On 27 July 2010 21:34, ivp wrote: > I've been looking at various options for short-range transmissions > at 434MHz. Less than 100m line-of-sight will do > > So far I've tried 1/2 wave (345mm), 1/4 (172mm) and 1/8 (86mm) > straight aerials, using both copper and aluminium. 1/2 is best although > 1/8 is still pretty good, apart from a couple of dead spots at 100m > > One application I'm evaluating would benefit from internal aerials. > This could either be an 1/8 or a PCB trace. PCB trace would be > preferable. My thought is to use a short link from the fixed-position > user to a repeater. The repeater can have a 1/1 or 1/2 wave aerial > to broadcast the longer range to the end receiver. This receiver > should also have an unobtrusive aerial (PCB preferably), and I'm > hoping that the power output of a repeater with its better gain aerial > will be picked up more reliably with this internal aerial than from the > user's short range transmitter > > I've Googled 434MHz aerial PCB and found this document, which > has several 434MHz examples. The Bode plots are very helpful > > http://www.rfm.com/corp/appdata/antenna.pdf > > Opinions and suggestions please ? > > TIA > > Joe > Joe, The pdf looks like it has plenty of good advice & examples. To get best range with low power you will need the antenna to be resonant at 434MHz and you will need to match it appropriately. A 1/4 wave whip on a ground plane will be close to 50 ohms at its base and its length can be trimmed for resonance. You'll need some equipment to get it perfect however - and then it will change with proximity to other things / people etc. (eg iphone 4) So a good starting point is to just cut to length as close as you can and see if it's good enough. Even a 1/4 wave long length of hookup wire may be enough, although probably not for 100m with the cheaper modules. Note that you need a metallic ground plane as the natural "earth" can be several wavelengths below ground level at this frequency. The feed impedance of the equipment may not be 50ohms either - although it's the best bet unless there is info to the contrary. Feeding a 1/2 or 1/8 wavelength antennae can be a bit more difficult as they will not be 50 ohms and possibly unbalanced. This can lead to additional losses & so reduce the actual transmitted and received power. This can be sorted out using baluns or transmission line stubs but would require suitable gear to fine tune & is likely to be more trouble than it's worth. A gain antenna (e.g a yagi) will give you longer range, but then again, may take a bit of setting up. If you know any hams you might be able to do some basic tests using simple gear (transmitter, receiver, VSWR meter) in the 70cm ham band. In NZ this is 430MHz - 440MHz (with some frequencies reserved for satellite use) so includes the 434MHz frequency of interest. I am in the position at the moment of working with RF gear and have access to test equipment. I measured one of my Wifi antennas and found it was slightly off frequency. A small adjustment to make it resonant and the performance has improved significantly so I can vouch for the fact that resonance does make a difference. RP --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .