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#11
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"Reg Edwards" wrote in message ... An 18 nano-henry inductor seems, to me, to be an impractical inductor value. The length of the connecting wires will form an appreciable part of the inductance. There must be another way of acheiving the desired circuit functions. However, to find the length, diameter and number of turns to make such a small coil you can use program SOLNOID3 which can be downloaded in a few seconds, free of charge, and run immediately from the the website below. Try it and see what happens. --- .................................................. ......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. ......... Reg, A 1/2 turn loop of the proper dimensions might be more practical. I recall using one that was about .5 in high between .5 centers, made of #14 wire. (it carried 10 amps). Don't remember the exact value, but it was probably a little more than what he is looking for. At any rate, as you say, it is important to add the inductance of the circuit board traces to the inductor value. BTW, the last job I was on used 402 SM inductors down to about 10 nH, but that was at 2+ GHz. Tam |
#12
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"Joe" wrote in message link.net...
"Reg Edwards" wrote in message ... An 18 nano-henry inductor seems, to me, to be an impractical inductor value. ;-) You just aren't working with small enough, high enough frequency circuits, Reg. 3 turns of 28AWG on a 4-40 (USA) screw (remove the screw, of course) will give you about 18 nH. Unloaded Q at 440MHz will be around 200. The link to the schematic is: http://www.radiotronix.com/downloads/433_pair.pdf Easy enough to use SMT components soldered to a piece of copper-clad for a ground plane. Just put down the two caps and the shunt resistor "tombstone" style, one end soldered to the ground plane and the other up in the air, separated by enough distance to put the series coil and resistor between them. You can keep the parasitic L and C very low indeed this way. You can also use tiny squares of copper-clad glued down to the ground plane as tie points. It's also possible to mechanically make a simple circuit like this on copper-clad using surface mount parts, by scribing lines with something like an X-Acto knife and removing strips of copper. In this case, I could see scribing four lines across the board, separated by about 1/16 inch, and removing two copper strips, one from between the first and second scribe, and one from between the thrid and fourth scribe. That leaves a trace about 1/16 inch wide. Cut gaps in the trace, about 1/16 inch long, where you want to solder down series components. Solder shunt components across from the trace to the copper ground plane. Bridge across the trace with a copper strap to connect the two gound plane sides, with the bridge up in the air over the trace. Nice to have a ground plane on the opposite side, with some holes and wires to connect to the top-side ground planes, but not necessary. I'm thinking 0805 parts with the sizes I mentioned...make things slightly larger for 1206. You can make the trace be a 50 ohm transmission line if you want, by sizing things right. Cheers, Tom |
#13
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"Tom Bruhns" wrote in message ... "Joe" wrote in message link.net... "Reg Edwards" wrote in message ... An 18 nano-henry inductor seems, to me, to be an impractical inductor value. ;-) You just aren't working with small enough, high enough frequency circuits, Reg. 3 turns of 28AWG on a 4-40 (USA) screw (remove the screw, of course) will give you about 18 nH. Unloaded Q at 440MHz will be around 200. The link to the schematic is: http://www.radiotronix.com/downloads/433_pair.pdf Easy enough to use SMT components soldered to a piece of copper-clad for a ground plane. Just put down the two caps and the shunt resistor "tombstone" style, one end soldered to the ground plane and the other up in the air, separated by enough distance to put the series coil and resistor between them. You can keep the parasitic L and C very low indeed this way. You can also use tiny squares of copper-clad glued down to the ground plane as tie points. It's also possible to mechanically make a simple circuit like this on copper-clad using surface mount parts, by scribing lines with something like an X-Acto knife and removing strips of copper. In this case, I could see scribing four lines across the board, separated by about 1/16 inch, and removing two copper strips, one from between the first and second scribe, and one from between the thrid and fourth scribe. That leaves a trace about 1/16 inch wide. Cut gaps in the trace, about 1/16 inch long, where you want to solder down series components. Solder shunt components across from the trace to the copper ground plane. Bridge across the trace with a copper strap to connect the two gound plane sides, with the bridge up in the air over the trace. Nice to have a ground plane on the opposite side, with some holes and wires to connect to the top-side ground planes, but not necessary. I'm thinking 0805 parts with the sizes I mentioned...make things slightly larger for 1206. You can make the trace be a 50 ohm transmission line if you want, by sizing things right. Cheers, Tom Hi Tom, Being so new at this, I don't even know what you mean by 'tombstone style', and it sounds like an awful lot of work to be scoring pcboard with an Xacto knife to create transmission line effects. I talked with a tech rep from radiotronix today. They called me because I ordered a half dozen modules from mouser. He explained that the pi circuit on the TX is so the TX sees 50 ohms, which is pretty critical. I have not done anything with the transmitter modules yet (they are from Velleman because they are thru hole), but I am building a receiver board on pc board using pcbexpress and single sided copper pcboard. It will be the first prototype. Now that I have it working on a breadboard I am going to build one and see how it works. I am planning on using a straight piece of (20ga) wire for the 18nH inductor and using the T network of 2 8pf caps beside it. The tech said this is just a low pass filter, but it seems to make a difference in receiver sensitivity. The noise on the receiver is supposed to be there according to him. It is between 1Khz and 1.5Khz. he said some people use the data slicer pin with a holtek ht12D decoder, which i am doing or you can also use a micro to look for the bit pattern and decode the signal. I am just using the TV (transmission valid) to set off the rest of my circuit which, right now, consists of a latch and an LED. Joe |
