Rx issues, mostly one radio...

MMDVM_HS Hat hardware
AF6VN
Posts: 821
Joined: Fri Jul 20, 2018 1:15 am

Re: Rx issues, mostly one radio...

Post by AF6VN »

SIMPLEX: radio transmits and receives on the same frequency
REPEATER: radio transmits on a different frequency than it receives on (for UHF, that is typically a 5MHz shift)

Most Amateur gear is programmed in terms of: Receive frequency, Shift Direction (+/-), Shift Offset (the latter may be a hidden menu entry as the rigs often have the "standard" offset and direction pre-set for the market area).

The TYT units I have (MD390/MD2017) are not programmed in direction/offset. They have separate entries for receive and transmit frequencies for every channel -- so any offset/direction could be created, but one needs to take into account that too-close will interfere [since the repeater receives and transmits at the same time], and using other odd offsets could cause interference with other normal offset repeaters. TYT channels also have an "Allow Talkaround" check box; if a button is programmed for it, one can toggle the channel between normal repeater mode and direct simplex mode.

--
AF6VN
Dennis L Bieber
W8DEX
Posts: 23
Joined: Fri Jul 13, 2018 1:40 am

Re: Rx issues, mostly one radio...

Post by W8DEX »

Yes, I do understand the concept of simplex and repeater very well, no novice there, thank you.

This is a DMR mode issue. The HD1 also uses tx and rx entries separately, or by shift if needed in analog.

My point and question is: why dies a cheap chinese radio communicate with repeaters and simplex without need to specify a mode, and a more exoensive radio requires to specify a DMR mode? In this case simeplex mode or repeater mode?
Is this related to the DMR protocol?

Just in case, the channel tx/rx settings were 447/442, and both the 'simplex mode" and "repeater mode" were behaving the same as far aa my sdr could tell. Both tx on 447 and received on 442, but the hotspot, listening on 447, only recognizes the HD1 when the radio is set to "repeater mode".
It sounds to me there is a diffeeence somewhere that is in the DMR protocol or ?

Cheers
AF6VN
Posts: 821
Joined: Fri Jul 20, 2018 1:15 am

Re: Rx issues, mostly one radio...

Post by AF6VN »

Nothing in DMR protocol itself that I know of.

If one of the radios is using a different transmit frequency even when set for simplex -- I'd be concerned that /that/ radio is the one that is not behaving correctly. Every radio I own (analog and digital), if set for simplex (no shift/"talkaround") uses the receive frequency for transmit. The receive frequency is also the display frequency on those that show frequencies -- the transmit frequency is the one that gets "adjusted" when the PTT is closed.

--
AF6VN
Dennis L Bieber
W8DEX
Posts: 23
Joined: Fri Jul 13, 2018 1:40 am

Re: Rx issues, mostly one radio...

Post by W8DEX »

Hi, the settings I am referring to on the HD1 are not the simplex/repeater commonly used in analog.
These are specific to the DMR settings only.
They do not affect the frequency settings and they are only avsilable to the digital channels settings.

Looks like I am having trouble explaining the issue here, but thank you for the effort.

I should probably move on, DMR is al VooDoo anyway 😁

Cheers
Chris
AF6VN
Posts: 821
Joined: Fri Jul 20, 2018 1:15 am

Re: Rx issues, mostly one radio...

Post by AF6VN »

Voodoo is Caribbean... DMR is European Union :mrgreen:

#11 on https://blog.retevis.com/frequently-ask ... lunce-hd1/ might be applicable (the response seems to imply that "simplex" mode also ignores time-slots, which might mean Tier-I behavior rather than Tier-II).

https://en.wikipedia.org/wiki/Digital_mobile_radio
DMR Tier I products are for licence-free use in the European PMR446 band. Tier I products are specified for non-infrastructure use only (meaning without the use of repeaters).
http://www.miklor.com/DMR/DMR-Tier1-2.php

https://doc-10-1s-docs.googleuserconten ... e=download (apologies for google overhead) page 14 also seems to imply that, since they list "Double Slot" as a mode option -- given poor Chinglish -- it sounds like "double slot" is what most others use as normal simplex with time-slot specification.

Interesting, the HD1 manual doesn't use the term "simplex" -- it is "Direct Mode", "double slot" is "Real Double Time Slots Mode" with the following section stating that "If real double time slots are active..." one has to specify the time slot.

One would think these companies could come up with visible differences in their products rather than just firmware in relabeled shells -- the images look a lot like the TYT MD380/390, but with VHF/UHF bands, and totally different firmware and no explanation of the terms used.

--
AF6VN
Dennis L Bieber
W8DEX
Posts: 23
Joined: Fri Jul 13, 2018 1:40 am

Re: Rx issues, mostly one radio...

Post by W8DEX »

Thank you, that starts clearing some confusion.

I found this cryptic message on the Retevis blog:

Q: "Is there a way to program a frequency into this radio that’s known to be DMRand decode the color code and time slot?"
R: Yes, Program two channels one with each time slot, Make sure you set the radio for repeater mode and not simplex or it won’t decode the separate slot


And this one:

Repeat (This is called repeater in software): when radio connects to repeater, please choose the Repeater mode.
Double slot: this mean DCDM( like RT82 DCDM function)
For digital radio like HD1, the time slot effects only connect to repeater.
For example, when you don’t connect to repeater, and you choose simplex, but not double slot in HD1 software.
In direct call mode, like HD1 talk with RT3, if HD1 communication channel select time slot 1, RT3 communication channel select time slot 2. Though different time slot, still they can communicate without any problem.
when you don’t connect to repeater, but you choose Double slot work mode in HD1 software. Then time slot will effect here. The channel that select time slot 1, can not talk with channel that select time slot 2.
What’s the advantage for double slot(DCDM)?
Generally, it enhanced the frequency utility


I honestly have a hard time figuring out the meaning.

My surprise remains with the RD-5R. There is no need to specify all these modes. It must have a smarter firmware that figures out when to use simplex (Tier I) and when to use repeater mode (Tier II).

Ok then. It looks like the fact that my JumboSpot is a true repeater (in a fashion), required the channel on the HD1 to also be specified on "repeater mode" or better, Tier II.
They should just call it what it is!!!

Thank you
Cheers
Chris
AF6VN
Posts: 821
Joined: Fri Jul 20, 2018 1:15 am

Re: Rx issues, mostly one radio...

Post by AF6VN »

Getting cross time-slot simplex communication basically means one of the radios is sending the same data in both time-slots with the other grabbing just its configured slot; or for a radio that is only sending in its time-slot, the other is somehow reading both and ignoring the one that is empty.

Tier-I is, from what I've read, only used in the European digital equivalent of US FRS (half watt limit). Some of the early Baofeng radios were Tier-I and played havoc with repeaters as they filled both time-slots.

A Tier-II radio, when transmitting within a few feet of my computer, induces a machine-gun noise audible in the computer speakers, since it rapidly turns the transmit on/off. I've not studied the protocol in enough detail to know how they synchronize -- but theoretically there can be a different conversation taking place in each time-slot at the same time (I can understand how a networked repeater could, for example, be receiving a local user in one time-slot while also fitting the other time-slot with data from a network server -- so one transmitter filling both time-slots -- but how two local users on different slots get into the repeater at the same time I don't know. TDMA as used in GSM phones I can understand -- since phones are always in light contact with the cell tower so all phones on the channel (8 time-slots) (they adjust power level based on signal strength and if they can't receive a tower produce the "no service" display) are synchronized. But ad-hoc radios that make contact on PTT? Somehow the second to key up would have to avoid interfering with the first, synchronize to the timing of the first, and then transmit in the holes when the first is not transmitting.

--
AF6VN
Dennis L Bieber
Post Reply