Re: LF: VK1OD's analysis of the MiniWhip antenna

[<jrusgrove@comcast.net>]

Roelof

Without adequate isolation between the feedline and e probe unit itself, the x meters of vertical 
feedline above ground level is part of the antenna.
Jay W1VD  WD2XNS  WE2XGR/2


----- Original Message ----- 
From: "Roelof Bakker" <roelof@ndb.demon.nl>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, July 05, 2013 9:09 AM
Subject: Re: LF: VK1OD's analysis of the MiniWhip antenna


> Hello all,
>
> Further to this discussion, I have done the ultimate test to demonstrate  that an active whip 
> antenna with a 1 meter long whip behaves as a  capacitance at LF.
> For the test I used the ground wave carrier of semi local NDB ONO at 399.5  kHz.
> As it is the only station at that frequency the carrier level is very  stable 
> at daytime.
> The distance is 59 km, which excludes probably all skywave propagation.
>
> The antenna was mounted vertical and the carrier of ONO produced a signal  level of -69.1 dBm as 
> received with a PERSEUS SDR.
> Next the antenna was mounted horizontal at the same height as the bottom  of 
> the vertical mount.
> This produce a signal level of -72.0 dBm.
>
> I reasoned that the mean height of the 1 meter long antenna when mounted  vertical is 50 cm 
> higher. So the antenna was then mounted horizontal 50 cm  higher from its previous position. This 
> produced a signal level of -69.9  dBm, close to the value measured when mounted vertical.
> The main point however, is that a horizontal polarized antenna should NOT  receive a vertical 
> polarized ground wave signal at (almost) the same  strength.
> So at LF, there is nothing gained in using a whip instead of a small piece  of 
> copper clad PCB.
>
> Comments are much appreciated!
>
> Best regards,
> Roelof Bakker, pa0rdt