Skip to main content

Another MMR40 fix

 

Another MMR40 fix

Filed in Kits on Jan.04, 2010

When I initially constructed the MMR40, I was going to use the original case.  So I put the band range switch on the bottom of the board to accommodate that.  Well with switching to the new case, I decided that I needed to move the switch to the front panel.  This had an unfortunate side effect.  It seems that the stray capacitance from the few inches of wire used to connect the new switch is enough to shift the VFO frequency down about17 kc.

 

Original Band Switch

I had spent a good amount of time adjusting the coils of the VFO to make it cover from 7025 to about 7150 kc on CW, which includes the most popular QRP frequencies of 7040 and 7030 kc.  With the 17 khz offset, the new range was shifted to 7042 to 7170 kc.

To rectify this problem, I pulled 1 turn off of the L2 toroid of the VFO circuit.

L2 Toroid

This shifted the VFO frequency up, and caused the rig’s final frequency to shift down.  So I now cover 7010 to 7147 kc in CW range, and 7126 to 7258 kc in SSB range.  I gave up some spectrum at the top, and gained some at the bottom.  I guess that’s OK, as 5 watts is a lot better using CW than it is using voice.  The Blue/White cable is the connection to the new switch.

MMR40 Mounted in the chassis

Large picture of band switch installation. I had a question about this, and found this higher res photo of how I wired the band switch. It looks like I wired the switch across the two terminals directly above the “S2” indicator on the silkscreen. I don’t remember why the wire colors are different here, but this looks like the connection…


 Migrated Comments:

3 Responses to “Another MMR40 fix”

  1. AC0AX Says:
    January 18th, 2016 at 3:01 pm

    How did you wire up the band switch. Im currently trying to wire mine up but the pto never starts oscillating. It was fine before I tried to wire in a new switch.

  2. wb0smx Says:
    January 18th, 2016 at 5:54 pm

    AC0AX, I added a hi-res photo to the post of how I wired the band switch. You can click on the photo and get a large one that will let you zoom in on the details. Good luck…. Randy WB0SMX

  3. ac0ax Says:
    January 19th, 2016 at 8:35 am

    Thanks Randy,
    I got it working. I must of had a cold joint. I touched up all the joints in the PTO and then it came back to life.


Comments

Post a Comment

Popular posts from this blog

Building the W8NX Short Trap Dipole

Image
  Building the W8NX Short Trap Dipole Filed in Antennas on May.31, 2021 For the past five years, I have been operating the lower bands (30, 40 and 80 meters) with a trap dipole that was modeled after a web article written by John DeGood NU3E. [1] While the antenna performed well, a monsoon storm last summer beat it up enough that the antenna wire broke at the center balun. So I climbed the tower and lowered the remains of the antenna to the ground for repairs. On closer examination, I discovered that the relentless Arizona sun had taken its toll on the traps. The insulation on the exposed ends of the coax had rotted away. They were still working, but would need to be rebuilt and weatherized to insure good operation many years into the future. Since I was going to have to rebuild the antenna, I started thinking about whether this antenna met my current needs and wishes. I had been wanting to get on 160 meters at this QTH for some time, but my small back yard would
Read more

Yaesu G-450XL Rotator Repair

Image
  Yaesu G-450XL Rotator Repair Filed in Antennas on Dec.30, 2007 In December of 2007, the rope support for the center element of my Cushcraft A3 broke, requiring me to climb the tower and bring the beam down for maintenance.  At the same time, at had been noticing that the rotator control was not indicating correctly, it was very erratic.  So I brought the rotator down for maintenance, as well. The first step was to mark the side of the case, where the top and bottom of the clam shells connected together.  This would allow me to assemble it in the correct alignment when the time came.   Marked Case of Rotator Next, I took the top cover off.  All of the bearings between the clam shells in the depression on the outside were safely stored.   Top Removed A little inspection revealed what the problem was.  The center gear had broken away from the shaft it was pressed onto.  I tried re-pressing it back onto the shaft, but it was too worn out.  I found the phone number for p
Read more

JuncTek Battery Monitor MQTT Controller

Image
 I recently installed some 48 volt Lithium Iron Phosphate battery packs at the Ranch to replace the 9 year old Lead-Acid batteries that had started to fail.   eg4-lifepower4-battery-48v-100ah   These are rack-mount battery packs that are intended for powering computer servers.  They are reported to work very well in an off-grid power system.  The Problem I had a problem to solve before the upgrade, in that the old 48 volt inverter I had been using in our solar power system required a programming interface to change its operating parameters to match the new battery specifications.  Unfortunately, the manufacturer wants over $400 for the required interface to make these changes.  I am unwilling to pay this extortion money for a simple device that should cost less than $100. The communications protocol and interface is proprietary, so it would take a considerable effort to hack the interface. There are two sets of parameters in dealing with the inverter/battery connections: 1. The chargin
Read more