Author Topic: Latency mystery  (Read 2462 times)

oh2xx

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Latency mystery
« on: 2013-11-02, 22:21:01 »
Hi,

I have posted a few questions here related to my issues with CW keying. I have tried to find out a workaround and have succeeded to some extent. Anyway the root problem is still to be resolved and it is a mystery for me. I have problems with the latency of my internet connection and I have spent tens of hours analyzing the problem as it seems to be RFI related.

I am using a 3G connection (3G router BandLuxe R300) and the 3G base station (UMTS 900 MHz) is quite near (<4 km) at the remote site. I have an outdoor yagi pointed there and the normal latency is between 60-90 ms, uplink about 1 Mbps and downlink 2 Mbps on average.

And here is the mystery. If I am running barefoot everything is fine but when using amplifier problems start (at about 600W and upwards). But the mystery does not start immediately - it takes from 4-10 minutes and after that the latency starts to go up and down heavily. Here is a screenshot of a ping trace between my home PC and the remote 3G router:

http://www.kolumbus.fi/kalehtim/ping.png

If I am not transmitting the delay stays under 100 ms for hours...

Unfortunately the RTT exceeds the critical 250 ms that is currently the maximum delay for CW keying. So my CW has some annoying errors there.

The thing that I can not understand is that the higher delay seems to last excatly 3,5 minutes every time - sounds like a SW or protocol timeout? It happens when transmitting on 160 meters or 10 meters. The delay propagates to all of the nodes between my home and the remote site. As you can see in the graph the delay is behaving the same way at the closets router to my home (vantik1.fi.elisa.net) and the remote 3G modem. My ISP has checked the lines and could not find any problems there. I tested the setup also by using a 3G modem at my home to bypass my ADSL access network and I could see the same problem with that setup as well.

I have put the remote 3G router in a metal box (grounded) with ferrites on power cable, current choke on the coaxial cable of the yagi and shielded CAT6 ethernet cable (1m long). So quite good RFI protection there. I bought also a 900MHz band pass filter for the modem  (yet to be installed)...

The Radio RRC is grounded, Ethernet is set to Auto-prefer 10 Mbps.

I am totally lost here. Any ideas are more than welcome.

73 de Kari, OH2XX

oh2xx

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Re: Latency mystery
« Reply #1 on: 2013-11-22, 19:06:22 »
Some update on the latest findings for the record.

I noticed that the 3G router seems to pass the ping request to RRC as it is configured to be DMZ. So the ping plot tells that it is the RRC that is involved in this latency issue. That explains why all my efforts to cure the 3G router RFI problem have not had any impact in the first place.

As CQWW is just around the corner I wanted to try alternative approach to have reliable CW in the contest. So I installed a local PC at the remote station with TeamViewer, logsoft and COM-port CW keying. And you know what - it works flawlessly. I just run the logsoft via TeamViewer and it works all day long. Ping stays at 60...90ms so it is now even better than my earlier setup with 250ms key delay.

But I would like to have the setup without the PC being involved. So I will continue analyzing the problem further.  It seems that the RFI is not going into 3G  router or RRC SIP stream but into the remote CW keying or the protocol behind it. Maybe I'll try some RF chokes on the RRC CW key cable next. That is perhaps one of the only cables there without ferrite at the moment ;-)

73 de Kari, OH2XX