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Author Topic: Homebrew QRP 10 meter 1 watt CW transmitter  (Read 16683 times)
KF4DDJ
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« on: August 09, 2005, 06:03:59 PM »

If anyone has plans, schematics, or any idea's on how to build or find a transmitter for the 10 meter band. I would appreciate it. I haven't had much luck looking thus far and I have been looking for a while. Something simple that will put out at least one watt. I don't know if a 74hct240 will put out a watt on 10 meters, at least I haven't had any luck so far. Maybe up to 100 milliwatts. Maybe something crystal controlled or if someone knows of or can draw up a simple schematic of how to drive an IRF 510 with an 74hct240 chip. I found plans for this, but they appear to be in spanish. Some of the values were metric. There is always a catch when you look for something on the internet. Any ideas?

Thanks,
KF4DDJ
Scott
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WB6BYU
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« Reply #1 on: August 10, 2005, 02:39:45 PM »

The IRF510 has a high input capacitance, so is difficult
to drive on 10m.  But it can be done - seems to me that
there have been a couple such transmitters built by W7ZOI
that appeared on "Solid State Design for the Radio Amateur"
and/or "Expermental Methods in RF Design".

I might instead suggest using a VHF transistor such as
the 2N4427, 2N3886, or 2N3553.  Or grab the final transistor
out of an old CB radio - most of them are similar and are
good for a few watts.  Most will be Japanese types such
as the 2SC1906, 2SC2025, etc.

The 74HC parts are usually good up to 20 MHz, and some
may work up to 40 MHz, but not reliably.

Most likely you will need a 3rd overtone crystal for 10m
with a fundamental in the 9.4 MHz range.  If you aren't
particular what frequency you use, there are a lot of
canned oscillators available on 28.322 MHz with a few
volts of output.  Otherwise  you can get a custom-programmed
oscillator for $6 or so from Digi-Key or Mouser on any
frequency from 1 to 125 MHz.  The phase noise may be
higher than a standard crystal oscillator, but it sure
reduces the parts count.

If you want VFO coverage, probably the best approach
would be to pick a crystal or canned oscillator just
above the 10m band (perhaps 33 MHz) and mix it with a
VFO on the necessary range.  One of the methods used in
"Experimental Methods in RF Design" is to use a digital
IC to divide the output of an oscillator by two, then
extract a desired odd harmonic from the square wave
output.  For example, a VFO running around 11.2 MHz
could be divided by 2, then the 5th harmonic extracted
with a couple of tuned circuits.  This process improves
the isolation between the VFO and the output frequency
to reduce problems with pulling, chirp, etc.
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KC8HZM
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« Reply #2 on: August 14, 2005, 08:43:57 PM »

This is something that I've been looking for also, and I'd be interesting in seeing what you find.  Be sure and post anything so we can read what you learn.

Marten
KC8HZM
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KF4DDJ
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« Reply #3 on: August 15, 2005, 04:15:48 AM »

OK,

Here is what I have found so far,

http://www.qrp.pops.net/transmit.htm :this is a very usefull page for someone who would like to build an amplifier. It may even work if modified for 10 meters. There are some other circuits that would be usefull on this page as well.

http://www.qsl.net/k0kp/hbrew/qrp_tx.html : I am currently building this transmitter for 10 meters and have been told it will put out about 500 milliwatts on this band.

http://www.qsl.net/kd7rem/5wpa.htm : This amplifier, I have built and can testify that it works quite well if built exactly according to the plans in the schematic. I am building a second one on the same board as the qrp transmitter on 10 meters.

http://www.qsl.net/kd7rem/qrpstuff.htm : Another good site for QRP projects

http://www.amqrp.org/kits/miniboots/miniboot.htm : This is just like the 5 gallon amp above, but with an RF switching circuit that works very well indeed. I am building my second one right now. Pay close attention to detail and stay persistant in the building process.

For any questions on the amplifiers above feel free to send an email. I will help out the best that I can. I have found a good supplier for toroids as well as silver mica caps for final filters.

Scott Griffith
KF4DDJ
73
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KC8HZM
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« Reply #4 on: August 16, 2005, 08:29:26 AM »

Great list of resources, I've been reading through them and my beacon project is in the works.

