GBPPR Stereo Zapping Experiments

Overview

While most people stutter and stammer when trying to think of something Sheikh Barack Hussein Obama has "accomplished," the residents of Wisconsin can name at least one thing - increased crime in their once peaceful neighborhoods.

Because places like Chicago are illegal alien sanctuary cities and nigger-infested, Democrat-voting, third-world shitholes, the first thing the useless shit-skins do when they pile all their welfare money together is to move - usually heading north.  In a textbook definition of "racial profiling," the third-world trash move to cities and neighborhoods built and run by hard-working white people.  (Where is the ACLU?  Hah!)

After settling in, their third-world "culture" usually takes root, thus destroying the once prosperous local school systems, businesses, hospitals, parks, or even entire neighborhoods.  One of the many annoying things third-world trash like to do is play their "ooking" rap music or their stereos and TVs very loud, especially at night.  They won't have to work or go to school in the morning, so what do they care?

In order to help prevent this type of behaviour, we'll try to build a device which will allow you to inject audio into a remote stereo system.  This will be accomplished by constructing an amplitude modulated, high-powered RF microwave transmitter.  Most ham radio operators are already aware of a phenomenon in which their high-powered AM or SSB modulated transmitters will easily interfere, or even in some cases, inject audio into their neighbor's TV, stereo, or telephones.  What we'll try to do here is to build a smaller, more controllable version of this "radio interference" causing device.

This device actually consists of several different experiments I was working on all rolled into one.  One was the modification of an old integrated-antenna California Amplifier MMDS downconverter to add an external N connector.  The next was trying to modifiy the VCO section in an old California Amplifier MMDS downconverter to move from the converters's stock 2.278 GHz local oscillator signal to something else, 2.4576 GHz in this case.  The final experiment was to see if a Motorola 1.9 GHz PCS-band, 4 watt hybrid RF module was capable of operating up in the 2.4 GHz Part 15/ISM/amateur radio band.

What we'll be doing is generating a RF signal at 2.4576 GHz and then AM "modulating" it with a common audio amplifier circuit and matching low-impedance microphone.  The AM modulated RF signal will then be linearly amplified using a surplus Motorola MHL19338 PCS-band pre-driver hybrid module.  These modules normally put out around 4 watts at 2.0 GHz with only 10 mW (+10 dBm) of RF input.  They appear to operate fine up in the 2.4 GHz band with only approximately 3 dB of output power loss (2 watts RF output).  Linear-biased RF amplifiers are required to amplify amplitude modulated RF signals without causing any additional audio distortion.

But, does this contraption really work?  Sorta...  The concept of injecting audio into remote stereo systems using high-powered, amplitude modulated transmitters does work, it's just that you'll need to be using a very high radiated power.  Also, higher carrier frequencies appear to be more effective against consumer electronics as they are not as attenuated by cheap RF shielding attempts.  This particular project doesn't really cut it, but the overall concepts do work.  I'd start looking out for some of those surplus high-power (100+ watt) PCS-band power amplifiers that show up at ham fests from time-to-time...

Construction Notes & Pictures

Parts overview for the 2.4 GHz linear RF power amplifier.

A surplus aluminum heatsink is off the to the left, the Motorola MHL19338 hybrid power module is the blue rectangle in the middle with the shield salvaged from an old Motorola bag-style cellular phone.

On the lower-right is an optional PCS-band isolator, and in the lower-middle is the homemade PC board for the amplifier module.  Be sure the PC board has a good RF ground plane.

The Motorola MHL19338 operates at +28 VDC and draws a continuous 500 mA because it is linearly biased.  Its maximum RF input is 10 mW (+10 dBm).

A LM317 adjustable voltage regulator supplies the +28 VDC for the MHL19338.  The LM317's input voltage will be from an old +32 VDC HP printer power supply.  Be sure the LM317's mounting tab is isolated from ground as it's at output voltage potential.  Some type of heatsink will also be required for the LM317 if it is not mounted to the MHL19338's heatsink.

Completed 2.4 GHz RF power amplifier.

The RF input is on the right and the RF output goes through an optional surplus 1.7 - 2.1 GHz PCS-band isolator.  These isolators also appear to work fine at 2.4 GHz, but with slightly reduced port-to-port isolation.  The isolator is used to protect the Motorola MHL19338 in case it is powered up without a load or antenna attached.

A slot was milled into the heatsink so the Motorola MHL19338's pins could rest directly on the PC board, thus making a more "RF secure" solder connection.

Completed 2.4 GHz RF power amplifier overview.

An optional Mini-Circuits ZMSW-1211 SPDT PIN diode switch is used to select the RF input source.  This is so the RF power amplifier can be used separately for other things, such as amplifying the RF output of those cheap 2.4 GHz video transmitters you can buy at Radio Shack or Wal-Mart.  0.1 µF capacitors were also added across the ZMSW-1211's control pins to the ground terminals.  One drawback to using Mini-Circuits ZMSW-1211 SPDT PIN diode switches is their relatively high insertion loss.

Modifying the VCO section of a California Amplifier MMDS downconverter.

The stock VCO is set at 2.278 GHz.  If you disable the PLL section, the free-running oscillator drops to around 2.1 GHz.  If you solder little copper extensions to the VCO stripline elements, you can lower the VCO to around 2.050 GHz.  If you shorten the VCO stripline elements using a Dremel tool or Exacto knife, you can raise the VCO frequency up into the 2.4 GHz band.

