Ferrite rod antennas in AM broadcast receivers

[[email protected]]

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

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.

 

[[email protected]]

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.

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

 

[[email protected]]

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.

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

 

[josephkk]

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.

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.

?-)

 

[amdx]

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.

This one uses an RTL2832U-based DVB-T USB dongle with the Elonics
E4000 tuner.

The modules consist of
1. A switching unit with a VHF broadcast band filter
2. A 300 KHz to ~60MHz pre-amplifier of around 18dB gain
3. An HF to VHF converter DC to 60 MHz input up-converted to 125 to
185MHz output
4. A VHF 50MHz to ~2GHz pre-amplifier of up to 18dB gain
5. A PC power rail filter
6. A voltage regulator for an external unit

http://makearadio.com/visitors/nick-sdr2.php

Mikek

 

[[email protected]]

[OP here]
To clarify my questions:
I'm building an AM broadcast receiver to be used in a non-standard application. It will use an existing wideband COTS software defined radio product that does not provide tuning information to the ferrite antenna. So I'dlike 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.
This non-standard application DOES require knowledge of the antenna delay vs. frequency.

There's nothing fundamentally wrong with using an untuned antenna.

Gain is cheap nowadays, and AM reception is generally dominated by

external noise, not receiver noise figure. A good opamp or jfet will

get you below 1 nV/rootHz noise, so resonant gain isn't necessary. If

delay matters, it's better to not resonate the antenna.



An untuned loop, or an untuned ferrite rod, would work, far below

self-resonance. A few-turn loop would act like an almost ideal H-field

probe, and its gain and delay behavior are calculable.



What are you trying to do? Do you expect to have a lot of signal? Is

the transmitter nearby?

Long-delayed follow-up ... )

You were right about using a mag loop followed by an amp to get broadcast band receive antenna performance equivalent to that to a ferrite stick but without the tuning requirement.

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

 

[iiiijjjj]

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?

 

[Phil Allison]

"iiiijjjj"

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?

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



..... Phil