Debugging Airmail and Pactor

[jalmberg]

Wow, I had no idea RFI could garble the signal, though it makes sense now that I think of it. I do have a portable SSB receiver, that I use to listen to Chris Parker in the mornings on (consumes a fraction of the power of my full-size rig even on receive). I've also ordered a new serial converter and a bag of chokes. I will fiddle with all until I get a clean signal. Thanks for all the advice.

[stormalong]

To determine if RFI is the problem turn down your TX power. I have run Winlink with only five watts. The other things to check are SWR and your ground. An antenna mismatch or bad ground can generate a lot of spurious emissions.

If this is a new problem with existing hardware and software RFI is a good guess. If the Windows 10 operating system is new you may have a driver issue with your RS-232 to USB adapter.

[jalmberg]

Turning down power sounds like a good tip.

The reason I boiled a new serial adapter is because I don’t know what the old one is. I’m using up to date FTDI driver, but don’t know if it’s an FTDI cable.

I think that’s the right acronym.

[donradcliffe]

I had power supply problems with my IIex. It would give your symptoms on cold mornings, and would respond if I put the tea kettle full or hot water on the top of the unit and turned it on for 15 minutes before I tried to send. If that fixes the problem for you, you can make a permanent fix by soldering a large capacitor on the board as shown in some instructions emailed from SCS.

The instructions have disappeared from my computer, but I got them by contacting SCS. I think Eric at Farralon Electronics may also have them.

[AA3JY]

I’ve been using this:

websdr.org

...to monitor my output signal via the internet.. Very helpful in adjusting and tuning..

[jalmberg]

So this morning I wound my serial cable even tighter, coiling it as close to the modem as possible, and secured it with twist ties.

Unfortunately, there is no way to lower the output power on my ICOM IC-M700 transceiver, so I couldn't try that.

I did try to monitor the output signal using the websdr station in DC (#1) which was the closest that could monitor the frequency I was using, but I could not hear the signal, so had to use my portable Tecsun receiver.

I put this as far forward as possible, switched it to 'local' and left the antenna down, but frankly I wasn't sure what a good signal was supposed to sound like, so I will have to do some listening on that frequency until I hear another station.

Bottom line, I was able to connect using airmail and send and receive mail with none of the usual crashing. Hard to believe it was that simple.

Next, I plan to check all the connections and make sure none of them are corroded. I have an SWR meter, but it is not hooked up. I just assumed the antenna tuner would take care of that, but it would not be a bad idea to add an SWR meter to the setup, obviously.

Anyway, thanks again for all the tips. I learned a lot.

[AA3JY]

Have you adjusted Amplitude adjustment in 'Terminal' ..then 'Control'..then 'Set PTC-II Amplitude'..?

[jalmberg]

I have fiddled with the amplitude adjustments, but don't know how to set them correctly.

I was just using the web sdr to monitor a Pactor frequency, and luckily heard a couple of connections. I would say that my tones were a little more raspy than the clear tones I heard on the radio. However, it could be that my little radio was getting overloaded by being so close. I need to take the portable radio down the block and see how it sounds at a more reasonable distance.

[AA3JY]

If it sounds "ragged" it's a good possibility your over deviated.. Set your Amplitude adjustment lower..

Unfortunately the commercial marine radios are unable adjust ALC (mic gain) externally like the ham gear Hf radios..

Also try using the K3FEF SDR site to monitor

[SoonerSailor]

Originally Posted by AA3JY

Unfortunately the commercial marine radios are unable adjust ALC (mic gain) externally like the ham gear Hf radios..

Mic gain is not ALC, and ham radios do not generally offer the option to adjust ALC. they do offer the ability to adjust microphone gain and compression. If you are feeding Pactor modem audio into mic input, you do need to have mic compression off, and you do need to set mic gain and Pactor modem drive levels at a point where ALC action does not occur or is at least minimal. If you are feeding Pactor modem signals into the radio via a separate line level input, like many ham radios and marine radios offer, mic gain and compression settings do not typically apply to that input, but the audio drive level of the Pactor modem itself is still important. ALC is a function of all modern transmitters to prevent driving the transmitter beyond its design limits. If you are driving the transmitter with high enough levels ( via microphone or the data port) to cause the ALC to kick in and limit output power peaks, you are actually creating clipping distortion which will negatively affect digital transmission quality.

The key to clean data transmission is to have modem drive levels set at a point that does not cause ALC action. With Pactor 3, you typically want modem levels set so that average output power of the transmitter remains below 50% of what the transmitter power is set to. Transient peaks will be close to 100% power at a setting that gives 50% average power. That is the simple rule of thumb and should keep you in a good zone.

Airmail and Winlink’s RMS Express both allow you to adjust modem drive levels. The exact settings that are best will vary among different models of radios. You may have to experiment to find the best levels.

[jalmberg]

Originally Posted by SoonerSailor

You may have to experiment to find the best levels.

How does one know if ALC is kicking in, though? I don't have any indicator on my simple marine transceiver to tell me that it is. Is it just a matter of listening to the output with a my portable receiver and experimenting with levels until it sounds right?

[SoonerSailor]

Unfortunately, except for some ham radios, there is usually no direct indicator of ALC action, so to set proper Pactor modem audio levels, you have to have some indication of the radio's power output, be that "bars" on the display, or an external power meter, and you have to know if that indication is peak reading or average reading.

If it is average reading, which is most likely, and your radio is set for 100 watts of transmit power, you want it to show no more than 50 watts of output when transmitting Pactor 3.

If your meter is peak reading, I would set modem output levels so that the meter shows something less than full output, maybe 80 watts on the peaks.

If your radio has no indication of power output, you should buy an external power/swr meter and put it in line to provide you with that information. Its good to have in any case.

The Sailmail program can automatically set drive levels with a procedure for the M802, but I don't know if that works with any other marine SSB.

[GMN]

Hi,
This is Topher from Global Marine Networks. I would like this opportunity to point out a very nice blog post that describes the differences in Pactor Modems and Satellite equipment.


HF Radio and Pactor Modems vs. Satellite Phones for Email at Sea

[stormalong]

Originally Posted by GMN

Hi,
This is Topher from Global Marine Networks. I would like this opportunity to point out a very nice blog post that describes the differences in Pactor Modems and Satellite equipment.


HF Radio and Pactor Modems vs. Satellite Phones for Email at Sea

This article presupposes that the only purpose of HF radio is for email. If that were true I would agree with the article.

However, Marine SSB and Ham radio offer many more uses. When you are out cruising you will make friends with other cruisers. Marine SSB and Ham radio both offer ways to keep in touch with them. There are maritime mobile nets on both services and it is easy to set up a schedule to chat with friends. Many cruisers on passage set up a net of their own for the passage. Word of mouth at the jumping off points is how these nets get started.

In addition, Winlink is free, after buying the hardware and (hopefully) contributing to the Winlink organization to help with their expenses. Besides general email you will be able to download weather faxes, weather forecasts and GRIB files on a regular basis. Some of these downloads are large enough that satellite airtime would add up pretty quickly if downloaded daily.

Winlink requires that you are a licensed amateur radio operator with, in the U.S., a general class or higher license. Each country has it's own set of rules so check with your home country if not a U.S. resident. If you do not have the inclination to get that license, Sailmail, for a fee can provide almost as good a service.