there are described two broadband transformers with transformation
ratio 1:5 and 1:10. First transformer could match 50 Ohm to 250
Ohm the second one could match 50 Ohm to 500 Ohm. The transformers
may be used to feed different types of hi- ohmic
antennas, for example, G5RV. The transformers provide symmetrical
output. The transformers provide SWR 1.15 AT 144 MHz, 1.1 at 70-
MHz, 1.0 at 50- MHz, 1.1 at 3.5- MHz and 1.15 at 1.9- MHz. The transformers
do not overheated at 500- Watts power going through.
Figure 1 shows design of the
transformer with ratio 1: 5 (50/250 Ohm). Main core of the transformer
is a ferrite tube taken from an RFI filter that was placed on
control wires of old CRT monitor. Such tube may have OD 18… 20-
mm, ID 8… 9- mm, and length 25- 28- mm. Permeability of the core
is near 800- 1000.
1 Design of the Transformer
with Ratio 1: 5 (50/250 Ohm)
ferrite core for the transformer should be 37... 44- mm.
So, two ferrite rings with equal to the tube OD and ID placed
from the both sides of the core. First winding of the transformer
(k1k2 at Figure 1)
consist of two copper tubes (pos.1) that are inserted into the
ferrite cores. The tubes should have a minimal gap between the
cores. The tubes are shorted by a jumper (pos.4). The jumper made
of a copper strip. The jumper is soldered (pos.5) to the copper
tubes. Second winding (k3k4 + k5k6) made by teflon wire in diameter 1.5- 2.0 mm (15… 12 AWG).
Figure 2 shows design of the
transformer with ratio 1: 10 (50/500 Ohm). The transformer has
design similar to the transformer with ratio 1: 5 (50/250 Ohm).
Difference is only in the second winding that design is cleared
from Figure 2.
2 Design of the Transformer
with Ratio 1: 10 (50/500 Ohm)
transformers were tested at real antennas. They worked perfect
at least much better the usual transformer made on a ferrite ring.
The transformers have equal frequency parameters from 1.9 to 144
MHz that could not provide the usual transformers on ferrite ring.
Credit Line: Radio Hobby # 6, 2014