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[aprssig] Prius Power for Field Day

Stephen H. Smith wa8lmf2 at aol.com
Fri Oct 12 23:22:21 UTC 2007

Robert Bruninga wrote:
> Rusty,
> I don't run HF, but suspect I have noise problems. I think  I
> even see redleuced receive range on APRS on 2 meters!  But then I
> have hacks goiing into and out of the HV battery compartment
> which is notoriouis for EMI.  SO much of this coiuld be my own
> doing.  Ill have to clean it up someday and see if it improves.
> When I first got the prius I did a quick test with a dusty old
> CB set sitting in the garage.  Only 2 S units of noise.  Not
> much...
> Bob

Did you actually have the CB ant mounted on the car or just nearby.   
The amount of noise RADIATED isn't that great, but the amount of noise 
circulating on the chassis is ENORMOUS!    Any antenna whose ground 
plane involves the car's chassis will have an S-9 noise level on every 
band from 160 through 6  coupled  into it's front end. 

I observed a noticeable degradation of APRS receive on 2 meters in my 
2005 Prius, even through the S-meter didn't show any signal.  (You don't 
have any indication anything is there when you open the squelch, since 
the white noise sounds exactly like open squelch noise.  A SINAD test 
using an iso-tee and service monitor showed I was suffering about a 6 dB 
desense of the receiver's effective sensitivity.)    

I did see a significant (about 3dB) improvement when I installed an 
end-fed half-wave no-ground-plane-required 2M/450 antenna (Comet 770), 
presumably because the chassis was no longer a major component of the 

NOTE: The hybrid Ford Escape actually uses Toyota's hybrid power train 
so I would expect similar noise issues in that vehicle.


Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
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