Variable inductor

Note that I said "two inductors". The voltages in the lower circuit cancel (to a first order) so that the control doesn't have to have a high impedance.

BTW: If you do this with a couple of 12V transformers, you can control the brightness of a 25W light bulb with just a flashligh battery.

--
--
kensmith@rahul.net   forging knowledge

"John Popelish"

** Of course he has not !

The know nothing f****it TROLL is having a wonderful time *pissing on* his technical superiors and sucking up to all the usual gullible NG dupes.

Mooooooooooo.............

...... Phil

Ah... those are actually two inductors up there so the fields don't couple; I did miss that -- thanks for the correction.

---Joel

Yeah, I had a look at some transformer offerings from Mini-Circuits. Maybe I'm wrong, and this is why I'm posting here, but to convert 200 to 50 Ohms impedance would require a turns ratio of 2 ( Zpri = n^2 Zsec ). This would produce a 3dB loss, and then you have about 1dB insertion loss too. Simulations of the tuned LC approach have a loss of

Where do you think that 3dB loss is coming from? Ideal transformers have no losses; real have have the dB or so insertion loss you describe.

A transformer is just an inductor or two or so where the coupling is very close to unity, after all...

You are all, of course, correct. I must've had a brain fart. So I wonder why the datasheet for the amp in question (AD8367) suggests an LC rather than a transformer?

If you only want it to work at one frequency, LC or transformer would both be OK and the LC might be cheaper. For a wide range of frequencies the transformer is much easier to use.

Chris

It may have something to do with the input having a lot of reactance, andnot being a purely resistive 200 ohm inpedance. See figure 15 on page 9 of:

A resonant impedance conversion takes thisreactance into account, while a transformer would pass this reactance upstream (though transformed by the transformer's impedance ratio).

Have you ever looked at the variable inductor tuner used by Delco and some other car radio manufacturers in the '60s & '70s? It tuned from <

540 KHz to >1600 KHz. The LO was offset by + 262 KHz, and tracked with the tuned RF sections. That is a 3 to 1 tuning range.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

That's right, I had forgotten those radios with inductor tuning. Didn't they use a long coil with a ferrite rod that was pulled through on a string, or something like that?

--
 Thanks,
    - Win

Yes, but Delco used a rack and pinion mechanism to allow the use of pushbuttons. I checked several of my Sams AR series manuals, but couldn't find a decent photo of the tuner that showed the coils. I know someone who repairs car radios and I can see if I can get some pictures for you if you need them.

It was a long thin coil with a long ferrite slug with a threaded brass insert that was used to align the tuner at the bottom end of the dial, and trimmer caps for the top end. A string was used on some radios to pull the pointer across the dial but most were mechanical pointers from the rack & pinion drive.

Fair Radio used to have new surplus inductive tuners from AM pay radios made for hotel rooms for about $20. I don't know what they have these days.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Poxy hell. I seem to remember an old Philco B&W tv with a rotary switch thingy to select channels with ferrite slugs for VHF low band and brass slugs for VHF high band with two or three slugs per channel (that had to be tuned before sales). My, how much the relative cost between labor and materials has changed.

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
--Schiller

On Thu, 20 Jul 2006 04:13:11 GMT, joseph2k Gave us:

Electronics. It gets better and better, and cheaper to make and cheaper to buy with no declination in quality. (ideally)

It is one of the last businesses that follow the American dream.

Some sleazeball landlord, or stickitinyourass lawyer certainly doesn't.