Ferrite rod antennas in AM broadcast receivers

"John Larkin"

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

... Phil

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" "Phil Allison"<

The one thing you are uniquely expert on.

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

... Phil

Oh, go fix another broken guitar amp or something.

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.

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.

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.

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. ;-)

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.

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.

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.

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

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

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.

?-)

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.

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?

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?

"iiiijjjj"

.... Phil

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.