More MH+30 Information
Schematics and Pictorials
MicroHunt Mode Selection
Major Features :
Power : 12 - 15 VDC
Size : 0.7 x 1.2 inches
RF Output : 1.0 Watts with 50 mW drive @ 14 VDC power
Frequency : 144 - 148 MHz
Schematics and Pictorials :
Download links to schematic diagrams and technical details for the MicroHunt +30 are provided here. For additional information about the MicroHunt +30 amplifier, inquire directly by e-mail : Bob SimmonsMH+30 schematic ( 7 Kb GIF file )
General Description :
The MH+30 is a 1 Watt / 144 MHz class C power amplifier, intended for use with the MicroHunt or SquawkBox transmitters. It provides +30 dBm output ( = 1 Watt ) with 50 milliWatts of drive, ( = +13 db gain ) with 14 VDC of power. Current draw while transmitting is typically 200 mA, and 5 mA when idle.
The MH+30 also has an external control input that can be used to enable/disable the amplifier, or "modulate" it with an audio tone. This means the MH+30 amplifier can also be used with a MicroHunt transmitter for European style ARDF hunts, which typically employ A1 modulation ( on/off keyed carrier ) or A2 modulation. ( AM tone-modulated CW, with a steady carrier signal ) The control input accepts a TTL signal with positive polarity. ( TTL low = off, TTL high = on ) The switching bandwidth is internally limited to about 2 KHz, to prevent excessive sideband generation when employed in this manner.
The MH+30 amplifier has the same footprint and size as the MicroHunt transmitter, allowing it to be mounted directly atop a MicroHunt transmitter, with connections provided between the two boards by simple direct / vertical wires.
MicroHunt transmitters shipped after 1 Jan 2006 will include new software routines to enable the use of these new MH+30 modulation features. ( mode selection is described below ) Older MicroHunt transmitters can still use the MH+30 as a straight amplifier for FM / CW operation, with no modifications. If operation with the ( new ) AM modes is desired, ( either A1 or A2 modes ) then the microcomputer in older MicroHunt transmitters must be replaced with a new chip. ( contact me for details and fees : Bob Simmons)
SquawkBox Operation :
Operation with a SquawkBox transmitter requires a jumper to enable the amplifier. DC power and RF input / output connections are also required. The jumper must be installed from the MH+30 control input to +V, ( 4-15 volts ) to enable the amplifier. The required strap is shown on the MH+30 board outline diagram.
If the jumper is not provided, the amplifier "shuts down" which reduces the DC load on the battery. Amplifier load ( enabled ) with no signal from the SquawkBox is about 5 mA, load with a signal is about 200 mA. About 5 to 10 mW of SquawkBox signal will still "leak through" the amplifier, if it is disabled. This level of RF power can still go a fair distance, ( possibly a mile or more on the ground ) raising the possibility that a switch can be provided to select / de-select the amplifier, to conserve battery capacity.
MicroHunt Mode Selection :
When employed with a MicroHunt CW transmitter, the operating mode is selected with a strap that is tested by the microcomputer in the transmitter, when power is applied. The test checks for the presence / absence of a jumper strap installed on pin 6 of the transmitter's microcomputer.
Technical Description :
The MH+30 amplifier is a basic class C RF amplifier, tuned for operation at 146 MHz. A parallel LC network ( Q = 10 ) is employed in the output circuit to achieve good spectral purity. Harmonics are suppressed typically 40 db or more into a 50 ohm load, across the normal DC supply range.
A PNP transistor in the supply lead for the Motorola MRF555 RF transistor allows the amplifier to be turned on or off from an external control source. ( default = off ) and a 2N7000 MOSFET ( driving the 2N4402 ) allows the use of TTL control signals.
The control circuits are fast enough to respond to signals operating in the audio frequency range, allowing AM tone modulation of the amplifier. The response of the control circuits is "rolled off" at about 2 KHz to prevent excessive sideband generation, when used in this manner. The control circuit is not suitable for use as a regular audio modulator, with a voice modulation signal. For AM operation with greater modulation bandwidths, ( possibly to send data ) enquire about ( simple ) modifications.
If the EXT MOD/CONTROL wire ( from a newer MicroHunt TX ) is not provided, ( or a jumper when a SquawkBox TX or an older MicroHunt is used ) the amplifier "shuts down", which reduces the DC load on the battery. Amplifier load ( enabled ) with no TX signal is about 5 mA, load with a signal is about 200 mA. About 5 to 10 mW of TX signal will still "leak through" the amplifier, if it is disabled. This level of RF power can still go a fair distance, ( possibly a mile or more on the ground ) raising the possibility that a switch can be provided to select / de-select the amplifier, to conserve battery capacity.
More Info :
For more info or inquires, send an e-mail to Bob Simmons