On 4/24/07, Don KA9QJG <[EMAIL PROTECTED]> wrote:
Can Someone Please put the Spectrum Analyzer thread in Layman Terms I have a Motorola Serv Monitor R2001C With the Analyzer and a Icom R-7000 Communications Receiver with a AVCOM Spectrum Analyzer I Can see 10 Mhz at a Time and I know that it's nice to Find Signals. But I always thought that a Actual receiver IE Scanner running the right Software would actually find and see more Hits because it is actually a Receiver. I know for a fact I can hear a lot more on a Cheap Scanner then using a Service Monitor on the same antenna. What do I not understand here Thanks Don KA9QJG
The easiest and closest you can get to "layman's terms" on this topic is this, Don... "Selectivity and Sensitivity always interact." If you want a highly sensitive receiver, you usually have to filter it heavily (making it more selective) and can only listen to a very narrow range of the RF spectrum. If you want a very non-selective receiver (e.g. a typical cheap scanner) you end up having to make the trade off of lowering the sensitivity, or you'll overload the front-end. Those are the generalities... Through good design, software defined radio, filters, yadda yadda yadda -- all sorts of interesting technologies, that many RF engineers out there apparently make a pretty good living creating and using -- you can usually find a nice balance for whatever you're attempting to do. In the case of most modern mid-range spectrum analyzer designs -- the type of equipment many Amateurs and small RF shops might have access to -- if you're trying to "look at" (receive) a large swath of RF spectrum, the analyzer simply can't "hear" as well as it can when you give it less to work with. For the gentleman who's trying to do a site survey... he will probably have to do smaller chunks of spectrum to get the maximum "listening" performance out of his spectrum analyzer, and then "stitch together" the resulting graphs for his customer, since they're wanting a "view" of a large chunk of spectrum, but the instrument simply can't do it. Thus, the comment by someone else... that there ARE devices out there that CAN do a quick and very sensitive site-survey way down into the noise floor, but their cost is prohibitive. The really fancy equipment usually has computer controlled RF filtering systems that track with the receiver in an automated fashion, and various other tricks (including multiple receivers operating at the same time, but being displayed as a single contiguous spectrum analysis) that allow them to internally make the trade-offs a simpler device can't make. Someone lesser quality or older non-specialized equipment might have to do this "work" themselves... "the hard way". Does that help? Unless the poor guy has $80,000 lying around burning a hole in his pocket, he needs to use the general principals of RF engineering to his advantage and ask the spectrum analyzer to "do a little less work", while he does a little more. Nate WY0X
