[arm-allstar] Video example of rfi getting into fob, and my setup.

[David McGough]

Hi Terry,

Try powering the RPi3 from another power source---like temporarily using 
a wall-wart plugged into an AC source (or perhaps DC-AC inverter).  Does 
the whining noise change?? The reason I'm asking this is that RPi3 power 
supply noise *WILL* cause noise in the FOB audio as well. 

Also, what happens when the 1225 repeater has a simple whip antenna on the 
RX and a small dummy-load on the TX?? ....Even with a dummy load on the 
TX you should be able to hear it for several hundred feet.

What happens when you run this setup in another location (like the house) 
versus the car?

As already mentioned, I'd be very careful getting any antenna very close 
the the FOB, RPi3 or RPi3 power supply. Even 1W of RF can damage these 
parts when in extremely close proximity.

I'll mention that I've setup several "backyard" repeaters using a pair of 
Baofeng 888 radios and have had no noise issues at all. Here is a photo of 
an early prototype, which has no noise:

https://hamvoip.org/hamradio/baofeng888/P1040191.jpg

73, David KB4FXC


On Wed, 5 Jul 2017, "Terry Bethlehem via arm-allstar" wrote:

> #1 Yes it is greater than 10mhz for the repeater. The friend that helped 
> with this said the duplexer is only used for rx filtering.
> 
> #2 Getting the tx antenna at point blank range is just to show the 
> problem. It is the same noise when the repeater is in its normal spot. 
> When the repeater is in its normal spot, the passenger floor, it is of 
> course farther away. I had to have the AC cranked in the car during the 
> recording. If it is quiet in the car, the buzz tone can be heard when I 
> listen to my output on another radio. The repeater I'm linked to has 
> mentioned they hear it too.
> 
> 
> As for your tin foil idea, I was thinking along the same lines. I just 
> found a altoids tin that isn't empty. It looks like it might be the 
> right size to put the fob inside to see if that helps shield it better.
> 
> 
> On 7/5/2017 5:46 PM, "Steve Agee via arm-allstar" wrote:
> > My observations:
> >
> > #1 You say the duplexer is tuned to more than twice a normal split. 
> > So, greater than 10 MHz? Does this duplexer spec out that far? Some of 
> > them tell you 6 MHz or so maximum split, so be sure you are within 
> > tolerances/specs of the duplexer.
> >
> > #2 You are ramming +35 dbm or so of RF straight down the throat of 
> > your FOB. I don't know of any of them that wouldn't shudder under that 
> > much RF. Try wrapping it with some grounded aluminum foil. If it 
> > creates a ground loop then try it without grounding (as a reflective 
> > shield only). Now if it still happens 50 feet away out of the near 
> > field of the device, then perhaps you would have an argument. 
> > Remember, the FOB is a Part 15 or similar device.
> >
> > N5ZUA
> >
> > On 7/5/2017 4:28 PM, "kd4ont via arm-allstar" wrote:
> >> https://youtu.be/wSA7DscoiZM
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