QRP Transmiters

The original Grenade Transmitter

A wished new design ..!

Inside The Grenade Transmitter
Joe Bean Prototype Pictures

Requirements

• 12-14 volts DC power at 1.5 amps, 2 or more amps peak, to handle the modulation.
• Crystal FT-243 style case, in the 40 meter frequency area (6000-8000 Kilohertz).
• Antenna cut for the frequency of the crystal. A Dipole is the best and easiest.
• Audio source, .5 volts 'consumer level' like that from home tape decks, VCRs, or computers. A boom-box or other portable can be used through the headphone output jack.

Specifications

• Power output: nominal 10 watts @ 12.5 volts, 1.2 amps
• RF output impedance: 50 - 75 ohms
• Harmonics: -30 dB

The Grenade Project RF-section
The "Grenade" is a 10 watt AM transmitter for the 40 meter band (6955 kHz).
  It was designed, built and sold by "Radio Animal" of WKND.

The Grenade originally came built with one x-tal (6955/6950) and a dipole antenna at just under 100 dollars U.S. It is a great little radio, roughly the size of a brick, and weigh in at well under half a kilo. With a dipole cut to frequency you can cover the USA from the Rockies to the Atlantic in the evening under decent conditions. Output power roughly 15 watts when running from a 12 volt battery (That is constant carrier, it peaks in the 50 watt range) and will do close to 20 watts when powered from a regulated power supply. The limiter/compressor is really what makes the Grenade great. Makes it possible for someone with no knowledge of radio production to plug in a walkman type tape deck and go on the air. The rig is cased is in a black steel box, with a finned aluminium heat sink covering the top. The transmitter can run continuously for 3 straight hours in hot temperatures (85+ degrees Fahrenheit) and the rig barely gets warm to the touch. Unlike ham transmitters, this one can run several hours per day with no problems and it is made so that it can handle running into mismatched or even no antenna.

The Grenade Project LF-section
The limiter/compressor is really what makes the Grenade great.

The limiter/compressor in the Grenade Project LF-section.

The Grenade has an automatic level control to keep the audio level from being too loud or too soft. The circuit tries to compensate for differences in input levels, but some sources might still be too loud or too soft. If using a portable, like a boombox or personal stereo, adjust it for an average listening volume through the speaker, then connect it to the transmitter.
A resistive optocoupler, comprising an LED coupled to a photoresistor, has some unique advantages when used as a control element in analog audio circuits. The devices consist of a high performance LED shining on a photocell inside a light-tight case. It's a light source and a photoresistor pointed at each other and sealed in an opaque package. It's pretty easy to make a limiter out of one: put a resistor in series with the photoresistor and drive your signal across the pair. Take the output across the photoresistor. Drive the light source (usually an LED) such that when the output level is too high, the light goes on and when it's too low, the light is shut off. When the light goes on, the photoresistor's value drops and the resistor divider's loss increases => the gain of the circuit drops. When the light goes off, the photoresistor's value increases and the voltage loss of the divider decreases, raising the gain. That's all there is to it...
The only subtlety is how quickly the light turns on and off (or becomes brighter or darker) as this and the decay time of the photoresistor itself determines the attack and decay time of the limiter. The photoresistor is a typical Radio Shack thing the size of a dime, which has the LED touching the lens and pointing directly into it, with the whole mess sealed in a mass of black heat-shrink tubing pieces to block outside light. The photocell has a dark resistance of about 10 megs and a LED-full-on resistance of a few hundred ohms.
Simple Modulators for Solid-State Transmitters: Simple AM modulators work by varying the amount of power supplied to the transistor which is serving as the RF output amplifier. By imposing an audio waveform on the power supply, amplitude modulation is achieved. A transformer less circuit is physically smaller and lighter than designs that use a modulation transformer. Transformer-based modulation methods have a more "warm" sound quality, while transformerless schemes have a "crisp" sound.

This is another Grenade Transmitter ...

