Peter Miles
Northam, Western Australia QRZ Page: VK6YSF
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70cm MAST HEAD PRE-AMPLIFIER REPAIR
Mini-kits EME221-70CM 70cm Mast Head Pre-amplifier. 23 July 2024
The
EME221-70CM mast head pre-amplifier was damaged when operating SSB
at about 20w at 432MHz. The set up at the time relied on the RF
sensing (Un-Sequenced mode) to switch the by-pass relays during
transmission. Shortly into transmission there was a complete loss of
all RF gain in the pre-amplifier.
Repairs
completed on the mini-kits EME221-70CM mast head pre-amplifier
involved the replacement of the surface mounted PGA-103 and
PSA-0012 MMIC amplifier chips. It was determined during the repair
work that the PGA-103 chip was not faulty, however it was replaced
as it was not worth undoing the work.
The EME221-70CM mast head pre-amplifier is now operated in the
Sequenced mode relying on the Yaesu FT-736R transceiver to trigger
the pre-amplifier relay switching. See below details.
IC1,
PGA-103 High Dynamic range MMIC Amplifier 0.05-4GHz
Low
Noise Figure, 0.6 at 1 GHz; 0.9 dB at 2 GHz
Gain,
11.0 dB typ. at 2 GHz
IC2,
PSA-0012 High Dynamic Range MMIC Amplifier 0.05-6GHz
Low
Noise Figure, 2.4 dB typ. at 1 GHz
Gain,
16 dB typ. at 1 GHz
Figure
1. Circuit schematic EME221-70CM mast head pre-amplifier
Photo
1. Completed EME221-70CM mast head pre-amplifier board.
Photo
2.Yaesu FT-736R
transceiver rear panel jacks and connectors.
Photo
2.Yaesu FT-736R 5 pin
switching jack (4) STBY DIN Jack.
This
5-pin jack provides transmit/receive switching line for controlling
external transmitter amplifiers. Pinout is determined by Band Module
installed.
Video
of repairs including on air test carried out with the International
Space Station repeater in a contact with VK6GC.
See construction of
the EME221-70CM mast head pre-amplifier kit:
