You'd be better off just coiling up some of that coax in some tight turns at the feedpoint. You shouldn't ned that many turns at that freq.
73, Chris, KG0BP ----- Original Message ----- From: "Mike Newman" <[EMAIL PROTECTED]> To: <[email protected]> Cc: "Jim" <[EMAIL PROTECTED]> Sent: Thursday, January 27, 2005 5:51 PM Subject: [Repeater-Builder] Ferrite bead choke balun at 70 cm? > > > Hi to the group. > > I'm looking for advice. > > I've modelled a 70 cm Moxon Rectangle - with impedance of 50+j0, and F/B > around 30 dB. The cardiod radiation pattern is ideal for my application - a > low-altitude 70 cm repeater on the perimeter of the service area, and > co-sited with a 70 cm link repeater. The service area covers less than 20 > square miles - filling in a gap in local coverage. I need the rearward null > of the cardiod to minimise interference problems with a co-channel high > altitude repeater 85 miles away. > > The antenna is balanced feed - so I need to decouple the coax feedline. > > The obvious choices (at least to me) are. > > 1. Quarterwave coaxial sleeve balun: this requires a bit of measurement > and cutting, also waterproofing, and is not easy to fit in the physical > arrangement. > > 2. Ferrite bead choke balun: dead easy to install, and doesn't > compromise weatherproofness of the coax feedline. > > I have some ferrite beads which the supplier specifies as having 200 ohms > impedance at 100 MHz, which snuggly fit on a short piece of RG400/U coax > connecting to the main LDF5-50 feedline. > > But who knows what impedance they represent at at 70 cm? > > Can someone tell me about the effectiveness of ferrite bead choke baluns at > UHF and how to test this. > > What other options would achieve the desired results? > > Thanks > > MikeN, ZL1BNB > > > > > > > > > > Yahoo! Groups Links > > > > > > Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
