Sage advice reminds us that using the antenna included as part of a certified antenna assures compliance with 15.239.
If experimental antennas are tried, it becomes necessary to measure compliance which I'm able to do with a spectrum analyzer by comparing the experimental setup against the reference of Wholehouse 2.0 in its fully certified state.
The telescopic antenna on my otherwise certified C.Crane FM 1 Transmitter is removed because of a defective connector which refused to accept solder, replaced with a plain wire.
Having stated the ground rules being applied to my antenna experiment, let me mention the problem I wanted to solve.
Using the manufacturers transmit antenna the Panasonic Table radio in the next room constantly went in and out of reception due to multipath caused as I moved around the building.
I have accidentally solved the multipath problem by running the antenna from the C.Crane vertically up the side of a doorway, and an equal length horizontally across the top of the door-frame, forming an L.
The signal strength seen on the analyzer is actually less than the Wholehouse reference signal, but the Panasonic reception is rock solid with no multipath disturbance.
It could be that your "L" antenna is producing both vertical and horizontal field components.
What antenna are you using with the spectrum analyzer? Perhaps, if it is a whip, try rotating it from vertical to horizontal and compare results with the original vertical only transmitter antenna.
Neil
Its interesting to note per HB that the C.Crane puts out -45dbm to the final stage of the transmitter (Stock condition). So the L sape could have actually helped by making it both virtical and horizontal which would also help car Radio's receive your signal. Did your C.Crane still only go 10-15 feet or did it actually transmit further using this method? The SainSonic was a little less in output at -48dbm and I could only receive a good signal at low power about 15 to 20 feet. I know -48 is less than -45 and I don't know why they didn't make it -45 but it also proves something and that is the wire antenna if set right can beat a rubber duck.
I've repeated the entire antenna experiment with fresh readings, and here's what we found:
Throughout this test the C.Crane FM1 Transmitter is atop a metal computer case next to a wall at a doorway, possibly having ground plane benefits.
The wire antenna placed vertically held to the wall with masking tape.
Spectrum analyzer antenna: Vertical = 53 dBu; Horizontal = 55 dBu.
Wire antenna vertical to top of door-frame, horizontal along top of door-frame.
Spectrum analyzer antenna: Vertical 44 dBu; Horizontal 46 dBu.
Now here's the fly in the soup bowl. In my previous report I said that the L-shape eliminated multipath at a receiving location in an adoining room.
Thus, logically, with the transmitting antenna back to vertical we should get multipath interference by walking around the rooms, but not today.
The receiving radio in the adjoining room has rock-solid reception today.
Go figure.
It proves my theory that temperature and moisture in the air has an effect even on part 15 FM. Hence why some days you may get 800-900 feet and the rest of the time you'll be lucky to leave your house. Many people don't believe it but I've read the same thing on Light O Rama when people tried to set up those transmitters for a Christmas light show. I've heard reports at times folks with a stock Whole House Transmitter would reach 1/4 mile but would not happen all the time and they talked about it happening at night. So I'll have to conduct the same test I did with my transmitter on low power when we have some moisture and see what I get again.
Also, I was thinking about any physical changes I may have made between getting multipath and not getting it.
One change was moving metal lawn furniture that was placed right outside the rear wall. To check this out tomorrow I'll put the 2-chairs and a table back where it was and see if I can get my multipath back.
Several have stated with confidence that their FM transmitters are placed in windows.
But most windows include screens, and screens are signal blockers.
How much does it block FM?
My screens are not metalic. I suppose they would be RF transparent.
Even the blinds in front of the window could make a slight difference too. Not too sure how much though.
Bamboo blinds or metalic?
Bamboo. I have those kind of blinds in front of my FM Transmitter's antenna.
Several earlier mentions have been made of a multipath problem at times in the house while walking around causing radios to lose signal and get very noisy.
Two nights ago things were quiet and I wasn't thinking about multipath, as KDX programming was performing clearly from the radio.
I laid down and planned to listen myself to sleep, which went well for a couple of minutes until a roar of multipath started issuing from the receiver even though I hadn't moved.
From the horizontal position I tried to think of a reason why multipath would suddenly erupt as if someone was up moving around, and my first thought was that someone was in the house besides me. But no floors creaked nor shadows moved so I began wondering if someone was outdoors in the yard with multipath acting as a "motion detector."
My conclusion was that it was a ghost, and I now claim to have discovered the previously inknown fact that ghosts cause FM multipath.
Many ghost hunters use FM radio to track ghosts. So it really could be. Also what about an animal or something like that outside?
And, you rarely hear those "Black" helicopters hovering nearby.