This is in a manner of applogy. the technology exists, and is being tested. The interference from Cuba plus the Turks and Caicos is so significant that the airborne broadcast can not be heard anywhere. This is, as best I can see, a boondoggle that only the government could have created as it defies all logic fromt he technical, operational and fiscal aspects. Again, my apology for doubting that the government could have invented such a thing.
The sad thing is that the US government has ruined the operation of a responsible eveangelical broadcaster, RVC. Now no one can be heard, and 530, used with low power in Costa Rica and Ecuador, is pretty much wiped out as a useful frequency.
>
That's something I don't understand about end fed Zepps. if one side of the bal. feed is connected to nothing, it seems to me, the feed is unbalanced and will radiate. i always thought a bal. feed had to be feeding a symmetrical antenna, for example, a center fed 1/2 wave in order for the feedline current to be equal but opposite and cancel each other's fields.
>
You're still thinking "Broadcasting". In their application, I don't think they care too much about what the field strength is at any given point(s).
As long as they're heard.
Couldn't be measured, anyway, with any degree of accuracy, as the plane is constantly in motion.
>
The Zepp is a horizontal half-wave fed radiator, fed by balanced, open-feeder transmission line. One side of the balanced line is connected to one end of the radiator (at the voltage maxima point) -- while the other side of the open feeder line is left floating in most ground-based Zepp installations.
Since the Zepp is a half-wave radiator, it is not counterpoised against anything. Even though one side of the open transmission line is left connected to nothing, the line still performs its function by canceling equal but opposite line currents to ensure that the line does not radiate.
>
I don't think so. The zepp antenna, evidently from the WWI era, predates coax. Here's a web reference on the zepp, and it's entirely made out of wire (no shields):
>
If memory serves ( which, as stated earlier, I did not look it up ) I thought Clive's description ( and mine ) WAS a Zepp ?
|
Direct, line of sight, just like FM.....
PLUS the over-the-horizon characteristics of MW groundwave ( which, according to some theories, is just an artifact of the direct wave passing over head anyway, and is induced on the surface of the ground as it passes ) PLUS the skip from the incident angles at which the ground is struck.
In other words, more than you would think !
>
Then there's the "zepp" antenna, an end-fed half-wave wire, so named because it was first used on Zeppelins. The zepp still needs at least a minimal counterpoise (which could be the airframe), but not much current needs to flow into it since the zepp is voltage fed. Clive's idea of a sleeved dipole is probably better than a zepp.
>
I should think that a sleeve dipole would work just fine.
All you'd need would be a half wavelength length of feeder and a quarter wave piece of outer foil for the return screen/screen.
>
In my long misplaced manuals for the ART-13 (WW-II aircraft xmtr by Collins tuning 2-18 MC) there were directions for using this type of antenna. for various bands.
With am additional unit installed (exact designation forgotten by me) it was possible to operate as low as 2,000 KC (I think that number is correct). Manual had tables for length of wire being towed and settings for initial tuning at various frequencies.
I believe that the transmissions were intended for aircraft communications and the intended for the general public.
The above is as best my memory can recall.
>
They also do this with other types of aircraft.
Definitely out of the box thinking here.
Magic, pure magic.
>
Hemos estado haciendo pruebas en 530, pero debido a las interferencias de los "Turcos" y del gobierno represivo de Fidel, no han sido satisfactrios ni productivos. No sé se seguirán ni si se harán todos los sábados.
>
A "Zepp" is basicly a coaxial sleeve variation, and is every bit as efficient as a 1/4 wave over a full ground plane.
Basicly, once the plane is aloft, you just spool it out, remembering to wind it back in before landing.
If memory serves ( without looking it up ) a true Zepp was a 3/4 wave antenna, not unlike a 1/2 wave over 1/4 and very, very efficient.
The coverage is not at all limited, and performs quite well.
>
Not a notable frequency for conventional propagation techniques, but you are talking about an airplane at 10-20 thousand feet. Look at the path loss it is direct line of site to everything in it horizon. I think we need to get outside of the broadcaster's box.
>
My guess is that the fuselage of the airplane is the counterpoise. Not a super efficient one, but one, nonetheless.
>
An antenna is an antenna. You are thinking inside the box and need to look at it differently. The old VOA in Punta Gorda, Belize used two horizontal dipoles. There was no ground connection, it was all skywave and that was the intent. A long wire from the plane would be just that and would be skywave direct to the receiver. Why not?
>
It must not be the most efficient transmission. But isn't this simply the way early aviation (i.e. dirigible) radio was conducted? Trolling for seagulls.
