Just to "receive", antenna need to be calculated?

Thread Starter

Willen

Joined Nov 13, 2015
313
Hi, I have few experience of receiving lightning strikes signals and far AM stations of thausands of km. In the case, antenna element needed as long as possible. That works well. Now I am trying to make an analog TV receiving antenna for 470MHz, half wave dipole. Do I need to calculate element length as formula or need to use as long as possible antenna? Resonant antenna is for transmitting or receiving both? I will make a half wave dipole and make a coiled balun near dipole to balance the signal. I think it works.
 

crutschow

Joined Mar 14, 2008
27,184
Yes, the requirements are the same for designing a good antenna no matter if it is for transmitting or receiving, other than a high power transmitting antenna may require higher voltage insulation.
 

Thread Starter

Willen

Joined Nov 13, 2015
313
Thank you crutschow.
After reding the reply, I made a Halfwave Vertical Dipole Antenna. Performance was WOW!

I still receive analog TV stations. There are two stations still alive as an UHF analog transmitter, one has 471MHz and another has 487MHz. But with common rabbit ear antenna, reception was horrible and irritating! Years ago, I was thinking to make a vertical dipole for my DIY FM transmitter. Since the transmitter has couple of mW of power, practically feeding the couple of mW to the dipole was not a practical step. Today made the same dipole and used as a reception antenna. Guided by a common formula, I trimmed the antenna element for 470MHz which is 1 feet each. (dipole element formula: 468÷470MHz=1.00 feet). the coiled coxial cable there, a poor man's BalUn.

Test result: in theory, vertical dipole works vertically, but not in the test. It worked very well horizontally instead of vertically. Using my eye and brain, here is the result of clarity:
1. Station 471MHz: before=30%, after 80%
2. Station 487MHz: before=90%, after 100%
It works well in horizontal position, does this mean vertical dipole transmits vertically and receives horizontally? Like the Yagi antenna has horizontal dipole element?

Irritation of adjustment antenna everytime and for every station, totally solved. 2nd station looking like a High Definition. Relief!
 

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LowQCab

Joined Nov 6, 2012
510
In the USA, all TV Transmitters have a Horizontal-Radiation-Pattern,
(it might be different in other countries),
so the Receiving-Antenna must also have a Horizontal-Reception-Pattern.

A Vertically-Polarized-TV-Antenna will usually have very poor reception performance.

FM-Radio is Polarized both Horizontally, and Vertically, at the same time,
this is done to improve FM-Reception in Cars, which usually have Vertical-Antennas.

Vertical-Receiving-Antennas tend to
pick-up more atmospheric "noise" than a Horizontal-Receiving-Antenna.

You must have a "Resonant" Antenna for best reception.
The proper Resonance of any Antenna is heavily dependent upon
having a matching Impedance between the Receiver and the Antenna.
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nsaspook

Joined Aug 27, 2009
8,382
Receiving is all about signal to noise ratio. At LF/HF a "Resonant" Antenna is less critical as the higher ratio of noise is external background noise to the receiver mixed with the signal. So while the absolute level of signal increases with better antenna systems, so does the level of noise if receiver signal bandwidth remains the same during the same atmospheric conditions.
https://www.govinfo.gov/content/pkg...VPUB-C13-4c22fdfcac581ce04eec8244130fcdac.pdf

At VHF/UHF and beyond the background noise is mainly generated by the receiver so better matched antenna systems (antenna and transmission line) can make a big improvement to signal quality.
 

Thread Starter

Willen

Joined Nov 13, 2015
313
In the USA, all TV Transmitters have a Horizontal-Radiation-Pattern,
(it might be different in other countries),
so the Receiving-Antenna must also have a Horizontal-Reception-Pattern.

A Vertically-Polarized-TV-Antenna will usually have very poor reception performance.

FM-Radio is Polarized both Horizontally, and Vertically, at the same time,
this is done to improve FM-Reception in Cars, which usually have Vertical-Antennas.
When I look at the FM Station antenna here, all of the antenna are vertical dipole and placed vertically (up and down). Does this mean I need to place my dipole vertically too?
 

LowQCab

Joined Nov 6, 2012
510
Looking up from the ground, it is very difficult to determine the Polarization
of a high-power Broadcast-Antenna.
Also, Antenna-Towers are almost always "shared" by other Organizations.
There may be 10 to 15 different Antennas on the same Tower,
you don't know which is which, and there are a huge variety of designs.

The best way to determine which orientation will be best is found by either
a Signal-Strength-Meter on your Receiver, or simply by experimentation.
The more Directional your Antenna is, the easier the experimentation will be.
A dedicated, FM-Band, ~5+ Element Yagi Antenna,
will tell you very quickly what works, and what doesn't work.
With no Trees in the way,
an Antenna like this will easily pull in Stations from 50+miles away,
but it must be accurately aimed at the Broadcasting Antenna.

A Vertical-Only FM Broadcast Antenna, is very unlikely.
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