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Increase TX speed

Using VarAC V8.6.2 / VARA HF v4.8.6

I'm getting very good RX speeds generally (over 200 bps on average) but my TX speeds vary wildly, and often are 18 bps.

Is there any configuration on the modem or software that might be affecting this? Is this all driven by the RF connection between myself and my QSO partner?

I'm looking for optimization advice.

73, Mark - KD2NOM

https://twitch.com/hamradiolurker

17 comments

Comments (17)

Todd

Apr 08

Developed in Spain by EA5HVK, "VARA" is a very sophisticated DSP data modem that runs on sound cards connected to radios with the typical "sound card interface". It comes in two versions: One adapted for HF over SSB transceivers, and a separate version adapted for the greater audio bandwidth of FM transceivers on VHF/UHF. Both versions are adaptive - they will automatically adjust modulation formats & transmission speeds upward or downward depending on the quality of the radio path and radio bandwidths in use.

Says nothing about file size being a condition of transfer speed.

Todd

AL7PX

Todd

Apr 07

I tried sending a large file yesterday to a station in Japan just to see if the speed increased. It did not. The strength/quality (roughly -20dB) of the connection was ok for chat, but not for file transferring. Speed never changed. Took 3 minutes for 1 kB. Speed never went over 18 bps. many repeats. Shortly after that contact with no change in band or settings with radio or software I made a connection in Australia. Signals were roughly -10dB +- 5dB at times and speed was nothing less than 250 bps. Again, no change with anything from contact with Japan station. Just my observations.

Todd

AL7PX

Edited

Todd

Apr 04

Having used VaraHF with Winlink I believe the modem speed increases with good SNR and 100% copy ability. The less repeats the faster it tries to go. It can't go faster no matter the size if the SNR is poor.

Todd

Apr 02

My question is about switching to 2300 Hz. What are the required conditions and how is transfer speeds affected?

Todd

AL7PX

Glitch

Apr 03

Replying to

conditions: a clear 2300 hz channel

transfer speeds: https://www.sigidwiki.com/wiki/VARA_HF

Todd

Apr 03

Replying to

Thanks Glitch:

I believe I've seen that chart before, thanks. I have seen some pretty high speeds using the modem with Winlink. All high speed connections transfers were with very good signals. I haven't had too many contacts with VarAC yet to compare. Maybe somebody else has had some experience with 2300 Hz using VarAC.

Thanks,

Todd

AL7PX

Albert Kleyn

Mar 29

Mark..

200 bps is crawling. many a time i am hitting far over 4000 or more, with WINLINK/VARA, connecting to HB9AK in Switzerland about 1200 km away from me. RADIO IS A YEASU ft991a.

but.... your SNR values must be very good to get near that.

i've been much higher but those occasions are very rare. max 60 watts on a Endfed l/w antenna, it is all I have for HF.

Albert

Mark Steele

Mar 30

Replying to

Wow - I've never seen anything above 300 bps on my setup on VARA HF.

What band(s) were you on when you see those types of speeds?

Oliver OH6CRU

Mar 30

Replying to

All depends on SNR and message length.

I had a QSO with PD0MBU on 20m 2300Hz. He was beaming me with 3 ele yagi 20W.

This was the only time I've got these speeds on other than 80m.

I was on my EFHW with 20W, about 1700km.

We achieved over 3200 bps on file transfer.

Really nice reminder what VarAC can do.

Edited

Oliver OH6CRU

Mar 30

Replying to

Also ping @Albert Kleyn and @hb9brj

This was in start of the solar storm as well, not the best conditions.

Mark Steele

Mar 28

Thank you all for your insights. I figured it was likely propagation. I do occasionally get very good outbound speeds (in excess of 200 bps) depending on the QSO partner. I'll go thru all my settings and make sure I have them tight. One question, I typically send so that there is NO ALC, although I see the documentation encourages ALC of 1/3 meter - is that a hard and fast rule?

Glitch

Mar 29

Replying to

I personally don't recommend any ALC at all. Turn your radio to the maximum power allowed, then adjust your soundcard so the actual power transmitted is where you want it. If you absolutely want it pegged at the maximum power output possible, turn it up, and you'll notice when you hit that limit ALC will start to turn on to keep you from overdriving the rig. From there, don't allow ALC to get above 1/3 or the loss in signal quality might cause annoyance or slower connection speeds. But even below 1/3, it does affect the quality of your signal, so just to make sure everything is clean (and to protect your finals), I would drive the rig to about 50-75% max power output.

Mark Steele

Mar 30

Replying to

Glitch,

Perfect - this is my normal operating configuration.

hb9brj

Mar 28

Even on a perfect channel, VARA will only switch to higher speeds if there is a sufficiently large amount of data waiting to be sent. Try to send a text file or a picture.

When I did a test on 10m with a local Winlink RMS, VARA did not go higher than level 12 of 16. So there might be other factors limiting maximum speed, probably related to your rig.

73, Markus HB9BRJ

Albert Kleyn

Mar 28

Replying to

Markus.

Gruss Gott.

What I tend to do is get an idea about sppeeds first. If good, I get WINLINK to update the stations settings VIA RADIO. That is about an 11K file. I have had that update come down in QUAM 32 mode like a bat out of hell ! Agree, that very very seldom happens and you need a near perfect SNR.

I have never send large files from VARAC.. so you will know much more about that than I do.

Verzeiung.. mein Deutch sehr slecht.

Albert.

Albert Kleyn

Mar 28

Mark....

Irad has hit the nail on the head: PROPAGATION is ULTRA important. Remember... VARAC is an ARQ mode and will demand PERFECT copy, unlike JS8CALL that will insert a few .... where it can't copy that particular bit of text..

As IRAD says: Audio levels have to be set correctly for high speed and yes, While I never run more than 60 watts... I know of people that run 500 watt into their Antennas !

But ultimately Mark, , the propagation Gods have the last say. All else being equal, they will be the deciding factor.

Albert.

irad d

Mar 28

Speed level is controlled by the VARA modem dynamically. it adapts the speed automatically.

The other side constantly report back to you modem how well (or not well) it is decoding, and based on that, it send your VARA a signal to increase or reduce speed.

Please note that for short messages, VARA will automatically chose a lower speed level just because high speed is not required.

If this issue is consistent - I believe it has to do with either:

audio issue on your end that prevent your QSO partner to decode high speed traffic. Check your ALC levels and also turn on MONITOR on your transceiver to hear your outgoing signal... There could be some noise there.
Your power is low when compared to the other side. Like they are doing 100W and you are QRP.

I by the way have the opposite problem. I have lots of noise where I live. So everyone received me well and I am receiing them weak. so my VARA triggers low speed transmission on their end.

One way to know this is to take a look at the SNR report (those green/Orange/Red) on the top right. If you constatly see that you give good reports and get lousy ones - then this is the reason for low speed on your end and you should look for why people give you bad SNR reports

73s

Irad 4Z1AC