#14
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Joe wrote:
Being so new at this, I don't even know what you mean by 'tombstone style', and it sounds like an awful lot of work to be scoring pcboard with an Xacto knife to create transmission line effects. You can easily build what you need using single-sided board: a continuous groundplane, components soldered on top, and connections made using sticky-backed copper tape (available at craft stores for stained-glass work). If you cut strips 0.1in wide, these will be a good approximation to 50-ohm microstrip, for the relatively low frequencies and short lengths that you will need. On the reverse side, use broader the copper tape to link the groundplanes of your extension and the Radiotronix module. Simply lay the SMD components against each other, and solder them together... but before you do, mark where the connections through to ground will need to be, for the two capacitors in the pi-network and possibly other places. Then drill the board and insert links of thick wire (14AWG) so that the ground connections will have zero length beyond the thickness of the board - but I really do mean ZERO, or else your network will not perform correctly. The ground links must be touching the ends of the capacitor chips before you solder them. Likewise, use ZERO lead lengths inside the pi-network. Butt the ends of the two Cs and the L chips directly together, and solder. Any "connecting leads" must be restricted to the places that can use 50-ohm microstrip. This construction method is very quick and simple. The SMD parts are well-enough anchored to the board for all normal conditions of use. I talked with a tech rep from radiotronix today. They called me because I ordered a half dozen modules from mouser. He explained that the pi circuit on the TX is so the TX sees 50 ohms, which is pretty critical. - so remember what I just said about zero lead lengths. I have not done anything with the transmitter modules yet (they are from Velleman because they are thru hole), but I am building a receiver board on pc board using pcbexpress and single sided copper pcboard. It will be the first prototype. Now that I have it working on a breadboard I am going to build one and see how it works. I am planning on using a straight piece of (20ga) wire for the 18nH inductor and using the T network of 2 8pf caps beside it. The tech said this is just a low pass filter, but it seems to make a difference in receiver sensitivity. On the face of it, this pi-network has a 1:1 impedance transformation (two equal capacitors) so it shouldn't make any difference. However, there may be stray capacitances and/or inductances in the module that we don't know about. Bottom line is, this network is what the Radiotromix techs have found to work. Since you don't have the design experience and the test equipment to measure how the whole thing performs, you would be very wise to copy EXACTLY what Radiometrix did, which includes building the whole network using the best possible construction practice. Also, a straight piece of wire is actually a short length of transmission line: it does not have quite the same electrical properties as an inductor. So use an 18nH chip inductor like Radiometrix said. This is really part of your "contract" with the module manufacturer. It isn't fair or reasonable to expect their tech support to second-guess what the effects of every individual user's network might be, if they're all slightly different. You might get away with it this time, but some of the worst tech-support problems are caused by people who decla "I did exactly what you said..." [Now follows 20 minutes of intensive cross-examination over the phone] "... oh, apart from all these things that are different." [Deleted: strange sounds on the phone line. The tech has the curly cord gripped in both hands. He's puling it out straight, and he has a red glint in his eyes. Be very thankful that you're several hundred miles away...] -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
#15
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Ian White, G3SEK wrote:
You can easily build what you need using single-sided board: a continuous groundplane, components soldered on top, and connections made using sticky-backed copper tape Sorry, that wasn't quite clear (not enough coffee yet this morning). The continuous groundplane is on the underside of the board. All the SMD components are on the bare fibreglass side. The SMD components are held in place by soldering them directly to each other, to the ground links, to the striplines, and to various other fixed points. No board etching is required, and this technique will is good to frequencies well above 1GHz. The 0.1in stripline width was for standard 0.064in FR-4. You can obviously refine that calculation if you want, but there's little point for this particular application. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
#16
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"Joe" wrote in message link.net...
