Thanks CENTINEL for thinking of me in this regard but I have no needs to talk over with the HAM gentleman.
My stations are all running below part 15 levels and I'm not pushing any range so a pro-meter wouldn't help.
Very grateful to you.
Bruce,
You can purchase the coil from Jameco p/n 372402. It is a 22 uH coil but is close enough.
The antenna connects across C2 which means the the 50 ohm feedpoint of the antenna connects to the lead of C2 that also connects to the coil. The ground end of the antenna connects to the other lead of C2 which connects to ground.
Carl began this thread by stating:
"A "serious part 15 research hobbyist", to my way of thinking, would be someone dedicated to trying all of the transmitter antenna installations that we talk about year after year and providing detailed numbers describing their comparative performance."
I ask what "detailed numbers" should be used?
Neil questions what Carl meant (in Post # 1) by "providing detailed numbers describing their comparative performance."
Neil asked: "what "detailed numbers" should be used?"
Each of us has some method of gathering numerical data about our transmitter's performance. If not, it will be difficult to be a "serious scientist".
Those with certain radio models such as the TECSUN PL-310 have dBu signal strength readings, some may have spectrum analyzers, even S-meters can be used to collect relative readings.
Distances between objects, height of objects, proximity between objects, meter readings, whatever numbers one can possibly gather to compare the performance of one transmitter to another.
Distances, uphill downhill angles of incidence, and word descriptions:
Where was your measurement device, was it handheld or stationary, what were the environmental conditions, was it hot, was the ground dry, were the tests all done with the same conditions or did conditions change during the testing period, what time of day was it?
Numbers and words should reflect every square inch of air, earth and surrounding materials of the physical and electrical domains.
Of course step one is to obtain all of the transmitters to be compared.
Which versions and revisions of the transmitters do you have, were they prebuilt, made from kits, who built them.
Was test done unmodulated and modulated or a mix of both or "can't remember"?
Then maybe someday we'll have a real answer when some simple new-be asks, "Which transmitter is best?"
In post #19 Carl has outlined the many factors which can make comparisons and predictions of different AM transmitter systems difficult. It would be nice if there is a meaningful specification for AM transmitters which would provide prospective buyers with some guidance.
Perhaps we can borrow some ideas from the audio and ham communities. Equipment made for hi-fi stereo state the audio output power into a particular load impedance. Amateur radio transmitters likewise are specified for a power output into a 50 ohm load. Such output power specs. can guide a prospective buyer as to what to expect from the equipment.
I suggest that an output power specification for a Part 15 AM transmitter might also provide guidance. Unlike the audio and amateur radio devices the expected load impedance is not well established yet using a standard load impedance for the specification could be helpful in comparing transmitters. Phil of SSTRAN has suggested a bench test load standard of 30 pF in series with a 30 ohm resistor based on the expected typical impedance of a 3 meter vertical radiator above a ground plane of radials. Though this would not represent all installations in terms of load it can be a rational basis for comparing transmitters.
For instance a transmitter delivering 50 mW into this test load would be expected to give longer range than one delivering 10 mW.
Though not a complete predictor of range for an installation it may serve as a starting point to get comparitive information for different transmitters..
Neil
Neil posted an example of a starting point in gathering detail needed to evaluate and compare the performance of transmitters.
There are many more accuracies that can be measured.
So many have said, "It went a mile".
But was that an estimated mile, an exact mile, a straight-line mile on level ground, in which compass direction?
Someone says "the antenna had wide bandwidth."
Oh? What was the audio frequency response? Was it electronically flat? What kind of reciever was used to measure it, how thick was the antenna?
I am still not convinced that any 3-meter antenna has bandwidth any different from any other given the narrow range of AM band-pass (50-10 kHz).
I tend to suspect that claimants make subjective judgements that "it just sounded better."
With regard to distance measurements, I like to find a spot were the signal is still usable to a car radio meaning good solid copy. No background noise. I note where this occurs and then I use the measuring tool with Google Earth.
DHR says: "I use the measuring tool with Google Earth."
Very useful piece of information gathered by this method.