For years now I have been using an indoor antenna for AM transmitting. This antenna is mounted horizontally on the ceiling in my basement with the tx. grounded to a cold water pipe near the base of the antenna. The antenna is resonated with a loading coil. Being indoors and horizontal it is suspected that this is a less than ideal situation to achieve range.
So to test this I did an outdoor antenna test. I laid down 11 10 foot radials and connected the ground of my "high efficiency" transmitter to the center point of the radials. The transmitter was positioned on the ground next to the antenna. As seen in this picture 
the loading coil and antenna are supported by a high tech insulator (an empty wine bottle). The loading coil is the same one I use indoors and has a trim coil for fine adjustment seen at the bottom.
The three meter high antenna is supported with Kynar rope as seen here: 
My wife ventured out and when she saw this she said "Oh, you're playing with an antenna.". Nothing surprises her anymore.
I used my current transformer arrangement to tune the antenna to resonance. It appears that being outdoors above the radials adds capacitive reactance compared to the indoor position since it required adding 8 turns to the coil to get resonance. It is almost amazing how sensitive this antenna system is to artifacts nearby. I found that by moving from about three feet away to 8 feet away shifts the phase angle by 45 degrees. It is really a sensitive adjustment.
Having achieved resonance it was time to do a comparative range check based on past experience with the indoor antenna. First with my portable I walked down the street and there was a very marked improvement in the signal strength. I could hear the signal at a distance where it was lost previously.
Now for a drive around test. The results are surprising. From my home to the exit of our neighborhood the signal was about the same on my car radio but making the turn onto a state highway the signal disappeared and there was very strong interference from the high voltage power lines on the poles (within our neighborhood the power lines are underground). With the indoor antenna I could travel down this road for 2 miles and still hear my signal. This wasn't the case now. Perhaps having my antenna indoors coupled a good bit of the RF signal to the power lines and the pole mounted lines were radiating this signal ala carrier current.
I continued and turned onto a street with underground lines and the noise abated and I could hear my signal at a distance where it could not be heard previously away from the overhead power lines. This was about 1 mile away. My criteria for this test is if I could identify the audio as being from my station then I was in range, if not I was out of range. Because it was rush hour I didn't drive further away to find this limit but at this distance of about a mile the signal had noise but it was listenable. The signal stayed listenable as I approached my home being heard as I entered my neighborhood by the back door route where previously I couldn't hear the signal.
Then I drove the other direction along the state route and again the line noise blocked the signal. About a mile away in this opposite direction I turned into a neighborhood with underground power lines and my signal was again listenable.
It seems that the range is much improved as I heard a listenable signal at distances and in areas where it was not heard with the indoor antenna but the antenna effect from the overhead power lines experienced with my indoor antenna is gone.
The conclusion from this is that an AM transmitter delivering 86 mW into a base loaded antenna over ground mounted radials can be listenable on a car radio out to at least 1 mile.
I haven't decided whether to go back to the indoor antenna or make the outdoor antenna permanent. This indoor antenna needs not be weather, people, deer, falling limbs, and other mayhem resistant but it is not the optimum for getting a signal out.
Neil
I can understand why it is tempting to have that outdoor setup, and I have some ideas on resolving the "what to do" dilemma, which I'll get to in a minute.
The wine bottle makes a fine insulator, and appears to be filled with water for ballast. Is there any way the water is influencing the RF field?
I didn't notice a ground rod for that extra type of ground connection, do you think that would affect performance if added?
To help with the decision of where to install things in the future, I would ask what is your objective with the station. If the indoor setup filled your needs, keep that for its convenience.
Another option that would appeal to me would be to have two systems, one in and one out. You could use the outdoor as your nighttime signal.
Great job, Neil! I wish I had more time to play again. I sure do miss it..
"Perhaps having my antenna indoors coupled a good bit of the RF signal to the power lines and the pole mounted lines were radiating this signal ala carrier current."
Highly unlikely. It is more likely that your range was doing good on the indoor setup due to the fact you were grounded to a cold water pipe, which that cold water pipe is connected to a huge array of cold water pipes ran all over the place, down every street, in every neighborhood, and yes even along the state highway in the area where you observed the signal before.
RFB
I'm curious as to what kind of transmitter you are using. You mentioned it's high efficiency.
