Author Topic: How Much ACTUAL Bandwidth Needed to support reliable operation  (Read 3816 times)

N4HPG

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Hi All,

I'm hoping to have secured a site on a tall building to put my remote base station and to use this wonderful product. My plan is to get an IC-706MKIIG. Because I want to have the station operational regardless of power conditions for ARES communications, the site I'm trying to get is mostly line-of-sight from my home QTH. I have 2 5GHZ Microtik access points that I used for bridging between 2 buildings a number of years ago. The supply a solid 30Mbps of bandwidth when they are LOS and the firewall is running. A bit faster without a firewall running.

HOWEVER, there is a tree between the building and my condo. The crotch in the tree doesn't have much foliage yet I'm not sure that I can push the 5GHz through it in the summer. So, my backup position is 900Mhz. When examining these systems, the manufacturer says that they pass 1.3Mbps, but from a practical matter, about 984Kbps bi-directionally. With a yagi, these will "burn through" the foliage.

So, my question to the forum is this. Has anyone actually run a test to determine how much bandwidth is actually necessary to have reliable communications? Our manufacturer is recommending 1.5Mbps as a minimum.

If I were to get this awesome location on a 13-story building, I would use the 706 for both HF and VHF/UHF so there could be 2 SIP channels coming back for audio.

***
And for those of you who might need some assistance with networking, firewalls, etc. I'm a computer geek, EE and creative problem solver. I've offered to edit the manual and clean up the English so that it is clearer. Speaking 5 languages, I hope to help out the kind folks in Sweden making the Remote Rig.

Say a prayer for me that I can get back on the air!

73,

Bill

dj0qn

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Bill,

That bandwidth is no problem. Although you will get different opinions from everyone, in general you need to add the following together to get the bandwidth required:

- COM0 serial port bps
- COM1 and/or COM2 bps if used (i.e. for CAT or rotor control)
- which CODEC you are using, refer to appendix A in the Manual. I use CODEC 0 for almost all of my stations, which has proven to be more than adequate for SSB and CW.
- If you are running single or dual-channel audio (this doubles the codec rate requirement)
- There is probably some overhead in the 20-50 bps range that I would just add-in as well

Remember also that this is doubled, up and down! Most DSL lines are asynchronous and have a lot less bandwidth going up than down, but the internet provider usually only advertises the down speed. You need therefore to take into account that the bandwidth used by RemoteRig  is the same in both directions.

A corollary is the serial ports sent over the RRC, including CAT. It is not always necessary to run them at 57,600 bps! When possible, reduce them down to e.g. 4800 bps and reduce your bandwidth that way.

I also need to point out that I believe that the latency is far more important than the bandwidth, especially once you are over about 250k bps. Often 3G lines have severe latency problems making them unusable, and satellite is not advisable at all.

73,
Mitch DJ0QN / K7DX


VE3ZI

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I can get full duplex speeds of better than 500kbps over a 15km NLOS 900MHz radio link. As Mitch says, that is way more than adequate. However, while the latency is usually only a few ms, it is sometimes up to a second or so for no apparent reason. This tends to mess up CW!

I have wondered whether it would help to reduce the MTU from 1500 to some lower number, but I am a little dubious about trying that before the spring in case the radios are then not able to talk to each other as I can't get to the remote site until the snow goes.

73 Roger

N4HPG

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Guys, thanks so much for the information. The manual recommends 1.3Mbps for the 2-channel link. I've also spoken with a fellow in our club who maintains the echolink system. And yes, latency is a much bigger problem with SIP. I've worked with wired SIP phones. A frame size of 1500 is pretty big when latency is the bigger issue. It just happens to be the default MTU.

The 900Mhz link would seem to be the better option. With some Yagi antennas, there should be enough gain to burn through the foliage. The distance is trivial.

I'm just praying to the RF gods that I get the location!

best 73

Bill

sm2o

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Hi

You do not need 1,3 mbit. Look at this page

http://www.remoterig.com/wp/?page_id=388

I my self run a K3 twin setup with two Receivers in audio quality= 1 (130kb/s x 2) and the total bandwidth from my summer house is 400-500 kbit/s, and it's never any bandwidth problem. The quality is also far enough for HF-listening. You can ofcourse not listen to music on wideband FM with that codec.

73 de mike