Visual Part 15 AM Tuning Indicator

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Visual Part 15 AM Tuning Indicator

Stolen from The ALPB Boards: 

Imagine placing a small NE2 neon bulb or a grain of wheat lamp at the tip of a Part 15 AM transmitting antenna. One leg of the lamp is attached to the antenna. The other leg is in free space. Then one can tune the transmitter for maximum brightness. Very easy. This could help with the complicated (perceived) tuning procedure on the AMT5000 IMHO.Read more:

Very interesting

I can see an NE-2 working.  I don't

know what the grain of wheat bulb

is made of.

There would have to be 90 volts 

(or more) at the tip of the

antenna???  Is that


(I guess I should read the link.)

Best Wishes To All

Brooce, Part 15 Hartford


Tried It...Didn't Work

Neon antenna tips were used during the CB craze and apparently worked with the 4 watts or so of input power.

Simulations using lumped parameter modelling of a base coil loaded 3 meter antenna at resonance predicts a voltage at the coil end of the radiator of about 120 volts with 85 mW of power applied which is enough to illuminate a neon bulb.

I just tried two experiments with a neon bulb using my resonant antenna and touching one bulb lead to the radiator at the coil connection and holding the other lead between my fingers caused the bulb to light.  Touching the lead to the tip of the radiator and holding the other lead between my fingers also caused the bulb to light and in both cases severe detuning was seen..  However, leaving the "finger side" lead to dangle in space did not result in the bulb lighting at either end of the radiator.  It seems there is not enough capacitance to the "universe" to provide the necessary current path.

Consulting my trusty General Electric Glow Lamp Manual, First Edition I note that a NE-2V (typical brightness type) bulb draws 0.6 mA at 75 Volts for typical operation.  This is 45 mW needed for the bulb so even if it illuminated it would require a huge percentage of the available RF power. The actual power used might be less since the bulb is conducting on only a part of the a. c. cycle but this would also draw a lot of power from the system..

I would also question if the bulb did illuminate then it would be generating harmonics of the RF frequency, but since it didn't light this is moot.



Thanks Neil.

It was a great idea while it lasted. :-(

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

To Neil

I really enjoyed your technical explanation.

Brooce Part 15 Hartford


Hang on a minute

What if you were to attach an NE-2

to a high voltage point, such as

Neil mentioned, and attach a wire

PERMANENTLY to the previously

unattached NE-2 lead.  This would

provide the capacitance to light the

bulb.  Then retune the system.


Brooce, Part 15, Hartford





Oh.  Power consumption.

Never mind.

It is fun thinking about

it though.  It's sort of a 

Science Fair experiment.



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