Subject: RE: [BC] AMs from Airborne Airplanes
> How does an antenna dropped from a plane radiate without a ground system
> or
> a counterpoise system? Any idea of how efficient such radiators are? I am
> intrigued by one on 530, where the wavelength is near 600 meters... I
> would
> assume the coverage is very limited.
>
My suspicion is that the 50Kw over salt water would be the better choice.
However. it wouldn't have been a visible monument that would have appeased those clamoring for anti-Castro propaganda in Florida. I think it was more a political motivation rather than a technical one.
Military friends explain that AM is used in aviation because two signals can be heard. That's important in emergency situations where the capture effect of FM would prevent an emergency or other warning signal from being received. My brother-in-law is the head of maintenance for US Air at Bradley International in Hartford. His explanation was the same.
Your question has been asked before. I asked a few friends in the military with whom I often have breakfast if they've ever heard of a medium wave station operated from a plane. None had. However, they had heard of shortwave being used for propaganda purposes in areas of the world where it was the only means of communication. Everyone had shortwave receivers.
>
When I first read this about an IBB/OCB Radio Marti transmission from an airplane on 530 kHz, I thought your information was mistaken since I work for IBB and had never heard of it. I had only heard of the airborne TV transmissions. Sure enough, it is listed on the frequency schedule on the Radio mart web site. It appears to be only 6 to 10 PM on Saturdays. It is listed as an airborne transmission.
I am very curious and fascinated now. I 'll have to see if I can find out any technical details. It isn't likely they are running very much power. I expect the antenna is a long trailing wire.
I'm the manager of an IBB site that transmits only VOA programming. We are located on the Equator off the west coast of Africa on Sao Tome Island.
>
The Commando Solo folks from the 193rd Special Ops Wing of the PA Air National Guard have been broadcasting PSYOPS messages from aircraft in the MW, SW, FM, and TV bands in virtually every major conflict involving the US since 1968. They presently operate 6 specially modified EC-130E airborne broadcast stations. The MW transmitters are frequency agile Rockwell-Collins 10 kw units. The MW antenna is deployed from the belly with a 500 pound weight on the end to keep it relatively vertical. One of the cable science channels produced a very interesting 1 hour program about these guys a couple years ago that I still see on the air every once in a while. In Iraq they also air dropped hundreds of single channel MW receivers tuned to their frequency and equipped with hand-crank power generators since there were very few radios available to the natives. Do a Google search for "Commando Solo" and you will find a huge amount of info.
The sad thing is that the US government has ruined the operation of a responsible eveangelical broadcaster, RVC. Now no one can be heard, and 530, used with low power in Costa Rica and Ecuador, is pretty much wiped out as a useful frequency.
>
That's something I don't understand about end fed Zepps. if one side of the bal. feed is connected to nothing, it seems to me, the feed is unbalanced and will radiate. i always thought a bal. feed had to be feeding a symmetrical antenna, for example, a center fed 1/2 wave in order for the feedline current to be equal but opposite and cancel each other's fields.
>
You're still thinking "Broadcasting". In their application, I don't think they care too much about what the field strength is at any given point(s).
As long as they're heard.
Couldn't be measured, anyway, with any degree of accuracy, as the plane is constantly in motion.
>
The Zepp is a horizontal half-wave fed radiator, fed by balanced, open-feeder transmission line. One side of the balanced line is connected to one end of the radiator (at the voltage maxima point) -- while the other side of the open feeder line is left floating in most ground-based Zepp installations.
Since the Zepp is a half-wave radiator, it is not counterpoised against anything. Even though one side of the open transmission line is left connected to nothing, the line still performs its function by canceling equal but opposite line currents to ensure that the line does not radiate.
>
I don't think so. The zepp antenna, evidently from the WWI era, predates coax. Here's a web reference on the zepp, and it's entirely made out of wire (no shields):
>
If memory serves ( which, as stated earlier, I did not look it up ) I thought Clive's description ( and mine ) WAS a Zepp ?
|
Direct, line of sight, just like FM.....
PLUS the over-the-horizon characteristics of MW groundwave ( which, according to some theories, is just an artifact of the direct wave passing over head anyway, and is induced on the surface of the ground as it passes ) PLUS the skip from the incident angles at which the ground is struck.
In other words, more than you would think !
>
Then there's the "zepp" antenna, an end-fed half-wave wire, so named because it was first used on Zeppelins. The zepp still needs at least a minimal counterpoise (which could be the airframe), but not much current needs to flow into it since the zepp is voltage fed. Clive's idea of a sleeved dipole is probably better than a zepp.