Marten
KC8HZM
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N2AXZ
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« Reply #5 on: August 21, 2005, 09:39:48 PM »

A really nice transistor that will work well for 10 meter CW is an International Rectifier IRFR110.  It is a power MOSFET that is generally used for power switching applications, but will work really well in the 10 meter band.  I have designed a 5 watt CW transmitter using this device.  I used a 16 volt DC supply, and an FZT651 bipolar NPN transistor as a driver amplifier.  Up at 10 meters the input impedance of the MOSFET is probably about 30 ohms or so, and you should be able to get a nice match from the output of the bipolar by using an L-section between the collector and gate.
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KF4DDJ
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« Reply #6 on: August 22, 2005, 08:23:39 AM »

David,

Please send me an email to kf4ddj@yahoo.com I would like to ask some questions about your design using the IRFR110.

Scott
KF4DDJ
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R_QRP
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« Reply #7 on: September 07, 2005, 12:59:01 AM »

check this site:
http://www.lu8eha.com.ar/microhobby/lab_ref2.jpg

//QRP
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KC8HZM
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« Reply #8 on: September 07, 2005, 07:35:33 PM »

kf4ddj, you should make a website after you finish showing what you learned, the different options you considered, and the final result.  I think that will be a big help to others who are also interested in getting a 10 meter 1 watt transmitter up and going.

I've ordered the Little Joe tx kit for 10m from:

http://danssmallpartsandkits.com/

and a crystal from surplussales.com.

I was also given an old CB by a friend and I'm in the process of locating the proper crystals to turn that into a 10m beacon.

Marten
KC8HZM
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KC8HZM
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« Reply #9 on: September 07, 2005, 09:07:11 PM »

oops.  That is:

http://danssmallpartsandkits.net/
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KF4DDJ
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« Reply #10 on: September 08, 2005, 05:47:59 AM »

OK,

The website sounds like a good idea and I fully intend to do that. I found a schematic for a transmitter called the ultra simple tranmitter. This can be found on the net. I have built the transmitter and it works great. So for a one watt output beacon, this would be a wonderful solution. I do prefer however, to have a little higher output and would like to build a PA and used the transmitter to drive it. The problem is that I have not found any real working (working being the key word) documentation or schematics to show a real output of say 2- 5 watts on the 10 meter band using an IRF510 for example. My knowledge of design is not good enough to even begin to start to experiment building a PA for a small transmitter. I have found designs and schematics (of course) but when it comes down to doing a smoke test on the amps and trasmitters I have built so far, they just do not work very well if at all. I have had some problems with spurious output on some of the tx's I built and noticed if I turn down the power it will go away. But what good is a design for a beacon if it will not put out but few 100 milliwatts to avoid the spurious output. It has been a big learning curve thus far. I have not found a single transmitter design for 10 meters that will put out an adjustable 2-5 watts. Which is what is really needed for a beacon on that band down in the low spot of the solar cycle at times. Maybe someone will come through and save the day that has a little more radio theory stored in their head than I do.

Thank You,

KF4DDJ
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KC8HZM
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« Reply #11 on: September 26, 2005, 08:11:57 AM »

I know this isn't exactly what you're looking for, but FWIW here is a brief web page that outlines how I converted a CB to the 10m band for a beacon.  It ended up being pretty easy, but it isn't as "elegant" as a simple TX.

It isn't quite finished yet, but here is what I have so far:

http://marten.beels.info/projects/beacon/beacon.html

Marten
KC8HZM
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KC8HZM
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« Reply #12 on: September 28, 2005, 10:36:15 AM »

Here is a 4 watt homebrew 10m transmitter based on an IRF510.

http://www.wn2a.radio-snow.net/beacon.htm

Marten
KC8HZM
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KB1IAI
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« Reply #13 on: January 22, 2008, 06:17:08 PM »

nice website martin. i also am converting a 40 channel cb to 10 meters. and i found a circuit right here on this site to inject cw into the mike input. i have lou franklins cb pll data book for reference. now i will have a 10 meter qrp cw rig.

73 all paul kb1iai
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KC2RLY
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« Reply #14 on: September 08, 2010, 08:15:19 AM »


 you can get a custom-programmed
oscillator for $6 or so from Digi-Key or Mouser on any
frequency from 1 to 125 MHz.  The phase noise may be
higher than a standard crystal oscillator, but it sure
reduces the parts count.


I have been searching the Mouser Catalog and Digikey all morning and I think i must be looking in the wrong places. Any one have any clue as to where I would locate the custom offerings?
 
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