The requirements were for an audio link not data and available in the UK. He also only wants transmitters and reading between the lines wants Watts of power not milliwatts. And wants a quick cheap solution. Otherwise I would have suggested modifying ex-pmr equipment. He specifically excluded off the shelf data modules. Regards Chris Carr ----- Original Message ----- From: "Sean Breheny" To: Sent: Wednesday, August 01, 2001 4:10 PM Subject: Re: [EE]: VHF and UHF mini modules > Hi Scott, > > On Wed, 1 Aug 2001, Scott F. Touchton wrote: > > > > > I've used the Lynx modules with good success (433 and 915 Mhz). Also, RF > > Monolithics has some nice small single chip solutions for both a > > transmitter and receiver. I've lost track of this thread, and not sure of > > I just used the Linx SC series (916 MHz)in a project and I can second the > notion that they work well. > > > your range requirements. These two solutions are typically about 0dBm > > output... and only will get about 300' of range or so. I did get close to > > 1000' at 915Mhz, but that was open line of sight and the BER was getting > > intolerable. Of course, these products are typically 50 ohm output. So it > > does help to design a matching network to line up with your antenna. I was > > using quaterwave monopoles on ground plane.. about 75ohm impedance. A > > simple LC section did the impedance transformation. Doing this added 25% > > to the range. > > I think you went the wrong way, a simple vertical monopole above a ground > plane has about 36 ohms impedance (it has the same radiation above the > ground plane as a 1/2 wave vertical in free space would, and almost no > radiation below the ground plane. This measn that ,overall, for the same > antenna current, it transmits half the power, so since power is I^2 *R, > this means half the R. R for a 1/2 wave dipole in free space is 72 ohms, > so 72/2=36) > > I'm a bit surprised, though ,that this tiny mismatch made 25% difference. > When you say LC section, are you referring to microstrip L and C? It > would be difficult to make an LC filter with discretes at 916 MHz. You > can just use a 1/4 wave long section of microstrip transmission line as a > quarter wave transformer from 50ohm to 36 ohm. > > > > > Also.. since these are 50ohm parts, its very easy to use a MMIC amplifier > > to get added output power. > > > > Yes, and also to improve their noise figure (if you include n RF sensing > TR switch and a second MMIC amp). From their specs it seems as though their > receivers are > quite a bit less than optimal. Too bad the FCC doesn't allow more than > 50mV/meter E field strength @ 3feet on this band, otherwise we could use > small yagis and get REALLY good range. Come to think of it, we could > still use a yagi on the receiver side, provided we had a TR switch, as > mentioned before. > > It's interesting that this thread should come up now as I am almost > finished with my online tutorial on wireless communications for > microcontrollers. I will be sure to post to the list when it goes up, in > a few days. > > Sean > > > Scott F. Touchton > > 1550 Engineering Manager > > JDS Uniphase > > > > > > > > Chris Carr > > > ET.COM> cc: > > Sent by: pic Subject: Re: [EE]: VHF and UHF mini modules > > microcontrolle > > r discussion > > list > > > A.MIT.EDU> > > > > > > 08/01/01 08:22 > > AM > > Please respond > > to pic > > microcontrolle > > r discussion > > list > > > > > > > > > > > > > > > Maxon SR-214 is a complete handheld transceiver operating tin the 70cm > > band > > > 10mW output runs off 4 AA batteries. Ideal as the basis for a higher > > powered > > > unit. > > > > > > Cost # 29.95 UK. Available from ourselves or Waters & Stanton ( as you > > > appear to be in Edinburgh JC, 20 Woodside Way, Glenrothes, Fife KY7 5DF > > > 01592 756962 > > > > > > Otherwise Vectronics have kits to build FM Receivers for 2, 6 and 10 > > metre > > > bands #35.95 and a 5 watt 2 metre transmitter at #99.95 > > > > > > Then there are the Ramsey and Ten-Tec Kits it all depends on what you > > want > > > to do. > > > > > > Regards > > > > > > Chris Carr > > > > > > > > > > > > Thanks for your answer. > > I am looking for small synthetized modules that can transmit in VHF or UHF. > > I do not need tranceivers or a normal LPD already industrial friendly > > boxed radio. A PCB (printed circuit board) module is enough for me. Do not > > need pretty boxes :-). > > The final system is going to be a speacial kind of Beacon for RDF. > > Thanks > > > > Sena > > > > As a quick and easy to implement solution you will have difficulty beating > > the SR-214. Just key the transmitter and forget about the receiver. Use a > > PIC to emulate keystrokes. 10mW will get you around a mile with the > > attached > > antenna. > > > > Otherwise you are going to have to look at building designs from a > > handbook. > > > > ARRL UHF/Microwave Experimenters Manual > > ARRL UHF/Microwave Projects Manual Volumes 1 and 2 > > > > are a good starting point and should be available at the University Library > > otherwise they can be purchased from the RSGB > > > > VHF Communications also supply boards, partial and full kits for the > > projects published in their magazine. > > > > Regards > > > > Chris Carr > > > > Please respond via the list and not direct, other people may want to > > contribute to the thread. > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > > > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics