[amsat-bb] Mast mounted low noise amps

Gregory Beat w9gb at icloud.com
Sat Jan 20 22:28:19 UTC 2018

Bill -

The Icom AG-series of mast mounted pre-amplifiers for weak-signal and satellite work are now legacy (I believe Icom has discontinued recently).  A lower noise figure of the active device (FET, MMIC) is important for satellite work (sky), than weak-signal work (noisy terrain/earth).
High noise-levels with the AG-series are often attributed to a Failed FET or an improper FET replacement by an earlier owner.

Newer FETs have ESD / static protection, while older designs — DID NOT !
Nearby lightning strikes can damaged the FET on the AG-series pre-amps.

Central States VHF Society annually performed Noise Figure tests on a variety of devices.
This may be useful, as you examine modern devices or recent surplus.

The Icom mast-mounted pre-amplifiers (AG-25, AG-35) used the dual-gate Toshiba 3SK121 Dual Gare FET (discontinued).  Schematics and manuals for the Icom AG-series are available via the Internet.
MODS.DK has the parts list and hand-drawn schematic for AG-35 (1999),
the othe file AG-25 etc. Instructions has schematic for AG-25 (last page).

Toshiba 3SK211 — GaAs MES FET, Dual-Gate, UHF, 10V, Idss>20mA, Up<4V

Icom AG-series (brochure)

In 2012 and 2013, Earl Andrews, VE3AB (Netty Electronics) 
did comparison testing of various Dual Gate FETs, used by Icom, Yeasu, and Kenwood since the late 1970s.

Earl also noted Eastern Asian counterfeit products (various FETs), largely from China.
The Phillips/NXP BF981 being a common bad Chinese export (March 2014 & June 2015)

RF Parts — Low Noise FETs
As far as a MMIC swap, I have not seen anything posted (YouTube, Icom boards, amsat-bb reflector), BUT that does not mean it has not be attempted or accomplished.
Beginning this month — Corey Abercrombie, N4NGZ, acquired the exclusive rights to manufacture, sell and repair the existing DownEast Microwave, Inc. (DEMI) VHF/UHF Transverter product line and all past VHF/UHF transverter products. 
Q5 Signal, LLC
17704 County Road 455
Montverde, FL 34756

Sales:  sales at q5signal.com

Support:  support at q5signal.com

Corey may be a source for current production UHF/Microwave devices, now or in future.
Jay Rusgrove, W1VD owner of Advanced Receiver Research (ARR) has a number of excellent Gallium Arsenide low-noise preamplifiers (LNA’s).
The ARR MSP144VDG-160 and MSP432VDG-160 models are often recommended for fixed satellite earth stations.

High Performance, 160 Watt Mast Mounted, Amateur Radio Preamplifiers

Greg, w9gb
From: Bill Acito <w1pa at hotmail.com>

What's the opinion/consensus of the older ICOM AG series, as an 
economical alternative? Can they be updated, with say, a different MMIC?

Bill W1PA

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