HobbyPCB.com

Built by Hobbyist for Hobbyist!
It is currently Wed Nov 14, 2018 1:43 am

All times are UTC - 5 hours




Post new topic Reply to topic  [ 7 posts ] 
Author Message
 Post subject: Undocumented Feature ?
PostPosted: Sun Jan 07, 2018 4:33 pm 
Offline

Joined: Thu Aug 18, 2016 9:05 pm
Posts: 12
I came across which I believe to be an undocumented feature dealing with the reception and demodulation of FM RF signals with signal strength around -96 dBm
(obtained from the SS comnand). My setup consists of a stock RS-UV3 intergrated with a RS-UVPA and connected to a SBB-224 antenna. When I tuned the weather station transmitting on 162.475 MHz in my area, I only hear noise coming out of the speaker with the squelch at 0; however, the SS command reports the presence of a signal with a strength of -96 dBm. When I tune the same frequency with a different radio connected to the same antenna, I can hear the station properly. After poking around, I discovered that if I enter the following command: RS32 followed by the return key, I magically hear the station's audio from the speaker. This works until I cycle the power on the RS-UV3/UVPA. I can't find any reference to the RS32 command that would explain why I'm able demodulate FM stations with strength values around -96 dBm. I just replaced the firmware with version 2.4a and I'm getting the ssme result.

Questions:
1- Why FM stations with signal strength of around -96 dBm don't demodulate after power up ?
2- What does the RS32 command do and is it it safe to use it ?
3- Does this feature affect RF signals on the amateur radio bands too ?

Thank you in advance,

73,
Rej. VE3MPV


Top
 Profile  
 
PostPosted: Sun Jan 07, 2018 8:41 pm 
Offline

Joined: Mon Jul 23, 2012 6:25 am
Posts: 1047
That's very strange behavior. I just put an RS-UV3 on the bench with a signal generator at 162.475MHz, FM modulation, and with the squelch open I could hear the signal from -127 dBm to -45dBm with no interruption and no distortion. So I'd have to say that the behavior you are seeing is not 'normal'.

The RS command is not undocumented, it's the 'register set' command, used to manually set the registers in the RDA1846S chip. It's companion, the RR, command can be used to read the registers. We use these commands to test features before we code them.

RS32 is probably setting register 32 to 0000 hex, although since you didn't supply any data this might not be guaranteed. The documentation I have on the RDA1846S indicates that register 32 is the 'AGC target power' and should be set to 0x4495 or 0x7564 depending on the operating mode but is independent of frequency setting.

Have you tried issuing a FD1 command to set the radio in 'factory default' then tuning to 162.475MHz and see if the problem persists?

You are running the latest FW.

73,
Jim WA2EUJ


Top
 Profile  
 
PostPosted: Sun Jan 07, 2018 10:22 pm 
Offline

Joined: Thu Aug 18, 2016 9:05 pm
Posts: 12
Indeed I find this strange too. I've been at this for a while and I assumed that the station on 162.475 MHz was off the air until I use a different receiver and bam the signal is there. I checked the register 32 (RR32) after the RS32<return> and I get 7475 which tells me that the RS32 command uncloaks the signal by changing the target gain from 0x15 to 0x11. I know that the register 32 is not well documented, and among others, I've been trying to get more info on this register without success. Also, as you suggested, I set all settings to 'Factory Defaults' (FD1) and I get the same results. It is consistent. Let me know if you find an explanation to this issue. I'll do more testing and let you know if I find something of interest.

73,

Rej. VE3MPV


Top
 Profile  
 
PostPosted: Wed Jan 10, 2018 8:33 am 
Offline

Joined: Thu Aug 18, 2016 9:05 pm
Posts: 12
What are the operating modes you mentioned in your previous update ? I assume you are referring to Narrowband / Wideband modes. If so, I tried to activate the Narrowmode with the BW0 command in order to test with the alternate value (0x4495) for register 32; but, the value in register 32 doesn't change, it stays at 0x7564. Should I manually change the value with the RS324495 command or is it done automatically ? What am I doing wrong ?

Thank you in advance for your support.

73,

Rej. VE3MPV


Top
 Profile  
 
PostPosted: Wed Jan 10, 2018 9:44 pm 
Offline

Joined: Mon Jul 23, 2012 6:25 am
Posts: 1047
Hi Rej,

The BW command requires a power cycle to take effect since virtually every initialization parameter has to change. Also remember to use the ST0 command BEFORE cycling the power to store the current operating set in flash memory.

73,
Jim WA2EUJ


Top
 Profile  
 
PostPosted: Thu Jan 11, 2018 1:08 pm 
Offline

Joined: Thu Aug 18, 2016 9:05 pm
Posts: 12
Jim,

Thank you for the information on how to enable the narrowband mode. I successfully switched the RS-UV3 to narrowband mode (BW0, ST0 and power cycle) and I no longer experience cloaked Klingon signals, at least the one I know of... I'm able to receive all weather stations properly when I enable the narrow mode. I don't recall having this problem with a stand-alone RS-UV3 (without RS-UVPA). Albeit the amount of work, I'm tempted to disconnect the RS-UVPA from the RS-UV3 to see what happen without additional components in the antenna path. To be honest with you, I'm having similar problems with the HamShield wide band transceiver board which uses the same single-chip transceiver (RDA1846S), and the way I see it, until we have a more information on the undocumented register's values pertaining to the receiver module, (to name a few: registers 0x13, 0x32, 0x33, 0x34 and the AGC table), we're bound to experience similar issues. I hope the transmitter won't exhibits similar strange behaviours.

73,

Rej. VE3MPV


Top
 Profile  
 
PostPosted: Thu Jan 11, 2018 8:59 pm 
Offline

Joined: Mon Jul 23, 2012 6:25 am
Posts: 1047
Hi Rej,

The RS-UVPA is carefully balanced on the receive side to have the tiniest bit of positive gain. There is a solder jumper that will increase the gain so if you use it with the Hamshield it will significantly improve the Hamshield's RX sensitivity.

I can't imagine that the PA would have any effect on the RX.

But I'm ready to haer your results.

73,
Jim WA2EUJ


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group