[TowerTalk] HF LOG-PERIODIC ANTENNAS Comments Please

[Tom Rauch]

> One point needs to be made, especially for contesters. The
LPDA is a very
> low Q antenna with very wide bandwidth... the SteppIR is a
high Q antenna
> with narrow bandwidth that is frequency agile.
>
> When the bands are very crowded with big signals, there is
a huge difference
> in the strength of unwanted signals reaching the receiver
front-end.

Hi Rick,
That isn't a valid reason (and I'm also not sure it is true
that signal levels are "hugely" less).

Virtually every receiver sold and used by amateur operators
has exceptional wide spaced dynamic range. The problem is
most have poor close-spaced dynamic range, and poor
transmitter bandwidth for close spaced signals. The new
big-dollar IC7800, for example, is just garden variety at
close spacing (in the high 70dB IM3 range). It's about like
any other mediocre radio. Most difficult to cure problems
are going to come from signals 10kHz or less away, so
antenna bandwidth is a non-issue for the bulk of receiving
problems.

The only exception is the TenTec Orion, which has good
close-spaced receiver performance (better than 90dB IM3
range). Yaesu's aren't bad either if you correct the noise
blanker issue the factory insists  on designing into the
radios. Fortunately that is a simple fix, and the Yaesu is
an acceptable radio when the NB issue is dealt with.

http://www.w8ji.com/receiver%20IM3%20sorted.htm

73 Tom