Quote:
Originally Posted by WM6
I don't know what of instruments do you have in your lab.
If you start from "Gold gun" which is real for you, you need first to measure all of (as you say) three frequencies of your AL707. Do not believe to producers data it may vary, but because of ferrite antenna ("widest" Q) real data can be inside of acceptable tolerances.
There are some way to measure antenna resonance but first rule have to be that we may not to over-burden input LC circuit by direct measure instrument connection in a way to change his resonate frequency.
So we will try to measure without to over-lasting antenna circuit. Maybe you have or can lent some sort of reliable audio signal generator or signal generator for general use. If so, you first wind your testing transmit antenna from about 10 turns (1mm Cul) 10cm in diameter (or 10 turns on ferrite rods) and connect such testing antenna together with serial connected 1k pot (trim to middle position) to generator output. Put generator output on unloaded (max peak to peak output) square signal (typically 15vpp). Now you have your testing measurement transmitter ready.
Put your AL707 "ON" and approximate it to test antenna at about 20cm. Now you start to gradually change generator frequency from 0Hz to about 35kHz and watch for react from AL707 speaker or led. If you catch signal, try to establish his maximum. Frequency at which signal reach his peak is resonate frequency of selected frequency position of your AL707. Try the same way to establish other two frequency. In case of strongest signal from receivers speaker you can use attenuator on signal generator to get weak signal or put AL707 so apart from TX antenna to get weak signal from speaker. By weak signal we can more accurate establish peak and by this more accurate resonate frequency too.
In case of no signal from AL707 you can first regulate serial pot to lower resistivity of about 100E, more approximate test antenna to AL707 and at the end try to open it and measure signal at amplification stage by mV-meter or scope. To prevent possible damage hope that this would not be needed.
After you establish all three of antenna circuit resonate frequencies your next step is transmitter adopted to middle of three frequencies (or on one of his lower harmonics).
Here may you suggest to buy very usable testing instrument Portable frequency counter with possible use as field strength meter. You can search for it on eBay under name "GE FC-1 Portable Frequency Counter 10Hz - 2.6GHz". Usable to detect in-depended of transmitter and receiver resonate frequency of TX antenna and cheap.
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Thank you very much for your help WM6.
The only thing that I have to ask you to explain me better is:
....After you establish all three of antenna circuit resonate frequencies your next step is transmitter adopted to middle of three frequencies (or on one of his lower harmonics). ....
Do you mean that if the lower freq. is 9khz and the higher is 10khz then the Tx must be adopted at 9.5Khz?