Hf
iakobos,
small correction......
The antenna itself is rarely resonant: the tuning circuit provides an impedance transformation such that the correct load is presented to the transmitter (usually 50 +j0). This may appear academic until you have to start working out how much power is radiated (or more usually, turned into heat!)
The argument as to whether or not the transmitter should match the load is a different one which has occupied technical journals in vituperative correspondance, and I won't raise that here!
small correction......
The antenna itself is rarely resonant: the tuning circuit provides an impedance transformation such that the correct load is presented to the transmitter (usually 50 +j0). This may appear academic until you have to start working out how much power is radiated (or more usually, turned into heat!)
The argument as to whether or not the transmitter should match the load is a different one which has occupied technical journals in vituperative correspondance, and I won't raise that here!
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Radeng,
You did not correct me, you just added a point intended for the non-experts.
An antenna is always resonant somewhere, the problem is, nowhere else.
Therefore the TU or ATU that will fool the transmitter to think he married the right bride.
You did not correct me, you just added a point intended for the non-experts.
An antenna is always resonant somewhere, the problem is, nowhere else.
Therefore the TU or ATU that will fool the transmitter to think he married the right bride.
When I were a lad, we thought that maximum deflexion on a meter was A Good Thing. So the ATU ('Wavemeter') attached to our school ex-WW II Wireless Sets No. 12 ('Twelve Set') was always adjusted to give peak meter values.....
That was in 1966.
15 years later, along comes (legal) CB radio in the UK. I learn about the mysteries of VSWR and tuning antennae for minimum SWR. After much tweaking and adjusting, I obtain a good match across...err, 80 channels in the 11 metre band in my car with a 'disguise' base-loaded 1/4 wave whip.
Which rather explained why there were so many complaints about the interference our dreadfully mismatched longwire antenna used to cause at school! And no wonder it was so difficult to contact other stations on our 5 HF spot frequencies (on or about 2-7 MHz. Or Megacycles as it was back then!)
A little knowledge is a dangerous thing!
That was in 1966.
15 years later, along comes (legal) CB radio in the UK. I learn about the mysteries of VSWR and tuning antennae for minimum SWR. After much tweaking and adjusting, I obtain a good match across...err, 80 channels in the 11 metre band in my car with a 'disguise' base-loaded 1/4 wave whip.
Which rather explained why there were so many complaints about the interference our dreadfully mismatched longwire antenna used to cause at school! And no wonder it was so difficult to contact other stations on our 5 HF spot frequencies (on or about 2-7 MHz. Or Megacycles as it was back then!)
A little knowledge is a dangerous thing!
Nope - it was quite legal to use the school shortwave transmitter and receiver on the official frequencies assigned for use by the Combined Cadet Force and Army Cadet Force.
And the FM CB frequencies were also legal; 40 channels were approved in 1981 and another 40 a few years later. Although I do admit to setting up the antenna to cover the whole frequency spectrum approved for use in the UK before the lower 40 channels were released!
88s (no tongues!)
And the FM CB frequencies were also legal; 40 channels were approved in 1981 and another 40 a few years later. Although I do admit to setting up the antenna to cover the whole frequency spectrum approved for use in the UK before the lower 40 channels were released!
88s (no tongues!)
iakobos,
>An antenna is always resonant somewhere, the problem is, nowhere else.
There's a nice area for argument! Depends on the antenna, and what you mean by resonance......e.g. a cavity backed spiral antenna used for Electronic Counter Measures is a reasonable match from 2 - 18GHz. Where is it resonant?
Sadly, the older I get, the more I realise that I know less and less about radio engineering, when it really ought to be more and more.....
>An antenna is always resonant somewhere, the problem is, nowhere else.
There's a nice area for argument! Depends on the antenna, and what you mean by resonance......e.g. a cavity backed spiral antenna used for Electronic Counter Measures is a reasonable match from 2 - 18GHz. Where is it resonant?
Sadly, the older I get, the more I realise that I know less and less about radio engineering, when it really ought to be more and more.....
Iakobos,
It certainly receives......But what about the whole family of travelling wave antennas? Log periodics (which you can argue use multiple resonances, although I'm not sure about the Green's equation boundary conditions), terminated rhombics and Vee beams, even Discones? Slots are another case, too - not sure how widely used these are on aeroplanes at HF these days.
Getting a bit academic for this fora.......
One problem is definitely that things you'd like to do for antenna efficiency on aircraft don't always sit well with either aerodynamics or structural requirements.
It certainly receives......But what about the whole family of travelling wave antennas? Log periodics (which you can argue use multiple resonances, although I'm not sure about the Green's equation boundary conditions), terminated rhombics and Vee beams, even Discones? Slots are another case, too - not sure how widely used these are on aeroplanes at HF these days.
Getting a bit academic for this fora.......
One problem is definitely that things you'd like to do for antenna efficiency on aircraft don't always sit well with either aerodynamics or structural requirements.
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Every good rule has an exception, hence the good rule.
Aerial systems (much more poetic than antenna isn't it ?) have their exception.
TW are not used for transmission.
Rhombics (terminated or not), vees (ditto) are resonant antennas, which can be used on a wide spectrum provided there is a matching device, in which case they are used in the non-resonant "mode", usually with a purpose (directivity/gain).
Discones are the poor man's antenna and the scanner delight...
Nowhere that good but nowhere really that bad.
Usually not intended for transmission either.
Terminated folded dipoles are resonant antennas to which a nice resistor has been added. The most sophisticated dummy load so far.
If aircrafts could just stay on the ground it would make radio engineers so much more happy and the quality of communications would be greatly improved. What can you do ???
Aerial systems (much more poetic than antenna isn't it ?) have their exception.
TW are not used for transmission.
Rhombics (terminated or not), vees (ditto) are resonant antennas, which can be used on a wide spectrum provided there is a matching device, in which case they are used in the non-resonant "mode", usually with a purpose (directivity/gain).
Discones are the poor man's antenna and the scanner delight...
Nowhere that good but nowhere really that bad.
Usually not intended for transmission either.
Terminated folded dipoles are resonant antennas to which a nice resistor has been added. The most sophisticated dummy load so far.
If aircrafts could just stay on the ground it would make radio engineers so much more happy and the quality of communications would be greatly improved. What can you do ???
Iakobos,
>If aircrafts could just stay on the ground it would make radio engineers so much more happy and the quality of communications would be greatly improved.
Yes, we could use plug in telephones and get reliability! Having made a living for over 40 years designing radio systems, I maintain that the use of radio should be the last resort, especialy where you want reliability..........
>If aircrafts could just stay on the ground it would make radio engineers so much more happy and the quality of communications would be greatly improved.
Yes, we could use plug in telephones and get reliability! Having made a living for over 40 years designing radio systems, I maintain that the use of radio should be the last resort, especialy where you want reliability..........
