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Author
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Topic: My Class-E AM Transmitter for 1610 kHz
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Will Snyder
General Troublemaker Posts: 11
Registered: Feb 2006
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posted 10-15-2006 03:15
   
I am posting for
comment and to assist anyone who might be interested my homebrew
Class-E AM transmitter that I use for my low power Part 15 AM station.
I am by no means an expert on Class-E, but basically Class-E is an
extremely efficient mode of non-linear RF amplification. Since the
final input power of a Part 15 AM transmitter is limited to 100 mw, I
found the high efficiency of the Class-E very appealing in terms of
maximizing the range of my installation. I was inspired to build the
circuit by listening to the AM operators on 3885 kHz who have built
their own high powered Class-E AM rigs, one of whom maintains a great
website at http://www.classeradio.com/. My undertaking was substantially less ambitious. I used the formulas posted at http://www.ussc.com/%7Eturner/mpm_class_e.html
to calculate the values for my circuit. I chose to use the very
inexpensive 2N7000 MOSFET for the final amplifier. The 2N7000 is fed
power directly from the output of the LM386 audio amplifier, which I
found to work better than using a modulation transformer or transistor.
Using the power limiting method that Lyle Koehler/K0LR has on his
website at http://www.mlecmn.net/~lyle/
, I added a 500 ohm resistor between the output of the LM386 and the
inductor that feeds into the drains of the 2N7000s to keep the input
power to below 100mw. The frequency source is a custom FOX JITO-2
oscillator that I ordered through Mouser for about $18.00. My antenna
is a 4 element Marconi flat-top antenna that has an effective length of
a little under 10 feet, and it is tuned to resonance with a tapped
loading coil that I wound with enamel-covered wire. I have 4 radials
made from aluminum shirt hangers from the cleaners that are terminated
with 10' ground rods. The circuit is housed in a plastic electrical box
with the loading coil, and the antenna is connected to a terminal on
the top of the electrical box. The electrical box is mounted onto an 8
foot ground rod, which serves as the transmitter's ground. The maximum
range is about 1/4 to 1/3d mile (and occasionally 1/2 mile) during the
day depending on conditions based on the reception on the radio in my
car. Power source is 18 VDC. Programming consists of various podcasts
(including Ragnar's "The Pirates Week, TWIAR, WOR, etc.), music, comedy
bits, and shortware pirate radio shows that I find on the Internet.
Anyway, I am linking in a schematic that I drew of the circuit and a
photo of the completed board. Although the schematic shows only 1
2N7000, I found that two of them in parallel seems to improve the
loudness of the transmitter. I have built a similar circuit for 13.560
MHz, and I can post some pictures of that rig if folks are interested.I
hope folks draw some inspiration from this little project of mine. I
would like to undertake another project to build Class-E AM rig using
the IRF510 MOSFET for 80 or 40 meters to get some more experience with
Class-E circuits. Thanks, and good luck.
Will Snyder KB4LFD
jwsnyder@radiofirsttermer.com.vn [IMG]http://www.jwsnyder.com/JWS Class-E Part 15 AM Transmitter - Schematic.jpg[/IMG] [IMG]http://www.jwsnyder.com/JWS Class-E Part 15 AM Transmitter-640.jpg[/IMG] [This message has been edited by Will Snyder (edited 10-15-2006).] [This message has been edited by Will Snyder (edited 10-15-2006).] [This message has been edited by Will Snyder (edited 10-20-2006).] Admin |
Bill O. Rights
General Troublemaker Posts: 368
Registered: May 2000
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posted 10-15-2006 11:13
Very cool Will. Admin |
Pigmeat
General Troublemaker Posts: 585
Registered: Apr 2004
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posted 10-19-2006 03:52
Yep. That's fun stuff to fool around with.BTW,Billo
and I have been using Class-E Grenades for years. Good transmitters.
