MFJ 945D Uživatelský manuál stáhnout pdf

Tee and SPC Transmatches

Gary E.J. Bold, ZL1AN Version 2, November 2010

1 Introduction

These transmatches are used to power match between single-ended impedances - that is, those where

one end of both the source and the load are grounded. This is the case if the source is a modern

transmitter, which expects to see a load of 50Ω for optimum operation, and the load is a coaxial

transmission line, terminated in the antenna.

If the load is balanced, as for open wire feedlines, a balun can be used at the transmatch output.

Baluns can be bought commercially, but they are not hard to wind yourself. I wind them on toroids.

Early single-ended transmatches for tube transmitters were almost invariably pi couplers. There were

2 reasons for this:

• Tube class “C” transmitters generated rich harmonics, which had to be attenuated. Pi trans-

matches do this, because they are low-pass devices, that is, they have a frequency response which

falls oﬀ very rapidly above the matching frequency.

• Tube ampliﬁers worked correctly into much higher impedance loads than those speciﬁed for mod-

ern transistor output stages, usually 50 Ω. When designed for transistor stages, Pi transmatches

usually require very large capacitance values to give a match, especially for low value loads, on

the lower frequency bands.

Modern Tee transmatches are conventionally constructed as high-pass devices. This, their response falls

oﬀ less rapidly with frequency above the matching frequency. This is acceptable for modern commercial

transmitters, which have excellent output low-pass ﬁlters already built in. Furthermore, high-pass

transmatches can be constructed with much smaller values of capacitance. Thus, the majority of

modern 3-element commercial transmatches are high-pass tee types, and I use and recommend these

myself.

I wrote three Break-In articles examining the design and performance of Pi and Tee transmatches in

detail. These are references 1,2 and 3. They are a bit theoretical for those who just want to build

one, but they do contain all the relevant design and performance equations, most of which I derived

myself and have never been published anywhere else.

2 Tee Transmatches

Figure 1 shows the simple tee high-pass transmatch (top) and the SPC (series-parallel capacitor)

transmatch. The SPC conﬁguration was devised by Doug DeMaw, W1FB, of the ARRL Headquarters

staﬀ, and published in the 1981 ARRL Handbook.

The simple tee is commonly used in commercial transmatches (such as the MFJ series), because it

is simple. The SPC has slightly better harmonic attenuation, and also enables “reasonably-sized”

capacitors to achieve a match on 160 meters. Both require two airspaced variable capacitors and

a tapped inductor. The SPC requires a double-ganged capacitor on the output side - that is, two

sections which move together on a single shaft, but this is no problem, as salvaged double-ganged

broadcast capacitors are at least as common as single ganged types. Capacitors having a maximum

value of about 350 pF per section are OK for 80 metres and up. The SPC always introduces more

loss (power dissipated in the inductor) than the simple tee, given inductors of the same Q. This is

1 2 3 4 5 6 ... 10 11

Shrnutí obsahu

Strany 1 - Tee and SPC Transmatches

1Tee and SPC TransmatchesGary E.J. Bold, ZL1AN Version 2, November 20101 IntroductionThese transmatches are used to power match between single-ended i

Strany 2 - 4 The ZL1AN Simple Tee

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 10dimensions 21 cm wide, 15 cm deep, 6.2 cm high. On the back, there are two PL259 f

Strany 3 - 4.2 Inductors

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 11The power detector is a toroidal transformer, the primary a single wire feed from

Strany 4 - 4.4 Winding the Coil

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 2Figure 1: Top: Simple Tee transmatch. Bottom: SPC transmatchbecause it is a “more s

Strany 5 - 5 Design Equations

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 34.1 Selecting Variable CapacitorsSpecial “wide-spaced” transmitting capacitors are

Strany 6 - 5.2 SPC Transmatch

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 4increased the pitch of the coil winding in what I assumed to be the right range for

Strany 7 - 8 Some Experimental Hints

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 5dropping to 3 to 5 on 15 metres, depending on the lengths of the wires to the capac

Strany 8 - 9 Tuning a Transmatch

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 6XL2=R0R2XC2(6)XL=XL1XL2XL1+ XL2(7)5.2 SPC TransmatchChoose R0> R1(50Ω) (8)and R0

Strany 9 - References

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 77 Power Loss in Tee TransmatchesIf the design parameters R1, R1, R0and QL, the indu

Strany 10

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 8important though, that the designated characteristic impedance of the SWR meter is

Strany 11

Tee and Pi Transmatches, ZL1AN Version 2, November 2010, revised. 910 Design ExamplesHere are some typical results for a simple tee matching a variety

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