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Monday, September 17, 2018

Review: N5BOC Duplex Hotspot Board

Quality of construction has proved important across all newer digital voice capable radios and related infrastructure.

Modes such as DMR, NXDN and P25 all require stable clock sources to ensure proper operation with DMR especially requiring this because of its capability to allow two simultaneous data or voice streams on the same frequency at the same time. 

As the old adage goes, "You get what you pay for" holds especially true for the most modern of amateur radio equipment.

MMDVM raspberry pi zero  duplex texas lone star
David Dennis N5BOC has created a high quality small duplex MMDVM board for use
with the Raspberry Pi Zero or any of the larger Raspberry Pi too 


This review provides some observations on the N5BOC designed duplex multi-mode digital voice modem (MMDVM) that packs a lot of capability into a very small form factor.

The key benefits of buying the N5BOC duplex board compared to the foreign manufactured ones are as follows:

  • Gold plated contacts for superior on-board connections
  • Thicker PCB material for improved DC and RF stability
  • Additional u.FL connectors for external "pigtail" connections
  • ECS branded TCXO for very stable frequency operation (No offset likely required)
  • 1/2 the size of foreign made duplex board
  • Lower power consumption compared to foreign made duplex board
  • Help support domestic US amateur radio community design talent
Further details about why David Dennis designed this product, his design goals and user manual can be found HERE.

This MMDVM duplex board is handmade in small quantity to ensure quality. They sell out quickly, so be
sure to get on the waiting list and purchase it as soon as they become available.

After creating a fresh Pi-Star image and setting up both time slots with active talk groups such as 91,310, 3100, etc and running it this way for an entire weekend on a 16000mAh power bank, here is what was learned.

Feedback #1: Running the N5BOC board on a Raspberry Pi Zero lasted 11 hours longer compared to using the foreign pictured duplex board with identical rechargeable power sources down to 50% battery capacity.

getting started MMDVM hotspot
Comparing the N5BOC duplex board to foreign duplex board

Feedback #2:  No offset was required on the N5BOC board compared to the pictured foreign board.  Better design and material likely attributed to this. 


Feedback #3: The N5BOC board is well thought out and designed compared to the single sided and less complex foreign board options




Critical Comments:  It is hard to find something to complain about with this product because all the underlying concepts are not new to me, but I would like to see:

What? User install-able SMA connectors for different mounting options and use of u.FL connectors instead which are great to see included.
Why?  Some people may not have good de-soldering skills and may want to use "pigtails" instead.
What? J3 connector placement for an OLED display if installed will block the on-board status LEDs 
Why? No big deal, but some may get annoyed by that. Good reason to consider other display mounting options or even a "wireless" display or just block out the LED by adding a display over the top anyway which can be turned off in software more easily then LEDs.

MMDVM OLED N5BOC
Connector pin out description for N5BOC duplex board


Final Comments: For the current price of just under $100, this is a very good piece of engineering. My current fully enclosed duplex board looks like an ancient prototype compared the smaller N5BOC board and am looking forward to an official case or creating something of my own.

Will the N5BOC duplex board look as cute when it gets an enclosure?

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