>
I should think that a sleeve dipole would work just fine.
All you'd need would be a half wavelength length of feeder and a quarter wave piece of outer foil for the return screen/screen.
>
In my long misplaced manuals for the ART-13 (WW-II aircraft xmtr by Collins tuning 2-18 MC) there were directions for using this type of antenna. for various bands.
With am additional unit installed (exact designation forgotten by me) it was possible to operate as low as 2,000 KC (I think that number is correct). Manual had tables for length of wire being towed and settings for initial tuning at various frequencies.
I believe that the transmissions were intended for aircraft communications and the intended for the general public.
The above is as best my memory can recall.
>
They also do this with other types of aircraft.
Definitely out of the box thinking here.
Magic, pure magic.
>
Hemos estado haciendo pruebas en 530, pero debido a las interferencias de los "Turcos" y del gobierno represivo de Fidel, no han sido satisfactrios ni productivos. No sé se seguirán ni si se harán todos los sábados.
>
A "Zepp" is basicly a coaxial sleeve variation, and is every bit as efficient as a 1/4 wave over a full ground plane.
Basicly, once the plane is aloft, you just spool it out, remembering to wind it back in before landing.
If memory serves ( without looking it up ) a true Zepp was a 3/4 wave antenna, not unlike a 1/2 wave over 1/4 and very, very efficient.
The coverage is not at all limited, and performs quite well.
>
Not a notable frequency for conventional propagation techniques, but you are talking about an airplane at 10-20 thousand feet. Look at the path loss it is direct line of site to everything in it horizon. I think we need to get outside of the broadcaster's box.
>
My guess is that the fuselage of the airplane is the counterpoise. Not a super efficient one, but one, nonetheless.
>
An antenna is an antenna. You are thinking inside the box and need to look at it differently. The old VOA in Punta Gorda, Belize used two horizontal dipoles. There was no ground connection, it was all skywave and that was the intent. A long wire from the plane would be just that and would be skywave direct to the receiver. Why not?
>
It must not be the most efficient transmission. But isn't this simply the way early aviation (i.e. dirigible) radio was conducted? Trolling for seagulls.
Subject: RE: [BC] AMs from Airborne Airplanes
> How does an antenna dropped from a plane radiate without a ground system
> or
> a counterpoise system? Any idea of how efficient such radiators are? I am
> intrigued by one on 530, where the wavelength is near 600 meters... I
> would
> assume the coverage is very limited.
>
My suspicion is that the 50Kw over salt water would be the better choice.
However. it wouldn't have been a visible monument that would have appeased those clamoring for anti-Castro propaganda in Florida. I think it was more a political motivation rather than a technical one.
Military friends explain that AM is used in aviation because two signals can be heard. That's important in emergency situations where the capture effect of FM would prevent an emergency or other warning signal from being received. My brother-in-law is the head of maintenance for US Air at Bradley International in Hartford. His explanation was the same.
Your question has been asked before. I asked a few friends in the military with whom I often have breakfast if they've ever heard of a medium wave station operated from a plane. None had. However, they had heard of shortwave being used for propaganda purposes in areas of the world where it was the only means of communication. Everyone had shortwave receivers.
>
When I first read this about an IBB/OCB Radio Marti transmission from an airplane on 530 kHz, I thought your information was mistaken since I work for IBB and had never heard of it. I had only heard of the airborne TV transmissions. Sure enough, it is listed on the frequency schedule on the Radio mart web site. It appears to be only 6 to 10 PM on Saturdays. It is listed as an airborne transmission.
I am very curious and fascinated now. I 'll have to see if I can find out any technical details. It isn't likely they are running very much power. I expect the antenna is a long trailing wire.
I'm the manager of an IBB site that transmits only VOA programming. We are located on the Equator off the west coast of Africa on Sao Tome Island.
>
The Commando Solo folks from the 193rd Special Ops Wing of the PA Air National Guard have been broadcasting PSYOPS messages from aircraft in the MW, SW, FM, and TV bands in virtually every major conflict involving the US since 1968. They presently operate 6 specially modified EC-130E airborne broadcast stations. The MW transmitters are frequency agile Rockwell-Collins 10 kw units. The MW antenna is deployed from the belly with a 500 pound weight on the end to keep it relatively vertical. One of the cable science channels produced a very interesting 1 hour program about these guys a couple years ago that I still see on the air every once in a while. In Iraq they also air dropped hundreds of single channel MW receivers tuned to their frequency and equipped with hand-crank power generators since there were very few radios available to the natives. Do a Google search for "Commando Solo" and you will find a huge amount of info.