The Animal was way ahead of his time when he designed those. Admin |
Grass Cutter Mannnn
General Troublemaker Posts: 731
Registered: May 2003
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posted 10-19-2006 21:47
Hey Will,I can't
get your links to open,I can go to your site,but you have no links
about the Class E Transmitter there,post a pic or schematic here
mannnnnnnn I am interestated in that.Never Mind I got the link to open
that is very cool mannnnnnn!!!I am also interestated in the IRF510
Class E transmitters,I have two IRF510s and would like to build a
transmitter myself,I also have four IRF540s any ideas out there
mannnnnnn!!!!!I am not very good with the math that it takes to get the
right values,but I relly would like to bulid one for broadcast
band& one for 6.9khz!!!------------------
Grasscutter [This message has been edited by Grass Cutter Mannnn (edited 10-19-2006).] [This message has been edited by Grass Cutter Mannnn (edited 10-19-2006).] [This message has been edited by Grass Cutter Mannnn (edited 10-19-2006).] Admin |
Ragnar
General Troublemaker Posts: 1140
Registered: Nov 2002
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posted 10-19-2006 22:00
quote:
Originally posted by Will Snyder:
My antenna is a 4 element Marconi flat-top antenna that has an
effective length of a little under 10 feet, and it is tuned to
resonance with a tapped loading coil that I wound with enamel-covered
wire. I have 4 radials made from aluminum shirt hangers from the
cleaners that are terminated with 10' ground rods.
Will,
I am really interested in this antenna design. Any additional info or Pics? rd
Admin |
Will Snyder
General Troublemaker Posts: 11
Registered: Feb 2006
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posted 10-20-2006 04:34
quote:
Originally posted by Ragnar:
Will,
I am really interested in this antenna design. Any additional info or Pics? rd
Yeah,
I'll take some pics of the antenna system and the interior of the
electrical box and link them for you and others. It's been very rainy
here and work & baby duty has been rough lately, so I have not been
able to get to the woods in the back yard to work on the rig recently.
1610 kHz is OK during the day, but at night that freq gets clobbered by
broadcasters south of the border. It would really be cool if the FCC
would adopt the NRPM to increase the allowable input power to 1W. I'll
go ahead and post those pics of the 13.560 MHz version of the circuit
here shortly. Stay tuned.
Will Snyder
Admin |
Will Snyder
General Troublemaker Posts: 11
Registered: Feb 2006
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posted 10-20-2006 04:51
Controls:
Left Knob: RF Input Power. Middle knob: RF output power attenuation.
Right knob: AF Input attenuation. Switch: Power.
[This message has been edited by Will Snyder (edited 10-21-2006).] Admin |
Will Snyder
General Troublemaker Posts: 11
Registered: Feb 2006
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posted 10-21-2006 02:26
Ragnar, per your
request, here are several pictures of the antenna for my Class-E AM
transmitter. The white wire is #12 THHN stranded house wire, and the
copper-colored strips on the flat-top are bronze weather stripping that
I bought at the discount building supply store near here. The spacers
are 1/4" square wooden dowels that I painted with wood stain. The four
elements are linked at the base of the antenna and connected to the
output terminal of the transmitter section. The purpose of using T or
flat-top antenna like this is to increase the capacitance of the
antenna so that it requires less coil inductance to tune the antenna to
resonance and so there is less in the way of coil losses. The
capacitance of my antenna is about 65 pF. From what I have read on the
Internet, the FCC is OK with the use of a capaciance hat so long as the
vertical portion of the antenna plus the radius of the capacitance hat
does not exceed the maximum length of 3 meters (10 feet). I am also
posting a picture of inside of the electrical box that contains the
transmitter and the loading coil. I got the idea to use this type of
antenna from a compilation of LowFER materials from the 1980s that
someone scanned and put onto the Internet.
(http://maxmcarter.com/lwantennas/1750mtxantennas.PDF) I have a run of
multiconductor cable running from the shack under the house across the
lawn and out into the woods where the antenna erected through which I
run the DC power and audio from the output of my computer's soundcard.
However, I have read about techniques where audio and DC power can be
run on the same twisted pair that I may try to implement sometime.Anyway, here are the pics:
Later,
Will
Admin |
Pigmeat
General Troublemaker Posts: 585
Registered: Apr 2004
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posted 10-21-2006 17:38
Thanks for the
pics Will. I'd seen distant shots of commercial "hammock" style
antennas from the early days of broadcasting,but I'd never seen the
details?Now I've got something to do with those clothesline poles out back of the house? The
op of WKNR,who posted another topic on this thread has designed two low
power Class E AM rigs called the Corsair and the Commando. I've heard
both on air and they sound good.
