To: <topband@contesting.com>
>Date: Thu, 23 Jan 1997 06:32:12
>To: K3BU@aol.com
>From: Dan Robbins <kl7y@alaska.net>
>Subject: Re: TopBand: HEARD better on xmit antenna, propagation
>
>At 12:05 AM 1/22/97 -0500, K3BU wrote:
>>
>>Hope this helps to forget the "bouncing" nonsense and sheds some light on
>>what is going on. Thank you for the bandwidth and hope CU in CQ 160. Hope
>>that winds are merciful to my baloons. (Lost one in Stew Perry at 3:00 am and
>>had to QRT)
>>
>>Yuri K3BU, VE3BMV
>
>
>Sorry, Yuri, bouncing is exactly what it does. I used to work at the
Relocatable-Over-the-Horizon Radar (operated at HF) and we always got earth
returns unless there was a blanketing E layer. At times we printed nice
color pictures of the radar's evenly spaced bounces all the way around the
world. I saw tilted ionosphere, sloped ionosphere, moving ionosphere, but
old Mother earth is just a huge target. Interestingly enough, the beam
heading from KL7 to VK0 was included in our radar's beamwidth, so those RTW
signals went right over VK0. You have to get a pretty low angle of
incidence to get chordal hops - which means very low angle of radiation and
operation near the MUF. The radar transmit site had 8 huge vertical LP
arrays with an extensive groundscreen. It was on a bluff about 700 ft high
directly overlooking the Pacific Ocean and it did throw some very low angle
photons. Certainly much lower angle than the average topbander can summon.
Yet this system did not yield regular "whispering gallery" signals, despite
thousands of unambiguous observations.
>
>I think ionosphere-earth reflection system is often underestimated. Once
in a while the radar would overload the receivers from the backscattered
radar signal. Visualize 1 MW ERP leaving Alaska, "reflecting" off of the
ionosphere, impinging upon that vast Pacific Ocean with only a minuscule
portion of that power bouncing back towards the transmitter. Once again off
of the ionosphere to a pair of phased verticals on receive. There the
signal passes through a 30 dB attenuator, through a multi-FET active mixer
that alone probably costs as much as your rig and certainly has better large
signal handling capability. From there to a DSP with 96 dB of dynamic
range. After all that the receiver was overloaded. I am no longer
surprised by anyone's signal strength.
>
>Let's hear it for earth bounces.
>
> Dan KL7Y
>
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Sponsored by Akorn Access, Inc & N4VJ / K4AAA
|