This particular modification is handy to know, as these surplus downconverters can now be adapted for use as simple 2.048 GHz, 2.097152 GHz, 2.304 GHz, and 2.4576 GHz PLL signal sources by simply replacing the stock 8.89843 MHz crystal with a 8 MHz, 8.192 MHz, 9 MHz, or 9.6 MHz crystal.

In the above photo, the stock crystal was replaced with a salvaged 9.6 MHz one, and the striplines were "ground" away between the red points using a Dremel tool with a small engraver bit.  Connect a frequency counter to the VCO's output just before it enters the mixer and monitor it while it is powered and the PLL circuit disabled.  Slowly grind or cut away the striplines, and watch as the frequency goes up to the desired range you need.  Try to get the VCO close, but slightly below, the targe frequency range so the PLL loop filter does not have to operate near the "extreme" top or bottom voltages.  This will require a little bit of experimenting.

Modified California Amplifier MMDS downconverter VCO connected to a frequency counter.

The Radio Shack frequency counter is reading "457.601 MHz."  This is actually 2.4567 GHz, as the Radio Shack frequency counter appears to drop the "2" when operating out of its intended frequency range.  The output RF power is believed to be around +5 dBm, though I could not measure it accurately.

The next modification will be to add an external N connector to a California Amplifier integrated-antenna MMDS downconverter.

These also show up from time-to-time at ham fests as they appear to still be made by California Amplifier.

The stock Yagi-style antenna specifications are:

          Frequency: 2.5 - 2.686 GHz
               Gain: 17 dBi 
Front-to-Back Ratio: 18 dB
    Side Lobe Level: -12 dB
     3 dB Beamwidth: 24°

Stock antenna solder connections.

They will be a little rough and corroded, so you'll want to clean them up.

Carefully take the antenna section apart, noting all the pieces and washers.

Thoroughly clean each of the parts and start to put the driven and reflector elements back together.  At this time, you'll want to replace the stock coax with RG-142, which has a Teflon dielectric.  This makes soldering much easier as it won't melt the dielectric.

Note the driven and reflector elements are tin-plated copper.  Try not to scrape away the tin plating as it protects the elements from corrosion when outdoors.

Add the N panel-mount connector as shown.  Try to use stainless steel hardware.

Completed antenna.

A good coat of paint protects the mounting hardware and some brass drawer handles make nice handles.  Note the antenna's stock 1/4-20 mounting bolt was replaced with a short 1/4-20 stainless steel bolt.

This antenna is now perfect for portable operations working the 2.4 GHz frequency band.

Next is the construction of the AM modulator PC board.

The 2.4576 GHz RF input is on the upper-left with the microphone amplifier section in the middle.

An optional RF switch will control the output of the signal so it will not always be transmitting.

A 2.45 GHz bandpass filter cleans up the final output signal.

Completed AM modulator circuit board.

Power supply regulation is on the upper-left.  The LM833 microphone amplifier is in the middle.  The 74HCT04 takes the input from the PTT line on a military surplus M-80/U microphone and controls the Alpha AW002 SPDT RF switch.

The actual AM modulation takes place by slightly amplifying the incoming 2.4576 GHz signal with a Mini-Circuits VNA-25 and splitting it with a Mini-Circuits SBA-2-22 two-way RF splitter.  One of the legs of this new split signal is passed to the LO port on a Mini-Circuits MBA-25MH mixer.  The incoming audio modulation is placed on the mixer's IF port.  The audio signal varies the conduction of the mixer's diodes and the result is an amplitude modulated RF signal.  It is then recombined with the original 2.4576 GHz carrier frequency using another Mini-Circuits SBA-2-22.  The optional Alpha AW002 acts as an "RF enable" switch, and another Mini-Circuits VNA-25 further buffers and amplifies the signal.  The final signal is then bandpass filtered and sent to the RF power amplifier module.

The VCO section of the California Amplifer was cut so its RF output is taken right after the stripline bandpass filter.

AM modulator circuit board, alternate view.

Overview of the ammo box case components.

An old HP dual-voltage (+32/+15 VDC @ 500 mA) printer power supply is on the left, with the incoming 120 VAC components in the middle, the AM modulator is housed in an old California Amplifier MMDS downconverter case, a 20 kohm potentiometer will be used for audio gain in the microphone amplifier circuit.  A surplus M-80/U microphone and the matching connector will be used for the audio modulator and PTT switch.  A regular low-impedance ham radio or CB microphone can also be used.

The completed RF amplifier section is on the upper-right.

Behind the front-panel.

From the bottom to top is a standard 120 VAC IEC power connector, a fuse holder, a SPST power switch, and a neon light power indicator.

The dual-voltage printer power supply is zip-tied to the back of the ammo box and has its two output voltages sent to a solder terminal block.

Mounting the AM modulator section.

The front-panel now has a matching connector for the M-80/U microphone and the 20 kohm audio gain potentiometer.

Addition of the RF power amplifier and the front-panel N connectors.  A DPDT RF input selector switch was added just in front of the AM modulator section.

RF COM goes to the input of the RF power amplifier.  RF1 goes to a front-panel N connector and RF2 goes to the RF output of AM modulator section.  This allows the RF power amplifier to be used externally by just flipping the selector switch.

Completed overview.

An additional use includes being used as a 2.4576 GHz beacon for pre-testing wireless network links.  Use a downconverter to receive the signal on a standard communications receiver.  If you can hear the beacon in a non line-of-sight condition, it should be possible to pull off a RF radio link.