Impedance match parallel Yagi antennas to a 50 Ohm radio

时间：04-08 整理：3721RD 点击：

We need to connect two 50 Ohm Yagi antennas connected in parallel to a SCADA radio (158.34 MHz). What are the specific components needed in the Impedance Matching Network to accomplish this ?

The attached PDF file is a copy of the concept.

Thanks!

"Connecting in parallel" isn't exactly a specification of the intended coupler behaviour. It can be assumed, that a Wikinson power divider would
best fit the problem. If you don't want to operate both antennas simultaneously, an antenna switch can give better performance, however.

Just search the net for "stacked yagi"

http://www.grantronics.com.au/docs/StkYagis.pdf

If I'm not mistaken, this would be to boost the gain in one direction. We are trying to connect two Yagi antennas simultaneously pointing in different directions. Our concern is how to compensate for any impedance mismatch and power loss between the two Yagi antennas and the radio transmitting at 158.34 MHz.

Please advise. just use a wilkinson divider as suggested above and point the yagi's in whatever direction you want.
Main feeder cable to N type T adaptor, feeding 2 x electrical 1/4 wavelength sections of 75 Ohm coax @ freq of operation will give 50 Ohm at the end of the 75 Ohm ends.
ie. ... The 50 Ohm to 75 Ohm transformer gives 100 Ohm at the T adaptor end of the 75 Ohm cable and paralleled in the adaptor takes you back to 50 Ohm for the main feeder. too easy :)

cheers
Dave
VK2TDN That makes perfect sense, Dave. Thanks for helping a newbie out! Knew just enough to be dangerous

As said, Wilkinson power divider is the obvious solution. But the transmitted power and receiving sensitivity will be reduced by 3 dB compared to single antenna operation.

yup that is true but easily made up with a bit of extra gain with the yagi :)

and when there is ~110dB at 158 MHz over the first 10km (LOS path) another 3 dB is neither here not there anyway its only 1/2 an "S" point

cheers
Dave
VK2TDN

What is your expert opinion regarding using Reactive Splitters for our project versus Wilkinson Splitters ? (see the attached PDF article)

Hi Netad,
just to clarify some of the above statement in relation to what we have been discussing. Usually/often, Wilkinson dividers done on PCB will have a 100R resistor across the ends of the 2 x 75R sections of stripline.
But in an antenna system it doesnt. Mainly cuz its impossible to do at the 2 ends of coax, as they could be some metres apart. So their statement about 100R resistors burning out is not applicable in the situation you want to use :)

I have used the earlier described coax splitter system a number of times over the years for feeding multiple yagis. The system has never failed me and returnloss (SWR) has always been excellent.

cheers
Dave
VK2TDN

As the only difference, when using a "reactive" splitter, a part of the received signal is transmitted at the other antenna and a part is reflected
back, possibly modifying the yagi directional characteristic a bit. No difference in transmission behaviour, as the paper explains. Gain is
identical to Wilkinson. Most likely, you wont observe a practical difference.