T antenna with matching network

T Antenna With Matching Network

Electrical Notes

This T antenna broadcast design by Guglielmo Marconi has been built and is used by Jim NN4AA on 160m, all details and

drawing are copied from Jim's Notes he sent me.

As Built,The Antenna will Resonate at 1640khz

This raises the radition resistance about 1 ohm over what would result from a resonant configuration.

If the antenna is built higher or longer, a still lower resonate freq will result.

Radiation Res. is 11.5 ohms current in the down lead is about 2.3 amps at 100 watts

Gnd resistance is about 6-7 ohms.

Tuning notes

Put the matching network at the bottom of the antenna where the ground radals terminate.1.

The antenna is fed at Jim's QTH via 400 foot of underground 1/2 inch hardline.2.

Since the antenna resonates well below the band, it was tuned up to 1860khz by means of a 1600pf fixed capacitor in

series with the down lead.

3.

Resonance can be determined by connecting the tuning cap directly to ground via a short clip lead. A grid dip meter

can then be coupled to the clip lead. A 2 turn loop maybe nedded here to get adequate coupling

4.

http://www.pcsystems-ss.co.uk/g7lrrweb/index.php?module=pagemast...

1 of 2 28.7.2009 20:29

Matching L design is then designed to match 50ohms to 18 ohms for perfect vswr at 1860khz. 1.5:1 BW is 45khz, 2:1

is 90khz.

5.

You do not have to duplicate the antenna dimensions exactly, with a shorter flat top resonance could be achieved at

your operating frequency. in that instance the series capacitor would not be needed, but you would still need the L

network.

6.

http://www.pcsystems-ss.co.uk/g7lrrweb/index.php?module=pagemast...

2 of 2 28.7.2009 20:29