As I mentioned previously, wiring and other conductive objects within the home and walls will attenuate that already weak signal from that C-Crane, which out of the box doesn't even hit 250uV at 3m anyway. It's no wonder your having problems with reception within a 10 foot range.
You said the reception antenna is directly below the transmitting antenna which is a cage monopole supported by bamboo sticks. I've seen the pics.
One thing you should realize is that the C-Crane thing was peaked and tuned for it's wire antenna. Attaching something else to that wire will throw off the tuning of the output because your changing the length of that wire antenna by attaching it to the cage monopole antenna. As far as I know, there is no tuning ability for the output circuit of the C-Crane, just a power adjustment pot buried under putty. Besides, attaching any other antenna to that certified C-Crane FM transmitter voids its certification. (shame on you!) :p
Your cage monopole wont put much signal below it or above it, but to the sides of it. Your reception point is below in another room, though directly underneath that cage monopole the signal is probably already so weak due to the fact that most of the signal is emitting out of the sides of that cage monopole and not shooting upward or downward, particularly downward where your receiver antenna is.
You will get better results by simply using the C-Crane by itself without any additional antenna and simply lay that on the floor above where the receiving antenna is. Lay the wire straight out on the floor and I bet your multipath problem ends. You got the polarities right, except your receiving antenna is below the radiation angle of the TX antenna and it's barely picking it up. Like having two microwave path dishes not quite aligned, as if one is shooting the beam too high because the TX dish is mounted or adjusted wrong and is not in line of sight to the receive dish.
RFB
Since the multipath problem stopped, all at once, it hasn't been back.
But I grasp everything said about this setup.
The one correction is that the transmitter feeding the cage-monopole is a Wholehouse 2.0, which comes with an instruction to cut an antenna to a multiple of the wavelength, and gives a formula for this. So I am within their certified specs, since that surely must be part of the certification since it's the way it comes packaged.
This FM tower also needs to reach a receiver on the same floor one room away, it is providing STL for two AM transmitters.
I think I will try to modify the antenna to provide a horizontal element for reaching down below.
Meanwhile, the C.Crane, with its own dinky antenna, is broadcasting four feet to a radio used to edit my radio blabber. It works for that.
I see. I recall mention of a C-Crane in use.
There is still the TX antenna being above the receive antenna issue. The field from the cage monopole is not radiating downward but out to the sides. Your receiver antenna is in a null zone and most likely receiving a reflected signal anyway and that is what is affected, not a direct signal as it would be if that receiver antenna was in the radiation field pattern emitted by the cage monopole.
If you have to run a cable to carry an RF signal, might as well just run some audio cable and direct feed that other system instead. Or move the STL TX and it's bamboo cage monopole somewhere so that it is in more line of sight to the receive antenna, or move the receive antenna more in the line of sight to the TX antenna.
Or..simply put up with the limitations as expected in this license free flea fling hobby of ours! 😉
RFB
I appreciate all the input on this STL-by-FM situation, and have been given many good suggestions to use for a re-design.
I will fiddle until it works reliably, then want to try alternative STL methods, backups for backups.
Meanwhile, I just put into service a triangular shaped loading coil I built for the AMT3000, and its in early tests. It is loading up, and may need finer tap points to peak it way up.
After that a ground system goes in for the AMT3000, and we'll have a report.
Also, I again toured the future sight of the future outdoor stick and radial installation..... sorry birds, some shrubberies will have to go. At least I waited until all the young birds have left home.
In fact, with the drought, I see very few birds at all. They waited for weeks, and then cleared out.
Permit me to time warp back a day to follow up on my post regarding the RF problems in my "shack". While sitting and staring I remembered that 20 years ago I had installed an underground 120V line to power some lights in the back yard and that the terminus was very near my new transmitter and antenna. The line had been disconnected and abandoned but I found it and prepped the end to connect audio, power, and audio/power ground to the transmitter using the old hot, neutral, and ground wire. Knowing it is risky in terms of interference to the audio it was worth a shot. And it paid off! Good, clean, and quiet audio signal heard and since the line is 10 inches or so below soil level it doesn't pick up RF from the antenna and dump it in the shack.
There is a noticeable lessening of the RF signal strength in the shack but the hum is completely gone.
A buried STL line can be a workable option.
Neil
Your outdoor buried cable experience is on target with what is planned here at the Internet Building.
All of the above STL multipath problems are only about indoor links, from room to room and floor to floor, so as to avoid drilling worm-holes in the woodwork.
But the soon-to-come outdoor vertical with radials will be mainly fed by buried cable, including phantom-power sent on the same cable with audio, the way microphones do it.
One thing I didn't understand in your "RF in the Shack" time warp was why there would be less RF in the shack because of your buried audio/power/ground cable (?)
One thing I didn't understand in your "RF in the Shack" time warp was why there would be less RF in the shack because of your buried audio/power/ground cable (?)
My theory on this is that originally the feed cable was placed on top of the soil and was acting as a radial by picking up induced RF current from the vertical radiator. This current appears along the entire length of the line since this length is a fraction of a wavelength, including the end of the cable in the shack. The exposed line acting as a conduit for the signal was confirmed when placing a powdered iron toroid over the line in the shack and grounding the shield to a water pipe virtually eliminated the hum.
My original thought on this was that the RF didn't penetrate the soil to reach the buried line but this is not in accord with the estimated skin depth in soil being 7 meters at X band frequencies. Another "guess" is that the RF is attenuated by being capacitively coupled to the soil and hence dissipated by the soil resistance. The problem with this is it works both ways in that the current induced in the soil is also coupled into the line by capacitance.
It could also be that since the transmitter signal ground is isolated from the antenna system radials by a RF coupling transformer, the current coming down the line was not significantly that induced by the field but rather was coupled in a common mode manner from the antenna system back through the transformer to the transmitter circuit ground. This would be a high impedance coupling and perhaps the line capacitance to the soil, being much higher than the winding to winding capacitance in the transformer, shunts this current into the soil.
Absent another good explanation, the only thing left is the observation that the RF is greatly attenuated in the shack and no longer causes hum problems. The question also remains as to how deep the line need be buried to have this effect and whether the transformer is a factor.
Maybe someone with another explanation of this will comment.
Neil
Hey Carl,
I had the same exact problem actually.
My studio is in the basement, transmitter is upstairs.
Im using my final working C Crane as an STL, it actually gets out pretty decently for being underground. However multipath became a huge problem when a number of people come to the house.
The way I fixed it was by moving the C Crane around untill I found a "sweet spot" and then adjusting the recieve antenna for the "sweet spot"
Its working much better now, theres occasional multipath, but not too bad.
Carl, you might try the leaky coax method.
RFB
I must be clear headed this morning, because the last several comments caused the brain to "whizz, whirrr" and come out with these ideas....
You may have noticed that I am setting the stage for "indoor antenna experiments", which originally was going to be about AM antennas.
But what are we talking about right now? Indoor FM antennas.
When the Spectrum Analyzer arrives we will be able to "see" the various results from moving antennas and looking for "sweet spots," and all that.
Phlotilla, please send out for more empty notebooks...also get more pencils."