Antennas & Transmission Lines (feedlines)

muDped · 2015.03.15, 20:26:48

Quote from: Centraflow
Wow a nice vacuum variable cap in those ATU's cost an arm and two legs

Yep motor driven ATU's at the base of the vertical antenna will sort the HF length, 1.5:1 is acceptable, I used to run a sigma 4 vertical on 28MHz it was a half wave length, pretty high, and no ATU, 100w out from a dual final valve transmitter, YASU 101, front end digital the best of both worlds, 5 and 9 from England to Australia with a high sun spot year, like speeking to the person in the same room, those were the days.

regards

Mike

Aye, those were indeed "the days!" Once the band "opened up"
voice communications were just like you said; "in the same room."

The final incarnation of Navy/Marine Corps MARS station N0EFA
(November Zero Echo Foxtrot Alpha) was in Cat Lo near Vung Tau.
Our principal gateway was located near Sacramento, California and
almost every evening at about 8:00 PM the band opened and
we could phone patch for several hours until it faded.

Collins Radio ham station equipment from Cedar Rapids, Iowa.

Some links:

Navy/Marine Corps. MARS in Viet Nam

The Original N0EFA

Viet Nam era N0EF(x) stations

Centraflow · 2015.03.15, 23:46:23

Quote from: muDped on 2015.03.15, 20:26:48
Aye, those were indeed "the days!" Once the band "opened up"
voice communications were just like you said; "in the same room."

The final incarnation of Navy/Marine Corps MARS station N0EFA
(November Zero Echo Foxtrot Alpha) was in Cat Lo near Vung Tau.
Our principal gateway was located near Sacramento, California and
almost every evening at about 8:00 PM the band opened and
we could phone patch for several hours until it faded.

Collins Radio ham station equipment from Cedar Rapids, Iowa.

Some links:

Navy/Marine Corps. MARS in Viet Nam

The Original N0EFA

Viet Nam era N0EF(x) stations

Thanks for the links, so you were a nam vet:?

Always liked the 10 meter band. In low sun spot years I worked sat's, both our own RSGB and associates, and the Russian sat's. Also worked the space shuttle Columbia with 2mtr & 70cm up and down links, attached a bit of press and a photo of Garrett on his return, I was a lot younger in that photo, around 30yrs ago.

I only maintain my G6 license in the UK as I have also a Spanish license for HF bands but don't operate now apart from 2mtr repeaters with 2.5watts when mobile using a hand held.

well 73's

Mike G6GVA out

Verpies · 2015.03.16, 00:21:23

Quote from: Itsu on 2015.03.14, 19:57:52
i agree, the mismatch stays (with the antenna) so no change in radiated power, only the indication on equipment measuring the standing wave .
Trimming the antenna would affect the degree of mismatch therefor the radiated power.

What if the feedline forms a quarter wave transformer that matches the transmitter ideally to the antenna?

Duncan · 2015.03.16, 11:21:22

I hate to disagree with Mike he was kind enough to sit and talk with me some time ago and I was quickly forced to realise I was a long way down the food chain from this guy , he's also IMHO one of the unsung hero's across these forums still even if I'm just playing the devils advocate here .. consider this

The data sent by Radio or Tesla's Wireless system is not limited to Morse ... To amplify this point if the Radio system were limited only to a carrier wave then it too could only deal with Morse and its ilk. Modulation and demodulation of course alter all that and so it is with the wireless system. Prof Myel makes that very clear in this video, which points out that large screen TVs must use this very different type of electricity because the radio/ electromagnetic/volts and amps system we are used to is no where near fast enough..... as for the modulation 'space' available, in the 'wireless' system it would seem there is a whole dimension available. if we were taught this system it would be a very different world.

See 47 min 0 h > to 1h02min https://www.youtube.com/watch?v=tKTkpC-DHZ8

All Hams including me know the importance of keeping the carrier wave a pure sin wave as well as all the frequencies within the envelope, That is why linear amps are so expensive (for those of you lucky enough to live somewhere your allowed to use one)
It is also taught that from the composition of a sine wave any other wave construct is possible, those scratching about building signal generators will know this to be true. The trouble is we are taught nothing of this alternative wireless and electric system, after all when did any of you last transmit with an SWR of infinity rather than unity ?
Here then is the start of the world of longitudinal wave theory and a totally different type of energy. Depending upon the perfect impulse (rectangle) composed of overtones rather than the (circle) sine composed of harmonics .
A complex subject the miss matched antenna this thread has long legs and could run a long way (I hope) considering the absolute miss match ... assuming the transmitter can withstand it ... spurious emission's across infinite wavebands me thinks
kind regards Duncan

Itsu · 2015.03.16, 12:07:51

Quote from: verpies on 2015.03.16, 00:21:23
What if the feedline forms a quarter wave transformer that matches the transmitter ideally to the antenna?

