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Author Topic: February 1984 QST 30 meter QRP transmitter Project Question  (Read 2380 times)
KU4UV
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Posts: 376




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« on: October 02, 2012, 06:35:21 PM »

Hello everyone, I found this article online regarding what looks like a fairly simple to build 30 meter QRP transmitter.  I think I can probably round up all of the parts needed to build the transmitter, but I have a few questions I hope someone on the forum might be able to answer.  Here is the link to the scematic

http://www.arrl.org/files/file/Technology/tis/info/pdf/8402046.pdf

The schematic is showing what looks like a 130 Microfarad (130 SM) silver mica capacitor.  Am I reading this correctly, as the schematic notes that all capacitors are in Microfarads?  I am having trouble finding a source for 130uF silver mica capacitors.  It seems there are a plenty of 130pF capacitors, just not any 130uF.  This looks like a really neat little transmitter, and I think I could build it without any problems if I can find all of the parts needed to build it.  Another question: I am assuming that the ferrite bead just slips over the lead of transistor Q2?  I is ok to simply place the bead over the lead, or should the lead be wrapped around the bead?  Has anyone on the forum built this transmitter, and how is the performance?  I was planning on using the transmitter and a second receiver to make contacts.  Any thoughts or advice would be most helpful.  Thanks and 73!

Mike KU4UV
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WD8AJY
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Posts: 60




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« Reply #1 on: October 02, 2012, 07:01:36 PM »

The ones with a decimal point (.01) are microfarads the ones without the decimal point are picofarads.

Bob
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K8AXW
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« Reply #2 on: October 02, 2012, 09:58:20 PM »

Bob's right Mike.  The note at the bottom right of the schematic explains the difference between the caps.

This is pretty much SOP for reading schematics.  (Normally, if you can't find a value, like 130ufd, then it's probably 130pf.)
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KA4POL
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Posts: 1972




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« Reply #3 on: October 02, 2012, 10:01:55 PM »

As can be read in the lower right corner of Fig. 1 all capacitance values are in pF except the decimal ones being µF.
Yes, the ferrite bead just goes over the connecting lead as indicated in Fig. 3 component side. In case you should not use the PCB you can put the bead over the base lead of Q2.
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KU4UV
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Posts: 376




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« Reply #4 on: October 03, 2012, 03:33:42 AM »

 :-\Thanks guys, I feel pretty stupid for not knowing some of this stuff.  I guess I am just used to the capacitance values always being listed alongside the component, but it helps to read the notes.  I am going to try to build this thing, hopefully in the next few weeks and give it a try on the air.  I operated strictly QRP CW during Field Day from one of our family farms in southern Kentucky and had a lot of fun.  It helps to have an opportunity to actually be able to put up a decent wire antenna in the trees.  I used an antenna launcher on Field Day and had an inverted L up about 50 feet or so, with about another 100 foot piece of wire for the counterpoise through an antenna tuner.  I have a longwire outside of my apartment that is about 150 feet long, much like what the designer of this project used.  I am planning on maybe just using a shortwave receiver  as the receiver section.  I know it's probably not the best setup in the world, but I think I can stir up a contact or two.  I will keep you posted when I get the transmitter built and let everyone know how it performs.  Thanks again for the assistance guys!

73,
Mike KU4UV
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G3RZP
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« Reply #5 on: October 03, 2012, 04:11:42 AM »

I don't like the lack of a DC return from the base of the 2N3553 to ground - asking for leakage problems. I'd put something like a 22 microhenry choke in there.
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W5FYI
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« Reply #6 on: October 03, 2012, 08:23:03 AM »

Another consideration: current FCC rules require harmonics to be at least 43dB below the fundamental, the article says the filter shown is good for only 34dB. When you design your board, consider adding a five or seven stage output filter, then you should be OK with the law.

Looks like an interesting transmitter. I'll keep the schematic handy in case I decide to build one myself. GL on your build.
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WB6BYU
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« Reply #7 on: October 03, 2012, 08:52:41 AM »

Quote from: G3RZP
I don't like the lack of a DC return from the base of the 2N3553 to ground - asking for leakage problems. I'd put something like a 22 microhenry choke in there.


Or at least a resistor, maybe 22K or 47K.  Probably not as much of a problem if you
are keying the DC to the whole rig, but it will keep the transistor off when when
the oscillator isn't running.

Put the ferrite bead over the leg of the transistor as close as possible to the case to
optimize VHF stability, even if it means elevating the case up above the board.

Last time I listened to the band, 10.106 seemed like a better choice for a crystal than
10.120 MHz if you are going to order one, otherwise you can use whatever you can find.
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