The Parts List for the Shortwave Transmitter

The Parts List for the Shortwave Transmitter:

• R1 - 33K ohms, ¼ watt, carbon.
• R2 - 4.7K
• R3, R6 - 100
• R4 - 10
• R5 - 100, 1 watt, or greater.
• C1 - 47 to 470pF, or greater, silver mica or disc ceramic.
  Better yet, a trimmer capacitor, to slightly change
  frequency ±1 KHZ.
• C2 - 10 to 140 pF trimmer.
• C3 - 100 to 220 pF, silver mica or disc ceramic.
• C4 - .01 to .05 µF.
• C5 - 300 - 800 pF, or (? ? ?) variable capacitor.   I used an
  Arco TC-4610 (260-900 pF) compression trimmer.
• C6 - .01 to .1 µF.
• C7 - 1000 µF or greater, electrolytic, 25 volts or greater.
• X1 - Fundamental mode crystal, 5 to 8 MHz.
• T1 - On an Amidon T50-2 toroid core, primary is 26 turns of
  #28 magnet wire closewound, secondary is 2 turns
  wound over the primary windings.
• T2 - On an Amidon T50-2 toroid core, bifilar wind 6 to 8 turns
  of #18 magnet wire.   See note 1 for details.
• L1 - 2 mH or greater, .5 ohm or less resistance.   I used the
  inductor from Radio Shack p/n 270-0030A HD Noise Filter.
  One could also use the 4 or 8 ohm secondary of a medium
  sized audio transformer, or the secondary side (6 to 24 volts)
  of an AC mains power transformer.
• L2 - .7 µH.   Wind 7 turns of #16 magnet wire on a 5/8 inch
  diameter form, then remove form.
• L3 - 1.4 µH.   Wind 11 turns of #16 magnet wire on a 5/8 inch
  diameter form, then remove form.
• Q1 - 2N2222
• Q2 - 2N2907
• Q3 - IRF510 or IRF511 (Radio Shack p/n 276-2072A)
  Maybe a MRF486 is more preferable.

... and this is another Audio section without compressor/limiter

A slight modification in the LF/RF section of the Grenade transmitter

Winding and Installing a Toroid Coil
The transmitter's low-pass filter uses a high-Q toroid inductor wound on a T37-2 form (T37 means the powdered-iron form is .37-inches in diameter). When winding the Toroid Coil, the number of turns are counted inside the form (not on the outside). This means, if the instructions call for a 12-turn coil, you must pass the wire through the center of the core 12 times. When winding this coil, be sure to pull each turn up tight before starting the next. If the coil is wound loosely, its inductance increases - a condition that may reduce transmitter output power. Count turns on inside of form. Tin leads with solder before installing. Pull each turn tight before winding the next. Finally, before installing the Toroid Coil be sure to tin both leads with solder. The coil wire is coated with heat-stripable enamel insulation that breaks down at soldering-iron temperatures. If you touch the tip of an iron to the end of the wire for several seconds, the insulation should start to melt, allowing solder to adhere to the copper underneath. If your iron is not hot enough to start this process, carefully scrape the insulation off with a small hobby knife and tin. If necessary, refer back to these instructions at any time during assembly.

A small two stage transistor AM transmitter

This is two stage transistor AM transmitter for the shortwave band wich gives about 1 watt in output. You can use a 2N2219 or a 2N3553 in the final stage. The output with a 2N3553 is aprox. 1.8 watt @ 12 Volt. The transmitter seems to give more output when you use 7 turns instead of 4 turns in the secundary section of T1 (the coil between oscillator and final stage). It will work fine between 6 and 8 Mhz. Try with differend (power) transformers to modulate the transmitter in Amplitude Modulation. You have to do experiments to find a suitable modulation transformer to produce a good Amplitude Modulation.
Also test with different transistors in the final stage, but be careful to not blow up the rig.
BD135 - gives 1.7 watt output @ 13.8 volt
C2314 - gives 2.4 watt output @ 13.8 volt
BLY88C - gives 3 watt output @ 13.8 volt

This is a very interesting transmitter from MicroHobby Lab. Reference

The output stages in 74HCxxx devices are designed to have equal pull-up and pull-down transistors.This minimizes even-order harmonics, simplifying the rig's output filtering. The 74HC240 can directly drive a power MOSFET amplifier (IRF510).

IRF510
POWER MOSFET TRANSISTOR
Metal Oxide Semiconductor Field Effect Transistor

 

Manufactured by Harris Semiconductors
Available at most Radio Shacks
Cost: $$ at Radio Shack (Cat. No. 276-2072)

DESCRIPTION
The IRF510, IRF511, IRF512 and IRF513 are n-channel enhancement-mode silicon-gate power field-effect transistors. These power MOSFET's are designed for applications such as switching regulators, motor drivers, relay drivers, and drivers for high-power bipolar switching transistors requiring high speed and low gate-drive power. These types can be driven directly from integrated circuits.

