Monday, May 19, 2014

An evening on 474kHz at WH2XES

Tonight I went and visited W5LUA to Christen his new experimental licence WH2XES on 475kHz.
 
In preparation I had built a modified Ultimate 3 Transmitter by Hans Summers http://www.hanssummers.com/ultimate3.html  When originally built with the 2N7000 the output spectrum was nasty, especially LF of the output signal so I looked at alternates. I ended up using the filtered sine wave output from the DDS (the original used the square wave output) to drive an ERA2 and a 2N5109 PA from kitsandparts to a lowpass filter. This produced 200mW into 50 ohms.
 
 
Ultimate 3 New output Stages
 
I also built the GW3UEP 100W IRF540 amplifier:-
100WAmp with Arduino Protection circuitry
 and a matching 100W Low Pass Filter to a design by WA1ZMS
 
 
We started the evening with the 200mW on WSPR into AL's 80m dipole with inner and outer strapped together and tuned against ground with an LC network resulting in a 2.8:1 SWR
 
We immediately got reports from the local
 
01:04   WH2XES   0.475722   -12   0   EM13   0.2   WG2XIQ   EM12mp   93km  
01:08   WH2XES   0.475723   -12   0   EM13   0.2   WG2XIQ  
01:12   WH2XES   0.475722   -11   0   EM13   0.2   WG2XIQ  
01:16   WH2XES   0.475722   -12   0   EM13   0.2   WG2XIQ  
01:20   WH2XES   0.475722   -12   0   EM13   0.002   WG2XIQ  
01:24   WH2XES   0.475722   -12   0   EM13   0.002   WG2XIQ  
 
(we adjusted the power to transmit EIRP at 0120)
Enthused we hooked up the PA which started taking a lot of current but was producing lots of output
 
01:32   WH2XES   0.475722   +10   0   EM13   0.002   WG2XIQ   EM12mp   93   175  
01:32   WH2XES   0.475728   -22   0   EM13   0.002   KF5JIA   EM15qe   194   11  
01:32   WH2XES   0.475729   -7   0   EM13   0.002   WG2XXM   EM15lj   213   0
 
(we forgot to adjust the power setting on WSPR) The signal at WG2XIQ increased 22dB and we were heard in OK. Unfortunately on the next transmit period the supply current limited with no output. We hooked up the exciter to the antenna while we investigated
 
  01:48   WH2XES   0.475722   -19   0   EM13   0.002   WG2XIQ
 
The received signal level had dropped 7dB. We noticed the SWR in the shack was now 8.8:1. We let it run while we braved the chiggers in the field to look at the matching unit
      
  01:52   WH2XES   0.475722   -19   0   EM13   0.002   WG2XIQ    
  01:56   WH2XES   0.475722   -20   0   EM13   0.002   WG2XIQ    
  02:00   WH2XES   0.475722   -19   0   EM13   0.002   WG2XIQ    
  02:04   WH2XES   0.475722   -19   0   EM13   0.002   WG2XIQ    
  02:08   WH2XES   0.475722   -20   0   EM13   0.002   WG2XIQ
 
Opening the box we were met with a nasty smell. There were scorch marks on the box and the red enameled wire on the 180uH toroid was now a brown scorched wire
 
 
 
 
Some more work needs to be done on the matching unit! Needless to say the $1.25 IRF540 needed replacing, but they are in stock at the local emporium 
 
 

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