Round two at building a simple transmitter - Page 1
Forum section: electronics / rf-microwave

author: yada
author_rank: Frequent Contributor
timestamp: April 28, 2017, 02:58:20 pm
content: I found this one seems really simple (on bottom of page)http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/433MHz_Data_TRX.gifUnfortunately it doesn't tell you the value of the inductor. I was thinking 3 turns of 22ga magnet wire with a 3mm dia. I just pulled that figure out of my ass but it looks like something I have seen before. Think it will work? I'm building this one on a tiny piece of perfboard with the leads acting as wires since I still don't have my copper board.

author: DimitriP
author_rank: Super Contributor
timestamp: April 28, 2017, 09:30:43 pm
content: 27 nH should do it

author: yada
author_rank: Frequent Contributor
timestamp: April 28, 2017, 10:54:22 pm
content: Quote from: DimitriP on April 28, 2017, 09:30:43 pmIf only I had a way to measure it. The coil was so sensitive on the last one. Just touching it could make the whole oscillator stop working or double the output.

author: yada
author_rank: Frequent Contributor
timestamp: April 30, 2017, 12:32:46 am
content: OK here it is before soldering. The LED lights but my supply says its drawing 0.000mA (it seems to be accurate down to about 0.001) So its not oscillating as far as I can tell. I don't have a scope so I will try and look for the signal in my SDR.This is an actual RF transistor, I have three to pick from, part# in picture but these trans. seemed identical in that other FM trans I made so I didn't try swapping them (wire wrapping takes along time). I'm guessing that's not the right coil, as I think all the connections are correct. If that was the coil is there just too much wire wrap wire? I was hesitant to cut the leads and solder because if this is not going to work I want to save the parts. But since it pulls <0.001ma I don't have even a clue to how to modify it. Antenna is the exact size from the schematic. Only mods are:Three 10pf in parallel for the 3.3pfWhere it says "data in" those leads are just open. Should they be shorted? Connected to high value resistor? A low value resistor?How much can I tell from the LED lighting? Does that mean the trans is conducting? Power is applied to the two leads of the mylar cap.

author: Don Hills
author_rank: Regular Contributor
timestamp: April 30, 2017, 01:15:22 am
content: Quote from: yada on April 30, 2017, 12:32:46 amVery likely one of the wrapped connections isn't making good connection.Also, long wire lengths are a bad idea at 433 MHz.QuoteDid you make the same mistake you made last time? Three 10pf in parallel is 30pf. Three 10pf in series is 3.3pf.QuoteThe lead with the resistor should go to 5 volts. You can connect it to ground, then a 27 K resistor from the base of the transistor to the 12 volt rail. That will put about 5 volts on the base of the transistor.I think you should go to the Talking Electronics pages mentioned in a previous post and look at the FM "Bug" transmitters. They'll be a lot easier to get working and you can test them with any transistor radio.

author: yada
author_rank: Frequent Contributor
timestamp: April 30, 2017, 06:18:17 pm
content: Quote from: Don Hills on April 30, 2017, 01:15:22 amYes the caps are in SERIES now, heh. So I made this again with a brand new trans just incase with no wire wrap all leads are wrapped around each other, was almost easier then wire wrap. I upped the coil to 25 turns, because the HAM radio inductor calculator said that was :0.0029718030670158003uH, which is 29.7nH? Or is it 2.9nH and I need to increase the coil by a factor of ten, which is not ten times as big (I still haven't made enough inductors to figure out what the relationship in size/turns is to value, When I think that its double its usually not even close) but the physical size just seems to be way bigger then any picture I have seen of any other circuit.So to give the DATA line signal : I add a 27k resistor, connecting one end to data in resistor and the other to +12 volts? What do I connect to the other data in to, just ground or do I leave it open?This new version also pulls 0.000A, first time I turned it on it went to 0.003A for less then a second, then down to 0.000A I have set the current limit to 0.005A then tried it at 0.015A it still wont light the LED that was coming on with the wire wrap circuit. So I don't think that the transistor blew up. I have read a lot on the site I got this from but this circuit has no explanation. Maybe it IS just an "idea".Thanks for all the help!Can you download this spice program for free?

