Description
AM transmitter with DSP processing, PWM modulator and DDS frequency generator
While for many mentioning AM transmitters brings back childhood memories, these are actually still used widely in some countries. Besides, AM can be lots of fun to play with. Long wire antennas, different signal propagation (even worldwide), the nostalgia that comes packed with it… well, it is something very different in this modern age.
Our old AM MAX units sold out many years ago and for a long time we wanted to make a new AM transmitter, this time with different, more modern approach, with new better parts and better specs. And we finally did. It is equipped with DSP which makes it possible to control parameters of the audio chain, such as the compression, low pass audio filter cut frequency and pre-emphasis via convenient LCD with menu system. Other features, such as the fully solid-state PWM modulator which ensures crisp audio, >125% positive peak modulation, compact form factor, plenty of audio input options and LCD display unit make AM transmitters based on AMMAX8000+ really something special in this modern age.
What is new in AM transmitters based on the new AMMAX8000 boards?
– New larger high power FET (300W)
– Robust PWM output stage based on larger FET, extra LC stage in PWM filter
– A number of small fixes and improvements to improve reliability
– Added anti-aliasing audio filter after DSP, less noise
– Larger heatsink
Manual is available under additional details above.
Technical specifications:
– RF Output Power AM: ~100W peak, 10-25W carrier (24V-50V DC stabilized, use 50V for maximum power), varies with band and frequency
– Output connector: BNC (1H version)
– Output Impedance: 50 Ohms
– Frequency Range (MW version): 540-1800KHz
– Frequency Range (shortwave version): 160m, 80m, 40m (other SW bands also available, please ask)
– PLL Steps: 1KHz
– Frequency stability: +/- 50Hz
– RF output: Harmonics: -30dBc typ (varies with frequency, if necessary use external filter or high-q resonant antenna)
– RF output (spurious): -70dBc
– Power Supply: 48V/2.5A DC stabilized (1H rack)
– Wideband design, no tuning required
– Audio performance: compressor, low pass filter, limiter, treble, bass adjustment
– RF output ruggedness: > 2:1 VSWR
– Modulation: AM (CW input on-board. TTL 5V for disable)
– Exciter board inside: AMMAX8000 board, PCB size: 100x125mm
– Audio input board inside: 2x XLR, 2x RCA + USB audio inputs, accepts either mono or stereo signal (transmission is mono, channels are added up)
– DRM support: On-board jumper inside can disable DSP processing which is great for DRM modulation
– Modulation: AM, >125% positive mod
– PWM circuit is opto-isolated and can be used to drive high power external stage
What is the audio input board:
– This is audio input board used in our AM transmitters. This board adds XLR, RCA and USB audio inputs to the transmitter. It is also equipped with extra input limiter, low pass filter and balanced input stage with ESD protection. You may think this is not needed, but believe us it is nice to have. Built inside all our 1H and 2H units.
What is AMMAX8000+ board:
– This is the AM transmitter board used in our AM transmitters. Built inside all our 1H and 2H units.
What is the Barix audio streaming with MP3 playback option?
– Barix instreamer with STL (Studio To Transmitter link) upgrade lets you play audio from remote IP audio streams via Ethernet or Internet. There is also automatic MP3 playback from USB that starts whenever there is no active IP stream. It can be used to playback MP3 audio from USB key with included playlist.
Suitable DIY antennas for the AM transmitters:
We are giving you a link to several 160m HAM radio antennas. These are operating just slightly above broadcast band at 1800KHz. To make these work for MW broadcast band they will need to be slightly longer. The further you go towards 540KHz the longer antenna will need to be. The same goes for capacitors and coils in any tuning/matching networks that are needed to bring impedance of antenna closer to 50 ohms. You can also look for 160m ham antenna designs here. Note antenna performance is critical for AM transmitter range and it does make a HUGE difference. A good antenna will ensure surprisingly big range with 100W, more than 20km-30km is possible.
Link 1, link 2, link 3, link 4
Isotron 225 antenna specifications :
Dimensions: H x W x D: 235″ x 16” x 15”
Bandwidth: 40 KHz*
Radiation resistance: 50-75 OHMS
Frequency: 1.35-1.599KHz
Maximum output power: 300W CW, AM, FM, RTTY
Wind loading: 1.7 Square feet
Radiation pattern: Omnidirectional
Weight: 13LBS
*BW is within 2:1 SWR. Will vary with environment.
Isotron 400 antenna specifications :
Dimensions: H x W x D: 324” x 12” x 15”
Bandwidth: 40 KHz*
Radiation resistance: 50-75 OHMS
Frequency: 1.0 – 1.349KHz
Maximum output power: 300W CW, AM, FM, RTTY
Wind loading: 2 Square feet
Radiation pattern: Omnidirectional
Weight: 20LBS
*BW is within 2:1 SWR. Will vary with environment.
Isotron 600 antenna specifications:
Dimensions: H x W x D: 456” x 12” x 15”
Bandwidth: 40 KHz*
Radiation resistance: 50-75 OHMS
Frequency: .5 – 0.99KHz
Maximum output power: 300W CW, AM, FM, RTTY
Wind loading: 2 Square feet
Radiation pattern: Omnidirectional
Weight: 32LBS
*BW is within 2:1 SWR. Will vary with environment.
What is included with CyberMaxAM+ in 1H rack
– CyberMaxAM+ transmitter in 1H rack
– Audio input board + AMMAX8000+ are installed inside
– 48V mains power supply is NOT included, please order if you do not own already
Optional parts for servicing or upgrade:
– Audio input board for service replacements
– AMMAX8000 boards for service replacements
– Ethernet control + Barix IP audio + MP3 playout is an upgrade for IP audio or MP3 playback
– Mains power supply is optional upgrade for 1H rack
Warning regarding using power meters:
– Most HAM SWR/Power meters will not work well for MW band. Even types that perform reasonably well at 160m will fail miserably at 540KHz or even 1500KHz for example. Sensitivity of directional couplers is very much frequency dependent and usually this means the needle is not even moving with power output actually at 100W peak. CB power meter won’t even deflect at 100W peak power at MW!
– With AM modulation peaks and using positive modulation in excess of 100% (this is done to make it sound louder and increase power efficiency) the carrier power with no audio applied will be less than ¼ of the peak power. So with no audio your power might be just 15W rising to 100W in peaks of modulation.
– The only way to accurately measure peak power (or any power at MW) is to use dedicated power meter or oscilloscope (you can calculate power from voltage and known load which is 50 ohms). Dedicated power meter needs to have peak power measuring capability and must cover the MW band.
CALL FOR FEEDBACK
Please e-mail us back and let us know what kind of antenna you’re using and how many Kilometers you were able to squeeze out of your transmitter. We had one report with ~20km with previous weaker version (about 50W peak).
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