Lots of theory about the multiple transmitter and how to do that best.
My question is do we have anyone on here running multiple transmitters on the same frequency currently?
Lots of theory about the multiple transmitter and how to do that best.
My question is do we have anyone on here running multiple transmitters on the same frequency currently?
Looking for general observations about the installations (broadcast transmitter, antenna type and distance between the transmitters).
Believing myself to be a person of uncanny good luck, I put both AMT3000s on 1680kHz and expected them to synchronize exactly, which they did not do.
What actually happened was a fluttering in and out of the two signals, like an underwater loudspeaker.
This experiment, however, did prove scientifically that I do not have uncanny good luck.
What actually happened was a fluttering in and out of the two signals, like an underwater loudspeaker.
Maybe if you submerge your transmitter underwater in the bathtub the fluttering signals will cancel each other out and produce a clear signal.
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Censoredship, as discussed previously, there exist a rather major difficulty in syncing of the audio of to two transmitters on the same frequency.
I highly suspect the only feasible way to accomplish it would be spacing the transmitters far enough apart so the two signal ranges do not overlap each other.
This of course will leave a non receivable portion area inbetween them
Carl,
How far apart were the transmitters? (assuming in same yard/field)...
I've seen several accounts of folks using multiple transmitters in same local lot to increase signal strength. Now wondering if that is even doable in light of your experience.
Censoredship, Perhaps I should clarify my comment..
I suppose I was speaking for myself when I said the only feasible way..
remove the word "feasible" and replace it with "affordable"!
It can be done, probably the most common way is by using the Barix units, as they are design for this specific purpose. However, it's going to cost $500 to $600 for the pair (Instreamer and Exstreamer).
Take a look at the methods and options described here:
Installing Multiple Transmitters
http://www.am1000rangemaster.com/zerobeat.html
The most reliable way to sync multiple transmitters in close proximity, say a couple hundred feet or more on the same freq is to hard wire them together with balanced audio lines like this:
http://www.am1000rangemaster.com/pdf/synctransmitters.pdf
... Only way to get near precision sync.
Otherwise, you will have to separate them wirelessly by the distances where the signal starts fading each way between, with good TX' properly tuned. This means you will need to send your audio via microwave, digital wireless LAN, etc., with AD/DA converters like Barix Instreamer, Extreamer, or maybe used computers, maybe 802.11 WiFi sets at each end from the base, directional antennas (dish) ... and even then there will still be enough difference between the TX' signals to cause a beat or flutter in the crossover zone(s). Won't last long if you're driving, buy not so good for listeners sitting in the zone.
Obviously the way out of that dilemma is to use different frequencies, as most commercial FM station translators do. The signal will be close enough since they don't have to be perfectly sync'd, but listeners will have to re-tune frequencies when traveling between. The key is to throw regular announcements as to frequencies to use in coverage area locations into the program content along with whatever other publicity you have to get the word out.
The other way to eliminate the audio delay factors is to have delay compensation on the first unit so that it can be adjusted to be behind the next transmitter..and so on.
Same approach with timing and color synchronization in analog video systems..called "Delay Modules".
RFB
Dang! .. I just finished posting a new thread 2 seconds ago on that subect!
When I tried 2 transmitters 1 frequency, they were 36-feet apart, the front of the house and the rear of the house.
Most of the space got filled with the fluttering motor-boat effect.
The audio was from the same hard-wired source.
I'm thinking that if one of the transmitters had a variable shifter control to give + and - control of the timing then at least a manual setting could be made until drift sets in.
Most of the space got filled with the fluttering motor-boat effect.
Probably the motor boat effect was due to the carriers not operating on exactly the same frequency.
This motor boat effect also should be present in the noise level in receivers of nearby, unsynced AM systems with the receiver volume turned up a bit, and with no modulation of the transmitters.
Once the carriers are exactly synced, then the audio fed to each transmitter needs to be synced in the time domain, as well as having the same negative-going and positive-going peaks, and modulate each transmitter in the same audio phase.
Rich touched upon a major point that has not been singled out prior to now, in these discussions:
"...modulate each transmitter in the same audio phase."
Audio phase becomes important when two audio signals get mixed together.
Many electronic hobbyists use unbalanced audio lines, so they may not encounter audio phase problems, but two identical audio lines going to two different transmitters results in audio being mixed in the air.
The phase of a single audio line can flip because of a balanced line being wired in reverse, or an audio signal amplifier inverting the phase.
Out of phase audio signals cancel, and it is important not to blame the problem on the transmitters.
I am not talking about thinking in the month of March. No. I am talking about the way thoughts march on, like thought soldiers, and arrive at other thoughts. An army of thoughts.
I got carried away there for a minute. Oh, another thing Rich said was...
"Probably the motor boat effect was due to the carriers not operating on exactly the same frequency."
Probably what happened, as I was using two AMT3000s which do not have a fine-tuning adjustment for achieving zero-frequency-beat.
Although I have never heard flutter against distant commercial stations on my same frequency, which indicates the AMT3000s are very accurate.
But for the manual synching of transmitters via fine-tuning the AMT5000 does in fact have an adjustment for reaching a very fine zero-spot.
Some day when I have a second AMT5000 I will do a "same frequency" test and march over here to file a report.
At one time this site's Library contained two publications of particular interest on this subject of operating multiple transmitters synched on a single frequency.
James R. Cunningham's LOW POWER RADIO BROADCASTING on page 7 contains a description of a cable AM method for driving a string of 3-meter antennas from a single transmitter.
Ernest G. Wilson's CARRIER CURRENT TECHNIQUES on pages 19, 26, 32, and in between, shows how to use a similar cable system to drive individual repeater amplifiers from a single "master" transmitter.
Trying just now to locate those links for you, I cannot find them in the Library.
If someone is able to locate these important works, please post links for the benefit of this forum.
"Rich touched upon a major point that has not been singled out prior to now, in these discussions:"...modulate each transmitter in the same audio phase." Audio phase becomes important when two audio signals get mixed together."
Nope. I brought this up using the analog video system as an example some weeks ago..remember?
And again a couple posts above.
"Remember!" Spock Star Trek The Search For Spock
RFB
Weeks ago......
Oh ya, it was on a Tuesday, mid afternoon.
But it is good to re-hash the phasing, because some readers might not be familiar with the problem.
I may have actually brought it up first, back in 2006.