[Collins] Power Inverter Question

[Dr. Gerald N. Johnson]

On Wed, 2006-07-26 at 12:01 -0500, Danny Lunstrum wrote:
> Good Afternoon Group,
> 
> US Cellular is planning on installing a cellphone site approximately 1300' from my amateur radio/short wave listening station and I am very concerned about possible interference.
> 
> In visiting with Mike Gruber at ARRL, he suggested that I take a portable communications receiver and monitor the amateur and short-wave bands with the rig around     1300' from a cellphone site and see what kind of interference I can pick up.
> 
> My question concerns using a 51S-1 receiver and powering it from a power inverter with a 12v input.
> 
> The two that I looked at stated that the output was a "modified sine wave output."
> 
> Would it possible to damage the power supply section of the 51S-1 if I used a 12 VDC to 115 VAC power inverter to power it?
> 
> Thank-you for your thoughts,
> 
> 
> Dan Lunstrum

I think the 51S-1 transformer will smooth the pulses adequately, though
there is a chance of some ringing from the pulses. A 1 or 2 mf AC rated
capacitor across the 120 volt line may help smooth the AC voltage.

The bigger problem may be hash and RF noise from the inverter.

Another limiting problem may be the small antenna used while mobile cuts
its sensitivity compared to the home station.

I have noticed increased noises in one of my 2m handhelds while close to
a cell tower. Likely its from a harmonic of the receiver LO beating with
800 to 900 MHz cell signals to mix them to something the receiver could
hear.

Using a 300 or 400 MHz low pass filter in the receive coax at home may
be of benefit. There are many available in surplus, often used for
military aviation communication equipment, sometimes with a power meter
coupler included (and those diodes could put back the harmonics and
intermod the filter removed). Its possible that the filter with cutoff
of 420 MHz will attenuate 800 MHz better than a filter that cuts of at
52 MHz (like the typical TVI filter).

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer