Ferrite rod antennas in AM broadcast receivers

"George"

I have been trying to find info on designing ferrite rod antennas into AM broadcast receivers. Googling so far has just produced general loop antenna principles and characteristics of the rod material itself.

** Yes.

Pre-selection of the antenna signal is crucial to getting good results with the AM broadcast band, otherwise the receiver will suffer badly from cross modulation effects and images of the IF frequency.

** No.

** The length of the rod is the main thing, longer = better signal strength and directionality. ** Irrelevant.

... Phil

[OP here]

To clarify my questions:

I'm building an AM broadcast receiver to be used in a non-standard applicat= ion. It will use an existing wideband COTS software defined radio product = that does not provide tuning information to the ferrite antenna. So I'd li= ke 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 v= s. frequency.

Can you create a voltage (say from a DAC) that you could use to resonate your loopstick using a voltage variable capacitor?

--Winston

A tuned antenna is important in a superhet, where with an IF of 455kHz, an LO frequency of 1005kHz could pull in two channels, 550 and 1460kHz. But since your detector is different, this doesn't need to matter.

So you need a Q of about 1. Size the L and C accordingly. That's the best you can do, and of course your antenna gain will be terrible (far below isotropic).

Could you define "antenna delay", and quantify how it must be known?

In general, a radio has absolutely no phase reference, and because bandwidth is generally narrow (e.g., 10kHz out of a >1MHz band), a radio is very insensitive to relatively sharp changes in phase vs. frequency (even if that phase shift lands in the middle of the channel)*. Is this a diversity application of some sort?

• Obvious exception: analog TV, which is notably sensitive to multipath. One could argue, because this signal is wideband, and more time- than frequency-domain oriented, it doesn't count.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"George"  wrote in message 
news:b2f8f837-5eac-4b7e-be97-0d3821024155@googlegroups.com...
[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'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.

This non-standard application DOES require knowledge of the antenna delay 
vs. frequency.

"George is a TROLL "

[OP here]

To clarify my questions:

I'm building an AM broadcast receiver to be used in a non-standard application.

** That is not helpful.

You are obviously yet ANOTHER idiotic code scribbler wasting our time.

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.

** Low Q and high gain are incompatible goals.

Your ideas are totally stupid.

This non-standard application DOES require knowledge of the antenna delay vs. frequency.

** Bullshit.

... Phil

On a sunny day (Sun, 2 Sep 2012 17:35:35 -0700 (PDT)) it happened George wrote in :

Yes

Its just a magnetic pickup for the eM field. And because of that very directional sensitive.

Most are black....

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.

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?

--

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

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.

You may be right about going with an untuned antenna. It's worth a try. I= f a high-gain amp in lieu of a tuned stick will give me the receive gain of= a traditional ferrite, that's all I need. And it avoids phase non-lineari= ty issues which my app is very sensitive to. Besides, I'm sampling the who= le AM broadcast band at once and can't tolerate a narrow-band front end due= to the high-Q ferrite antenna.

Two concerns:

1. The Websites I have seen talk highly about the performance that is achi= evable with high-mu ferrite over ordinary loops in the same board space. M= akes me wonder if I can get to that antenna gain without ferrite, even with= a good amplifier. That amplifier is going to have its own problems like 3= IM overload, etc. I understand the high environmental noise argument. =20

1. The ferrite loop would have reduced the near-field impulse noise E-fiel= d pickup which now may become a problem.

Well, all I can do is to try it.

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.

frequency.

Electrically small antennas have a pretty sharp tradeoff of sensitivity vs bandwidth. See e.g.

There's a bibliography at

.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

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.

frequency.

high-gain amp in lieu of a tuned stick will give me the receive gain of a traditional ferrite, that's all I need. And it avoids phase non-linearity issues which my app is very sensitive to. Besides, I'm sampling the whole AM broadcast band at once and can't tolerate a narrow-band front end due to the high-Q ferrite antenna.

achievable with high-mu ferrite over ordinary loops in the same board space. Makes me wonder if I can get to that antenna gain without ferrite, even with a good amplifier. That amplifier is going to have its own problems like 3IM overload, etc. I understand the high environmental noise argument.

pickup which now may become a problem.

I think you may want to concern yourself also with front end saturation if you're sampling the whole AM band at once. Agc in the IF stage works good because it only acts on the selected pass freq.

