Years ago I learned that antennas, transmitting different frequencies that are near each other on the dial, need to be located far apart in physical proximity to avoid the two signals mixing in the antenna through induction.
That’s why 1550kHz is transmitted from the Wintenna (a resonated metal window frame serving outdoors and indoors) on the north end, and 1680kHz is radiated from the Wintenna on the south, opposite end of the building, separated by 36’7″
But that’s not far enough apart, I learned this morning. With 1550kHz already on and transmitting the Alex Jones Show, I turned on 1680kHz and turned the modulation to zero for testing the carrier, but on a radio in a different room a frazzled sounding image from 1550 was clearly audible on the 1680 carrier.
As long as the two transmitters carry the same audio at the same time, this mixing of signals seems to be harmless, but it certainly is an unexpected event at the given distance.
Inductive Mixing/Intermod
Interesting isn’t it! Now imagine what happens beyond the audio anomalies..such as all those carriers combining to form new carriers elsewhere in the spectrum. The close proximity of them is enough for them to combine and create the issues you described in your post and is why separation of antennas on different frequencies while transmitting is key to preventing the problem. Filtering, even the location of one TX site to another all play a role in minimizing the problem.
RFB
Mixing
There is no harm in multiple signals existing in an antenna per se since the signals just add. There is harm though if the signals encounter a nonlinearity such as the final stage of a transmitter or even a rusty bolt or loose connection. Such bad connections need not be in the antenna itself to cause problems. A pile of rusty nails will radiate mixing products of two or more signals. A nonlinearity represents multiplication rather than simple addition. Anytime there is multiplication of the signals there will be sum and difference frequencies produced.
So, your observation and solution of separating the antennas is valid since it is highly probable that nonlinearity is there in the finals.
Neil
Good Point
As I try to get DRS2 back on, I
can tell you this, I know for
certain now, there will be
an FM on 90.9 (because it’s
already running, although it’s
a nat, compared to the other
transmitters I have here.)
I expect to have 13.560 going soon.
Then there will be the CC on 1020, which I
will be reworking soon.
And finally, the SS-Tran hopefully
will be back on 1690, although I
might actually come down to 1590,
which is clear during the day. More
radios tune there. I had a friend years
ago who was willing to listen in his
workshop, where he spent a lot of
time. But his radio only went up to
1610. I really should have gone down
to 1590 just for him. I wish I had.
Anyway, I’m not sure if I even want to
run all of these transmitters at the
same time. I will study it very carefully.
CARL has said he has checked all over
the spectrum with his receiver, so it
looks like his set-up is clean. But that
is a lot of RF clashing there.
Bruce, DRS2
At Close Range
At close range, mostly indoors, there are many rays across the whole dial from my antenna ranch configuration.
But I have walked many of the spurious signals outdoors, and they fade out very soon.
Have not discovered any big jamming signals that go anywhere worth mentioning.
Fortunate
“I have walked many of the spurious signals outdoors, and they fade out very soon. Have not discovered any big jamming signals that go anywhere worth mentioning.”
That’s fortunate. With all those transmitters sending out signals and receivers with their local oscillators and IF circuits I am amazed that any portion of the dial within 30 feet of everything is working.
Here is a test. Feed each TX with different audio, then see if there is an intermod problem!
Ha ha!
RFB
I personally run on 1570,
I personally run on 1570, precisely because older radios (and there are still a lot of them out there) generally can’t tune above 1610. And in my locale, there is a strong station on 1600.
I use an old Farnsworth tube AM radio to monitor my station. There’s something just natural about using a vintage tube AM radio to listen to vintage music. Plus it has the added bonus of heating up the studio during the winter.
Similar Situation
We have a very similar situation here, Radio Artisan.
There is a 5kW on 1600, and although I have a signal at 1680, I also get the idea of serving the old radio sets.
At 1570 we have a station across the river and through the woods which can be enjoyed just barely. They do good local talk in their little town.
But 1550 is a wonderful gobble of about four stations off in every direction that put a real barble-de-fobble on that channel. So I plop a signal there and all is well.
Ground lead no longer than whatever it takes to get 3-meters, counting antenna and lead in. Just trying to save that other guy the trouble.
