You've Built it - You Don't Hear Anything - Now What?


david cripe <ai9e_qrp@...>
 

I've heard from a number of builders of the Ozark Patrol radio who have assembled their radios, connected an antenna, and heard.....nothing.

They have double checked solder joints, component values, antenna connections, circuit voltages, and reapplied power...and still hear nothing.

Yet there is nothing wrong with their radios!

How can this be?

Well, the simple answer is that the Ozark Patrol is a regenerative receiver, and for anyone not well familiar with their operation, it behaves very much different from any other radio you have used.  Unless you know how to operate it, you will hear....nothing.

This radio has an extra knob!  Aside from the Tuning, Bandspread, Band, and Volume controls there is another control marked REGENERATION.  That control is the key to making this radio work!

The Regenerative radio circuit, invented by Edwin Armstrong, takes a portion of the amplified antenna signal, and feeds it back into the amplifier input. Too little feedback does not give enough amplification. Too much feedback creates an RF oscillation in the amplifier, permitting reception of CW and SSB signals.  But right at the proper REGENERATION setting, the receiver is capable of amplification of the signal by thousands of times, and a weak signal suddenly comes in at good listening volume.

But how does one use this?

Operating a regenerative receiver is definitely a two-handed operation.  Left hand on the regeneration control, right hand on the tuning or bandspread control.

Rotating the REGENERATION control counterclockwise increases the feedback, sending the receiver in to oscillation.  Rotating the tuning control, you will hear the chirps of carrier signals as they pass through the receiver range.  Stop the tuning control on a loud carrier tone.  Then, slowly rotate the REGENERATION control clockwise.  You'll notice the pitch of the carrier signal varies as you adjust the regeneration control.  Simultaneously adjust the BANDSPREAD control to keep the carrier at a more or less constant pitch.  You'll notice its volume increases as you continue adjusting the REGENERATION control clockwise.  Very abruptly, the signal will leap in volume as the regeneration of the circuit hits the sweet spot.  Gently adjust both regeneration and bandspread controls to get the best volume of the signal. 

When both controls are in the right spot, you will hear signals that are completely inaudible with the controls just a few degrees off.  But when the controls are set properly, this simple circuit with only three transistors can match the performance of a receiver with much more complexity.  With practice you can tune in CW and SSB signals too.

So, if you have completed your Ozark Patrol receiver and don't hear anything, there may not be a problem, it just takes the right knowledge of how to properly tune it.  Give it a try.

73 Dave NM0S


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