WARNING!!!!!!!!! This same scheme (scam?) happened quite a few years ago. Don't remember the name of the "device", but is was a "black box" type "proprietary" antenna coupler. The price was rather high ($300-400) and it was guaranteed "flat SWR" between 3-30 Mhz. SO-239 input and two standoff insulators with wing nuts (output). Was said to match a random wire or a balanced line dipole! Someone finally "x-rayed" one and it turned out to be a dummy load actually. It was enclosed in a cast aluminum "Bud box" and potted with some sort of opaque epoxy if you took the lid off! They didn't last too long, but long enough for the manufacturer to make a bundle! It was not guaranteed to radiate with high efficiency but was guaranteed to have an input VSWR no greater than 2:1! BEWARE of ANY "MAGIC DEVICE" that makes these claims. More than likely it is a large pile of bovine fecal matter that they are feeding you!
No, I didn't buy one, but in some "unusual installations" it was tried on some commercial marine limited coast station installations. The results were very mediocre no matter what 'antenna' was tried. Low SWR....BUT! Not much radiation! 73, Sandy W5TVW ----- Original Message ----- From: "Vic K2VCO" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: <elecraft@mailman.qth.net> Sent: Friday, October 27, 2006 12:01 PM Subject: Re: [Elecraft] Attic Antenna | [EMAIL PROTECTED] 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 | _______________________________________________ | Elecraft mailing list | Post to: Elecraft@mailman.qth.net | You must be a subscriber to post to the list. | Subscriber Info (Addr. Change, sub, unsub etc.): | http://mailman.qth.net/mailman/listinfo/elecraft | | Help: http://mailman.qth.net/subscribers.htm | Elecraft web page: http://www.elecraft.com | | | | -- | No virus found in this incoming message. | Checked by AVG Free Edition. | Version: 7.1.408 / Virus Database: 268.13.17/505 - Release Date: 10/27/2006 | | _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