author: yada
author_rank: Frequent Contributor
timestamp: April 30, 2017, 09:14:10 pm
content: This is actually a transmitter, not receiver. So first I'm going to fix my coil sizes now that I have my D's in order. How would that have worked a 4.5mm dia. wire wrapped into a 0.64mm coil?! No wonder why the readings were wrong!I'm still a bit confused about how to hook up the data input. Take the 22k resistor end in the schematic attach to another 27k resistor and apply +12 to it. Leave the ground end unconnected as its already connected to ground. So this is what biases the trans and gets it to transmit?I bought a bunch of RF trans from USSR, (they're red too!), I wonder how you would model those in spice.Will this circuit not work if the data line is just open? I guess if its not receiving data it doesn't have to transmit, but that seems like bad design, I would want to keep the carrier signal always on.I knew those inductors looked wrong. The actual turns for 27nH is three, I guessed five so I was close. And with the right data all the fields are populated on the site. Always trust your intuition I guess.

author: yada
author_rank: Frequent Contributor
timestamp: May 01, 2017, 07:48:37 am
content: Quote from: evb149 on April 30, 2017, 11:54:12 pmSS9018FBUSS9018HBUThose are two trans of four RF trans I have now. I think the data sheet said they went to 2GHz. The 199 was an old metal can package and cant be found.I think the HBU is in the circuit. My other FM trans used these and they seemed to all work the same, like shit but worked, gen purpose trans didn't work at all.I would love it if I could get this working to send telemetry or a digital audio signal into a rasp.pi with an Arduino on the TX end.I need a bug for the office to see what an employee is doing and don't want something that can be picked up on FM radio. Or too high tech that would run through the computer, and easy to find. I would like to pick it up on my cheap Chinese 455mhz walkie talkie radio plugged into a VOX tape reorder with squelch turned up. Other option would be to buy a commercial "bug" that transmits FM on 455MHz, hopefully in cheap DIY kit form and runs off a nine volt.I do have an Arduino Should that be set up to make a square wave go out? I would hate to set that up only to find this doesn't work for some reason . Now to download spice.

author: yada
author_rank: Frequent Contributor
timestamp: May 01, 2017, 05:08:31 pm
content: So now its soldered together with no wire wrap it pulls0.006A and does make a signal when its sitting right on top of the receivers antenna. I don't think its weak but rather needs a ground plane. I'm going to find some copper at the hardware store. The components have almost no lead length (rule out that variable) on them so now it needs a ground plane to make it work? So just put a copper plate under it with all points that attach to the - of the power supply soldered to this ground plane? What exactly does this do? The transmitter just came alive as soon as the metal sheet from the receiver antenna was placed under it. Was very weak when it was in between the antenna elements.

author: yada
author_rank: Frequent Contributor
timestamp: May 01, 2017, 07:51:47 pm
content: So I hope this counts as a ground plane.

author: Teknow
author_rank: Regular Contributor
timestamp: May 01, 2017, 08:50:25 pm
content: I remember building this transmitter some years ago. I used the BFR91, and BFG135, high power! And the most powerful was the Siemens BFT98B, now it is obselete! Although I had some success building this Xmitter, it was not reliable at all, and I had some transistors damaged! I found one version I once built, and leave you to judge for yourself its wild oscillation covering the 300-600 spectrum with jumping spikes and spurs!

author: yada
author_rank: Frequent Contributor
timestamp: May 01, 2017, 10:56:58 pm
content: Quote from: Teknow on May 01, 2017, 08:50:25 pmI'm wondering if that happened to this one. Wouldn't the mA change to 0 or go to a different value if it was damaged? I just plugged this one in again. LED lights still pulls 0.007A but I cant find the signal. The antenna is only a few inches away.Is the key to getting a reliable DIY xmitter that works by picking a design with a crystal? I did order some crystals they are 13.56MhZ and 36MHz. I ordered a bunch of stand alone transmitter chips but I messed up on the package size and they have 8 pins and are 2X3mm! I know of no way to hand solder to those leads.

author: BigBoss
author_rank: Regular Contributor
timestamp: May 16, 2017, 12:23:15 am
content: I couldn't understand exactly what you intend to do but if you wish to send a digital data you should use a kind of modulation.The simplest one is OOK ( On-Off Keying) but you can choose more sophisticated one such as FSK.LTSpice is not a frequency domain simulator, it's just a simple transient simulator and it's not very convenient for such circuits.