[Elecraft] Attic Antenna

[Vic K2VCO]

n2ey at aol.com wrote:

> I would want a lot more info before spending any money.
> 
> The BB7V is priced at US$400. It's a 22 foot vertical aluminum radiator 
> with a nice mast clamp (mast not included) and a cylindrical feedpoint 
> device.
> 
> The big question is: What's in the feedpoint device?

Here's some more information (but no mention of what's in the magic 
cylinder): <http://www.hamradio.co.uk/pdf/Diamond/BB7V.pdf>

However, it is possible to see that the radiator is a continuous 
conductor.  Therefore, the counterpoise function must be provided by the 
mast, coax shield, or lossy ground (depending on mounting).  This means 
the antenna's performance would be highly dependent on mounting, and it 
would be prone to RFI and RF-in-the-shack issues.

The antenna supposedly works from 3-30 MHz with SWR less than 2:1.  The 
SWR curve shown is suspiciously similar to that of a resistively loaded 
antenna.  Such antennas can be useful in certain circumstances (B&W 
makes several versions), but the efficiency can be quite low on 
frequencies where the impedance of the radiating part is high or 
reactive.  The B&W antennas are well designed and relatively large; even 
so, the efficiency is significantly below that of a dipole.

A 22-foot vertical without top loading will be inefficient on 7 MHz (it 
will be a dummy load on 3.5), especially without a decent counterpoise.

Even if one only has room for a 22-foot vertical there are lots of 
better choices.

I agree with Jim.  Put up a dipole and spend the leftover $395 on beer.
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco