MMDVM Dual Hat Duplex Setup

MMDVM_HS Hat hardware
Post Reply
ke8owx
Posts: 2
Joined: Fri Jan 01, 2021 7:02 pm

MMDVM Dual Hat Duplex Setup

Post by ke8owx »

So, I decided to build a second hotspot and split D-Star from DMR now that I have started using both for a while. I decided to use a duplex hat since the price difference and availability is about the same. It is installed on a RPi3+B. I have it tuned up as s simplex node (according to the band plan, and 300kHz from the DMR hotspot) with 0.0% BER. Instructions indicate using the STM32-DVM/MMDVM_HS - Raspberry Pi Hat (GPIO) modem choice. It works great in simplex mode, updated firmware and current pistar software.

I have a few questions when using it in duplex mode. Instructions say turn on "Duplex Repeater (or Half Duplex on Hotspots)". When I do that, I assume I need a split in TX & RX frequency? I tried the same frequency, and a 0.3MHz split. Neither work. With the 0.3MHz split, It recognizes the transmission for less than 2.0s, even if the radio stays keyed. Keep in mind, in simplex mode, I have 0.0% BER. I also notice that it appears I get a pulse of a transmission from the HS ever second without stopping. This leads me to a few questions:

1) For this to work, do I need the traditional 5.0MHz split?
2) With a 5MHz split, do I need to move the frequency into the repeater portion of the band plan (and possibly contact the repeater coordinator).
3) Is there something else I am missing that should be simple?

Thanks,
KG6RUT
Posts: 75
Joined: Thu Dec 24, 2020 7:28 pm

Re: MMDVM Dual Hat Duplex Setup

Post by KG6RUT »

No expert but I have the same hat....not sure you are required to use a 5mhz split but that is what I am using. Not sure I fully follow the second question but I think as long as you stay away from the Satellite frequencies I think you are fine.
I am using 429.0 for RX and 434.0 for TX as an example
KE7FNS
Pi-Star Team
Posts: 1782
Joined: Wed Apr 17, 2019 11:11 pm

Re: MMDVM Dual Hat Duplex Setup

Post by KE7FNS »

ke8owx wrote: Wed Jan 20, 2021 3:47 pm I have a few questions when using it in duplex mode. Instructions say turn on "Duplex Repeater (or Half Duplex on Hotspots)". When I do that, I assume I need a split in TX & RX frequency?
Yes.
ke8owx wrote: Wed Jan 20, 2021 3:47 pm I tried the same frequency, and a 0.3MHz split. Neither work. With the 0.3MHz split, It recognizes the transmission for less than 2.0s, even if the radio stays keyed.
You need more of a frequency split than that or you need greater antenna separation.
ke8owx wrote: Wed Jan 20, 2021 3:47 pm Keep in mind, in simplex mode, I have 0.0% BER. I also notice that it appears I get a pulse of a transmission from the HS ever second without stopping.
In simplex mode you are only using one of the two ADF7021 chips on the PCB.

Your radio is looking for that pulse to continue the transmission, if it is missing your radio will report a connection error if enabled in the codeplug.
ke8owx wrote: Wed Jan 20, 2021 3:47 pm This leads me to a few questions:

1) For this to work, do I need the traditional 5.0MHz split?
Technically, no.

But for your equipment to operate properly you need some sort of a greater offset than you have previously set or you need greater antenna separation.
ke8owx wrote: Wed Jan 20, 2021 3:47 pm 2) With a 5MHz split, do I need to move the frequency into the repeater portion of the band plan (and possibly contact the repeater coordinator).
Technically yes, however with such low power from the stock hat I don't think a repeater coordinator is going to waste the time or frequency on assigning you a coordinated repeater pair. For example in the Los Angeles metro area there are no unused repeater pairs left. They will probably just request you use a pair dedicated for portable repeaters.

