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Ferrite rod antennas in AM broadcast receivers

And a good opamp, or a BF862, is way better than a Hallicrafters.

I took a banana lead, plugged it into both sides of a dual Pomona bnc adapter, and ran that into our spectrum analyzer. That made a single turn loop about a foot in diameter, basically an untuned H-field probe. The whole AM band was picket-fenced with lines, and the bigger ones were around -70 dBm, roughly 70 microvolts RMS. Noise floor maybe

20 dB below the better peaks. Adding a second, longer lead and wrapping a few turns got me to -60, about 200 uV. Tons of signal.

Using the 3' banana lead as a single-wire antenna, basically an E-field probe, I got similar amplitudes but a much higher noise floor. That was into 50 ohms, a terrible mismatch to a short antenna.

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John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
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Reply to
John Larkin
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"John Larkin"

** The OP is crapping on about a device that fits in the palm of the hand, samples the whole AM band at once and does some kind of magic trick.

I would say he was " off with the fairies" but that is a big insult to fairies.

... Phil

Reply to
Phil Allison

I don't know what the magic trick is, but a small several-turn untuned loop, some gain, and an ADC could easily capture the AM band for digital signal processing.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply to
John Larkin

"John Larkin" "Phil Allison"<

** You are merely crapping on about your own, false imaginations.

The one thing you are uniquely expert on.

Yawwnnnnnnnnnnnnnnnnnn.....................

... Phil

Reply to
Phil Allison

Oh, go fix another broken guitar amp or something.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply to
John Larkin

Sounds right. Our spec an measurements agree (in the ballpark) with predicted receive signal level of -80 dBm using a -35 dBi antenna receiving a 1 kW transmitter at 100 km distance.

Reply to
George

This is done (software defined radio) but I think the problem with it is overloading the receiver with a strong signal. It's sorta the same problem that FFT based spectrum analyzers have.

Reply to
krw

In the AM band, you could oversample like crazy, say 12 bits at 100 MHz or something. Noise dithering is no problem... noise is free here. So the dynamic range should be pretty good, and sub-LSB signals should be useful. A little front-end gain switching wouldn't hurt.

You could also software phase-lock to each carrier. We were thinking about doing that in another situation where we had to do I-Q sort of processing. Our idea was to make a PLL using a DDS as the virtual VCO, all digitally in an FPGA. Lotsa code but not much hardware.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply to
John Larkin

But once the front end is saturated, you're dead. There's TOO MUCH noise in the AM band.

FPGAs are *way* too expensive for anything on AM. ;-)

Reply to
krw

If you have plenty of power to burn (i.e. _not_ battery powered), use sufficient collector/drain current, say 1 A, use push-pull, use negative feedback to linearize and the front end is not going to be the problem, the problem starts with the ADC.

Reply to
upsidedown

I don't think the OP is building a radio. It has something to do with measuring the phases of the various carriers, maybe some geo-location thing or something. Or something.

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John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation
Reply to
John Larkin

receive signal level of -80 dBm using a -35 dBi antenna receiving a 1 kW transmitter at 100 km distance.

Well, we're in a wooden building in plain sight of Sutro Tower.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation
Reply to
John Larkin

If you're standing next to the transmitter, the front end is the problem. Well, everything is the problem.

Reply to
krw

It's the same problem, though. Once the system goes nonlinear it's all over.

Reply to
krw

noise in

Any way you want to slice it, OP wants to do something with radio signals in the AM band. That implies a receiver of some kind.

?-)

Reply to
josephkk

cation. It will use an existing wideband COTS software defined radio produ ct that does not provide tuning information to the ferrite antenna. So I'd like to be able to get enough antenna gain across the broadcast band from the antenna to avoid having to tune the antenna to resonance on each freque ncy. But space limitations dictate use of a ferrite.

y vs. frequency.

Long-delayed follow-up ... :o)

You were right about using a mag loop followed by an amp to get broadcast b and receive antenna performance equivalent to that to a ferrite stick but w ithout the tuning requirement.

We contracted the design and will have a demo unit in a few weeks. Thanks.

Reply to
broadbandglobalpositioning

application. It will use an existing wideband COTS software defined radio product that does not provide tuning information to the ferrite antenna. So I'd like to be able to get enough antenna gain across the broadcast band from the antenna to avoid having to tune the antenna to resonance on each frequency. But space limitations dictate use of a ferrite.

vs. frequency.

receive antenna performance equivalent to that to a ferrite stick but without the tuning requirement.

Just curious, but how big a loop did you use? What sort of signal levels (microvolts) are you seeing?

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation
Reply to
John Larkin

It has taken many person hours to answer this question. Since it is so simple the OP should just try it in the lab with an oscilloscope. Is that not the easy answer?

Reply to
iiiijjjj

"iiiijjjj"

** You have totally missed the central issue in the story.

.... Phil

Reply to
Phil Allison

the OP should just try it in the lab with an oscilloscope. Is that not the easy answer?

Please explain how that measurement would be performed.

Reply to
John Larkin

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