Meter for the Mitrek Conversion by Karl Shoemaker, AK2O

Introduction

The SRG version ("A") has a handy feature of a panel mounted AGC meter. After plotting an AGC curve on the finished product, the R.S.L.(Received Signal Level) can be determined at the station. It's also useful for tuning the front end. This meter takes the place of a test set, using the "M-1" function, plus can be calibrated in a more meaningful scale, logarithmically speaking, and provide a 0-full scale reading for a broader range. Since the radio's to be mounted on a 2U rack (3 1/2") the meter needed to be small, and more importantly, have a small hole required for mounting to keep the structural integrity of the panel itself. A few type were obtained a few years ago, however the source ran out. The pictures provided, here, are enlargeable by clicking in the center of them. Some of these are the following:

 



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This shows what mounting area is set aside for the meter. The import feature, here, shown, is the small "body" area that goes into the panel.



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To accomplish this extensive "shopping" on the web was needed to find a vender/source of such a meter, yet low-cost. Most of the meters found were between 3-15 each, plus S&H. Some features were desired, thus looked into. They were:

  • 0-100 (something)scale. This provides a good AGC plot.

  • Low current or voltage is needed, i.e. 100 mA or 100 uA is desirable. Over a 5 volt meter won't work because of the maximum output of the (LM324) op amp meter driver output.

  • Low cost- most found were between 3-12 $.

  • Small mounting hole, preferably down at the bottom of the meter, so a notch could be made on the bottom edge of the panel.

  • Mounting bolts would eliminate gluing the meter. Glue eventually lets loose, especially in time and vibration variables.

    Some of the venders (their web sites) were:



     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     



     

     

     

     

     

     

     

     

     

     

     

     



     

     

     

     

     

     

     

     

    These are some general sites visited in search of the proper meter as well:



     

     

     

     

     

     

     

     



     

     

     

     

     

     

     

     

    As of 2009 an overall meter was found, mainly due to the help of Doug, N7BFS. It satisfies most of the requirements (size, cost, etc.). Even though the scale is not perfectly linear it's duable for an AGC curve. You also have the option of re-surfacing the scale, thanks to the simple "scotch" tape hold the face plate on. They can be reach on the web or phone at (800) 647-1800, or (662) 323-5869.



     

     

     

     

     

     

     

     

    Front, side and back views which are enlargeable by clicking on the image....



     

     

     

     

     

     

     

     

     

     

     

     

    Copy write: AK2O 2008

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      http://www.ak2o.org/srg/tech.html





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