Under present plans, there will be four distinct outdoor antennas, two for MW, and one each for LW and SW. Each of these installations requires ground radials.
Under present plans, there will be four distinct outdoor antennas, two for MW, and one each for LW and SW. Each of these installations requires ground radials.
1680 AM will be about 110-feet way up in the rear, placed as far away as possible so that indoor reception comes from “off in the distance.” 3-meter vertical with transmitter at the ground;
1550 AM will be about 20-feet toward the front side and share its tower with flowering vines. It is understood the vines could impede the efficiency, but will be a design factor. 3-meter vertical with transmitter at the ground;
13.560 SW does not yet have a definite location, but the idea of using the house or chimney for the high point of an inverted-V is being considered, but the main antenna element needs to be away from the building, so maybe not. But keeping it close to the building would minimize the length of the transmission line. The transmitter will be indoors;
164 LW is baffling because erecting a 50-foot vertical is desirable but possibly not feasible, so we need a “plan B.”
These installations each need ground radials. But instead of four distinct situations, perhaps some of them can be combined… like SW and LW sharing a single set of radials. An opportunity to experiment and invite opinions.
mighty1650 says
In Theory
In Theory they could all share a ground system.
So long as proper filters are in place.
In Fact,
you could probably just Diplex the AM stations.
Carl Blare says
Not Sure
Hello The Crow… I am interested in the concept of sharing radials among transmitters, but I’m of the impression that AM transmitters that are nearby in frequency, let’s say 1550 and 1680, need to be far apart to avoid the transmit antennas acting as receivers and back-modulating the audio from the other transmitter.
Do the filters go on the ground radials, or on the RF antenna outputs?
If the transmitters are diplexed, can this be done without significant power loss?
I have a post elsewhere about the idea of diplexing, or combining, before the final stage, so that the sum output could be kept at 100mW to the final. Of course such a system would have the same audio on both frequencies, which is fine for me.
RFB says
AM Diplexing
Diplexing AM transmitters, especially those in the 100mW power range is not a complex matter at all. And it wont require massive resonant tanks or huge coils the size of your house and all that. I recall someone posting something about this saying the diplexer would be huge.
Wrong.
Now if we were attempting to diplex two or more high powered transmitters, then ya you need a diplexer capable of handling those power levels as well as the reject loading.
An example of this is the size of the loading coil inside an AMT5K versus a final tank coil inside a 1Kw transmitter….very BIG difference!!
I’m not so sure about combining prior to a final “final”. That final would have to be incredibly wide band and extremely linear across that bandwidth range. Not saying its impossible, just not easy.
Plus if you combine everything prior to a final, then to meet the 100mW limit of that final, each signal combined going into it would have to be reduced by a factor of the number of combined signals so that the 100mW limit is not exceeded by that combining. So that means each signal will be less than they would be going into their own final at 100mW and then into their own antenna or combiner and then into a common antenna.
RFB
Carl Blare says
DIPLEXER DISCUSSION
Regarding having the diplexer before the final stage, your statement RFB that each (of two) signals would need to be reduced to 50mW in order to sum up to 100mW at the final. I thought so, but I was hoping someone else would say it to verify what I thought. However I think there is another way of looking at the problem.
I belief that each (of two) signals, 1550 and 1680, could be combined as 100mW + 100mW = 200mW into the final, because the intent of the rule 15.219 is that EACH INSTANCE (each individual frequency) is permitted 100mW into the final.
RFB also indicated that the outputs of two transmitters can easily be diplexed. Can you draw a diagram for combining 1550 and 1680? I will try it.
RFB says
Drawing
“Can you draw a diagram for combining 1550 and 1680? I will try it.”
I can save us both time on this. Give thanks to Neil for linking to it.
There is one on the Jim Hawkins site Neil linked on another thread..here is that drawing…
http://hawkins.pair.com/wcbs_wfan/diplexer_schematic.jpg
A basic drawing, but a great starting point. As you can see, one part of the diplexer rejects the other while allowing resonance to its input so it can pass through to the common antenna.
Principles of a diplexer are similar to a low pass filter or high pass filter, even a band pass filter. These filters allow passing of one frequency while shunting unwanted frequencies to ground through tuned circuits. In a larger diplexer, this is done usually in resonant cavities or canisters.
For our much smaller diplexer, the inductors can be simple air wound coils with a tap, or variable inductors. Each section of your diplexer will have two inductors, one to tune your pass frequency, one to tune the reject frequency.
Now keep in mind that the two frequencies your going to work with are very close to each other, so this diplexer will have to be capable of narrow bandwidth notching otherwise you may run into the reject side of each part of the diplexer shunting out some of the signal that you want to pass. So each inductor circuit will have to be designed carefully and very close to the resonance of the frequency being worked with. In other words, you do not want the inductor built for 1550 reject to be too “loose” in bandwidth and partially reject 1680 at the same time.
Same in the opposite direction, where the inductor for 1680 pass does not have too big an opening in its window and let 1550 slip through too. This is crucial because if any of the inductor circuits are too wide in bandwidth, then the isolation between the transmitters will also be affected and the diplexer just becomes nothing but a mess of coils and caps absorbing the signal energy and very little isolation between the TX’s and little signal going to the antenna.
