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AMT3000 and AMT5000 AM Radio Broadcast Transmitter Kits

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AMT5000 Transmitter Specifications

 

The AMT5000 AM transmitter kit is an FCC Part 15 compliant transmitter designed specifically for high efficiency to provide nearly the highest RF output level practical for any 100 mW transmitter.

 

Frequency Coverage

Model AMT5000:  530 to 1700 kHz in 10 kHz steps.

Model AMT5000-9K:  522 to 1710 kHz in 9 kHz steps.

Carrier Frequency Generation

Crystal controlled PLL synthesizer

Frequency Selection Method

8-position DIP switch

Frequency Tolerance @ 25șC

±.003%

Modulation Type

Amplitude Modulation (AM)

Maximum Modulation Level

Normal 100%,  130% positive modulation with external processor

Power Input to Final RF Stage

100 mW, adjustable to compensate for varying load conditions

RF Circuit Configuration

MOSFET Class E switching mode, 98% RF transistor efficiency.

RF Spurious Emissions

43 dB below carrier level.

Antenna

Standard: 118” wire (supplied with kit)

User-supplied: 102” CB whip or 118” copper or aluminum pipe

Antenna Matching

Low-loss iron-powder toroid loading coil series resonates with antenna capacitance. Jumper-selectable option for user-supplied external loading coil.

Output Tuning

1350kHz - 1700kHz: jumper select toroid inductance, screwdriver adjusted air piston trimmer capacitor for peak tuning.

530kHz - 1350kHz: jumpers select supplemental inductors and toroid tap, screwdriver adjusted FILMTRIM trimmer capacitor for peak-tuning.

RF Output Metering

Test points on circuit board for measuring RF stage input voltage and current with inexpensive user-supplied digital or analog multimeter.

RF Grounding Options

Jumper options for including/excluding RF isolation inductors in power feed lines to suppress conducted emission

Modulation Circuit Configuration

Common-source MOSFET modulation driver in series with RF output MOSFET drain.

Internal Audio Response

20 Hz - 20 kHz ± 0.5 dB 

Jumper selects flat response or NRSC standard pre-emphasis.

3 dB RF Bandwidth

23 kHz with typical 20-30 ohm RF ground resistance.

3 dB Audio Modulation Bandwidth

11.5 kHz with typical 20-30 ohm RF ground resistance.

Audio Distortion

Less than 0.5% THD through audio stages to final high-level modulator stage.

Audio Input Level

Consumer Audio: -10 dBV, 0.316 Vrms

Pro Audio: +4 dBu, 1.228 Vrms

Audio Input Impedance

Consumer Audio: 18k ohms at 1 kHz

Pro Audio:  14.3k ohms differential at 1 kHz

Audio Compression

Compression ratio adjustable from 1:1 to 5:1.  Attack time less than 1 ms. Medium release time suitable for both voice and music. 

Audio Limiting

Adjustable threshold.  15:1 compression above threshold. True RMS limiting ensures no distortion in limiting region.

Front Panel Controls and Indicators

Audio input GAIN, MODULATION level, COMPRESSION ratio. Green LED power light.

Rear Panel Jacks

Consumer Audio (unbalanced): 2 RCA audio-in jacks mixed equally on board for stereo-to-mono conversion or two mono sources.

2.1 mm power input jack.

On board screw terminals

Antenna

RF ground

Mono Pro Audio (balanced): +, -, Gnd

Power: AC or DC(+, -)

Input Power Options

12VAC wall adapter, DC wall adapter, 12V battery.

On-Board Power Conditioning

RF bypassed bridge rectifier for 12VAC operation mode.

Low-dropout 12V regulator provides stable, regulated and filtered voltage even when operating from 12V battery (nominal lead acid battery voltage is 12.63V). Below 12.3VDC, input voltage is passed to output without regulation.

Separate 5VDC regulator provides stable, regulated and filtered power to ICs.

Power Consumption

120 VAC, 2 watts with standard 12VAC wall adapter.

Circuit Board

7”W x 3.9”D x .062”H FR4, two layers, 1 oz. copper, top and bottom solder masks, top silkscreen with component identifiers and labels.

Enclosure Options

Indoor option: 1.5”H x 8.1”W x 4.2”D  ABS plastic, color bone and black.  Drilled, silk-screened front and rear panels.

Outdoor option: NEMA 4, 4X.   8.66”H  x 4.72”W x 3.54”D, fiberglass, color gray

 

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