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     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:

https://vk6ysf.com/pre_amp_70cm_kit_202011.html

 

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Page initiated 20 August, 2024

Page last revised 20 May, 2024 

 
 

   Space Weather

   https://www.swpc.noaa.gov/

    

   Notice Board

VK6YSF JS8Call and Olivia 8/250 operations.

Current activity is generally focused - though not restricted to - JS8Call operations on the 20m, 30m, and 40m bands.

Currently there is a particular emphasis on JS8Call on the 10 and 12 m band between 00:00 and 12:00 Z, often extending beyond this period.

Olivia 8/250 is used occasionally on the 20m band.

Proposed band and mode activity is often communicated on HamSpots: https://hamspots.net/js8/ or my profile on 

X: https://x.com/vk6ysf97230 .  

Feel free to contact me to discuss or arrange a schedule for a contact.

Post date: 7 December 2025

 

Western Australian SSTV net 

Popular Western Australian SSTV net for both digital and anolog SSTV.

Generally found at 7214.0kHz LSB every afternoon from 08:00 UTC (4:00pm WST)

For more details: https://www.wasstv.net/wasstv.net/index.html

Post date: 8 December 2025

 

VK6MJM LF (136kHz) and MF (474kHz) Beacon

VK6MJM is a  LF/MF station located in Manjimup, Western Australia.

Common Mode: FST4W 300 (Similar to WSPR)  

Note: other modes and sub-modes may be used.

Station details were presented by Peter Hall (VK6HP) at PerthTech 2024.Presentation PDF: Peter Hall VK6HP at PerthTech

QRZ Page: VK6MJM on QRZ.com

Post date: 10 March 2025

 

 

 
 

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Amateur Radio Station VK6YSF - Promoting amateur radio communication and experimentation.