Another thing to keep in mind is the main resonance impedance of the antenna being used. Your diplexer inputs and output will have to maintain this impedance for both transmitters and impedance for the antenna at the output. This maintains maximum energy transfer efficiency as well as reject efficiency and isolation efficiency.
Hope that helps.
RFB
Carl Blare says
Spinning Wheels
The description of what needs to be done and the component parts is good, and I hope experiments are done in this area for Part 15.
But the specialized transmitting components that would permit such a project do not exist.
It would be a whole new design project for Part 15 in the future, but could be useful to those who want to build scale-models of real-world transmitter antenna clusters.
RFB says
Nothing Special At All
“But the specialized transmitting components that would permit such a project do not exist.”
On the contrary. Parts for constructing a diplexer are all around you.
Wire for winding the inductors, capacitors for coupling, some sort of enclosure, and reject load resistors depending on operation impedance.
Again since this is flea power and not watts, the thing will probably not be any larger than a typical outdoor weather proof box most use right now on their 3 meter sticks.
Basically this thing is nothing more than a collection of resonant circuits, where one part passes the signal to the antenna, while the other part passes the reject signal to a dummy load or to ground.
It really is nothing different from a loading coil arrangement for a radiating element like that found in 3 meter stick setups.
RFB
Carl Blare says
Simplification
Making life simpler I am tonight closing 1550kHz and putting all 3-meter antenna activity on 1680kHz. After all, the two footprints were just about identical. All it achieved was making kdx more prominent on the upper end of the dial, but that’s at odds with my objective of operating a personal radio station for my own benefit and not a community radio station.
However, somehow 970kHz Carrier Current will be opened up, when we find a way of gathering the needed equipment. Will that be a community radio station? Uh, dunno.
But for now we have just cut the need for towers and radials by 50%.
MICRO1700 says
That’s A Lot Of Stuff
Y’know, Carl that’s pretty ambitious.
Of course, do what ever you want. But after
putting a bunch of Part 15 set-ups outside,
I can tell you this.
You might want to get one going first, and
improve it as it goes along. When that first set-up
is working the way you want, then you will be able
be able to go from there and add more.
I bet the AMT-5000 will work GREAT in an outside
set-up with the internal inductor. I really think that’s
what Phil wanted to do for all of us. He wanted to
make a transmitter that you could put outside – tune
up – and run. (Without having to build that loading coil
for the 3 meter stick.)
I always start with 2 radials, then 4, and then 8. After that
I fit whatever I can fit. As you do this, you can watch the
performance improve and retune the system as needed.
You will get excited as you see the range go up. In my
last set-up I got up to 17 radials, but I lost one of them
in the ground, so it really turned out to be 16.
Putting radials down is not that hard. The problem is you
have to do a lot of kneeling on the ground. I get a little
spade and pull the ground apart and shove a length of
wire in the ground. Then there was that other guy who
anchored radials down with coat hangers that were shaped
like upside down Vs. After a while the grass grew up and
the radials disappeared. And some people do water the
radials. One guys had some kind of contraption on his
hose that was on some kind of timer, and it ran water
into the system at certain times.
I have never been able to do ground rods. You should have
them, but my yard is so full of rocks underneath, that I have
never been able to get anything in there. Some of my ground
radials were 20 feet long and some were 10. Based on the
Part 15 AMT-3000 test video that we all watched recently –
well – that guy had 20 foot radials all around. So – I really don’t
know – but 20 sounds better.
As for the longwave thing – a guy had success with just a 30 foot
pole. I still think at most – on longwave AM – you will just get
a couple of thousand feet. With a really really good radio. Most
multiband portables have terrible LW sections. Even my Sony 2010’s
LW section is not that great. That goofy $5.00 boat radio works
much better. (But it doesn’t have a BFO.)
The plan here is actually to get the CC on and then the outdoor set-up
for AM. My friend in NJ has wonderful intentions and he is a fabulous
engineer. (I had given him the LPB RC-6A to work on.) He is also
a very very good hearted soul. But I really don’t think he has the time for
the RC-6A. So I’m going to endeavor to get it back from him. The plan
is to replace the tubes (all 6AL11s.) I think this rig is really made for
the low end of the band. So the plan is to get a crystal for 1020 kHz from
AF4K, and run it daytime only. Crystals for less than 1000 kHz cost a
fortune. But a 1020 rock from AF4K is only $14.00 – assuming he still
has them.
Meanwhile I putt away on the Gates board. I’ll post some of that info on
the Vintage Control Board thread. We may have to move – and if that
happens – the outside Part 15.219 set-up may be history. We’ll see.
In some ways – right now – my Part 15 station is more like a little radio
museum that a working broadcast set-up.
I guess that’s OK.
Best Wishes,
Bruce, DOGRADIO STUDIO 2
andre_pro20g says
Radial length
Hi,
My radials are 20′ long. The reason I chose 20′ is because I read somewhere that longer was better and in my mind (a very lonely world), it made sense that radials should be at least as long as the antenna is high. Since my 3 meter antenna is mounted on a 2 meter mast, I rounded it out to 20′.
RF is not my expertise so I based a lot of my installation on ideas and opinions from those who know more (most of you guys).
But I am curious on how a common radial/ground setup works out.
Good luck Carl.
Andre
RFB says
Sharing Is Giving
“I based a lot of my installation on ideas and opinions from those who know more”
That’s what this forum and its members are her for…share what we know and help others discover!
Carl will get that ultimate antenna going soon!
RFB