"We are talking UHF and microwave here" Then we will consider the 6" Motorola quarter-wave UHF antenna built in great quantity in this country ... a very simple antenna again containing no matching network per se and interfacing quite well to 50 coaxial cable ... I have also seen extremely simple designs at 5 GHz of the "monopole" variety - intended as an MLS receive antenna. As to contentions of extremely 'tight' link budgets owing to low power xmitters and high noise figure receivers - these factors do indeed serve to limit range ... but the fades and 'nulls' due to destructive multipath do FAR more to limit reliable range that the ever-so-cited and glorified "link budget" - as we indeed see in the real world ... Some of the 'bad' experiences with RF are due to other factors usually *not* considered - such as CPU clock noise, in-adequate grounding/counter-poise A/K/A "ground plane" for the classical monopole. One more thing that should always be remembered - *anything* used (and usable) at 10 MHz, 150 MHz or 450 MHz can be *scaled* for use at OTHER desired frequencies. That is a just fact of nature ... As most people simply lack the background, the insight required for troubleshooting RF problems *and* most don't posses the requisite test equipment or access or ever spent time on an antenna test range - "things RF" tend to remain obscure and make the job of bringing up and RF-based data system just that much more difficult ... Oh yeah, one more thing. It's ALL been done before. See the IRE (now IEEE) series dating back to the twenties ... Jim ----- Original Message ----- From: "Peter L. Peres" To: Sent: Tuesday, May 14, 2002 5:53 PM Subject: Re: [EE]: RF modules > On Tue, 14 May 2002, Jim wrote: > > > "A simple monopole needs more careful matching > > and tuning than a dipole" > > > >Practical experience in the real world will not > >bear this out ... ever seen or used the classical > >Motorola 19" whip on 2 Meters? No matching network, > >mates up directly to RG-58 50 Ohm coaxial cable and > >deleivers reasonable preformance for the simplicity > >and size ... > > We are talking UHF and microwave here, low power, no voltage or power > margin on the Tx, very poor noise figure on Rx (relative to what is > possible), high noise background from FCC compliant (pun intended) nearby > office computing equipment. Matching is everything. Tuning improves the > noise margin on Rx and the useful in-band power (a little) on Tx. I don't > have to tell you this. A legal 433MHz 1mW transmitter at 5V had better be > matched *perfectly* to a *tuned* whip to be heard at 30 feet by a > similarly prepared receiver. This is NOT the case in 99% of the cases (see > millions of usenet postings - also on this list - from people who are > disappointed by the range obtained), because the ground plane/shield/box > whatever is not appropriate or because of nearby wires and metal objects, > even if the layout, and antenna are perfect (you wish). Remember that > this is not twinax in the lab or on some high end navy ship stuff or the > best dreamland manufacturer figures obtained in an anechoic chamber and > rounded up or down, as appropriate. > > > "A vertical 5/4 lambda will outclass it" > > > >You *might* be alluding to a "5/8 wavelength antenna" - and > >you would be closer to corect ... > > Yes, that's right. Whew, I'm posting after midnight again ... > > > "a lambda/4 whip probably costs them 6dB in transmitted power" > > > >Again, practical experience will not quite bear this out ... > > This one I HAVE to insist on. Believe me, real life sucks, engineering > wise, 99.999% of the time. I know because I make my living out of > engineer's mistakes ;-) ;-). They are sort of, paying my salary, you see ? > > I'll stop now. I state based on my experience that by adding a tiny load > coil (1 turn 4mm dia) and/or a 0.8pF-6pF trimmer at a whip at both Tx and > Rx you can up the range by at most 30% in many cases (at 433MHz). > > Peter > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.