Check the link to his website in his post for schematics? They go from
MW through mid-HF bands w/ small mods and the parts are readily
available. If I'm not mistaken the Commando uses the IRF 510/511's? The
Corsair takes a IRF 530. Several stateside pirates have built Corsairs. Dave is good guy and will give you all the tech support you need. [This message has been edited by Pigmeat (edited 10-21-2006).] Admin |
Ragnar
General Troublemaker Posts: 1140
Registered: Nov 2002
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posted 10-21-2006 18:13
Damn You Will!!
I have spent all day here surfing the web looking at AM antennas. Actually
thanks for the pics and the websites. I pulled out my little 1w AM kit
& warmed it up. I don't have a proper antenna for it so I hooked up
directly to the 6925 Dipole, got out 3 blocks. Then I hooked it up to
the A-99 11m vertical, went 4 blocks. Thats without a tuner or
anything. I was listening to the radio in the jeep as I drove around.
So now I have to build a proper antenna. If I can increase the range
40% over the unmatched 11m vert. I will be able to cover most of my
town.  Killed a rainy Saturday anyway. RD
*Actually if I could somehow match that A99 for 1700KHz...
[This message has been edited by Ragnar (edited 10-21-2006).] Admin |
Pigmeat
General Troublemaker Posts: 585
Registered: Apr 2004
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posted 10-21-2006 20:55
Heck,I just saw where you are Will? I'm through there a few
times a year. I'll have to pull off to the side of the road and see if
I can hear you?Admin |
Will Snyder
General Troublemaker Posts: 11
Registered: Feb 2006
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posted 10-22-2006 01:16
Pigmeat, by all
means drive by when you are in the area and see if you can pick up the
signals from my 1610 kHz and 13.560 MHz rigs. They can be barely copied
during the day along Hastings Hill Road between Kernersville Road and
Sedge Garden Road and along Kernersville Road between Old Winston Road
and Harmon Creek Road. The signals get really good in the development
of Wyndfall (which is why I have started calling the station "Radio
Free Wyndfall." I have also copied it while driving along Masten Road,
and I have heard short bursts of the 1610 kHz signal while driving
along Union Cross Road near its intersection with Glenwood Road
although I think that those signals may be the result of sympathetic
radiation from some power transmission lines that run through that
area. I have transmitted JASON (http://www.weaksignals.com/) output
into the 13.560 MHz version, and I was shocked to be able to copy it
while parked in the Harris Teeter parking lot with my laptop,
IC-706MKIIG, and 10 meter mag mount (near the intersection of Century
Blvd and S. Main).Here's
a Google Earth snapshot of the area with references to the roads to
which I refer. [GULP!] I guess I had better start checking my tire
pressure a little more often. <cringe!>
Will
 Admin |
Will Snyder
General Troublemaker Posts: 11
Registered: Feb 2006
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posted 10-22-2006 01:37
quote:
Originally posted by Ragnar:
[B]Damn You Will!!
I have spent all day here surfing the web looking at AM antennas.
Yeah,
yeah, yeah. Serves you right for playing that song about ragging on
those of us in the legal profession. Even yours truly has been called
for jury duty. (This is all in jest! Please do not tell my mother that I am a lawyer. She thinks I play piano in the local bordello. My
law licenses (yes, plural) are another reason I like to keep my radio
activities in the legal arena notwithstanding the apparent
laissez-faire attitude of the FCC towards professional shortwave
pirates who steer clear of the ham bands, international aircraft
frequencies, 2182 kHz, etc. etc. I
ran the Gulch on the rigs today, so folks within the field strength
envelope of them got to partake of the Halloween episodes of Kracker
Radio, WBNY, Radio Free Speech, etc. Oh
yes, the antenna for the 13.560 rig is a 1/2 wave dipole mounted under
the house to attenuate the signal. The range is comparable with the
range of the Part 15 defined 1610 kHz rig. I also have a low pass
filter on the output from the final section because of the more
stringent requirements for suppression of harmonics under the Part 15
rules that apply to the 22 meter band. Good
for you on getting your 1W AM rig on the air even with non-resonant
antennas for testing purposes (been there, done that). Yet another
outlet for "The Pirates Week!" Later, my friend.
Will
Admin |
QRP
General Troublemaker Posts: 181
Registered: Feb 2005
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posted 10-22-2006 17:59
![]()
Admin |
Pigmeat
General Troublemaker Posts: 585
Registered: Apr 2004
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posted 10-22-2006 21:48
Looks like Commander Bunny bought a new outfit?Admin |
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