In AZ they recommend these: (your area may be different)

Code: Select all

440.4000 (+) Low-Level/Locally-Shared & Portable (Digital or Digital/Mixed-Mode) ***
440.4250 (+) Low-Level/Locally-Shared & Portable (Digital or Digital/Mixed-Mode) *** 

446.5500 (-) Low-Level/Locally-Shared & Portable (Digital or Digital/Mixed-Mode) ***
446.5750 (-) Low-Level/Locally-Shared & Portable (Digital or Digital/Mixed-Mode) *** 
ke8owx wrote: Wed Jan 20, 2021 3:47 pm 3) Is there something else I am missing that should be simple?
Not really, had you used a standard UHF 5 MHz split you probably wouldn't of ran into any issues.
If someones previous actions are any indication of their future actions, then I predict the deletion and removal of access will happen at any moment. 7-11-2020.

"07/13/20 This Website Has Been Taken Down" ... again :lol:
ke8owx
Posts: 2
Joined: Fri Jan 01, 2021 7:02 pm

Re: MMDVM Dual Hat Duplex Setup

Post by ke8owx »

KE7FNS wrote: Wed Jan 20, 2021 6:20 pm
ke8owx wrote: Wed Jan 20, 2021 3:47 pm I have a few questions when using it in duplex mode. Instructions say turn on "Duplex Repeater (or Half Duplex on Hotspots)". When I do that, I assume I need a split in TX & RX frequency?
Yes.
ke8owx wrote: Wed Jan 20, 2021 3:47 pm I tried the same frequency, and a 0.3MHz split. Neither work. With the 0.3MHz split, It recognizes the transmission for less than 2.0s, even if the radio stays keyed.
You need more of a frequency split than that or you need greater antenna separation.
ke8owx wrote: Wed Jan 20, 2021 3:47 pm Keep in mind, in simplex mode, I have 0.0% BER. I also notice that it appears I get a pulse of a transmission from the HS ever second without stopping.
In simplex mode you are only using one of the two ADF7021 chips on the PCB.

Your radio is looking for that pulse to continue the transmission, if it is missing your radio will report a connection error if enabled in the codeplug.
ke8owx wrote: Wed Jan 20, 2021 3:47 pm This leads me to a few questions:

1) For this to work, do I need the traditional 5.0MHz split?
Technically, no.

But for your equipment to operate properly you need some sort of a greater offset than you have previously set or you need greater antenna separation.
ke8owx wrote: Wed Jan 20, 2021 3:47 pm 2) With a 5MHz split, do I need to move the frequency into the repeater portion of the band plan (and possibly contact the repeater coordinator).
Technically yes, however with such low power from the stock hat I don't think a repeater coordinator is going to waste the time or frequency on assigning you a coordinated repeater pair. For example in the Los Angeles metro area there are no unused repeater pairs left. They will probably just request you use a pair dedicated for portable repeaters.

In AZ they recommend these: (your area may be different)

Code: Select all

440.4000 (+) Low-Level/Locally-Shared & Portable (Digital or Digital/Mixed-Mode) ***
440.4250 (+) Low-Level/Locally-Shared & Portable (Digital or Digital/Mixed-Mode) *** 

446.5500 (-) Low-Level/Locally-Shared & Portable (Digital or Digital/Mixed-Mode) ***
446.5750 (-) Low-Level/Locally-Shared & Portable (Digital or Digital/Mixed-Mode) *** 
ke8owx wrote: Wed Jan 20, 2021 3:47 pm 3) Is there something else I am missing that should be simple?
Not really, had you used a standard UHF 5 MHz split you probably wouldn't of ran into any issues.
I appreciate all the help. I did set it with a 5MHz split and it works just fine. The only odd thing I notice now, when in duplex repeater mode, the screen scrolls "Idle" after a while of no activity. It only ever scrolled the MMDVM screen saver before.
KE7FNS
Pi-Star Team
Posts: 1782
Joined: Wed Apr 17, 2019 11:11 pm

Re: MMDVM Dual Hat Duplex Setup

Post by KE7FNS »

ke8owx wrote: Thu Jan 21, 2021 5:11 pm I appreciate all the help. I did set it with a 5MHz split and it works just fine. The only odd thing I notice now, when in duplex repeater mode, the screen scrolls "Idle" after a while of no activity. It only ever scrolled the MMDVM screen saver before.
Maybe you just didn't notice it, if the scrolling is enabled all the banners on the various modes scroll.
If someones previous actions are any indication of their future actions, then I predict the deletion and removal of access will happen at any moment. 7-11-2020.

"07/13/20 This Website Has Been Taken Down" ... again :lol:
Post Reply