Loop Antenna

Is the old fashioned loop antenna the best antenna out of all antennae (I wanted a reason to say "antennae") for indoor digital tv reception? I believe I read or saw this somewhere?

In some locations yes, but in most locations no.

The locations where they work best have the following characteristics:

-Close to TV transmitter (high signal strength)
-No muti-path problems
-All TV stations transmitting in UHF frequency band

Classic 7.5" diameter loops only work in the UHF band. They don't work worth squat with VHF signals. Many areas in the US do have VHF digital stations.

Loops have low gain, so they won't work well for distant reception.

And loops are not very directional, so if you have multi-path problems with your TV signals, they don't tend to work very well.

(Muti-path means that TV signals are reflected off of objects such that your TV antenna receives more than one version of the signal from a single station. This causes "ghosts with analog reception, but it can easily confuse a digital TV tuner such that the reception breaks up.)

2009-05-04 15:48:31 by papa_de_q

This is the loop antenna calculator page I used design my loop: www.angelfire.com To see my ham radio and radio related T-Shirt online shop click ...

A loop antenna is an antenna that the center conductor is connected to the shield or the two conductors of the twin lead feed line are connected to each other through the loop. UHF loop antennas are usualy round but some UHF loop antennas are shaped like a bowie. For lower frequencies there needs to be more inductance and length so the loop if wound around a ferrite core. The ferrite core loop antenna is the most common AM radio antenna. The Coalinear antenna and folded dipole are both loop antennas. Loop antennas have the advantage that they are effectively an electrical short at low frequency current and this can reduce the effects of lightning and some type of interference.

2007-03-18 21:51:33 by kb_25

Price: $49.99 $24.95

Use with direct wire connection or wirelessly for radios without AM antenna input
9-Inch diameter loop design with tuning knob
Enhances AM reception with frequency coverage from 520 KHz -1,510 KHz
Passive (no battery required) loop AM antenna
30-Day money back guarantee 1-year manufacturer's warranty

Is this true they said the UHF antenna is capable of receiving a digital signal,

Digital signals that are broadcast over the air are received with the UHF part of a regular antenna - including high definition digital. However, if you have an analog tv and no digital TUNER, you still need a digital converter box to convert your tv's tuner to digital.
New tv's with a digital tuner, only need a UHF antenna, to get signals broadcast over the air.

2008-09-29 06:06:03 by rgs821

I installed an AM loop antenna on my receiver. There are two radio stations, of similar strength, that I get equally well in my car. However, I am only able to receive the one on my home receiver. Does anyone have any suggestions for increasing the strength of the antenna, or maybe I need a different antenna? Perhaps the location of my house and/or stereo has something to do with it regardless of the antenna? Thank you for your help.

AM loop antennas are highly directional but most car antennas are not. You may have accidentally nulled out the 2nd station with the position of the loop (the 2nd station antenna is along the line of the loop, while the first is more perpendicular to it).

Try slowly rotating the loop antenna. You'll probably find that it picks up the 2nd station just fine, but in a different orientation from the original one. If you're lucky, the stations will not be 90 degrees apart and you'll be able to hear both of them without having to move the antenna again.

2007-10-09 20:16:06 by Chef Mark

Q= 20
L= .71664 microH
operating frequency = 13.6 MHz

i want to know how to do the impedance matching, the values of the various circuit component. (capacitor, resistor etc.) and if there is a internet site that can help me with this.
thanx

First, you need to know the impedance of the antenna and the impedance of the system (i.e., transmission line) that you are matching it to. You haven't really stated the impedance of the antenna in an obvious form. Do you mean that the antenna impedance looks like an inductance of 0.71664 microhenries with a Q of 20? Reading your question, that's the conclusion I make. If that is true then here is how to match that impedance to a 50 ohm system at 13.6 MHz.

First, change your antenna impedance to a more user friendly form. At 13.6 MHz an inductor of 0.71664 uh has a reactance of X = 2 pi f L = 2 * pi * 13.6e6 * 0.71664e-6 = +j61.24 ohms. Let's find the series equivalent impedance, so R = X/Q = 61.24/20 = 3.06 ohms. So your series equivalent impedance is 3.06 + j61.24 ohms at 13.6 MHz. By looking at these values it is apparent that this will result in a very narrow bandwidth match.

The next step is to decide what matching network topology you want to use. Your matching network must do 2 things. It must remove the reactive part (+j61.24 ohms) and change the real part (3.06 ohms) to 50 ohms. Certain circuit topologies may do this better than others, and certain circuit topologies will give you more reasonable matching component values than others. This is where lots of experience doing this comes in.

Let's say we will use a simple 2 element network. You can design this on either a Smith Chart if you know how or using equations for an "L" network. To match on the Smith Chart you could start at the center (50 + j0 ohms) and add components until you arrive at the complex conjugate of the antenna impedance (3.06 - j61.24 ohms). Or you could just plug your source (50 + j0) and load (3.06 + j 61.24) into the appropriate "L" network equations. When I did this I came up with two matching circuits that should do the job and give reasonable component values.

Circuit #1: 50 ohm source - series C = 48.2 pf, shunt C = 144.4 pf - Antenna.

Circuit #2: 50 ohm source - series L = 2.84 uh, shunt C = 236.9 pf - Antenna

Both of these were plugged into a circuit simulator and they do work.

If you were to actually build this you would probably want to make the shunt C adjustable to tune the antenna right on.

BTW, I don't recommend stub matches at HF. The stubs are too big and lossy. Also, never use resistors in matching networks. All they do is waste power. If you can't get the match using only L and C values, try a different circuit topology, don't add a resistor.

2008-03-24 22:40:56 by captaincrash_001