What is it about low(er) frequencies that make reflections less of an issue=
?

I'm tempted to just pick up a simple transmitter and receiver and log=20
RSSI for a couple days, just to see what I get in this environment.

Cheers,
-Neil.



On 10/7/2019 2:21 PM, David Van Horn wrote:
> At 2.4 GHz, the reflections are such that I can watch the antenna impedan=
ce change while I'm sitting 2 feet away, just breathing.
> There used to be 915 MHz alarms that work that way.  A short monopole on =
top of a box, and since pretty much everything has a different dielectric c=
onstant than air, motions in "stuff" cause changes in the antenna impedance=
 that trip the alarm.  "Stuff" can include stratified air in a closed room.
>
> It will be problematic at most (all?) frequencies, just different problem=
s.
> At 457kHz, reflections aren't much of a problem, and almost nothing atten=
uates the signal, but the path loss is some 60dB per decade distance inside=
 100m (radiansphere) but local noise produced by your drone will deafen you=
 except at short ranges.
>
> 10m and shorter distances are easy.
>
> The book by Joe Moell on transmitter hunting is a classic, though somewha=
t dated now.   I've hunted with him, and N6JSX who is an evil genius at hid=
ing a transmitter.
>
> Pseudo-Doppler rigs tend to be rather deaf, and reflections drive them nu=
ts.
>
> The "Double Ducky" direction finder might work for you, since it switches=
 quickly enough that you shouldn't get much change in RSSI over that time p=
eriod.
>
> When I was in Wisconsin, I helped Bill with the "Foxcopter", a continuous=
ly rotating 5 el VHF beam mounted in the back of his pickup truck, using RS=
SI and a storage scope to plot the antenna pattern in the direction of the =
signal.  Reflections were easy to see and ignore.
> http://www.homingin.com/hmgindx.html
>
> --
> David VanHorn
> Lead Hardware Engineer
>
> Backcountry Access, Inc.
> 2820 Wilderness Pl, Unit H
> Boulder, CO  80301 USA
> phone: 303-417-1345  x110
> email: david.vanhorn@backcountryaccess.com
>
>
>

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