| Home |
| Search |
| Today's Posts |
|
#17
April 2nd 08, 01:07 AM
posted to rec.radio.amateur.antenna,sci.electronics.design,sci.electronics.basics
|
|||
|
|||
Do receiver antennas need matching or not?
Joel Koltner wrote:
"Homer J" wrote in message .. . All this talk about noise while important to minimum detectable signal more greatly influenced by the internal Noise Figure (NF) of the receiver (RX). 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. 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. 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.) 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 Zrx_port ). You can match very short antennas with antenna tuners to make them transfer efficently to the RX antenna port but now the nasty parameter of effective antenna aperature (square feet or meters) reduces it caoture ability 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 yes |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| matching masts as vertical antennas. | Antenna | |||
| FS: Mosley CM-1 Receiver and Matching Speaker | Boatanchors | |||
| Z matching of antennas | Antenna | |||
| FS: Knight R-100A Receiver and matching speaker. | Boatanchors | |||
| FS: Knight R-100A Receiver and matching speaker. | Boatanchors | |||
Threaded Mode