I also think your range is very good considering the transmitter is at ground level. I know this sounds stupid, but I thought the antenna and transmitter would have to be on a 10 or 20 foot tall mast in order to reach over a mile. I always thought an on the ground setup wouldn't even reach the neighbors.
It's amazing what 100mW will do!
I'm so glad you brought the
set-up outside. It's a real
adventure to do an outside
set-up. I think it's exciting
to drive around and see where
it goes.
The nulls and peaks and such
can really be puzzling. But it's
very interesting.
Also, I'm sure we all appreciate
the photographs. They look
really good!
To ChannelX1610, Neil built the
transmitter himself.
If you go to the thread that says:
Radio8Z Part 15 Transmitter Design
You can read about it.
Bruce, DRS2
Just curious. (I hope you're not
dragging the SuperPro around in
a wagon with a big long extension
cord.)
Some portables are a lot more
sensitive than others.
Bruce, DRS2
The wine bottle was soaked in hot water to remove the labels just before the photo so there was a little water left inside. Water is death to RF in this instance because the dielectric constant is 83 (if my memory serves).
There was no ground stake used and I don't think it would make much if any difference. The ground stake is primarily for lightning protection.
For Channel X, the transmitter used is one I designed and built and it is in the gray box at the antenna base. The details are at these links:
http://www.part15.us/node/2791
http://www.part15.us/node/3636
It is just recently that transmitters with claimed high efficiency have become available. As far as I know this one is the only one where the power output has been documented and reported and it delivers 86 mW into the antenna shown in this project. I am not saying that there are not other high efficiency units out there but I know of none with documentation of the output power into an antenna.
I regret that a more complete and better documented test could not be done but this is a start. Maybe as time and energy permits I will spend some more time on this.
Bruce, I used a GE el cheapo $15 portable with moderate sensitivity for the walk up the street test. For the drive I used the stock radio in my Armada. It seems not to have the sensitivity of car radios I had 20 or 30 years ago but it is adequate. As an example, with my previous truck I could hear WLW during the daytime in Bay City Michigan but with the Armada radio WLW fades away around Ann Arbor.
Neil
The thread was right in front of me! I can't believe that I missed it!
But anyway...
I wish I knew how to build from a kit. I bet it would be cheaper than buying a transmitter already assembled. And his transmitter seems pretty powerful. 80 some odd percent efficiency? Isn't that better than the procaster? It might even be better than the rangemaster.
I would love to see a side by side between his unit and the SSTRAN AMT5000.
And his transmitter seems pretty powerful. 80 some odd percent efficiency? Isn't that better than the procaster? It might even be better than the rangemaster.
I would like to know this but I know of no published data by which to make a comparison.
Neil
I would love to see a side by side between his unit and the SSTRAN AMT5000.
I suspect that the two transmitters using the same antenna and radials would have almost the same range. The big difference is that with the AMT-5000 the loading coil is internal and none is needed at the antenna.
Neil
RFB,
I tend to agree about the coupling to the power lines since the drop transformer is set in my neighbor's front yard and it serves only his house and mine. This would likely block the signal.
The water line from the street is black plastic and if there is a messenger wire buried with it this doesn't enter the house. Are you saying that the RF could be going through the water in the pipes?
What about the CATV and the telephone lines? The cable runs within a couple of feet of the antenna in my basement and the phone line stops at the network bridge adapter on the outside wall. They both share the same electrical ground with the cold water pipes indoors.
Neil
"Are you saying that the RF could be going through the water in the pipes?"
Could be. Are you familiar with the water antenna? They are antennas that use a stream of water shot out of a spout mounted above an inductive coupling coil. Just like a metal conductor's length determines the resonant frequency, the length of the stream of water determines the resonant frequency. They have been proven to work very well even at HF frequencies.
Since the pipe is non-conductive from the street to the house, that would allow any signal riding on that water in the pipe to radiate, perhaps even couple to other conductive objects below..like the electrical conduit pipe underground, which would carry your signal onto other objects that could inductively carry the signal even further.
Another possibility is the messenger wire, or the pipe itself may have a layer of protective sheeting between the layers of the pipe itself for strength reasons.
Radio..gotta love it's many mysterious ways of getting around!
RFB
Are we drinking radio programs?
Can a filled bathtub be used for reception?
"Can a filled bathtub be used for reception?"
Try a kiddie swimming pool. You will be surprised at how much that will improve things..both RX and TX.
RFB