About a transmitter - Page 1
Forum section: electronics / beginners

author: M-E
author_rank: Newbie
timestamp: August 18, 2020, 05:48:45 pm
content: Hi everyone!I found the schematics of a transmitter, but it's not complete.I hope some of you could help me.How many µH should each half or L1 have?-How far away from / close to -each other should they be?-How long should each core be?-How many µH should L2, L4 & L5 have?-Does the wire-diameter matter?I've found many inductance calculator online, but the don't ask for the wire diameter.Does it matter if i use a coil with the same µH inductance -air or ferrite -core?-Is the power test necessary?-can i change the bulb to some kind of meter?If i can: -what should it be? (like W-meter, A-meter) -what range?-can i use 2SC3320 (hFE=30) instead of BD139 (hFE=40)?-what other transistors can i use?-what hFE ? -lowest? -highest?-how do i do to make this transmitter a 15W? ...or more.How do i do to make the out-effect adjustible? (1 - 12 / 1 - 15W)-How low frequence can i make it transmitt? 1,4MHz the lowest?I've read that the 3 - 30 MHz signal will reach farest, but which frequence reach most farest?I found this info:"A good rule of thumb for the time of day is that the higher frequencies are best during daylight (10 to 29.9999 MHz) and lower frequencies work best at night (2 to 10 Mhz)."-which frequences reach most farest of them? -in the day? -at night?C14 & C15: I guess 100pF is the maximum, but whatabout the minimum -how many pF?-can i use just one * - 200pF?-Which kind of antenna should i use?-How many Ohms should it be from RF OUT to the antenna?-Anything else i should know -tell me!Thanks a lot!

author: bob91343
author_rank: Super Contributor
timestamp: August 18, 2020, 09:33:35 pm
content: L1 must resonate with C1 at the crystal frequency. The details are not important as long as the Q is reasonable. That is determined partly by wire size and the other details. Build it and see how well it works.The bulb acts as a dummy load to help tuning without dangerous stress on the transistor.The best frequency for long distance is 14 MHz. Best time of day is near sunrise and sunset.Yes you can use one capacitor instead of two 100 pF. The antenna question is important. There are many books written about the subject and the main consideration is that it be around 50 Ohms and as high above ground as possible.

author: M-E
author_rank: Newbie
timestamp: August 19, 2020, 05:57:21 pm
content: The whole L1? ...or each half of it? The whole i guess...-Should i use only ONE core for L1?Does this:MHz L1-µH1,4 ~391.6248591,5 ~341.1487661,6 ~299.83778310 ~7.67584714 ~3.916249...sounds right?I cange the buld to a resistor, -how many Ohms should it have? 7,2? (The bulb has) -how many Watt? 12? -more?Which is the best frequence for allaround the day? (day-night-morning-evening)-Anyone who know about the rest?

author: fordem
author_rank: Regular Contributor
timestamp: August 20, 2020, 04:54:15 pm
content: Is it only me, or does any one else have questions about the legal aspects of this discussion?In my neck of the woods, transmitters have to be licensed, and the only way a home brewed transmitter could be licensed is under the amateur radio regulations which require the operator/constructor to be licensed, and that involves testing on the theory.

author: bob91343
author_rank: Super Contributor
timestamp: August 22, 2020, 04:47:32 am
content: The computed inductance would be the entire winding.The discussion isn't illegal. But it's certainly true that the government regulations must be observed and transmitting a signal usually requires a license. When you are tested for a license you generally are proving your knowledge of these regulations.Be all that as it may, I try to encourage people to learn the technical aspects and on the way they need to realize the legal ones too.

