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Building my portable PLL coil

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LAN_403

flannelhead

Wed Feb 06 2008, 01:52PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Hi all!

So, I'm building a portable PLL coil. I didn't post it to the projects forum because I have some questions about it. Here are the specs:

Power: two 6V 3Ah SLA batteries in series (so 12V 3Ah)
Secondary:
4.5cm x 13cm with 0.315mm wire (fRes ~2.3MHz)
OR
3.1cm x 4.5cm with 0.1mm wire (fRes ~2.5MHz)

Primary: I don't know yet, maybe will try with some 5 turns first. Voltage to primary 12V.
Driver: PLL DWSSTC II driver, but with 74HC4046 (VCO tuning cap 39pF)
Gate drive: PLL VCO out -> 74HC4049 inverter gates in parallel -> 47R resistor -> BD179/80 totem pole -> IRFP240

So, because this is gonna be portable, where should I ground the secondary? I want it completely portable, so no external grounding wires. What would be the best solution?

Also, will my circuit work? (I mean my gate drive thingy) I've built the gate drive part already and tested it. Strange problem: the 47R resistor is heating a lot

What's wrong with it?

I maybe also will try class e, although that's gonna be hard, I haven't got a scope

I've got also a unique audio mod idea for this portable coil, but I'll keep it a secret until I finish the coil!

Linas

Wed Feb 06 2008, 03:03PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

i am also bilding small portabe, but high power sstc :) it will be something like 3 litres of all sstc
Box will be 17*25*90mm

spark, (i hope <50cm)

MRacerxdl

Wed Feb 06 2008, 04:22PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Ok, I am wrong :P It cant be on the DC Supply Ground

Dalus

Wed Feb 06 2008, 04:36PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

Just build it bipolar.

flannelhead

Thu Feb 07 2008, 01:30PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Dalus said:

Just build it bipolar.

That would be one possibility, but
1. I don't like bipolar coils
2. I'm also going to try secondary base feedback.

Kolas

Thu Feb 07 2008, 09:00PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

There is the possibility of using a large conductor as your RF ground. I've used everything from large heat sinks to large planes of AL foil on the ground. It is my understanding that you only need a "sink" which is a capacitance larger then the sec self capacitance and the toroid combined. in my experiance, a couple square feet of surface area does the job.

flannelhead

Fri Feb 08 2008, 01:33PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Kolas wrote ...

There is the possibility of using a large conductor as your RF ground. I've used everything from large heat sinks to large planes of AL foil on the ground. It is my understanding that you only need a "sink" which is a capacitance larger then the sec self capacitance and the toroid combined. in my experiance, a couple square feet of surface area does the job.

That's a good idea. I also thought of something similar.

flannelhead

Mon Feb 18 2008, 01:21PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Yippee! First light

I'll post the coil when I have it cased. But for now two more questions:
I'm gonna use an aluminium case. I thought about grounding the secondary to it. I'm also gonna mount all the switches, pots, etc on it. But I recognized that at least my DC jack and audio jack have the ground connected to their bodies. What would be the best way to isolate them from the casing, but they could be still connected to it?

Another question, is the audio output of a PC sound card enough to audiomod the PLL without any amplification?

MRacerxdl

Mon Feb 18 2008, 07:45PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Its depends the soundcard, the realtek ones have a good gain (it very loud with a hearphone), but other ones maybe not. You can make a mini pre-amplifier like that schematic:

The out is on Sinal Amplificado.

If you want to use 12v with that pre, change the 10k resistor near the cap of sound out, to 22k instead 10k.

...

Tue Feb 19 2008, 03:50AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I would personally never connect a sstc to a computer, especially since the one time I connected my laptop to it I fried the amp on the motherboard >.<

If you insist on doing it, make sure you ONLY connect/disconnect the cable while the coil is off, and make sure that both sides are grounded.

As to having enough volume, I did some testing and found that as long as you set it so that there is small window of possible frequencies (like, there will always be plasma produced regardless of the position of the tuning pot) the 1v p-p from a normal source if fine. But otherwise you need a very well shielded amp to get a bit more volume out of it.

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