Well, it will match the impedance's, but will not remove the mismatch.
That way we would be able to match a 50 Ohm transmitter via a 50 Ohm coax with an open end to this infinite impedance.

Don't think the transmitter would be transmitting full power for very long.

Regards itsu

Centraflow · 2015.03.16, 13:10:56

Quote from: Itsu on 2015.03.16, 12:07:51
Well, it will match the impedance's, but will not remove the mismatch.
That way we would be able to match a 50 Ohm transmitter via a 50 Ohm coax with an open end to this infinite impedance.

Don't think the transmitter would be transmitting full power for very long.

Regards itsu

Yep I think it would have a fever

Regards

Mike

Smudge · 2015.03.16, 14:39:10

Quote from: Itsu on 2015.03.16, 12:07:51
Well, it will match the impedance's, but will not remove the mismatch.
That way we would be able to match a 50 Ohm transmitter via a 50 Ohm coax with an open end to this infinite impedance.

Don't think the transmitter would be transmitting full power for very long.

Regards itsu

A quarter wave transformer can't match to an infinite impedance. If I remember correctly the impedance Z_m of the matching section has to be Z_m=sqrt(Z₁*Z₂) and the square root of infinity is what??

Smudge

muDped · 2015.03.16, 14:52:05

Quote from: Duncan
...after all when did any of you last transmit with an SWR of infinity rather than unity ?

Hmmm. Interesting question Duncan. But, what
does it mean?

There are systems which operate into otherwise
intolerable Standing Waves. By use of a Directional
Coupler any reflections from the 'mismatch' are
prevented from returning to the transmitter/source.
The reflected energy is usually absorbed by a Dummy
Load to assure that it doesn't cause 'problems.'

Mike,
73's to you and the XYL! You've done some amazing
things.

Verpies · 2015.03.16, 14:53:50

Quote from: Smudge on 2015.03.16, 14:39:10
A quarter wave transformer can't match to an infinite impedance. If I remember correctly the impedance Z_m of the matching section has to be Z_m=sqrt(Z₁*Z₂) and the square root of infinity is what??

...but Poynt99 wanted to match a 50Ω transmitter to a 150Ω load and when he started this thread, he was seeking an answer to the general question whether the length of the coax between a transmitter and an antenna can affect its effective radiated power (ERP) when the resistive losses of the coax are disregarded.

Verpies · 2015.03.16, 15:01:54

Quote from: Itsu on 2015.03.16, 12:07:51
Well, it will match the impedance's, but will not remove the mismatch.

so what quantity will remain mismatched?

muDped · 2015.03.16, 15:12:33

Some links which may lead to an answer to the
original question:

Standing Waves and Antennas

Antennas and Standing Waves

VSWR

poynt99 · 2015.03.17, 00:53:39

Quote from: verpies on 2015.03.16, 14:53:50
...but Poynt99 wanted to match a 50Ω transmitter to a 150Ω load and when he started this thread, he was seeking an answer to the general question whether the length of the coax between a transmitter and an antenna can affect its effective radiated power (ERP) when the resistive losses of the coax are disregarded.

Well, not quite.

I was only seeking an answer to the question whether the coax length would affect the ERP. I was not seeking a method to match the antenna to the coax or transmitter.

It is impossible to perform any matching or tuning of a mismatched antenna simply by changing the feedline length. All that does is affect the impedance and VSWR that the transmitter sees. So if you have a dumb transmitter that just keeps pumping out its set power no matter what, the antenna ERP will remain constant, regardless of coax length (minus coax losses).

One reason one would want to cut the coax length would be to minimize VSWR at the transmitter end, because most of them are designed to throttle back their power or turn off completely once a VSWR of 3:1 or so is detected. The other reason one would cut the coax length to a multiple of 1/2 wavelength, is so one can know what the true VSWR of the antenna is.

BEP · 2015.03.17, 01:54:52

.99,

Sorry for not offering an answer earlier but your conclusions were correct anyway.

I just checked with folks on the local 2-meter net just to get an idea of how Hams understand this and it was unanimous with 6 contacts in the local area.

As one put it, 'Are you using your HT with an antenna mounted directly to it or a piece of coax connecting it to the antenna? Does it even matter except to the SWR display?'

There has been too much hype about SWR, T-line lengths, etc.

The only exception is when any portion of the coax is serving as an antenna match or antenna element (easy to do by mistake by many). At that point that portion can't be considered part of the transmission line anyway.

Verpies · 2015.03.17, 03:02:00

Quote from: poynt99 on 2015.03.17, 00:53:39
I was onBuly seeking an answer to the question whether the coax length would affect the ERP. I was not seeking a method to match the antenna to the coax or transmitter.

...but according to MPTT matching the impedance of the antenna to the impedance of the transmitter will maximize the power transfer between them, when their impedances are real.
A quarter wave transformer is a wavelength dependent element that will accomplish this feat.
For example: an 87Ω coaxial section will match your 150Ω ohm real load to a 50Ω transmitter, as long as its length is quarter of the wavelength.

For complex impedance mismatches, a complex conjugate impedance matching must be used to maximize the power transfer between the transmitter and a load (a simple impedance transformer is not sufficient for this purpose ...but with stubs - it is).

poynt99 · 2015.03.17, 12:26:04

Thanks WW, I was wondering why you hadn't posted yet! Thanks for the confirmation.

Verpies, yes one wants impedance matching for maximum power transfer, agreed. That just wasn't part of my question. Does this quarter wave transformer also work at multiples of a quarter wave? If not, then it would only be useful in some situations.

Centraflow · 2015.03.17, 12:30:50

Quote from: verpies on 2015.03.17, 03:02:00
...but according to MPTT matching the impedance of the antenna to the impedance of the transmitter will maximize the power transfer between them, when their impedances are real.
A quarter wave transformer is a wavelength dependent element that will accomplish this feat.
For example: an 87Ω coaxial section will match your 150Ω ohm real load to a 50Ω transmitter, as long as its length is quarter of the wavelength.

For complex impedance mismatches, a complex conjugate impedance matching must be used to maximize the power transfer between the transmitter and a load (a simple impedance transformer is not sufficient for this purpose ...but with stubs - it is).

The stub becomes part of the antenna, yargi's often have one built in for tuning, verticals as well, my sigma 4 had one, full power will be radiated, all other things being correct.

regards

Mike

Verpies · 2015.03.17, 13:42:49

Quote from: poynt99 on 2015.03.17, 12:26:04
Does this quarter wave transformer also work at multiples of a quarter wave? If not, then it would only be useful in some situations.

No it does not. The quarter wave Q section is not useful in broadband applications.

For broadband, the imaginary impedances must be cancelled out first and the remaining impedance mismatch can be handled by a broadband impedance transformer (e.g.: toroidal). L and π networks can do it too with some compromises.

Verpies · 2015.03.17, 13:51:45

Quote from: Centraflow on 2015.03.17, 12:30:50
The stub becomes part of the antenna,

Shorted stubs do not radiate any RF energy but they can cancel the imaginary part of antenna's impedance quite well.
Once you get rid of the imaginary part (subtract reactances) then the road to maximal power transfer becomes open.

Centraflow · 2015.03.17, 14:21:44

Quote from: verpies on 2015.03.17, 13:51:45
Shorted stubs do not radiate any RF energy but they can cancel the imaginary part of antenna's impedance quite well.
Once you get rid of the imaginary part (subtract reactances) then the road to maximal power transfer becomes open.

agreed

regards

Mike

poynt99 · 2015.03.18, 01:11:11

Quote from: verpies on 2015.03.17, 13:42:49
No it does not. The quarter wave Q section is not useful in broadband applications.

For broadband, the imaginary impedances must be cancelled out first and the remaining impedance mismatch can be handled by a broadband impedance transformer (e.g.: toroidal). L and π networks can do it too with some compromises.

Quarter wave of 800MHz is on the order of inches. How useful is the quarter wave transformer if I need 150' of coax?

Verpies · 2015.03.18, 09:03:20

Quite, because the quarter wave xformr can be followed by 150' of the target impedance coax.

T-1000 · 2015.03.18, 09:03:49

Hi,

Anyone tried radio communications using longitudinal (Tesla) waves instead of transverse (Marconi) with Earth as signal medium?
Would be interesting to see if anything interesting is being picked up there...

Duncan · 2015.03.18, 10:24:12

A stunning silence can be expected T1000 folks want to wax lyrical on things that are known about and spoon fed in modern text books (however complex). ... Introduce the other resonance ... SWR = infinity and the result will be just what tptb intended ! Indeed the thread shows the in - between to be a grey area also. All as RCA intended ... Kind regards Duncan

Verpies · 2015.03.18, 15:14:41

Quote from: T-1000 on 2015.03.18, 09:03:49
Anyone tried radio communications using longitudinal (Tesla) waves instead of transverse (Marconi) with Earth as signal medium?

No. I don't know how to generate and detect such waves.
I can make a Tesla coil with infinite SWR but that's about it.

Itsu · 2015.03.18, 15:24:16

Quote from: T-1000 on 2015.03.18, 09:03:49
Hi,

Anyone tried radio communications using longitudinal (Tesla) waves instead of transverse (Marconi) with Earth as signal medium?
Would be interesting to see if anything interesting is being picked up there...

Not with earth as a medium, but "the old scientist" used the air with some results:

https://www.youtube.com/watch?v=wjz-5Lqtxow

Regards Itsu

Antennas & Transmission Lines (feedlines)

BEP