Total posts : 45366
If you have the test equipment to do so, I would urge you to measure the inductance and Q of your very interesting coil. The coil form and coil look very nice in the pictures. Testing your coil only with a transmitter would really not give very much information.
To measure Q, it would be very good to have a Q meter, but that is not at all necessary. Very good results can be obtained with an RF signal generator, a frequency counter, and an oscilloscope with a 1X probe. Other recent posts in this Forum describe a Q measurement method of Ben Tongue (of Blonder-Tongue fame,) which gives excellent results.
It is useful to also determine the low-frequency inductance of the coil. If the coil is cylindrical, and not too short, the well-known Wheeler formula can be used to get very accurate results. This famous formula is of the form L = [(r^2)(n^2)]/(9r + 10l). It is in a great many publications, including the ARRL Handbook. When looking for the formula, don’t look for Wheeler’s name. For some reason, he is usually not given the credit for his formula, which he published in 1928. He continued publishing inductance formulas for a long time. I saw a 1982 (or thereabouts) edition of the PIEEE in which he reported several additional inductance formulas.
The coil described in your thread is is not cylindrical, so the Wheeler formula does not apply. In this case, the coil can be resonated with a large known capacitor at an audio frequency, using a variable audio generator, and an oscilloscope to detect resonance. I use the frequency counter function of my DMM to accurately measure the audio frequency. Using the operating frequency inductance and the low-frequency inductance, the self-capacitance of the coil can be calculated.
I am currently measuring several kinds of coils to gain a general understanding of loading coils. For my tests, I have purchased many styrofoam cylinders of various sizes from an art supply store. I am using both Litz wire and solid wire. Because the styrofoam forms are rather fragile, I am reinforcing the surface of each cylinder with polyethylene tape. Both polystyrene and polyethylene have low dissipation factors compared to PVC, so they should be good to use as coil forms. I am not trying to design practical loading coils right now. I am just trying to gain knowledge.
I will begin posting my results only after completing all of my tests, so that I can report general trends and conclusions. It would not be very helpful to just report my raw data.
There has been some discussion in this Forum about Qs to 1500. I don’t think that there is any possibility of the coil Q being nearly this high. I hope that I am wrong, however. A very-high-Q coil would make it possible to make a VLF oscillator with much lower noise than has been yet obtained. Such an oscillator would be very useful in another application that I am working on, which is not directly related to radio.