I suppose if you are doing this a with a high res DSP you could pull out the weak ones with DFT's.

Jamie

"George is a TROLL "

You may be right about going with an untuned antenna. It's worth a try.

** He says, clutching at straws.

If a high-gain amp in lieu of a tuned stick will give me the receive gain of a traditional ferrite, that's all I need.

** It will not.

And it avoids phase non-linearity issues which my app is very sensitive to.

** Your app is bullshit.

Besides, I'm sampling the whole AM broadcast band at once and can't tolerate a narrow-band front end due to the high-Q ferrite antenna.

** My god , what is this idiot doing ?

He won't answer, so you KNOW it is 100% stupid.

.... Phil

AM broadcast receivers. Googling so far has just produced general loop = antenna principles and characteristics of the rod material itself.

frequencies with the 0.5 - 1.6 MHz band? Or can decent performance be = realized across the band without re-tuning? Are there gain vs. frequency= curves available for given ferrite rod antenna designs?

across the AM band for a given design.

Read thread, disappointed by how many could not avoid resonating the antenna. =20 Well maybe, but with a Q of no more than 1/2. The biggest problem after that is amplify a bit first then filter down to AM band or filter first then amplify? =20 In either case the filter design will be at least 6th order to be useful and that gets you into possibly ugly phase/frequency/delay issues. And very likely difficult implementation problems. Inverse Chebychev or Bessel may be possible choices. After that most of the tough stuff is done, just an serious 16-bit, 10 MS/s digitizer, and analytical software (oops maybe i spoke too soon, sounds like medium sized FPGA).

?-)

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.

Agree an un-tuned loop or rod followed by an amp is the way we should go. = Any suggestions on who to contact for engineering services in order to sub-= contract the design?

You asked about signal levels. The signals are ordinary AM broadcast carri= ers which should be plenty strong for our needs. And yes, external noise p= redominates in this application.

George

"George = IDIOT "

Agree an un-tuned loop or rod followed by an amp is the way we should go. Any suggestions on who to contact for engineering services in order to sub-contract the design?

** Try the tooth fairy.

You asked about signal levels. The signals are ordinary AM broadcast carriers which should be plenty strong for our needs.

** Horse poo.

And yes, external noise predominates in this application.

** No, insanity does.

Cos it is all your mad idea.

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.

suggestions on who to contact for engineering services in order to sub-contract the design?

Bruce...

does research and design for us now and then, when we can't get around to potentially interesting stuff ourselves. You might ask him if he's interested.

which should be plenty strong for our needs. And yes, external noise predominates in this application.

You should be able to look up typical AM field strengths in cities, and calculate the H-field, and see how much signal you'd get from a given loop. Or measure it.

--

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

What's wrong with an untuned loop? Old tube AM radios had loop antennas, pretty small ones. Q couldn't have been very high, or else they wouldn't have tracked the LO.

Longwire antennas, untuned, make gobs of signal into an old Hallicrafters receiver. A foot is all you need to pick up AM in a city, and that's an e-field probe with a ghastly impedance mismatch.

--

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

"John Larkin" "Phil Allison"

** They were NOTHING like what the mad OP is on about. ** Nothing like what the mad OP is on about.

Fuck knows what the colossal idiot is really trying to do - radio location maybe.

Can't you tell a TROLL when you see one ?

( Rhetorical question .. )

Hint:

They ignore all questions and criticisms and only pick the one reply that seems to back their f****it, secret idea up.

... Phil

While I have not seen the original message from the OP, there are some issues.

1.) A small (relative to the wavelength) loop antenna will have a very low radiation resistance (in milliohms), well smaller than the 50/75 ohm input impedance assumed by most receivers.

2.) The atmospheric noise level at VLF/LF/MF bands is extremely high, so good results can be obtained with very poor antennas (such as loopsticks with gains in the -30 .. -40 dB range).

Tuned loopsticks work quite OK due to the impedance transformation between the resonant LC and the pick up coil.

Trying to use untuned (ferrite) loops at VLF/LF/MF would require some very low input amplifier stages (such as hefty common base stages) to actually take advantage of the current available in the loop.

go.=20

Better than you might think, it is the dominant property in image rejection. Resonated with another section of the variable capacitor that generated LO. Q of maybe 50 most likely, more than that would hurt RX bandwidth.

A Hallicrafters is a bit better than an average AM receiver.

?-)