[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Discuss-gnuradio] Maximum antenna input voltage on LFRX
From: |
Mark J. Blair |
Subject: |
Re: [Discuss-gnuradio] Maximum antenna input voltage on LFRX |
Date: |
Fri, 24 Dec 2010 16:20:42 -0800 |
On Dec 24, 2010, at 3:37 PM, Nick Smith wrote:
> I've looked through the mailing list archive and found a few messages related
> to this, but they referred to signal generators and power in dBm.
> In my case, I plan to use it with an antenna and eventually a pre-amp.
> However, I've found that by measuring the voltage from even a 3ft (90cm)
> antenna using a multimeter with a probe on the antenna and a probe to ground
> gives a reading of four volts RMS. With a 25ft (7.6m) antenna, I can slightly
> light up an LED (I don't remember the voltage), and with a 100ft (30.5m)
> antenna, I got about 140V.
A multimeter has very high input impedance. If you attach a 50 ohm resistor(*)
between the antenna and ground to simulate the input impedance of a radio
receiver, then you should no longer see a measurable voltage with a multimeter.
Also, a multimeter won't properly measure RF voltage. You're probably just
seeing 60 Hz power line noise, unless you're very close to a high-powered
transmitter. If there's a 100kW broadcast transmitter next door, then all bets
are off. :)
(*) or any other value you can get your hands on between around 25 and 500 ohms
--
Mark J. Blair, NF6X <address@hidden>
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.