author: radiolistener
author_rank: Super Contributor
timestamp: August 22, 2020, 05:08:19 pm
content: Quote from: M-E on August 18, 2020, 05:48:45 pmIt depends on many factors. For example it depends on frequency, your antenna, day/night time, year season, Solar activity, weather and other things.For 3-7 MHz usual distance is about 600-1500 kilometers (one-two reflections from ionosphere). With good propagation you can listen for stations at 6000-12000 kilometers distance and even more. It is possible even to listen yourself, when the wave goes around the whole Earth and comes back to you. But it needs very good antenna and enough power 100W - 2000W. It depends on many factors and needs good experience, good receiver and antenna in order to make qso on so long distance.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 22, 2020, 11:27:15 pm
content: This is a low power AM Ham transmitter. AM is not used much in Ham radio anymore. You use different crystals to change frequency. Probably somewhere in the 7 or 14 MHz bands is best. You need to find a correct crystal or two or three.....This thing looks like an old design "home brew" when transistor were relatively new things. Lots of transistors would work, But they must ALL be capable of RF MHz frequency, not just audio frequency. T3 and T4 are "power" RF transistors, bigger. I do not know that the 3320 is RF transistor. It supposedly is the equivalent of a 2SC5200 which is a RF transistor with a Ft of 30 MHz, if so, it should work at 14 MHz and below.Transistor 1 up to the capacitor C5 is an oscillatorYou might want to build oscillator section first and see how well it works. It might need a trimmer capacitor.Or you could use an air variable capacitor in place of C 1 value range about 10-50 pF. Would let you use different crystals.L 1 is wound around a small toroid core I think.L2, L4 and L5 are just coils of hard wire wound around something like a pencil (pencil then removed). These are air core because any core would change the inductance value greatly and possibly heat up. These are in the range of something like ONE micro Henry in value. Hard to measure if you do not have fancy equipment. Common multimeter like instruments will not measure this low. If you have access to old broken transistor CB radios, they have the coils in the output stages. Easy to modify. Pretty big hard copper wire. I think the schematic calls for .5 and .8 mm copper wire. Close is good enough here.C 14 and C 15 are probably big old fashioned air variable capacitors, easier to find some at 100 pF than 200 pF. A 100 pF air variable would be in the range of maybe 20 at minimum to 100 max pF.You use these to tune the output to Maximum using the bulb. You do not tune for anything other than max output because this places too much stress on the final transistor and could blow it. You can change this to a meter with a modicum of additional parts including a "diode detector". If you build this then we can talk about a meter.You might be able to change location of C 4 to before the L 5 and get an easier tune, it would then be what is known as a Pi network.This thing would be interesting to build, and cheap.Probably this is built for a common Dipole antenna, Pretty big. And maybe not 50 ohm coax feed line, maybe old 300 ohm TV antenna twin lead (just a guess, since this thing seems to be made for someone to build at home with limited resources, in the OLD DAYS HA!!) You can make a physically shorter "folded dipole" antenna and the feed line both out of old TV twin lead if you can find the stuff. Look this up. The tuned output should let you "match" different antennas with different impedance.https://en.wikipedia.org/wiki/Twin-leadDo you have any test equipment? Let us know.

author: M-E
author_rank: Newbie
timestamp: August 27, 2020, 09:38:13 pm
content: 2SC5200 has hFE 55 -not to much / to high?I have a Fluke multimeter and an oscilloscope (tektronix)

author: bob91343
author_rank: Super Contributor
timestamp: August 27, 2020, 10:09:16 pm
content: The brand of the test equipment is not as important as which model.The 2SC5200 is a big transistor with a transition frequency of 30 MHz so it probably will work okay up to maybe 7 MHz. The transition frequency is the frequency at which the beta drops to unity, the highest frequency that it will work as an oscillator. For ordinary use, you need more beta; the beta at moderate frequency would be 30 MHz divided by the operating frequency so at 7 MHz it has a beta of maybe 4.

author: M-E
author_rank: Newbie
timestamp: August 29, 2020, 07:39:36 pm
content: Is beta and hFE the same?Which beta do BD139 have at 7 MHz?This website:https://alltransistors.com/transistor.php?transistor=24713...have a search for alternatives to a transistor, -which fields is important?...and what should i write in the MHz -field?

author: bob91343
author_rank: Super Contributor
timestamp: August 29, 2020, 09:03:18 pm
content: Yes beta is the same as hFE. I don't know anything about that transistor; consult the data sheet or ask the company who makes it.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 29, 2020, 10:43:57 pm
content: Here is a link to the BD 139 Datasheet, there are different 139s according to the sheet. Look at the hFE.. It will vary greatly from transistor to transistor.I cannot find a chart that has the gain vs Freq, that would be helpfulI think you want the BD 139-16https://www.st.com/resource/en/datasheet/cd00001225.pdfInteresting article:https://create.arduino.cc/projecthub/akarsh98/transistor-basics-bd139-bd140-power-transistor-tutorial-5e112aHere is the BD 139 used in a FM transmitter at about 100 MHzhttps://www.homemade-circuits.com/15-watt-transmitter-circuit-500-meter/

author: M-E
author_rank: Newbie
timestamp: August 30, 2020, 08:48:39 pm
content: I'm thinking of getting "bigger" transistors then BD139, -which ones should i get?Any of theese?hFE 40 10A 40VA MHzTIXP40 10 150BD113 10 60BD111A 10 50BD111 10 602N5940 10 1502N5039-1 20 602N3919 10 8080VTIXP39 10 150FT34A 10 80BUX35 15 70BU127 10 70BU128 10 802N5939 10 1202N5584 30 702N5331 30 802N5330 30 802N5329 20 80