"Tom Bruhns" wrote in message ... .... Easy enough to use SMT components soldered to a piece of copper-clad for a ground plane. Just put down the two caps and the shunt resistor "tombstone" style, ... Joe: "I don't even know what you mean by 'tombstone style'," Tombstone style...just solder one end to the copper-clad board, and the other end sticking up in the air. Looks like a micro-size tombstone sticking up from the board. .... Cheers, Tom Hi Tom, Being so new at this, I don't even know what you mean by 'tombstone style', and it sounds like an awful lot of work to be scoring pcboard with an Xacto knife to create transmission line effects. It's really not all that difficult. Just use a ruler to guide the knife, use a sharp knife, and the strips you want to remove can usually just be pulled up in one piece (each). Or do it as Ian suggested, with sticky copper tape. As Ian wrote, keep lead lengths extremely short, like "zero." He suggested putting a piece of heavy copper wire through the board where you want to connect to the ground plane. Another way is to simply drill a hole through the board and drop an 0805-size surface mount part into the hole, and solder both ends. A 1/16" hole would work, but you'd do better to pick a size that just fits the part you want to use. Not all 0805 parts are quite the same size, but the body lengths are pretty accurate and work nicely in 1/16" thick board material. Any of the methods mentioned by Ian and myself will work well, and all are reasonably easy to implement with a bit of practice and patience. Cheers, Tom |
#17
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Tom Bruhns wrote:
Any of the methods mentioned by Ian and myself will work well, and all are reasonably easy to implement with a bit of practice and patience. One method of "etching" that worked for me was using a reamer bit on a drill press to cut through the copper and barely into the PCB material. This has the advantage of leaving a ground plane in between the active traces. Also great for scouring and sizing PCBs. -- 73, Cecil, W5DXP |
#18
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On Wed, 06 Oct 2004 12:20:57 -0500, Cecil Moore
wrote: Tom Bruhns wrote: Any of the methods mentioned by Ian and myself will work well, and all are reasonably easy to implement with a bit of practice and patience. One method of "etching" that worked for me was using a reamer bit on a drill press to cut through the copper and barely into the PCB material. This has the advantage of leaving a ground plane in between the active traces. Also great for scouring and sizing PCBs. This is where those Dremmel tools come into their own! -- "What is now proved was once only imagin'd." - William Blake, 1793. |
#19
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Paul Burridge wrote:
Cecil Moore wrote: One method of "etching" that worked for me was using a reamer bit on a drill press to cut through the copper and barely into the PCB material. This has the advantage of leaving a ground plane in between the active traces. Also great for scouring and sizing PCBs. This is where those Dremmel tools come into their own! As a matter of fact, when I did this stuff at home, I used a Dremmel tool. |
#20
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Thanks all for the suggestions, I have a dremel, and this might be a good
project for me to learn how to use smt stuff. I will need to get a small lighted magnifier tho, cause my eyes ain't what they used to be, even with my reading glasses. Joe |
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