MORNING STAR OBSERVATORY
  • Home
    • Contact
  • Astrophotography
  • Observatory
    • New Observatory
    • Lancaster Dome
    • ExploraDome
  • Equipment
    • Accessories >
      • RA Drive Corrector
    • CCD Cameras >
      • Orion Starshoot Pro
    • Mounts >
      • Orion HDX110 (EQ-8)
    • Telescopes >
      • 1956 Questar 3.5
      • Astro-Tech AT6RC
      • Celestron C-11 XLT
      • Zhumell 152mm Refractor
  • Projects
    • C11 XLT Mods
    • Dome Automation
    • Orion SSPRO Camera >
      • Disassembled Views
      • Noise Reduction Mod
      • Temp Controller Mod
    • Ultima 8 Mods
    • Zhumell Refractor Mods
  • Non-Astronomy
    • Amateur Radio >
      • Accessories >
        • Station Boom Microphone
      • Ameco >
        • Ameco AC-1
        • Ameco OCM
        • Ameco PT-2
        • Ameco R5A
      • Vintage Equipment >
        • Knight Kit T-60 Transmitter
        • Heathkit SB-102 Station
      • Yaesu FT-817 >
        • Yaesu FT-817ND
        • LDG Z-817 Autotuner
        • Windcamp LiPo Battery
    • Antique Radios >
      • Building A Radio Workbench
      • Radio Dial Neon Clock
      • Radios >
        • Boat Anchor Radios >
          • BC-348N Receiver
          • Collins 51J4 HF Receiver
          • R-392 HF Receiver
        • 1938 Zenith 6-S-254
        • Echophone EC-1
        • Eltz Radione 2
        • Knight Kit Span Master II
        • Panasonic RF-5000A
        • Silvertone Model 4465
      • Test Equipment >
        • Hickok >
          • Hickok OZ-1 (550X)
          • Hickok 19X RF Generator
          • Hickok 225K VTVM
          • Hickok 288X RF Generator
        • Simpson >
          • Simpson Genescope
        • Supreme Instruments >
          • Supreme Model 385 Automatic
          • Supreme Audolyzer
          • Supreme Vedolyzer
          • Supreme 563 Audio Generator
        • Military Test Equipment >
          • BC-221-AF Frequency Meter
          • I-177 Tube Tester
          • LM-21 Frequency Meter
          • MX-949 Adapter
          • TS-323/UR Frequency Meter
          • TS-465 C/U Sweep Generator
          • TS-505D/U VTVM
          • TV-3C/U Tube Tester
        • Rider Chanalyst
        • Tektronix 326 O'scope
        • Tube Testers >
          • Alternating Current Sink
          • Drug Store Tester
          • Hickok OZ-1 (550X)
          • I-177 Tube Tester
          • MX-949 Adapter
          • Precision Model 10-12
          • Supreme Model 385
          • TV-3C/U Tube Tester
    • Star Trek Communicator

A Station Boom Microphone

This page is now several years old. I don't know if you can still get the same mics anymore, and this is just for my reference now.

There are tons of cheap microphones online but are any of them suitable for a ham station microphone? I didn't have a good answer until I came across G4IZH's web page on the widely available and cheap BM-800. He provides detailed info on converting these into good performing mics for ham radio use.
​
​
The BM-800 comes in a variety of color choices and I chose blue and silver. On the inside it's an electret condenser microphone requiring a separate power source (phantom power) to operate. In testing with my FT-817 it was operating on only 5VDC. Obviously the gain was reduced at 5V but I was still able to adjust the output to match the level from the dynamic hand microphone for my FT-817.

The G4IZH modification converts the output to unbalanced and tailors the frequency response for better performance with an amateur transceiver.  

It's probably not going to beat out an expensive, high-end amateur microphone, but then I wasn't willing to pay the high-end price either. And I prefer DIY projects whenever possible - for me that's what the hobby is about.

​
Picture

BM800 Microphone Conversion

Although these mics are inexpensive, they are still well constructed. The shell and frame are all metal and only the internal electret mount is made of plastic. It's easy to disassemble the BM-800 - just unscrew the end and the metal shell slips right off. Then there are two screws inside that hold the screen in place. And there's plenty of room inside for the conversion.
Picture
There is one circuit board in this mic. Some of these have or had a second unused blank PCB mounted on the opposite side but not this one.
Picture
The screen removed to expose the microphone element/holder. The screen now has a foam insert unlike older BM-800's I've seen online. 

Picture
Picture
Thanks to the foam insert, the internal microphone element is not visible through the screen even when backlit, unlike older versions where the element was easily seen. Shouldn't be any need to add the external wind cap. Also, the front of the mic element faces the lettering on the body.
Besides the foam cap, the accessories include a metal shock mount and 2-wire microphone cable. The shock mount works fine as is, but the original conversion circuit required a 3-wire mic cable because it uses a separate lead for power. My FT-817 Windcamp interface puts phantom power on the audio lead, so I altered the mic circuit to use phantom power too, eliminating the need for a third wire. Now I can use the supplied 2-wire mic cable along with my Windcamp adapter.

