Monday 26 May 2014

N7ART Audrey II 432MHz Amplifier 240V Conversion

A week ago I was taking stock of my 432MHz amplifier collection. The one I had used the most was the N7ART Audrey II 2x3CX800A7 amplifier I bought 20 years ago. Steve made a wonderful job of building the amplifiers as the pictures below show. Unfortunately the PA was wired for 110V so couldn't be used in the UK. The 2600V PSU was not an issue as it was wired for 240V. It was time to investigate what would be needed for conversion.

Luckily I still had the original Documents in which Steve gives the part numbers for the 240V components used in his 240V version. The relay supply transformer in the amplifier (Triad FD-4-12) was already dual voltage primary so did not need changing. The heater transformer was a Stancor P8857 which being 115V only primary would need changing to a Triad FD-7-16 which would also mean changing the resistor in series with its primary from 20ohm 20W to 150 ohm 20W. The blower was a Dayton 4C446 115V 50/60Hz which would need changing to a Dayton 2C915 230V 50/60Hz. The search was on
The Dayton 2C915 is no longer made but I found an equivalent on ebay for $68. Mouser had the FD-7-16, but on 4 week delivery but someone had one on ebay at $10 shipped, so both were bought along with a 150 ohm 30W resistor from the local emporium
This weekend the components were installed. The blower had a different shaped outlet flange so some chassis filing was needed but fitted otherwise. The new transformer had different fixing centres which needed to be drilled along with the mounting holes for the new resistor.
Top View of amplifier after modification
Bottom View of amplifier after modification
  The amplifier is now ready to go on UK mains!

Tuesday 20 May 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  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 

Thursday 8 May 2014

Auto External Reference switching for the ANAN-10 HPSDR

Over the period I have owned the Anan-10 SDR Transceiver the only issue for me has been that to use an external 10MHz reference it has to be taken apart and links changed, which runs the risk of damaging the tiny RF cables. Last August G8ONH/G7OCD mentioned on the OpenHPSDR reflector they were working on a small PCB to be mounted in the ANAN-10 that would automatically switch the ANAN-10 to use the external reference when one is plugged in. This week I managed to obtain a board from G7OCD and set about installing it.
The board is very small:-
PCB size compared to a quarter
ANAN-10 Innards before Installation
All I had to do was plug the 4 headers into PCB and solder the pins to the PCB:-

PCB after Installation

 The 2 holes on the PCB are to allow a jumper to be fitted to ground the SMA connector "outer". A header wasn't supplied so I fitted a right angle 2 pin male connector to the PCB and used one of the now "spare" jumpers  on it

Jumper block added

Including assembling/disassembling the ANAN-10 and putting the board in place it took only 15 minutes to complete. 

My Rubidium drives a DEMI 10-4 four way 10MHz splitter. Attenuating the output with 50Ohm attenuators the minimum level to achieve "autoswitch" was -3dBm which is just fine for my setup
Note that when using the board NOTHING needs to be done to the PowerSDR settings to accommodate the board.

Friday 2 May 2014

MTR3 kit

Steve KD1JV is a prolific producer of compact rigs for mountain topping. A few years ago I bought and built an ATS3 and an ATS4 5 band rigs which were great fun, Unfortunately I sold them to finance the KX3.

I really miss them, so was excited when Steve announced that he was going to do another run of 150 Triband MTR (mountain top radios, AKA MTR3). The sale was the usual "first come first served" after the web page was launched, but I was lucky enough to get one of the kits. When the kit arrived it sure was small, it makes the KX3 look enormous!:-

Shortly after it arrived Steve announced he was sending all buyers an updated cpu chip to fix a bug, so I waited for that to arrive before starting construction to avoid having to desolder the original chip. I decided to build it for 40/30/20m. Building it took around 3 hours, including alignment. It was christened with a couple of QSOs on 20m using the Alexloop antenna Comparing the two,  I prefer the ATS due to its lcd frequency display avoiding the need to memorise the scrolling digits on the lcd display, but the MTR3 is much smaller!