AMATEUR TELEVISION




Yes Amateur Television, come on, you did know that Radio Amateurs used television. Did you also know that the
television transmissions were in fact Amplitude Modulation. Yep! That's right and also Frequency modulation. The
frequencies used mainly in the Buffalo area are 439.250 Mhz with audio 4.5 Mhz higher at 443.75 Mhz. There are
some locals that specialize in low power and also other frequencies such as 100 milliwatts on 902 Mhz and 1296
Mhz. No one seems to be on 2304 Mhz yet other than Myself.

The WB2FCN ATV station is in two forms, first there is the TUBE portion, and secondly there is the Solid-State
portion. The tube-type station runs about 325 Watts of video carrier power, and 75 watts of FM audio power.

My low power solid-state station is a VHF Engineering 420 Mhz 1 watt solid state exciter, which drives a Motorola
MHW 710 power amp which drives an MRF-646 UHF RF transistor operating class "C" at an adjustable power
output from 5 to 45 watts. I also have a VHF Engineering 145 Mhz 1 watt solid state exciter which drives an
intermediate amp which provides the solid state system with 5 to 15 watts of FM audio.

The solid-state station is mounted in an old PYE repeater rack cabinet that contains the pair of MRF-901 preamp
assemblies, and a tuner assembly from a VCR. It also holds a 13.8 volt DC power supply that provides up to
20 amps for the MRF-646 and the MHW-710 module and also the VHF Engineering UHF exciter. There is a
video modulator and audio insertion mixer to drive either the VHF Eng strip or to collector modulate the MRF-646
at almost 45 watts out. The collector modulator transistors can be seen to the right of the rf module and the MRF-646
amplifier (class "C"). The low power mod schematic is here, and the high powered collector modulator is here .

I also have a "SURPLUS" " Agile Modulator" made by Blonder Tongue, which is tunable over the range of 400 Mhz
to 800 Mhz. This modulator has a power module also made by Motorola which was used to drive a CATV
system. The unit takes an audio signal in, as well as a standard NTSC video signal and provides a mixed video
and audio output of about 5 watts into a 75 ohm load. A transformer was required to match up to my system
50 ohm impedance.









The high power section is a converted Military surplus module from Fair Radio an AM-1178/GRC, this module
is really unique in that it is two modules in one case. First there is a Tripler section, consisting of a 4X150A which was
changed to a 4CX250B, that takes 146 Mhz drive in and triples to 443.750 Mhz the Audio frequency. Then
there is the amplifier section, consisting of a 4X150G which was changed to a 4CX250K which takes drive at 439.250
Mhz and amplifies it. The two sections are "Diplexed" together in a coaxial "Ring Diplexer" which mixes (high level) the
75 watt audio signal with the 325 watt video signal to produce vestigal TV with the video separated 4.5 Mhz from the audio.




The tripler uses a 4CX250B tube as the active component, while the amplifier uses a 4CX250K (has a coaxial base)
as the active component. Both tubes are rated at 500 watts maximum up to 450 Mhz and are ideal for this application.

The Ring Diplexer is actually a waveguide arrangement (Homebrewed) made of 1.25 inch copper pipe. I had a smaller
one made of 50 ohm coaxial cable, however when I went to the high power mode the coax exhibited heating, which
changed the dimensions and subsequently moved the frequency of the diplexer over time.

The Antenna system consists of a Cushcraft 44 element Beam Array horizontally polarized. I connect the transmitter
to the antenna with 60 feet of  "Hard-Line" coax 7/8 inch diameter.

For running remote setups, I have portable cameras (Color) that run on internal batteries, AC mains, or the
car cigarette lighter connection.


  

  
I also have a Pioneer LD-V4400
Laser Disk Player, so I can run training info over the air. In addition
to the

  
color cameras I have several Black
and White (B&W) cameras for things
like showing off circuitry to folks

  
that want to see what some of the
equipment innards look like. Mostly in
cases where color is not required.

  


  

  

  

  
Also for putting up weather warnings
and other info, I have a video
titler that is basically a character generator

  
in full color with line editing
capabilities. Animation and graphics are also available with this unit.



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