Tuesday, September 13, 2011

VK5 with V4

Looking for something to pique my interest enough to overcome my lethargy I decided to have another look at the V4 Chat digital mode. I tried it first at the end of last year and made one contact with it, but the alpha software was a bit flaky, then the developer Rick KN6KB had a bereavement and nothing happened for a while so I forgot all about it.

What attracted my interest was discovering that the ARQ mode had now been implemented. V4 Chat supports two conversation modes: Forward Error Correction (FEC) in which the data is sent with a lot of checks and redundancy so many receiving errors can be corrected but you have one chance of getting it correctly, and Automatic Repeat reQuest (ARQ) in which the receiver can request a repeat if a transmission is received with errors. Using ARQ a receiver can repeatedly request a repeat (up to a limit) so even if conditions are marginal a QSO is possible as long as propagation is adequate for short periods of time. Under the same conditions conventional (non ARQ) digital modes would print so much garbage that a contact would not be possible. People who own expensive SCS modems like to boast about how Pactor gets through under difficult conditions but V4 ARQ offers the same kind of performance and requires only your PC and a bit of open source donationware.

I re-subscribed to the V4Protocol Yahoo Group (which is where you can get the software from), downloaded and installed the latest version. Then I set my K3 to 14.073MHz (which is the 20m "calling frequency" for experimental narrow data modes) and waited. After a while I heard the sound of V4 ARQ bursts, and found that VK5PO was in QSO. I saw him disconnect from the other station and sent a CQ. He then connected with me and we had (just about) a QSO.

Signals were marginal both ways and I had to crank the K3 up to 50W to help John copy me but over about 10 minutes names and signal reports were exchanged. One of the nice things about the ARQ mode is that when the text prints up you know the other station has received it error free.

OK, it wasn't much of a chat, but ignoring WSPR spots I have only ever made one contact with Australia before and that was using JT65A which is not a keyboard chat mode. I was pretty chuffed to exchange words with a ham 16,000km away using my stealth radio station!

I think I'll be spending a lot more time trying out V4 Chat digital mode and I hope you will too because the more people use it the more contacts we can all make. The V4 signal is 200Hz wide so if 14.073 (or 21.073) is busy move up in 250Hz increments to avoid QRMing someone else's QSO.


Paul Stam PAØK said...

Hi Julian, that's a nice QSO with V4. I tried a few times a year ago. Very odd software /mode. I couldn't make any contact so I lost interest. Maybe I will try gain. 73 Paul

PE4BAS, Bas said...

Interesting read Julian, I too did try V4 for a while and made some tests but found it too difficult to make a proper QSO then. May be we should ave a look again. 73, Bas

BX2ABT / PA2BX said...

Pity it is written with the .NET framework. Doesn't run on Linux using Wine, so that excludes some folk like me wanting to give it a spin. Good luck on your effort though.

Bob G3WKW said...

I discovered V4 from your original blog last December and have persisted through the various Beta iterations. I suspect many have dropped along the way as it is an iterative process but Rick is persistent despite the often unhelpful feedback and he has just made a fork with a "solid" release and the "edgy" version with bugs which is more interesting to some of us. But you have to keep checkin the progress, though the Auto-update should help from now onwards.