Vectronics HFT-1500 User Manual download pdf (Page 6)

From February 2003 QST © ARRL

TEN-TEC 238A

The Ten-Tec 238A is the only tuner

in our roundup to utilize an L-network.

Using an innovative switching arrange-

ment, the 238A actually provides five dif-

ferent circuit configurations to maximize

efficiency. A look at the low loss figures

in the table confirms this. The well-con-

structed tuner makes us of a single vari-

able capacitor and a smooth turning wire

wound roller inductor to match imped-

ances up to 3000

Ω

. Additional capaci-

tance is switched into the circuit by

means of a front panel switch. Five set-

tings each are available for high and low

impedances, as well as a bypass choice.

A ceramic feed through post on the back

panel provides a connection to add an

additional 1000 pF capacitor (included

with the tuner) to the circuit for match-

ing 160 meter antennas. The small dual

use meter can be switched to display

SWR or RF power in either a 2000 or

200 W range. The meter lamp is pow-

ered by 12 V on the back panel.

The 238A handily matched all bands

on both test antennas at full legal limit

power. On 10 meters using the G5RV, the

capacitor and inductor controls were a bit

sensitive to small adjustments. One mi-

nor complaint: Measuring forward power

in the high power range on the meter

caused the indicator to slap the right ex-

treme position during CW keying.

In laboratory tests, the 238A did not

match on 160 meters into a 6.25-Ω load

until 2700 pF of external capacitance was

added. Ten-Tec indicates they will provide

additional capacitors to purchasers at no

extra charge. Also, the power losses on 10

meters were considerably greater than those

on other bands. However, the 238A per-

formed very admirably on most other

bands, quite often exhibiting the least losses

on given band and load combinations.

The four-position antenna switch on the

front panel allows selection of four coax

outputs or a balanced/random wire. The

balanced output and one coax connector

share position four. A two-core balun

is provided for matching the balanced

output.

Front panel of the Ten-Tec 238A. Rear panel connections on the Ten-Tec 238A.

Interior circuitry of the Ten-Tec 238A. The 238A is the only one of the

five tuners reviewed here without an air-core inductor. The inductor

here has a linen phenolic core.

Since we purchased our review unit,

Ten-Tec has produced a substantially

identical antenna tuner, the 238B. The

Tennessee manufacturer is now selling

only the 238B model.

Manufacturer: Ten-Tec, 1185 Dolly

Parton Pky, Sevierville, TN 37862; tel

865-453-7172; fax 865-428-4483; www.

tentec.com. Price: $475.00 (current

model 238B).

Table 5

Ten-Tec 238A

SWR

Load (

Ω

)

160 m

80 m

40 m

20 m

10 m

8:1 6.25 Power Loss % No Match <10 <10 <10 28

1.5 SWR BW >5 >5 >5 2

4.1 12.5 Power Loss % <10 10 <10 <10 22

1.5 SWR BW >5 >5 >5 >5 2

2:1 25 Power Loss % <10 10 <10 <10 17

1.5 SWR BW >5 >5 >5 >5 3

1:1 50 Power Loss % <10 <10 <10 <10 <10

1.5 SWR BW >5 >5 >5 >5 >5

2:1 100 Power Loss % <10 <10 <10 <10 20

1.5 SWR BW >5 >5 >5 >5 4

4:1 200 Power Loss % <10 <10 <10 <10 20

1.5 SWR BW >5 >5 >5 >5 4

8:1 400 Power Loss % <10 <10 <10 10 13

1.5 SWR BW >5 >5 >5 >5 1

Notes

“No Match” means that a 1:1 SWR could not be obtained, even with the included 1000 pF

external capacitor attached. A match on 160 m at 6.25 Ω was achieved with 2700 pF of

external capacitance; the power loss was less than 10%, and the 1.5 SWR BW was

greater than 5%.

Power losses are expressed as a percentage. A 21% loss of power is 1 dB.

The 1.5-SWR Bandwidth (SWR BW) represents the bandwidth over which an SWR of 1.5:1

or less was maintained as a percentage of the measurement frequencies (1.8, 3.5, 7.2,

14.2 and 29.7 MHz).

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