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
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