TV antenna impedance plotting...

[Externet]

Good day. Can anyone direct/point me to any television antenna specifications with an impedance vs. frequency plotting ?

 

[danadakk]

Google "tv antenna impedance chart", quite a few charts/images on web.


Regards, Dana.

 

[Externet]

Thanks, Dana.
Am incompetent : text search shows one result, which is this thread . Unable to find it on a couple of pages of images results.

 

[BigBoss]

Antenna Impedance varies with different factors.Therefore measuring of an antenna should be done in a non-reflecting chamber.
This is a professional method but you can simply connect a VNA to measure the impedance but it will be erroneous.Because polarization,reflections,position etc. will definitely impact the impedance.

 

[BradtheRad]

Seems like directionality is a more prominent factor, which determines voltage and current produced by the antenna at a given frequency.

Impedance relates directly to voltage and current, or rather, the ratio of voltage to current.

If there's any current flowing, then it implies a load is attached.

I wonder how much an antenna's impedance might vary? Does it ever generate an unchanging voltage but varying current? If so then load impedance is a main factor since it's in the current path.

Or does an antenna ever generate unchanging current yet varying voltage? And does it ever generate substantial current, yet voltage is so minuscule as to make the signal unusable? In that sense I suppose we want a high impedance for an antenna, because it goes with greater voltage and lesser current.

 

[FvM]

"television antenna" is rather unspecified, could be e.g. simple dipole or Yagi antenna. Specification of commercial products is rarely more than nominal impedance and gain. For the elementary antenna types, I would rather refer to antenna text books.

 

[G4BCH]

I think that you will find that the only TV antennas that have a characterised impedance over frequency are those that are found on the transmitter tower.
For domestic use no manufacturer is going to bother; how many of their customers would understand it, and would it matter in a real life sitauation? As far as the reciever is concerned the antenna impedance will be masked by the loss in the transmission line. I doubt many installations would measure worse than 6dB return loss if the antenna was not even connected at the far end.
All I have ever seen for specifications appart from size is a gain figure proabaly that probably the advertising department dreamed up, a polar plot if you are lucky and a nominal impdaence of 75ohms,

 

[Externet]

Thank you, G4BCH
Not the ones on a transmitting tower, truly made and meant to present whatever (50Ohm?) impedance at the single transmitting frequency to match a transmission line and TX
- Plain RX ones, of any type, dipole, yagi, omni, folded, bowtie, loop, rabbit, log periodic, parabolic, your choice...

They connect usually to 75 Ohm cable, to a 75 Ohm plug to a 75 Ohm jack to the tuner module.
All this 75 Ohm concert tells that at some frequency, the antenna sources a 75 Ohm impedance signal... At what frequency ? Impedance is tightly linked and in function of frequency.
But never published, never exposed, never analyzed in decades of TV antennas being 'engineered' and sold. For consumer or not; there has to be a mathematical/scientific rationale making sense to feed a TV tuner properly *. Can find nothing. Like using a coathanger instead of the fancy pricey 'cutting edge antenna' is the same, nothing is rational science. As you mean, products of a marketing dream with all the empirical signatures.

* Which is another subject I tried to explore before in another thread a long ago. TV tuners with a 75 Ohm input jack and NO published impedance vs. frequency plot, working at large frequency spans. Where in the span are they 75 Ohm ?

The point is, how much of a farse/fraud are TV antennas supposed to work on several hundred MHz span with a nobody-knows (nor cares) its impedance and electrical matching behavior.
If front end TV tuners with very high impedance fets are the norm now; what is this "75 Ohm" for ?