Antenna matching for RF chips

[gxti]

I want to use Microchip's MRF49XA transceiver (datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/70590b.pdf), and like several trx I've run across it has differential, open-collector outputs. This and all the related chips recommend a balun made of a few inductors and capacitors (page 76 in the datasheet) to convert to a 50 ohm, single-ended output. All of these examples, though, are for use with a quarter-wave monopole antenna and don't make any mention of dipole. Do I still use the same balun if I want to use a dipole antenna, for example http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ANT-916-CW-HW-ND? The datasheet hints that it can drive a loop or dipole antenna "directly", but also says that coils are required for all antennas due to the open collector outputs. Would something like a Pi filter handle both the coil requirement and the impedance matching? How do I go about choosing values for it?

[gregariz]

My approach would be to forget about their recommended matching circuit. Since both outputs are out of phase open collector, I would tie each to your supply rail via identical RF Chokes. The chip says it has an Automatic Tuning Unit in it - I've not used that chip so I can't say how good it is.

[Mechatrommer]

How do I go about choosing values for it?

i hate to say it but you need a big buck for this. i have a non working radio in stock and have no clue why albeit everything according to datasheet. you may keep try and error with the value, and enthusiasm as your "faith", or you are going to need to measurement device such as spectrum analyzer or vna to measure the signal strength for real. radio is not something you can ask people for the value and expect it to work 100% otimum, my 2cnts from limited experience at least.

[vk6zgo]

The example you gave is an end fed antenna,& probably includes a matching section so it can be driven from a 50 ohm unbalanced output,so you will probably need the balun.

A balanced dipole does not need a balun (but may need some matching circuitry),& is nominally of 75 ohms impedance.
A folded dipole is a balanced antenna,does not need a balun (but may need some matching circuitry),& is nominally of 300 ohms impedance.
You are unlikely to run into the latter two types with commercially available antennas for your application.

VK6ZGO