DMR can Tx only if Tx and Rx frequencies are the same

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N1KY
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by N1KY » Wed Jan 04, 2023 8:16 pm

The radio has to digitally handshake with the DMR repeater before it will transmit. If the radio cannot handshake with the DMR repeater (settings error, distance too great, etc.) it will time out after trying for a few seconds and display "timeout".

When Tx and Rx frequencies are the same the radio operates in DMR simplex mode. Since there is no repeater in simplex mode the radio will always transmit.

N1KY

N1KY
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by N1KY » Thu Jan 05, 2023 12:32 am

Rosssin wrote:
Wed Jan 04, 2023 11:16 pm
Although, I cannot see how it would transmit the same frequency it receives
It is possible to have a single frequency DMR repeater (SFR) which receives on one time slot and transmits on the other time slot.

OpenGD77 cannot do SFR due to the limitations of the RF electronics in most/all of the supported radios.

N1KY

SA0BUX
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by SA0BUX » Fri Jan 06, 2023 5:26 pm

N1KY wrote:
Thu Jan 05, 2023 12:32 am
Rosssin wrote:
Wed Jan 04, 2023 11:16 pm
Although, I cannot see how it would transmit the same frequency it receives
It is possible to have a single frequency DMR repeater (SFR) which receives on one time slot and transmits on the other time slot.

OpenGD77 cannot do SFR due to the limitations of the RF electronics in most/all of the supported radios.

N1KY
Maybe it's a single frequency link or "Hotspot" with greater coverage?

SA0BUX
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by SA0BUX » Fri Jan 06, 2023 5:36 pm

Rosssin wrote:
Wed Jan 04, 2023 11:16 pm
Thank a lot for explaining N1KY!

There is this "repeater" near where I live, F5ZJP, and it is set with the same Tx and Rx frequencies: 145.037, on the notes it'S written "simplex test", which I noticed only now and I understand thanks to your explanation. Although, I cannot see how it would transmit the same frequency it receives - to me it feels like it would create a strong feedback loop in it's own circuit. Apart from that such a thing may serve to spread a nearby signal far away. Put the receiver low, shield/screen its top and put the Transmitter very high??

As for the other repeaters, from what you say it must be the distance too far reason. I do communicate with no problem with the UHF and VHF sections of this installation though. It is 60 km from here. The 145mhz section comes cleaner than the 440 mhz section.

..So if people don't get this "time out" they know that they have reached the repeater even before using the 9990 parrot?

Cheers
R
I guess it's a Hotspot with greater coverage?
I searched in brandmeister for the callsign but couldn't find anything there.
But there are other DMR networks.

Do you have a callsign?, if you have problems finding a nearby DMR repeater it's practical to setup a Hotspot instead.

/Lars SA0BUX

G4EML
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by G4EML » Fri Jan 06, 2023 9:17 pm

That's exactly what is expected.

There are two different modes for DMR operation. DMO (direct mode) and RMO (repeater mode).

All DMR radios select DMO when the Tx and Rx frequencies are the same and RMO when they are different.

When attempting to access a repeater the radio sends a very short single burst wake-up transmission. That is the click you are hearing. If the repeater hears this burst it will start transmitting. The radio will then hear the repeater and will start voice transmission.
If the repeater doesn't respond, the radio re-trys several times at about half a second intervals before it abandons the attempt and indicates a timeout.

Colin G4EML.

G4EML
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by G4EML » Fri Jan 06, 2023 10:48 pm

DMR and FM range is normally very similar with good commercial equipment. However some home-brew multimode repeaters do not perform as well.

You also need to make sure you have the correct Tx and Rx frequencies, it is easy to get them swapped. Also you must have the correct Colour code programmed.

SA0BUX
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by SA0BUX » Sat Jan 07, 2023 12:46 pm

Rosssin wrote:
Fri Jan 06, 2023 7:43 pm
SA0BUX wrote:
Fri Jan 06, 2023 5:36 pm
I guess it's a Hotspot with greater coverage?
I searched in brandmeister for the callsign but couldn't find anything there.
But there are other networks…
Hi, this repeater is listed on this map: https://www.f4igo.fr/
It is near Toulouse to the southwest, following the Garonne river, near the town of Carbonne.
At which site you search the repeaters?
I looked on https://brandmeister.network , https://radioid.net , https://www.repeaterbook.com/ , https://www.dmr-marc.net/MAP/fullscreen.html

The Toulouse area seems to be somewhat sparsely populated with DMR repeaters.

ok1pt
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by ok1pt » Sun Jan 22, 2023 5:59 am

Rosssin wrote:
Sun Jan 22, 2023 2:12 am
…one more question:
Since I’m interested for now in moly listening/receiving DMR, is it possible to “scan” or tune to a DMR frequency and listen to it WOTHOUT having initiated this “handshake” to the repeater?
If yes, what are the settings I should put the open gd77 on, I’ve been trying by putting all DMR filters off (to sort of imitate promiscuous mode) but no success, even when being close to a given repeater (although that I’m not certain any repeaters in this part of france work at all, as mentioned earlier on the thread..)

Thanks!
Hi!
You have to switch off the DMR filter (so it will receive any talkgroup/private call) and Timeslot filter (to be able to listen on both timeslots). If the Color Code is known, it's wise to set it and let the CC filter ON (or by other words, don't turn the CC scan ON). CC scan is a relatively complicated procedure and may cause various side effects like missing beginnings of transmissions, various audio artifacts etc. Together with appropriate frequency (TX frequency of the repeater, i.e. your RX frequency), it's enough to listen on a repeater.

With regards / 73,
Pavel OK1PT

VK3KYY
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Re: DMR can Tx only if Tx and Rx frequencies are the same

Post by VK3KYY » Sat Feb 25, 2023 12:56 am

Rosssin wrote:
Wed Jan 04, 2023 7:37 pm
Hi,
Thank you for such an AMAZING firmware and interface!!!
I Installed it on the RT3S radio. It works so fine, day and night difference between it and the original firmware.

The only thig I cannot figure out so far is the following problem:

I've created a few DMR channels for repeaters around Southwest of France near Toulouse.
When I press the PTT button only one channel starts to transmit, counts Tx time on the screen.
All the rest of the channels display 0 Tx count, and in 3 sec cut the Tx displaying "timeout" (despite that TOT is set to "off").

I've spent a whole day searching what the difference between the successfully Tx channel and the "timeout" nonetransmitting channels could be,
also fiddled with every possible option setting variation, experimenting back and forth.

The only thing I found was that the radio will not Transmit on DMR mode if the Tx and Rx frequencies are not the same (!!!???).
In the quick VFO menu there is an option "Freq. Bind" (receiving and transmitting frequency bind, says the readout voice), this option on eithr ON of OFF changes nothing about this problem. Also, this "Freq. Bind" is not mentioned in the manual.

So, I just couldn't understand where this impossibility to Tx on DMR when Tx and Rx freq. are different comes from...

Thanks for kind attention
and Happy New Year!
R
What is your callsign ?

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