Maybe. I thought it was Cape Cod, but I read it at least 100 years ago.
I remember enormous rhombic, something like one mile on each side. Is that the same place?
Hmm. I wonder if you're old enough to remember Murray the K, Dick Biondi, Dan Ingram, and those guys? Up until 1967 or so, that *was* music radio for anyone under 25. In the NYC area, FM started with its prog-rock format around 1966 or '67. ("Roscoe, don't you know?")
I used to try to get Wolfman Jack on that 100,000 Watt Mexican station, but I could never quite pull it in on my much-modified Hallicrafters S-107. With the 250 foot longwire I could tell it was his voice, but that was about it.
I thought Jerry said it worked because it *did* couple to the vertical element.
It doesn't have to *be* any particular size to do that, it doesnt have to be longer than 1/4 L to do so, in the same way that the car antenna whip is certainly shorter than that (at 1 MHz), yet it works just fine to couple to the incident rf field.
Doesn't have to be. Radials at the base of a true resonant antenna are elevated above gound, and are attached to the shield of the incoming feedline. They're not at 'ground' potential at the base of the mast, yet the serve quite well.
I think this statement is at odds with the information in the handbook. Rf currents flow in the radials and there will be rf voltages along their length, with respect to a ground rod at teh base of the antenna.
There is no requirement for them to be at some arbitrary voltage for the antenna to work.
Looking in the handbook, there seems to be very few instances where the term "ground plane" is used in reference to antennas. There may be a reason for this....
There is alot-alot of conflicting information from recognized professional antenna gurus on wire size, length and number of radials for a 1/4 wave stub antenna fed against a set of wires that represent the "ground". Although I have *my* oppinion about how the 1/4 wave stub above the ground works, I sure wouldnt try to convince anyone that they dont know as much as I do. In other words - the ground plane is just about anything you want to make and call a ground plane.
If you want to get a crowd together to give their thoughts, try posting the question on Rec Radio Amatuer Antennas.
rec.radio.amatuer.antennas has a thread still being posted to concerning radials. Roy Lewallen has gotten involved with it. He might be one of the best sources of good antenna theory information available.
Something I recently learned thru the antenna group is that only two radials can result in excellant performance of a 1/4 wave antenna.
Well, it's not at odds with the information in the ARRL Antenna Handbook. If there is RF on the radials, the radials are radiating -- partly into the ground, and partly at a very high angle, in a polarity opposite to that of the vertical radiator.
You have a kind of bent dipole, asymmetrical, with higher-angled polarization than from a true ground plane and with losses dependent upon the height above ground. One characteristic of a true ground plane is that the losses, and radiation angle, are independent of height above ground.
You'd also have current flowing on the shield of your feedline, but that, of course, can be eliminated by inductive coupling to the antenna.
Again, you can load it, and it will radiate, but the result is not the same as with a true ground plane.
The old Antenna Handbook discusses them in several references, for different frequencies and applications, but not in enough detail to satisfy me.
Jim, the "ground" or "image" plane is a concept, not an object. It is the assumed perfectly conducting plane that you use when you calculate the charges. Like the physics guys- "assume a spherical auto". How close you have to get to that perfectly conducting infinite plane depends on what you need out of the antenna. Kraus gives a rule of thumb of about a half wavelength for a counterpoise for a 1/4 wave stub, then goes on to say "it should be noted that the radiation pattern of a vertical 1/4 wavelength stub on a _finite_ ground sheet differs appreciably from the pattern with an infinite sheet". So one of the deciding factors for the question of how long the "ground" radials have to be is the desired takeoff angle.
I'm still missing the relationship, but I miss a lot of things. And I learned a different definition of coherent.
So I should translate this as: "an antenna has a bandwidth if you design it that way"?
Most I see look like log periodic antennas. A group of dipoles in an array. And as antennas gather energy and filters block it, I don't see much of a resemblence. But if it helps you visualize something, go for it.
We have already gone over why MF broadcast antennas are not optimized. I forgot to disabuse you of the notion that transmitting antennas cannot be broadband. Offhand, I can point you to about 300,000 antennas that transmit over a 3f range.
Again, making a better MF antenna doesn't buy you anything, so why would you do it?
The whip on most cars (or fast helix if they use that) is cut for about
100 MHz. That means the antenna is resonant at that frequency. At that frequency, it doesn't need any lumped elements. And the power limit is determined by the Ohmic resistance in the wire and radiating element. And 100 MHz is a VHF frequency.
Only in limited cases. Like low frequencies.
We will have to agree to disagree on this one. Perhaps you can point out a receive antenna other than those used on LF and MF (even HF receivers use antenna tuners) that is "untuned".
Thanks. I was perusing my arrl handbook last night, and there was a design for exactly such an item. Basically a wire vertical with two drooping radials off the bottom.
The 'radials' were nothing more than 1/4L wire, with an insulator twisted in the middle of it. They sloped off to trees. From the insulator there was one more vertical element that went up into another tree. The feedline connected at the insulator.
There's always some current flowing on the feedline, unless there's a balun or some ferrite beads on it.
There's the crux of the matter. The result is 'not the same' which I suspect means 'not as good.' 100% correct.
Any antenna for 1 MHz in a car is not going to be as good as, can never be as good as, a true resonant system. That doesn't mean one cannot use the same terminology to describe it though.
You might say this is imprecise - that a 400 MHz antenna in the same location on a car does indeed have the exact same sheet of metal as a "true" goundplane, because of the wavelenght involved. And that extending that nomenclature down to *one* MHz amounts to an error, a mistake - because it's less descriptive.
Well Jerry, since there's not enough room on my bench for the car, is there a way I can get the radio to work well on the bench? My shop is a metal building. Could it take the place of the car? Thanks, Eric
Thanks Don, I'll give that a try. The radio sounded real good in my car and since it was replaced with a cd player it would be nice to use it in the shop. ERS
Forget about the ground plane, etc. If your radio worked ok in the car and doesn't work ok in your METAL SHOP, then I suggest the problem is the metal shop. Put up an outside antenna above and away from the shop, run that samewire to the antenna input on your radio and your reception troubles will be over.
The fact is - I dont really know if the car antenna will be adequet for your receiver needs even if it gets located up on the roof. I would advise you to try it with some temporary supports before spending alot of time and energy. I know that there are alot of guys who spend alot of time and build electronic devices in an effort to get stub antennas on the roof to provide decent signal for an AM receiver. There might be a difference between a car, isolated from ground, and a building thats attached to ground, That building ground might impose different conditions on the feed point conditions. Also, the long coax feed from the roof really shunts alot of the received signal away from the receiver.
I hope you do try mounting that car antenna up on the roof. I'd be interested in the results.
PS After hearing about big AM loop antennas thru Don Foreman, I just began building one. If it works in the desert, I'll post the result.
PS2 There are some cars that include amplifiers at the base of the antenna. VW did it and probably still does on some models.
Btw Jerry...just out of curiosity, since you are too modest to mention it on your own..would you care to tell me what your background in antenna construction/art/theory is? And perhaps give some examples of your work?
Gunner
It's better to be a red person in a blue state than a blue person in a red state. As a red person, if your blue neighbors turn into a mob at least you have a gun to protect yourself. As a blue person, your only hope is to appease the red mob with herbal tea and marinated tofu.
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