Bifilar Coils and Software Defined Radios

[boris_blackmilk]

Hello all,

First post here, I hope its a good one.

In a distant past, I was a Foundation Radio Amateur in Australia, but discontinued my licence due to problems from other local amateurs. However, I still possess a Universal Software Radio Peripheral, which is a software defined radio made by Ettus Research. After spending all this morning transplanting my original radios guts (along with a clockcard suitable for GSM - a totally different story of my life) with a radio that has a "Basic Tx" and "Baisc Rx" RF frontend card, I spent most of this afternoon setting up my ODROID-X ARM board with GNU Radio and X11 forwarding to my temporary Windows 7 laptop.

From what I've been reading of bifilar coils made to work with the rudimentary, and you could say, model World Wireless System, they resonate in the HF spectrum - which is what the Basic Tx and Rx will do - from 1MHz to about 64MHz, although according to what I was told about Nyquist zones this morning by my adopted brother (whose USRP I am swapping with), I don't really want to be up near 64MHz.

However, my thought is this - a Basic Tx could be used as a function generator, and the computer running the show could sweep through the frequencies, until a response is picked up from the second bifilar coil, at which it stops - there lies the resonance point. If anything, it would make tuning for resonance of an arbitrary coil alot faster.

Rationale: I have been "trained" in the "accepted" arts, and while acknowledging them as an explanation, I know a few things that are odd, like one of the most fervent adherents to Einstein saying to me three months before his death "Shane, if the speed of light was not a constant, we could travel forwards and backwards in time..." Unfortunately, I didn't think to ask to go through his effects or computer files after his death - rest in peace Professor Sabine, I suppose I can only really wonder now if you had any theory for me...

Anyway, I note that many of Teslas inventions that were patented, like binary code, induction motors, and polyphase AC, are used everyday worldwide, without so much as the general populace once mentioning (or thanking!) JP Morgans "crackpot." Indeed, if I were Tesla, producing all these amazing things, I don't think I would've stopped at 50 cycles and called it a day, I would've been topping my previous inventions until I was well in a grave.

However, I have read plenty about the effects of the patent I am interested in, the foundation of the World Wireless System, and the system to have been completed at Wardenclyffe, I have Professor Meyls Scalar Waves textbook, which I intend on reading this week coming, although at 600 odd pages, I really hope it has a few diagrams, I learn more from a good sprinkling of diagrams ("Does it have pictures...?"), and I fully intend on getting the parts to build a set of two bifilar coils, initially, expanding the system to four a little later.

I have some questions, and they relate to not blowing up a very expensive piece of radio gear that I'm going to use as a signal generator and spectrum analyser, the USRP - I could really do without a $2,000 hole in my wallet, especially considering I'm foregoing the chance to build my own GSM base station because that'll take far too long.

I figure, if I have a model Wardenclyffe, it'll leave GSM for dead...

Anyway, the questions - I need to keep the impedance of the primary of the transmitting bifilar coil at 50 ohms to "convince" the radio there is a load there. Now, realistically, the amount of signal power output and the fact the output is directly wired to an DAC through a matching transformer should put my mind at ease somewhat, essentially, the analog output comes off the DAC, though a transformer to match the output to a 50 ohm load, and hey presto, you have a HF radio signal of a very low power. I am going to look to see if one of the interface pins on the card gives me a direct to the DAC output, sans matching transformer, although I was advised not to modify the radio frontend card, and given the cost, I am heeding that warning. Plus I suck at soldering surface mount. Damn frayed nerves.

So, assume I can't actually get a nice analog output off the DAC, I have to go through the matching transformer, to get the impedance up on the primary coil on the bifilar, I'd need a few more than the five turns recommended by Meyl in his Scalar Wave experiments book. Can I assume, if I were to have a turn ratio of say 5:200, if I was to make it 15:600, I'd still get the same effect? Or is this different from conventional transformers? Just remember, I'm keeping an open mind on this one, its going to cost me $50 to build the two bifilar coils, and take about two weeks, by which time, my adopted brother will have finished his (legitimate) demonstration with my USRP, and I can pick it up and get to work.

As for me? I like the appeal of the World Wireless System, as the great man himself said, maybe it wasn't its time, and the system would have to have a hard birth through a tirade of crap from the bankers. I've had a life of persecution at the hands of the Australian Government (although those bastards will never admit it), and I really like the appeal of jamming one in their pipe and ordering them to smoke it. I've always been interested in wireless technology, my interest in amateur radio, my training as a telecommunications technician, and I was going to go onto uni and do mechatronics engineering specialising in grid connected geo-dispersed robotics systems... but if I were to pull off some interesting results with this, I'd certainly concentrate on this.

For what its worth, I'm one of those people who doesn't believe it until he sees it. Doubting Thomas am I. However, I can follow a recipe, and thats what I'll be doing, firing it up, and measuring it with some instruments, trying to make sense of what its doing. I'm not looking for how it does it, I'm just looking for what it does. Believe you me, I understand cars go along the road just fine, but I've never once wanted to understand the guts of how one works. I just accept if I push the accelerator, it goes, hit the brakes, it stops, and if it don't do either, you ring a mechanic (who are usually criminals).

This is just some thoughts and questions I've had, and I'm tending them the community. Certainly, open source gave me the proper education I enjoy today, but I've never had the money to really make anything special, except for this. So I'm willing to share my findings and experiences with you all, in the name of wiping the crap off the map.

Lastly, this particular effort in my life is dedicated to a special woman who adopted me as her son while I was 29 years old, and while I'm unable to speak to my "Mum" for the duration due to issues with her family members, I've decided, if this thing does half the stuff it says on the patent application, and I can prove it, she'll be rather interested.

Ok, enough thoughts. Thank you for reading my rambling thoughts, and I hope that I can contribute some meaningful results to the community.

[xee2]

I am not sure I understand your question, but it seems like you want to make sure your transmitter is terminated in 50 ohms so it will not be damaged. Since you are not actually transmitting, and therefore are not worried about getting a lot of power into an antenna, the easy way to do this is to use a 6 DB 50 ohm attenuator which you can buy with almost any type connectors or make yourself from three resistors. When this is put on the transmitter it will always see a 50 ohm load and you will be able to connect the output of the attenuator to any impedance you want.

[boris_blackmilk]

Hi,

Pretty much, thats the answer I was looking for - how to protect my radio from blowing. Of course, the powers used here are minuscule, but the first thing I learned in technical college training to be a technician was to never run a radio without a load - I noted for many months the OpenBTS wiki didn't note this... then noted it "might be a good idea to terminate" the antenna... horror stories of paperclips, etc.

Of course, with a 6dB attenuation, I'm probably not going to get much power into my bifilar coil in any degree, but if the resonant frequency lies within the HF bands, I should be able to get a 45W amp with pre-amp specifically for SDRs. As for the sensitivity of the ADC, I think I'll be ferreting through the datasheets... perhaps hit the receiving coil with a multimeter tuned to millivolts AC range...? Although most HF signals wouldn't be in the volts range either...

Thanks for that, I'll purchase one when I get my radio back, along with the SMA cables.

[artiechoke]

Hi boris,

Here is something that I found helpful. 

It is worth a study.

I am new here and may be this can help you with your radio.

I worked on radios, but only a small one my sister had or did have until I broke it.

Feed forward control is often combined with feedback control to optimize performance.

See below for details.

Artie

http://en.wikipedia.org/wiki/Feed_forward_(control)