MAXIMUM RATINGS IRF510 IRF511 IRF512
--------------------------------------------------------------------

Vds Drain-source voltage 100v 80v 100v
Vdgr Drain-gate voltage 100v 80v 100v Rgs=20K
Vgs Gate-source voltage +/-20v +/-20v +/-20v
Id Continuous drain current 5.6A 5.6A 4.9A

ELECTRICAL CHARACTERISTICS (All types unless otherwise stated)
--------------------------------------------------------------------

Igss Gate-source leakage 500nA (forward) -500nA (reverse)
Idss Drain current, Vg=0v 250uA
Id-on On state drain current 5.6A IFR510, IFR511 4.9A IFR512, IFR513
Rds-on Drain-source "on" Res. 0.4-0.54 ohms (device ON resistance)
Cis Input capacitance 135pF (at Vds=12v, Cis=180pF)
Cos Output capacitance 80pF (at Vds=12v, Cos=130pF)
Td-on Turn-on delay time 8-11nS ) These parameters define
Tr Rise time 25-36nS ) how fast the MOSFET turns
Td-off Turn-off delay time 15-21nS ) on and off when gate is
Tf Fall time 12-21nS ) driven with a square wave
Vsd Diode forward voltage 2.5v
(dropped across the source-drain due to the internal diode)

SOME DATA FROM THE PERFORMANCE CURVES

Output drain current (Id) vs. gate-source voltage (Vgs) at Vd=+12v
Vgs=4v Id= 0.0A
Vgs=5v Id= 1.0A
Vgs=6v Id= 2.8A
Vgs=7v Id= 4.8A
Vgs=8v Id= 6.8A

NOTE:
Therefore, for a 5W QRP power amplifier, the gate-source voltage should not exceed 5-6v; otherwise excessive current will attempt to flow. A continuous applied Vgs >7.5v will cause Id to exceed the maximum drain current rating of 5.6A (IRF510). This will cause "catastrophic substrate failure".

What is the maximum frequency? Max. frequency is not specified, but since Tr= 36nS (rise time) and Tf = 21nS (fall time), a total device delay of 57nS occurs, worse case. f=1/t = 1/57nS = 17.5 MHz. Total "typical" device delay is 25+12ns= 37nS for f= 27 MHz. This does not take into account L/C loading of the output filter, etc., which will lower the maximum frequency which the MOSFET will toggle on and off.

IRF510 MOSFET

For a 5-15 watt transmitter, the IRF510 is a pretty good choice. Its Drain-source breakdown voltage is 100V which gives a reasonable amount of headroom. (on mod peaks the supply voltage will be 24V , assuming a 12V powersource. The RF voltage on the FET will be something more than 2 times that, say peak voltage of 60-70 Volts.
The input capcitance of the IRF510 is quite low (Ciss ~= 150PF) which makes it easy(er) to drive than larger mosfets with higher gate capacitance.
Why not try to get more out of the IRF510? The problem is Rds - the on Resistance, which is 0.4 ohms for the IRF510. The output impedance seen by the FET is roughly V*V/2P where V is DC supply voltage and P = power out.
If P = 10 and V=12 then the output impedance is about 12*12/2*10 = 7.2 Ohms
If P = 20 and V=12 then the output impedance is about 12*12/2*20 = 3.6 Ohms
As the value of Rds gets larger relative to the output impedance the efficciency drops and you stat producing more heat and less RF.
At the small end of the scale, you could try MTP3055Es. They are tested at 7 Mhz, but they are gate capacitance is about 3 times that of the IRF510, and thier breakdown voltage is rated at 60 Watts. If you can drive them you may be able to get more out than an IRF510, assuming you adjust the output network ...

ANTENNA

This is the recommended antenna for use with the Grenade transmitter. As with any transmitter, always have an antenna connected before applying power.You can use a 50 ohm dummy load for testing, as long as it's rated at 10 watts or more.

A good antenna to get the job done
Most QRP operators use modest wire antennas that have been carefully installed and tuned for minimum VSWR. It is best to avoid compromised or severely shortened designs along with long lossy feedlines and inefficient matching schemes. Like most of today's solid-state radios, your Transmitter uses a "no-tune" broadband output network designed to match into 50-ohm loads. While it can tolerate a wide range of mis-matches, you shall get more usable power and better harmonic filtering with a low VSWR load. Experience has shown that a full-sized 1/2-wave dipole or sloper installed as high as possible is hard to beat. The following chart suggests dipole wire lengths for various sub-bands. These dimensions are sensitive to ground conditions and near-by objects, so you may need to prune the length slightly to obtain minimum VSWR at your location. Information is also provided for adding a very low cost "choke" balun to your installation. A balun helps eliminate unwanted feedline radiation on transmit and noise pick-up on receive. Heavyweight or premium cables are not required for QRP stations, and inexpensive RG58 is usually sufficient to do the job. The lighter your coax, the higher you can pull the center of your antenna! For additional antenna information on a wide variety of HF antennas, consult the ARRL Antenna Handbook, a publication of the American Radio Relay League in Newington, Connecticut.

