OpenGD77

hi all,
I state that this is not a firmware bug because the defect was also found with the original firmware.
It would appear to be something generated by Hardware.
On 4 gd77 tested I found that a signal is generated exactly at 430.075 Mhz.
In practice there is always a fixed carrier at 4-5 of rssi.
With the external antenna it decreases but does not cancel.
This can disturb the rx of any repeaters on that frequency.
I have tried with other radios like Anytone 878, TyT Md-380 in the same place as the gd77 and on this radio the signal do not exist.
approaching one of these radios to the gd77 the signal also appears on these devices.
Can you confirm that this also happens on your gd77?

Regards,
Fabio IU4LEG

Yes, it will happen on all GD77s. The actual strength of the signal will vary between radios.

The theoretical frequency is actually 430.080 MHz but again this will vary slightly for each radio.

The crystal clock for the processor and DMR encoder is 12.288 MHz. There will be spurious signals at all harmonics of this frequency and there is nothing that can be done in firmware to prevent this.

12.288 x 35 = 430.080

There is also a second crystal at 26.0 MHz. This will also produce some spurious signals.

More expensive radios often have the ability to slightly shift the crystal frequencies to avoid such problems but the GD77 does not have the hardware to do this.

Colin G4EML

Thanks Fabio and Colin, very interesting.
Honestly I had not noticed it.
Even if it is not necessary, I confirm that more expensive transceivers often have the ability to slightly shift the crystal frequencies to avoid such problem, for example digital C4FM handheld FT1, FT3 and FT5 by Yaesu.

73 best regards de Fabio IZ2EIB

Hi!
These "autogenerated signals" are obviously known as "birdies" and they are very common on radios with digital circuits inside - like CPU/MCU, various frequency synthesizers, displays, GPS receivers etc. You can find them on every modern radio with wide reception bands including such valued brands like Kenwood, Yaesu, ICOM etc. It's just normal and for some models, these frequencies are listed in their manuals with a short explanation.
Even purely analog radios can have birdies, depending on their frequency plans (obviously they are two- or even three- stage heterodynes so there are local oscillators, which can have some harmonic frequencies passing to the received bands).
With regards / 73,
Pavel OK1PT

thanks guys for the explanation!

73, Iu4leg