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Watts Up With Those Amps? |
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This article
will provide a little insight into the world of VHF amplifiers. The test
subject is the RF Concepts 2-417. This particular series of amps is no
longer in production, but should be applicable to similar products by
other manufacturers.
The RFC 2-417 is
a VHF amplifier with the following specs:
Frequency Range: 143-149 MHZ
Input Power: 200mw to 50w
Output Power: 170w with 45w input
Max Input Power: 50 Watts
Modes: FM/SSB/CW
GaAs FET Preamp: Gain 20db nominal, Noise Figure 1db nominal
SWR Protection: 3:1 SWR Auto shutdown
Temp Protection: 175F Shutdown
Keying: Automatic RF sensing or external 3-12VDC keying line
Current Requirement: 22 amps @ 13.8VDC
Weight: 5lbs
If you take note
of the specs, you will see that this amp could be operated via a low drive
HT transceiver albeit with reduced output.
The RFC2-417:
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The test setup with ICOM IC-7000 driving the RFC 2-417,
Astron RS-50M power supply, Bird wattmeter, and Bird coaxial resistor (not
shown). The amp is being operated via RF sensing. |
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The following
statistics of input power vs output power vs current requirements are only
accurate within the limits of the analog measuring devices being used,
lengths and type of coax used, and of course my analog eyesight. While not
lab standard by any means, I think that the info provided will give some
useful insight into the operational considerations of using an amplifier.
All testing was
conducted in FM mode. |
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INPUT POWER
(Watts) |
INPUT CURRENT*
(Amps) |
OUTPUT POWER
(Watts) |
OUTPUT CURRENT**
(Amps) |
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147.54 MHz |
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5 |
<6 |
70 |
16 |
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10 |
>6 |
108 |
<20 |
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15 |
<8 |
125 |
21 |
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25 |
>8 |
135 |
>22 |
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35 |
<10 |
142 |
24 |
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40 |
10 |
148 |
25 |
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145.00 MHz |
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40 |
10 |
160 |
30 |
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144.00 MHz |
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40 |
10 |
165 |
30 |
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In this
particular setup, the amp was a bit more efficient near the SSB end of the
2 meter band.
(The < and > indicate slightly more or less than the stated values).
(*) IC-7000
current draw.
(**) Combined
IC-7000/RFC 2-417 current draw.
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Showing 108 out
with 10 in, a bit under 20 amps total draw:
(250W
element/top scale) |
Showing 125 out with 15 in, 21 amps total draw: |
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Showing 135 out with 25 in, a little over 22 amps total
draw: |
Showing 142 out with 35 in, 24 amps total draw: |
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Showing 148 out with 40 in, 25 amps total draw: |
Showing 160 out with 40 in, 30 amps total draw: |
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Showing 165 out with 40 in, 30 amps total draw: |
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It was a fun experiment showing the
efficiencies/inefficiencies of a transceiver and amplifier for VHF
operations. |
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Disclaimer: I have no financial interests in Icom, RF
Concepts, Bird, or Astron. Opinions are my own.
Photos taken by WB7X
http://www.wb7x.net |
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