K3QEP - Bob


Escondido, CA

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The latest K3QEP project, an 'experimental' transmitter covering 160, 80 and 40 meters.  The final  amplifier runs a 4-1000A tetrode which is modulated by a pair of 572B zero-bias triodes.  Separate power supplies are used for the final plate, the final screen grid and the modulators.  This necessitates the use of self modulation for the tetrode screen grid by inserting an audio choke in the screen supply. The Johnson Ranger at left functions as the exciter.  The current power level for the transmitter is a 375-watt carrier with the 4-1000A operating far below its ratings.   

A closer view of the RF deck of the transmitter with the 4-1000A easily visible  through the viewing port.  The rack is a genuine Gates Radio unit, so the RF deck gets a bit of the Gates flavor by proximity.  The transmitter is well metered and improved overload-protection measures are currently being implemented.   



The K3QEP Operating Position:  At left is the Johnson Desk Kilowatt, excited by the Johnson Ranger above it.  The Collins 75A4 is the primary receiver while the Collins R-388 serves as an all-band auxiliary.  The Johnson Kilowatt Matchbox at right  interfaces to a loop antenna fed with balanced line.  The setup is completed with a Heath SB-614 station monitor and a decidedly retro-looking D-104 microphone.  Behind the D-104 is a Hammarlund SP-600 receiver.



The Heavy Metal Dept. at K3QEP:  Large grey box at right is a Gates BC-1G  ex-broadcast rig used on 160 meters.  Racks contain other Home-Brew Transmitters and Amplifiers as well as a National NC-303 receiver, mod monitor and scope.  Audio chain is a Gates 'Producer' Console  driving a Gates Limiting Amplifier.

(Click here for larger photo and detailed equipment list 



The Balanced-Line Tuner at K3QEP:  Each coil is wound with 50 feet of quarter-inch copper tubing and the variable capacitor  has a 1-inch plate spacing.  Bob reports the inductors show no sign of heating and the capacitor does not arc-over when he drives his full-size loop antenna on 160 meters with full legal-limit power through this impedance-matching network.



Whatizzit??  A desk display made from the neutralizing capacitor and final-tube mounts of a Gates BC-1F broadcast transmitter.

(Click here for larger photo 

The HF mobile antenna system on the K3QEP service van.  The weather-proof box contains a DC motor coupled to a heavy-duty gearbox that can raise and lower the Hustler antenna is about 5 seconds.  K3QEP is frequently heard on 75 and 40 meters AM during the day as he tends to his electronics businesses around Escondido.

The HF mobile antenna system showing the Hustler antenna in the stowed position.

The Hustler antenna in the raised position and listening on 7293.

Inside picture of the motor/gear enclosure. The big gear box on the left was orginally attached to a 110 volt AC/DC motor (Not reversible) which could not be removed from the gear box without some trouble.  The solution was to connect a NEW motor at the rear of the old motor, the latter having a one-quarter-inch through-shaft which facilitated the coupling.

As can be seen, all of this is mounted on a plywood board which is screwed to the fiberglass weatherproof enclosure, one of several purchased at the Mesa Hamfest a few years ago.  The rest of the parts came from the extensive K3QEP junkbox and from local electronics/surplus stores in San Diego.  

A closeup the insulator and the machined aluminum block. The insulator is a type used in electrical power installations and was found at the local swap meet. All of the screws are stainless steel.


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