Forums

RF transformer

Started by Robert Baer July 29, 2013
On Sun, 28 Jul 2013 21:48:14 -0800, Robert Baer
<robertbaer@localnet.com> wrote:

> I understand, that with the proper winding configuration, that a 90 >degree phase shift can be achieved between primary and resonant secondary. > That is done with a tapped secondary on a FM discriminator transformer. > What are the guidelines and requirements needed to construct such a >transformer at a given frequency OTHER than the standard 10.7Mhz? > Say, on a form in the one inch diameter region, and frequency below 1Mhz? > Ideal coil diameter, length based on chosen frequency? > Turns / inductance (no resonating cap)? >
At 455kHz, and modern OpAmps available with high GBW, just do this... http://www.analog-innovations.com/SED/Pat-4472816.pdf ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Jeff Liebermann wrote:
> On Sun, 28 Jul 2013 23:54:03 -0700, Jeff Liebermann<jeffl@cruzio.com> > wrote: > > There's a detailed explanation of how to design an FM discriminator > for AFC in the Radiotron Designers Handbook 4th edition (1953) Pg > 1152-1156. > <http://www.paleoelectronics.com/RDH4/CHAPTR29.PDF> > Note the concern for controlling the Q of both the primary and > secondary. > >
Ineresting; have recently been looking at my old dusty Radiotron pgs 1090-1097 (same version). Q control _and_ coupling control. A bit messy for one that has not wound any transformers for 25 years, and those were power xfmrs.
RobertMacy wrote:
> On Mon, 29 Jul 2013 08:23:20 -0700, Jan Panteltje > <pNaonStpealmtje@yahoo.com> wrote: > >>> ...snip... >> >> Oh, I use LTspice, usually for small sub-circuits, >> but hey, human mind has a trillion ? of neurons (or it should be ;-)), >> and more than 60 years E design experience in my case. > > I know. I saw the 'smiley' I just used the opportunity to vent my spleen > on three entities that should know better. > > Using my own brain? I pride myself on looking at a schematic and > actually view it 'moving' Instantly see what it does, where it's weak, > etc. But, this topology has driven me NUTS! Using my intuition to > increase bandwidth, the change reduces bandwidth. Increase gain, nothing > happens - constant gain! I sat with a tablet of equations for two days > solid to no avail, even with super simplifications. Now even with > LTspice this !@#$#@! circuit doesn't 'act' right! where the circuit > should null and be the same voltage, it's not! I'm starting to simply > take the attitude, it works, because it works. > >> I wind 100 faster than I can write this. >> And 100 you know, as the grocer says when weighting the cheese: >> Can it be a little more? >> It is easy to remove a few turns... if you end up too high. >> >> Now, now it works, you can ask the online calecujilator what L is for >> 1 MHz, >> and put the in LTspice, and show it to customer, >> he (the custardtomer) now feels much more secure after seeing >> 'mathematical proof'. >> > > I carry 'data points too, especially the 'stacking factor' and coil > cross section size. > >> Hey I just had a discussion at CNN.com. and found out how to get rid >> of the US deficit: >> Advertising on dollar bills, on banknotes, >> how much does google make ... FED can do it too. >> Made available to all for free. >> (And in that discussion I invented gambling on banknotes too). >> So there you are, I like LTspice, in runs in wine (that is a windows >> emulator for the microsof users), >> so I can actually use it. >> It is the best I have seen (LTspice, not wine). > > Great ideas!! If Facebook can turn a profit of $480M in this economy > then the govt should be able to do the same thing! > > Uh, who paid that $480M? and, did THEY make a profit? Who's spending > this money?
...and $480M is a drop in the $20+ trillion deficit.
On Mon, 29 Jul 2013 07:04:15 -0700, RobertMacy wrote:

> TI who likes to make TINA-only models.
They provide Pspice models, too. Ones that actually work something like the actual devices. I downloaded a Burr-Brown rail to rail instrumentation amp from TI today. Remarkably like the datasheet says it should perform/ -- "Design is the reverse of analysis" (R.D. Middlebrook)
On Mon, 29 Jul 2013 13:41:47 -0700, Fred Abse
<excretatauris@invalid.invalid> wrote:

>On Mon, 29 Jul 2013 07:04:15 -0700, RobertMacy wrote: > >> TI who likes to make TINA-only models. > >They provide Pspice models, too. > >Ones that actually work something like the actual devices. > >I downloaded a Burr-Brown rail to rail instrumentation amp from TI today. >Remarkably like the datasheet says it should perform/
It's really not hard to write nice behavioral models. If you bother to actually measure the performance of the device to be modeled >:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
"Tauno Voipio" <tauno.voipio@notused.fi.invalid> wrote in message 
news:kt6744$3ha$1@dont-email.me...
>> Ratio Discriminator: >> http://www.radio-electronics.com/info/rf-technology-design/fm-reception/ratio-fm-detector-discriminator.php >> > > The circuit (while quite correct) in not too carefully drawn: > the signal from the diodes charges the electrolytic capacitor > in reverse polarity.
Probably a careless reprint of a circuit from the Navy's electronic manual (I don't remember the website, but it turns up often on these subjects). They, of course, used *electron current flow*, just to be different. Often, the diodes in those old schematics (when electron and conventional current were still open for debate) would specify with a + and -. So you'd see a diode drawn anode-to-cathode with a plus and minus respectively (i.e., the rectifier makes the minus side negative, because the symbol is pointing *electrons* in that direction). Don't forget those old circuits with germanium PNP BJTs, with a negative supply on the top and backwards-pointing emitters on bottom. :) Tim -- Deep Friar: a very philosophical monk. Website: http://seventransistorlabs.com
On a sunny day (Mon, 29 Jul 2013 11:05:14 -0800) it happened Robert Baer
<robertbaer@localnet.com> wrote in <v9yJt.4849$El3.2999@fx20.iad>:

>Jan Panteltje wrote: >> It is actually really simple: >> Find a nice C value, 220 pF is my favorite. >> Use online calculator to find L for resonance, or estimate from Xperience. >> Use standard coil formers (8 mm diameter, or 6 mm diameter, whatever), >> with adjustable cores. >> Add some turns (how about 100? for 1MHz), >> apply your F from source or generator. >> Tune for maximum. >> >> Now make 2, put them, 1 cm next to each other, >* RCA Radiotron indicated tight coupling to achieve a double-humpped >response for better linearty and AM rejection.
I had good AM rejection in the TV demod 5.5 MHz, 8 mm diameter formers, at 1 cm spacing those almost touch. You propbably want a good limiting amplifier. But please tell us: Is it narrow band FM (at 1 MHz????) It should be... other methods may be better (PLL, quadrature). I had some nice formulas for calulating bandfilters, no idea where that is. LC coupling LC and LC -C- LC etc Once had to do a whole lot a 19 inch rack full ...
On a sunny day (Mon, 29 Jul 2013 11:22:47 -0800) it happened Robert Baer
<robertbaer@localnet.com> wrote in <YpyJt.216626$f_.47850@fx12.iad>:

>> Great ideas!! If Facebook can turn a profit of $480M in this economy >> then the govt should be able to do the same thing! >> >> Uh, who paid that $480M? and, did THEY make a profit? Who's spending >> this money? >...and $480M is a drop in the $20+ trillion deficit.
You have to start somehere... http://en.wikipedia.org/wiki/J._R._D._Tata
On Mon, 29 Jul 2013 18:22:15 +0200, Glenn <glenn2233@gmail.com> wrote:

>On 29/07/13 08.54, Jeff Liebermann wrote: >> On Sun, 28 Jul 2013 21:48:14 -0800, Robert Baer >> <robertbaer@localnet.com> wrote: >> >>> I understand, that with the proper winding configuration, that a 90 >>> degree phase shift can be achieved between primary and resonant secondary. >>> That is done with a tapped secondary on a FM discriminator transformer. >> >> That would be a Foster Seeley Discriminator, except there is no 90 >> phase shift involved: >> <http://www.tpub.com/neets/book12/51c.htm> >> A 90 degree phase shift demodulator would be a quadrature demodulator.
The original 1938 Foster-Seeley (RCA) patent: <https://www.google.com/patents/US2121103> Note that it's for a TV receiver.
>I hope I some day will design a Foster Seeley Discriminator or better >yet a Ratio detector. The Ratio detector because it has built-in limiter >functionality.
Why? There are much better circuits that can be crammed into an IC, don't require messy xfomers, and often require no tuning. For example, using DSP: <http://www.silabs.com/products/audiovideo/fmreceivers/Pages/default.aspx> With the garbage generated by HD Radio transmission spewing garbage into the adjacent channels, an IF and demodulator that hear absolutely nothing from the adjacent channel is a must. <http://802.11junk.com/jeffl/crud/KCSM.jpg>
>According to this site there is a 90 degree shift needed: >http://www.radio-electronics.com/info/rf-technology-design/fm-reception/foster-seeley-fm-detector-discriminator.php >Quote: "... >To obtain the different phased signals a connection is made to the >primary side of the transformer using a capacitor, and this is taken to >the centre tap of the transformer. This gives a signal that is 90 >degrees out of phase.
Guilty as charged. It's been such a long time since I had to deal with a real discriminator circuit, that I forgot how it worked. I think the last discriminator circuit I dealt with used tubes (valves). The radios I helped design in the 1970's uses Sprague ULN2111 and ULN2136 IC's with quadrature FM detectors.
>By chance I found a schematic some months ago, with a Ratio >Discriminator with AFC functionality. I did not imagine that it could, >because I read some decades ago that only a Foster Seeley was associated >with AFC functionality.
The basic required for an FM demodulator to also act as an AFC is frequency response down to DC. Just about all the FM demodulators will do that. The rest is a matter of deciding on the lock range and modulation acceptance bandwidth. If the lock range is wider than the allocated channel width, the AFC could easily lock onto the adjacent channel. For this reason, the AFC lock range is often less than what the demodulator is capable of converting to audio. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On a sunny day (Mon, 29 Jul 2013 23:00:07 -0700) it happened Jeff Liebermann
<jeffl@cruzio.com> wrote in <ngkev8llo0aulo9vmu84m9k2nelo7bce2u@4ax.com>:

>The basic required for an FM demodulator to also act as an AFC is >frequency response down to DC. Just about all the FM demodulators >will do that. The rest is a matter of deciding on the lock range and >modulation acceptance bandwidth. If the lock range is wider than the >allocated channel width, the AFC could easily lock onto the adjacent >channel. For this reason, the AFC lock range is often less than what >the demodulator is capable of converting to audio.
Yes, and one old way to demodulate FM with a AM radio was 'slope detection', http://kom.aau.dk/group/05gr506/report/node30.html So, basically OP can use any MW radio for 1 MHz.. ;-) This gives some other detectors, like 'ratio detector' that I like personally: http://en.wikipedia.org/wiki/Detector_(radio)