Activity here on the site has been very slow. I hope the Part 15 hobby is still alive and strong.
Activity here on the site has been very slow. I hope the Part 15 hobby is still alive and strong.
I got to wondering about the unused capacity of the SSTran, with 100mW to the final amplifier stage. As we already know, the used capacity is whatever happens with a 3-meter antenna.
The unused capacity is whatever result might or could happen with a longer antenna.
The Rules allow brief experiments not to exceed 30-seconds.
So I raised a 6-meter vertical antenna and tuned the output for peak. Amazingly, the result was NO DIFFERENT WHATSOEVER than a standard 3-meter antenna!
After hearing your comments I’ll post the next experiment in this inquiry.
Doubling antenna height
This is no trivial experiment. Setting up a 20-foot monopole for just a brief test is a lot of effort. You are to be congratulated.
Your experience is a common one. Some people have tested 1 W of input power to the final stage to get a 10 dB of power increase, and were surprised that their range was hardly improved at all. The power increase near the antenna is more noticeable than at a significant distance (like a mile or more) from the antenna if the ground conductivity is poor. Far from the antenna, there is a significant power loss due to the ground, and range increases as approximately the fourth root of the power increase. Near the antenna, range increases as the square root of the power increase.
Doubling the height of an electrically short antenna increases the radiation resistance by a factor of 4. This results in a power gain of 6 dB. This should double the range near the antenna, and increase the range by a factor of 1.4 far from the antenna. Unless you make very careful measurements, a 6 dB power increase is just not very noticeable.
The figures I mentioned apply to an open field. Your local conditions can change the results a great deal.
Your Comments Match Experience
Yes, Ermie Roos, your comment about what most probably took place matches the experience I described very exactly, so I am certain that explains it.
What I believe I’ve come to understand is that the actual rules, a 3-meter antenna and 100mW input to final, may be verbally exact but they are technically pretty meaningless, since large excursions in either power or antenna length make virtually no difference.
Yet, conversely, there’s no advantage to exceeding the meaningless rules, since it doing so provides no meaningful gain, therefore the temptation to exceed the rules is a false illusion not worth entertaining.
This is the second time I’ve replied to this string, the first time did not show up.
The way it is here.
Carl, I agree with your experimental results and Ermi’s
comments on it. (By the way, putting up a 20 foot
vertical is a lot harder than a 10 foot one.)
I think Part 15 broadcasting is alive and well. My station
is not going very far. The AM is off and the FM is compliant
so it doesn’t break any distance records.
Lately I have been working on the Gates board. And the
13.560 MHz transmitter experiment hasn’t been completed
either. And the AM ground system repair project is not
done either. (I have 16 radials.) Life has gotten in the
way.
But I think there are quite a few Part 15 stations out there.
That’s my two cents.
Best Wishes
Bruce, MICRO1690/1700
About More Part 15 Stations
Bruce MICRO1700
With your input on the 20-foot antenna experiment we have full consensus on all sides about the results and what’s been said about it.
And the comment about Part 15 being alive and well answers the very beginning of my first comment, about a slow down in activity here at Part15.us. Perhaps, as with you Bruce, life is getting in the way for other members right at this time.
Not only should this be a popular hobby, it really ought to be spreading into a major pastime as many people would love having their audio over private radio stations. I try to come up with ideas for encouraging others to join in the hobby, and I solicit ideas anyone might share for spreading the fun of this hobby.