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doc_nomad

Anyone else mod'ed a Hong Kong system

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I recently purchased a Hong Kong wireless system and I have been fairly impressed. I determined it was running right between 1050 and 1150 mhz depending with a 9 volt. I would like to solve this problem.

I cut the Tx antenna to 65 mm, this made the largest improvement.

I was wondering if anyone has changed out the cheap tuning dial with something a little more accurate.

What is the optimum antenna for the Rx?

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I was wondering if anyone has changed out the cheap tuning dial with something a little more accurate.

A voltage regulated power source will help stabilize the tuning drift.

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A voltage regulated power source will help stabilize the tuning drift.

ok, but how do I deal with the Tx frequency drift?

"One of the things I discovered was that the Tx frequency drifted with battery voltage. Drift is about 7Mhz per volt. A Tx voltage change of as little as 100mV affected the received image. A voltage drop of 250mV caused the image to become unstable and required retuning the Rx (a knob on the Rx is used). I suspect that the Tx could be nearly drift free if it was operated on a voltage regulated battery source (hint, power it using a Voltage Regulator IC)"

Anyone have a wiring diagram on how to do this? I am thinking of using three of the CR123A lithium batteries.

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Three of those cells would only give you 9V. For a simple series pass solution, you will need a higher voltage, followed by a 9VDC voltage regulator circuit. Maybe someone will help out with a schematic.

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If it is an LM317 based design then the minimum input voltage needs to be *several* volts higher than the output.

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Try a 'LM2940CT' with a 4v zener diode on the centre leg.

Terry

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