have
>>not been so successful (like the ZD8 group in late February).
>>
>>I put mine over my 80 meter test range. It consists of about 32
>>radials each about 65 feet long. It worked quite well as stated
>>above but the VSWR is poor at 2.5-3:1. However, if your feedline is
>>short and the transceiver has an antenna tuner, this is OK.
>>
>>For a small low cost antenna, it is not bad. I hope this information
>>helps.
>>
>>73,
>>
>>Joe, W1JR
What Joe is hinting at is shown on pages 9 and 10 of the MA160V manual
available on line from Cushcraft at:
http://www.cushcraft.com/comm/support/pdf/956895.pdf
It says that adding radials may make the radiation resistance below 50 ohms.
On page 10 it says that enhancing the radiation can be done by adding
radials. Cushcraft says 16 radials 50-60 feet will help, but will lower the
radiation resistance requiring a matching network such "a shunt inductor,
fixed-ratio Ununn, transmission line transformer, or adjustable L-network."
What Joe has done with his antenna is doubled the "recommended enhancement".
With an SWR of 2.5 to 3.0 the radiation resistance has dropped from 50 ohms
to 17-20 ohms, so about 30 ohms of ground loss resistance has been
eliminated. This increases the efficiency by about 4 db.
I would recommend the L-network tuner matching network with a series
variable inductor and parallel shunt capacitor across the coaxial cable on
the transmitter side, either at the antenna or at the radio. Since RG213 is
low loss with a 3:1 SWR at 1.8 MHz, it is better to put the L-network at the
radio.
Better yet, try to put up an inverted-L antenna with at least 15-20 meters
of vertical wire, and the rest of the 1/4 wavelength wire horizontal, or
shunt feed a tower with yagi antennas on top. Either alternate should
result in at least 3 db more signal strength over at least 32 radials
approximately 20 meters long.
Remember that the MA160V is only about 24 feet from base to the loading coil
and top loading wires and vertical "stinger" which gives about 0.05
wavelength effective radiator length.
In summation, I personally believe this antenna will be a compromise at any
power level over any radial system compared to typical 160 meter antennas in
use. It will allow a radio amateur to get on 160 with a low profile
antenna, that will not take too much effort to install, and will perform
accordingly.
73 George K8GG
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