Using Old Vaccum Tube Radios As Air Monitors
In my kitchen is an AM/FM
Zenith from the early 1960s.
This must have been a high end
radio at the time. It’s BIG and
has fantastic fidelity. (It’s just
a big table radio, there is no
stereo or anything like that.)
Anyway, it has to be recapped. You
can’t listen to the AM because too
much hum comes through. But on the
FM, especially if you turn up the
volume and set the bass and treble
controls correctly, most of the hum
goes away, and it really does sound
very very good.
Some day I would like to recap it.
Also, it doesn’t really tune. The dial
cord slips, so it is stuck on 90.9, my
FM frequency.
That’s fine for now.
Best Wishes,
Bruce, DRS2
Best Channels
“I personally run on 1570, precisely because older radios (and there are still a lot of them out there) generally can’t tune above 1610.”
Not entirely true. I’ve got a very old Emerson console radio/tv combo..black and white tv btw, circa 1962 and it can tune 1610 just fine. I love that console, nice Earth tone and REAL oak wood cabinet, not that flaky fake stuff, heavy as heck too!
Around here the daytime is great for MW frequencies between 1430 and 1570. Going beyond 1570 get’s too close to the TISk station here (WQH744) on 1610. At sunset everything between 1430 through 1650 is filled with junk and noise, making that part of the band useless. 1660 thru 1680 is clear during the day and night, 1690 has a Disney radio station in Colorado that comes in quite well for a 1kw nighttime station. (probably not lowering power like they are supposed to..perhaps our resident rule thumper can do something about that).
Even with older vehicles, most end up with after market radios installed and they can tune the extended band. A lot of folks have surround sound theater systems equipped with AM/FM stereos capable of tuning that extended band as well. New vehicle radios can obviously tune the extended band.
I put quite a considerable amount of time planning which frequencies I would use taking into account the ratio of radios that can tune 1670 and those that cannot. I see far more newer vehicles (1992 and up) on the road so no problem there. However I found that during the winter months the lower portion of the MW band works better for the CC system than the upper part of the band. So I have two CC stations, one on 1670 and one on 710. Later this summer after I get caught up with a few things a 3rd CC station will hit the power line airwaves on 920Khz…or maybe 1130Khz have not decided just yet..if at all. With the way things have been going lately with “LEGAL LICENSE FREE BROADCASTING”, and the obvious “go after em hot and heavy” prospective, I too am wondering if it’s time to let it all go silent. So far I have not been persuaded, or intimidated to go silent. It would take a lot more than even an inspection or threat of a shut down to make the decision.
In the meantime, the show must go on.
RFB
Don’t Let It Go Silent RFB
The Show Must Go On
Bruce, DRS2
A New and Different Antenna Observation
The antenna observation at the opening of this thread turned out to be a mistaken description of what was actually happening, which got explained on another thread.
This is a different report.
When the AMT5000 was first installed, I tuned it up for the “Wintenna” which serves indoors and outdoors from a souped-up aluminum window frame.
The original signal went a lot farther than the AMT3000s I’d been using, but although this setup has not changed, the transmission range changes everyday. I attribute this to weather related conditions.
During this mega-heat-wave the AMT5000 range has been very reduced, I imagine the drought has a lot to do with this. The ground is rock solid with no moisture.
But today the AMT5000 is shooting way out, like it did those first few days. Yet the only thing different is that the sky is loaded with fake storm clouds that are not producing rain.
But, is it the clouds? They are way up high, maybe miles up. How could a mousy part 15 signal be influenced by clouds a mile or more high?
What else could it be?
Clustered Antennas
My subject line was clustered antennas because i felt the other term was a bit to colorful lol anyway this thread brings to mind the cluster of antennas on a short tower in my town. The tower i am referring to is the London Police Dept./911 call center. There has to be at least 5 or 6 antennas on that 30 foot tower. Most of them do not have stand off mounts so they are less than a foot or two from the tower and each other. Judging by the frustration in the police officers voice when trying to communicate away from town. The reception is horrible when a police cruiser gets out further than a few miles from Main St and the officer has to repeat his message. I don’t know who did their radio install but with all those antennas at close proximity of each other it is not surprising they have this problem.