[hpsdr] Munin problem

[John]

Hi Helmut,

Thanks for your answer.

The bias current is stable when there is no 
drive.  When drive is applied, the bias 
current  change is quite different on some bands.

I have a fan mounted close to the heat sink on Munin to improve the cooling.

My SWR bridge is an old MicroMatch made by M C 
Jones many years ago.  It is used to manually adjust my antenna coupler.

I am wondering if I should build a reflectometer 
SWR bridge and then remove the filtering of the 
reflected output signal.  I don't want to open my 
MicroMatch.  Maybe I could see the reflected 
signal on an oscilloscope and get some idea of 
the frequency of the spurious with a modified reflectometer.

Unfortunately, it would be very difficult for me 
to remove the final transistors because of the 
way I have mounted the copper straps on top of 
the board using homemade spacers.
http://www.n-connect.net/radio/Ham_Pix/Munin/Assemled%20Munin%20Board.JPG

Since the photograph was taken, the single 
thermistor bias stabilization circuit was added.

73,  John  WoGN



At 07:45 AM 5/18/2014, Helmut Oeller wrote:
>Hi John,
>
>Munin is well designed, but a lot can happen during assembling, soldering
>etc. with the components. Some things you mentioned would concern me:
>You talk about strange behavior of bias current. Without drive power the
>bias or quiescent current of the finals and driver stages should be stable
>on all bands, otherwise it can be clue for self oscillation.
>Be careful with stressing the amp when see high input and unusual little
>output. Power must be dissipated somewhere.
>You mentioned that Hermes VNA probably together with a measuring bridge is
>available. It's always a got idea to control transmission or at least
>reflection of the transformers and compensation capacitors before placing
>the semiconductors.
>
>In the current situation look for the 'power traps' first before applying to
>much drive power .
>
>Good luck.
>
>73, Helmut, DC6NY
>
>-----Ursprüngliche Nachricht-----
>Von: Hpsdr [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von John
>Gesendet: Sonntag, 18. Mai 2014 13:12
>An: hpsdr at lists.openhpsdr.org
>Betreff: [hpsdr] Munin problem
>
>***** High Performance Software Defined Radio Discussion List *****
>
>
>
>I'm trying to get my Munin working with Alex and Hermes, now using
>PowerHPSDR v 3.2.10 (4/10/14) and Windows 7 Pro 64 bit.
>
>I did not notice any problem when running Munin without Alex into a
>50 Ohm load using a signal generator for a signal source.  The output
>power was a little low on the higher bands and on some bands the bias
>current readings were strange to me.
>
>I calibrated my 30 dB power attenuator and cables for the ham bands
>to 54 mHz using Hermes VNA and calculated the correct Voltmeter
>readings to be used to set up the gain and Wattmeter settings in
>PowerHPSDR.  My Voltmeter is not fully  calibrated, but it agrees
>with each of my two signal generators.  I used this setup to set the
>gain in PowerHPSDR on all bands.  At 12m I could not get 100W and the
>supply current was lower than expected.  The output was also low on
>6m, but the supply current was very high.  The PowerHPSDR wattmeter
>was calibrated at 1.8 mHz using the same test setup.
>
>However, when connected to an antenna having a low SWR and running
>reduced power, PowerHPSDR indicated very high SWR and reflected power.
>
>I then ran power from my TS-440 rig through Alex at 3.5mHZ (no PA,
>Hermes on a dummy load with no drive and keyed in CW) and checked the
>PowerHPSDR readings:
>      Forward Power  82 Watts
>      Reflected Power 1.0 Watts
>      SWR  1.3:1
>
>This seems to indicated my problem(s) is not caused by Alex.
>
>I also used an external SWR bridge and found very low SWR when using
>a 50 Ohm load and very high SWR using an antenna.
>
>The only explanation I can come up with is that my Hermes/Munin/Alex
>system has very high spurious output and the antenna system is
>reflecting the spurious output.  I don't have access to a spectrum analyzer.
>
>Is there another explanation for the above results?
>
>73,  John  WoGN
>
>
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