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. https://csvhfs.org/index.php/vhf-101/24-csvhfs-history/noise-figure-results
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. http://www.radiomanual.info/schemi/ACC_preampl/Icom_AG-35_user_IW2HEU.pdf 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 http://pdf.datasheetcatalog.com/datasheets/134/499109_DS.pdf
Icom AG-series (brochure) https://www.icom.co.jp/world/support/download/manual/disp_down.php?SWT=&...
In 2012 and 2013, Earl Andrews, VE3AB (Netty Electronics) http://www.nettyelectronics.com/ did comparison testing of various Dual Gate FETs, used by Icom, Yeasu, and Kenwood since the late 1970s. http://www.earlandrews.com/dgshootout.html
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) http://www.earlandrews.com/dgmosbadagn1.html
http://www.earlandrews.com/dgbadagn.html — RF Parts — Low Noise FETs https://www.rfparts.com/rftransistors/transistor-misc/transistor-misc-lownoi... === 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. https://www.downeastmicrowave.com/ Q5 Signal, LLC 17704 County Road 455 Montverde, FL 34756
Sales: [email protected]
Support: [email protected]
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 http://www.advancedreceiver.com/page10.html
Greg, w9gb == From: Bill Acito [email protected]
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