Howdy,
Howdy,
A local ham who is at novice or maybe above and I were discussing what will happen if I set up two transmitters on my boat, i.e., in close proximity. We thought there would be some directionality, which is OK, but trouble with harmonics, e.g., unpredictable differences between fractal doubling and cancellation.
Thoughts please ... ?
Because the antennas will be close together, there will not be much phase addition and cancellation due to distance that will cause directivity. There will be a beat note with a frequency equal to the difference in frequency between the two transmitters. If both transmitters are at nearly the same frequency, there will be flutter due to the inevitable difference in phases between the two transmitters. Rangemasters are made for synchronizing the phases between two or more transmitters. Crystal control is needed for such installations. Since the transmitters will be very close together, there can be problems with one transmitter interfering with the other in some unpredictable manner.
When I ran 2 AM Transmitters one was on 1560 the other Was and still is on 1650. (The 1560 is off now)
I never noticed any interference between the two.
This is redundant, but - a while back
I came up with the idea of feeding two
transmitters (one in my front yard and
one in my back yard) with the same
crystal oscillator. That way they would
both be on the same frequency.
Or would they be? If a central crystal
oscillator is feeding 2 transmitters through
2 coax lines (one coax line to one transmitter
and the other line to the second transmitter) -
If the coax lines were of different lengths, would
there be a phase difference resulting in a slight
frequency difference?
I never did get around to trying this. But a local
broadcast engineer friend of mine said that he
thought there would be nulls in some
areas and somewhat stronger signals in other places.
Because of life and family and that sort of thing,
my single AM transmitter has not been on. I hope to
have it up and running soon. Some day maybe I'll
try this.
Best Wishes
Bruce, MICRO1690/1700
Bruce MICRO1700, I just spoke to you on the thread next door.
Until I am informed otherwise, by best guess is that the cables should be exactly the same length AND be cut to wavelength or some fraction thereof to not only attain phase but also the best match within the cable, where you want to avoid a standing-wave signal getting generated.
There STILL might be nulls or peaks as well as some directionality in the combined signal, which might be minimized by having the antennas a wavelength apart from each other.
I have a feeling someone told me some of this on a long ago thread right on this website.
Also, I did a thread about feeding repeater amplifiers from a common exciter based on a design in a manual available on this website describing just such a cable radio system with as many 10-foot antenna outputs as space allows. Wait here. I know where it is...
The manual is CARRIER-CURRENT TECHNIQUES by Ernest G. Wilson.
Since the two transmitters are separated by 100 kHz, they do not interact with each other unless they produce interference due to the large field strengths involved.
My experience with transmitters very near each other, one at 1550 the other at 1680, was that the 1680 signal got received by the 1550 antenna and the audio from 1680 could be heard on 1550 in a distorted version.
By putting those transmitters 30-feet apart the trouble stopped.
TEST 2
Test 4
What about the CB rigs ruckers use ... of course that's with one TX. As I understand it interfereometer antennas work well for receiving over a wider directional area ... but what about transmitting?