AMERITRON ALS-500M Manuel d'utilisateur télécharger pdf

18 December 2005 RadCom www.rsgb.org

THE PETER HART REVIEW

In this month’s column, Peter Hart reports on two HF linear amplifiers – the SGC SG-500

and Ameritron ALS-500M – that can help mobile operators boost their power.

he enthusiastic mobile operator

keen to improve his HF DX per-

formance might very well think

of adding a linear ampliﬁer to his

equipment line-up. Such a decision

needs to be properly planned and

engineered. High power doesn’t lend

itself well to 12V power supplies

where current drains can reach

100A or more. A heavy-duty battery

or a second battery needs to be safe-

ly installed with thick, short and

fully fused cable runs from the bat-

tery to the ampliﬁer to prevent volt-

age drop. The power output from low

voltage ampliﬁers will drop heavily if

the supply voltage sags. Another

consideration is the antenna. Very

high RF voltages are generated on

short high-Q resonant mobile anten-

nas and even corona discharge or

ﬂashover is possible. At high power

levels safety is of course of para-

mount importance.

There is a select but limited choice

of suitable ampliﬁers available, and

mainly from manufacturers in the

USA. This review looks at two such

offerings in the 500W power class,

the SGC SG-500 SmartPowerCube

and the Ameritron ALS-500M. Both

have been available for some years

now and as a consequence are well

established designs. Both are fully

semiconductor broadband ampliﬁers

with no tuning required and no

warm-up time needed.

AMERITRON ALS-500M

The ALS-500M is rated at 500W PEP

output on SSB or 400W output on

CW and covers all bands from 1.8 to

30MHz. The standard version sold

off the shelf in the USA requires an

internal modiﬁcation to cover 24 and

28MHz. This is a legal requirement

for all ampliﬁer sales in that country.

Early versions of the ampliﬁer need

to be mounted where the operator

has access to the front panel con-

trols. Later versions can also be

remotely mounted with all front

panel controls and indicators repli-

cated on an optional remote control

head unit. An upgrade kit is avail-

able to allow earlier units also to be

used in conjunction with remote

control.

The ampliﬁer uses a total of four

Toshiba 2SC2879 bipolar power tran-

sistors arranged as two separate

250W push-pull ampliﬁers coupled

together using hybrid splitters and

combiners. A separate PCB contains

the temperature compensated biasing

circuitry and control for the fan and

trips. The output from the ampliﬁer

assembly is followed by a low pass

ﬁlter to reduce harmonics to an

acceptable level, and a bandswitch

on the front panel or on the remote

unit selects one of six ﬁlters to cover

the entire frequency range.

The whole assembly is constructed

on an aluminium chassis with a

wrap-around case 23.7cm wide,

9.7cm high and 37cm in depth. It

weighs about 3.4kg. Internally, the

RF power ampliﬁer is mounted on a

ﬁnned aluminium heatsink and is

cooled by a fan. This is fairly quiet in

operation and also only operates

when the heatsink temperature rises

so there is no fan noise during

lengthy periods on receive. The

ampliﬁer is switched from the trans-

ceiver via a ‘ground to transmit’ line

(12V open, 100mA closed). The main

DC power feed is via a plug and

socket on the rear panel. The high

current lines remain permanently

connected but a separate lower cur-

rent line is used to switch the ampli-

ﬁer on and off. Although the power

connector is quite substantial, the

current passing through the pins is

as much as 80A peak. This is a 10-

way connector but only two pins are

used to carry the positive feed and

two for the ground return. If this

were my ampliﬁer, I would parallel

up the remaining vacant pins to

share the high current load. A power

cable is provided but it is quite long

and should be shortened to be no

longer than necessary. The current

drawn by the ampliﬁer is indicated

on the front-panel meter.

Protection circuitry is built-in to

guard against damage to the power

ALS-500M linear

ampliﬁer

ALS-500M front panel

Inside the ALS-500M

showing ampliﬁer,

ﬁlters and control

boards

Empowering mobile operators

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Résumé du contenu

Page 1 - Empowering mobile operators

18 December 2005 RadCom www.rsgb.orgTHE PETER HART REVIEW18In this month’s column, Peter Hart reports on two HF linear amplifiers – the SGC SG-500and

Page 2 - Peter Hart, G3SJX

19www.rsgb.org RadCom December 2005THE PETER HART REVIEWPeter Hart, G3SJXThe Willows, Paice Lane, Medstead, Alton, Hants GU34 5PRE-mail: [email protected]

Page 3

20 December 2005 RadCom www.rsgb.orgTHE PETER HART REVIEWnal. SGC claims that this takes just15ms but of course this does involvean element of ‘hot sw