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Do receiver antennas need matching or not?

I did not see all the replies nor the original post but in the world of radio frequency (RF) match yes this would be an ideal situation since maximum energy transfer occur when Imepdance of the antenna (Zant) = Imedance of the Receiver Antenna Port (Zrx_port).

All this talk about noise while important to minimum detectable signal more greatly influenced by the internal Noise Figure (NF) of the receiver (RX). In my line of work, which is Radar engineering, we use a standard temperature T = 270 Kelvin to model the noise originating by natural extgernal sources of which the Sun is the biggest contributor.

The short end answer on HF you will probably not notice a big difference as long as the antenna is close between a 1/4 to 1/2 wavelength long [e.g. wavelength = Velocity of Light (C) / Frequency of Operation (Fo)]. However, if you use one of those collaspable whips found on the portable shortwave receivers you will. This is because the anyenna impedance is a lot less than the usual 50 Ohm impedance of the RX antenna port (e.g. Zant

Reply to
Homer J
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My understanding is that this is not the biggest influence at HF -- there's so much atmospheric noise down there that even with a pretty poor receiver (noise figure-wise) the MDS is usually just about the same as with a much better receiver.

Have you seen the graph in, e.g., Krauss's antenna or EM book? T=270 is a poor model at many frequencies. (Granted, if you're doing narrowband designs, it'll just be some offset error that's probably not too much worse than, say,

+/-3dB.)

From watching this thread I get the impression that -- at least on HF again -- the (lack of) capture area is the much bigger problem than the mismatch is.

---Joel

Reply to
Joel Koltner

I never knew that "aperature" could be measured in square feet or metres! Is there a book that describes it in such a way ? Art

Reply to
Art Unwin

yes

Reply to
LVMarc

What has not been mentioned much is that AM band broadcast receivers and FM band receivers are designed to to tune over a fairly wide band of frequencies; so very difficult to build antenna that will mtach at all those different 'wavelengths'.

For example; the broadcast band (North America) is roughly 550 kilohertz (that's 545 metres wavelength) to about 1.7 megahertz (about

176 metres). That's 3:1 ratio!

On FM, 88 to 108 megahertz (3.4 to 2.8 metres) the ratio is less but still cnsiderable at 1.2:1 So again very difficult to design and build an 'all frequencies' antenna.

For stations designed to receive only one frequncy the antennae can be constructed for that only; hence the matching can be as optimum as possible.

Reply to
terryS

HOWEVER, if you will look at the Antenna Design for a AM Broadcast Receiver, using a Ferrite Loop Antenna, you WILL notice that the Loop IS Tuned to the specific part of the band that the receiver is being tuned to, by Linked Ganged Variable Capacitors, in the Receivers Frontend. These designs have been around for MANY years, (1940's anyway) and are a very mature technology.

Reply to
You

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