Picture
Picture
This mic has a different electret module than the one shown on G4IZH's site. This one is smaller and has the FET built into the module hence there is no FET on the PCB. 
The only components on the back of the PCB are two 47uF electrolytic capacitors. The caps stick up about level with the frame and I added washers under the add-in board mounting holes to space it up a little higher so nothing shorted to the top of the caps. Or just avoid the area of the caps on the add-in PCB.

Picture
A closeup of the PCB gives a better look at the traces and components. The red and black wires for the mic element connect on the left and the XLR wires on the right.
Picture
The mods to the PCB and connections to the add-in board. The blue cap is the 2.2uF across R4. The violet wire picks off the audio from Q5, sending it to the input of the Lo and Hi audio filters. The PCB traces from C5 to the collectors of both Q1 and Q2 were cut to remove them completely from the circuit. The white wire from the power filter connects at C5. Also, C3 and C4 were removed.

Picture
The add-in PCB has the capacitors and resistors for the power and audio filters, and the VR1 audio out level adjustment. Using an o'scope I adjusted VR-1 to provide the same level out as my hand mic.

I modified the original mod, adding phantom power on the audio lead, by removing the yellow power wire from pin 3 and connecting it to the red audio wire on pin 2. Then a 4.7uF capacitor was added between the red wire and the wiper on VR1, to block DC voltage from getting to the potentiometer. 
Picture
Schematic with the component values in my converted BM-800.  A few of the part values in my mic circuit vary from the G4IZH schematic.
Picture
The converted microphone mounted on a scissor boom arm using the included metal shock mount. Not bad for less than thirty dollars including the scissor arm. 

Last update 5/11/2017
Powered by Create your own unique website with customizable templates.
  • Home
    • Contact
  • Astrophotography
  • Observatory
    • New Observatory
    • Lancaster Dome
    • ExploraDome
  • Equipment
    • Accessories >
      • RA Drive Corrector
    • CCD Cameras >
      • Orion Starshoot Pro
    • Mounts >
      • Orion HDX110 (EQ-8)
    • Telescopes >
      • 1956 Questar 3.5
      • Astro-Tech AT6RC
      • Celestron C-11 XLT
      • Zhumell 152mm Refractor
  • Projects
    • C11 XLT Mods
    • Dome Automation
    • Orion SSPRO Camera >
      • Disassembled Views
      • Noise Reduction Mod
      • Temp Controller Mod
    • Ultima 8 Mods
    • Zhumell Refractor Mods
  • Non-Astronomy
    • Amateur Radio >
      • Accessories >
        • Station Boom Microphone
      • Ameco >
        • Ameco AC-1
        • Ameco OCM
        • Ameco PT-2
        • Ameco R5A
      • Vintage Equipment >
        • Knight Kit T-60 Transmitter
        • Heathkit SB-102 Station
      • Yaesu FT-817 >
        • Yaesu FT-817ND
        • LDG Z-817 Autotuner
        • Windcamp LiPo Battery
    • Antique Radios >
      • Building A Radio Workbench
      • Radio Dial Neon Clock
      • Radios >
        • Boat Anchor Radios >
          • BC-348N Receiver
          • Collins 51J4 HF Receiver
          • R-392 HF Receiver
        • 1938 Zenith 6-S-254
        • Echophone EC-1
        • Eltz Radione 2
        • Knight Kit Span Master II
        • Panasonic RF-5000A
        • Silvertone Model 4465
      • Test Equipment >
        • Hickok >
          • Hickok OZ-1 (550X)
          • Hickok 19X RF Generator
          • Hickok 225K VTVM
          • Hickok 288X RF Generator
        • Simpson >
          • Simpson Genescope
        • Supreme Instruments >
          • Supreme Model 385 Automatic
          • Supreme Audolyzer
          • Supreme Vedolyzer
          • Supreme 563 Audio Generator
        • Military Test Equipment >
          • BC-221-AF Frequency Meter
          • I-177 Tube Tester
          • LM-21 Frequency Meter
          • MX-949 Adapter
          • TS-323/UR Frequency Meter
          • TS-465 C/U Sweep Generator
          • TS-505D/U VTVM
          • TV-3C/U Tube Tester
        • Rider Chanalyst
        • Tektronix 326 O'scope
        • Tube Testers >
          • Alternating Current Sink
          • Drug Store Tester
          • Hickok OZ-1 (550X)
          • I-177 Tube Tester
          • MX-949 Adapter
          • Precision Model 10-12
          • Supreme Model 385
          • TV-3C/U Tube Tester
    • Star Trek Communicator