Testing and aligment
The Grenade is a "no-tune" design that has no adjustable alignment trimmers or coils to set up prior to operation.For initial testing, you shall need a 50-ohm dummy load. Any 50-ohm non-inductive resistor capable of handling up to two watts will provide a satisfactory transmitter load. If a dummy load is not available, you can make one using two (2) 100-ohm 1-watt metal oxide resistors (Radio Shack 271-152). These should be connected in parallel across a standard RF connector that will plug into your RF wattmeter or VSWR bridge. In addition to a dummy load, you shall need a calibrated RFpower meter with a low-power range to measure the output of your transmitter. This provides your best indication as to whether or not the transmitter circuitry is working properly. If you do not have access to a calibrated watt meter, an inexpensive CB-type VSWR meter will provide a relative indication of transmitter output.

This is not a QRP

The original Design was by VK3XU and appeared in 'Amateur Radio' October 1988. The drawing you have is obviously a reprint from some European source.

The output power was quoted as 5 W PEP
T1, is 11 turns trifilar #22 B&S on a FT50-43 core
T2, T3 are 11t bifilar #22 B&S on a FT50-43 core for the 7.0 Mhz LPF
L1,2,3 = 12 t #22 B&S on T68-2 cores

R2 was to be adjusted for 200-300mA standing current.

ARRL handbooks have a 2 x IRF510 design that is about 40W PEP output, running off 28 V.

Thanks for Your information, 807.

Some low power transistor transmitter links:

The Grenade Project
The infamous Grenade Transmitter is being 'decoded' - the work in progress is here
Free Shortwave!
Another experimenter is attempting to homebrew a shortwave transmitter
to broadcast in AM mode; ncludes updates on progress
Low Budget 1 Watt Shortwave Transmitter
Two-stage transistor design will broadcast in AM mode
Radio Morningstar Schematics Page
Most are in Dutch, but there's tons here, for many bands.
Harry's Homebrew Homepages
Amazing selection of well-written schematics for
a wide variety of broadcasting gear
AM Stereo Exciter
Wenzel's transmitter
Bowden's transmitter
NCR AM88 kit
7 Watt Prototype
1 Watt Shortwaver (Espańol)
SM0VPO's Morse/AM transmitter

Here are some other QRP projects:

http://cs.okanagan.bc.ca/ve7ouc/eng/kc6wdk-mirror/transmitter.html
http://www.al7fs.us/AL7FS2.html
The AL7FS website is now at http://www.al7fs.us/
http://www.qsl.net/k5lxp/projects/QRPTX/QRPTX.html
http://www.qsl.net/qrp/tx/317-tx.htm
http://www.qsl.net/qrp/tx/vu2vwn.htm
http://w1.859.telia.com/~u85920178/tx/hf-osc1.htm
http://w1.859.telia.com/~u85920178/tx/5watttx.htm
http://www.madisoncounty.net/~kj5tf/n7ksb.html
http://www.fix.net/~jparker/norcal/miniboots/miniboot.htm
http://www.qsl.net/k4msw/rigs.html
http://www.radiohc.org/Distributions/Dxers/ultra-simple-transmitter.html
http://www.qsl.net/qrp/tx.htm
http://www.pirateradio.us
http://worldwidedirt.tripod.com/gproject.html
http://www.angelfire.com/bc/radio/index.html
http://1watt-am.port5.com/
http://www.angelfire.com/de/RadioAnarchy/
http://www.usinternet.com/users/kyledrake/schematic/

AF4K Crystals

Give the Magnetic Loop Antenna a try:
http://www.antennex.com/preview/myloop.htm
http://www.g3ycc.karoo.net/loop.htm
http://www.qsl.net/mnqrp/Loop/Mag_Loops.htm
http://www.alphalink.com.au/~parkerp/nodec97.htm
http://www.qsl.net/pa3hbb/magloop2.htm
http://www.funklab.de/mloop.html
http://www.s-line.de/homepages/dl4sz/magloop.html
http://www.iri.tudelft.nl/~geurink/magnloop.htm
http://www.rys.nl/mat-div.htm
http://ftp.castel.nl/~levee01/antenna