Psk31

[MM0BSM]

Just some info for the pskers out there

1 Dont type in capitail letters
2 make sure your processor on the radio is off
3 set up your sound card for the best audio out and in
4 learn the software
5 use macros to their best saves a lot of hassle


To check that the soundcard is not overdriving the transmitter, first set the mike gain control to the normal level used for SSB voice and start with the soundcard output level at zero on the mixer control panel. Then key the software to transmit a tuning tone and slowly turn up the soundcard output level while watching the transmitter output power. Stop when the power is just reaching maximum. The ALC meter will start to read. This is the correct setting. If the transmitter power jumps to maximum on the first step of the output control, you will need to make an attenuator to reduce the soundcard output level going to the transmitter. If you are using the transmitter mike input, you will certainly need to make an attenuator! The best way is to make the attenuator big enough so that you can leave the Mike gain at the normal setting and the soundcard output level at maximum. It will then be impossible to accidentally overdrive the transmitter. When you have reached the correct setting, you will see that changing from the tuning tone to typing text, will make the transmitter power swing from 50% (no typing) to 100% (typing or tuning-tone). This change in power is correct. It's quite OK to let the transmitter ALC line operate on PSK31. The ALC line will control the drive level without clipping in the same way that it does on voice operation."

[MM0BSM]

psk article i had


PSK31 The Digital King
ZL3JT

There are occasions when I am working on PSK31 trying to call a DX station, and someone thwarts my attempts on the frequency by transmitting a poor signal. Over modulation of the tiny carrier is the worst offence, and it truly can be offensive at times. It can be likened unto a loud ‘boisterous’ SSB guy running as much bandwidth as he can, and when told about his signal, he is offended, because his sycophants on his frequency don’t know unless they tune off his frequency a little. It always sounds ‘great’ to a sycophant!
Many times I have noted even low power transmitters emitting spurious signals thus destroying the possibility of working something close by. In fact they sometimes have multiple, readable traces!
People play with ‘mic gain’ controls to alter their ‘power’. It is a myth that your ‘power’ is altered by turning up the ‘mic gain’. There is a control on most modern rigs which adjusts the power, the ‘mic gain’ control only alters the modulation of the carrier, which is suppressed in SSB mode of course. When you are using PSK the sound card produces a ‘twin’ carrier 31Hz wide. This is visible on the waterfall of the receiving station, and called a ‘trace’.
I never have cause to alter my ‘mic gain’ once I have set it up for the mode I am using. I use the power control to do that power adjustment.
On PSK on have watched persons playing with ‘mic gain’ controls, and have someone tell them “how is it now?” It’s still terrible, but the receiving station tells him it’s better but still not good, he doesn’t want to offend of course! “Your IMD is now -14dB”
IMD should be at least –25dB, and could be even better!
We have the best tool available to check someone’s signal, and we don’t do it often enough. I’m talking about the ‘waterfall’ on your screen. It is the best ‘spectrum analyzer’ that could be gifted by it’s inventor!
Tuning your ‘set up’ can be a laborious process, but it will pay dividends if it is done properly, and if you remember a couple of things that will affect your output dramatically. Before you start to tune it up to get the most out of this delicate mode, you need to know that it is your computer sound card that does all the processing of the reception and the transmission, not the radio! The radio is only a means of converting the audio into RF, and vice versa. A good receiver will be better naturally, and a stable transmitter is imperative. As an aside, you may well have seen signals on the waterfall that your AFC in the program cannot follow? Yes, it is not a stable rig the guy’s got!
We use SSB with a bandwidth of 2500Hz in a ‘narrow’ part of the spectrum. It is well to remember this when you are operating. The bandpass filters are not linear, but instead they are curved like the hump of a camel. If we tune our ‘set up’ in the middle of the bandpass, and then shift the cursor to one end of the waterfall, our signal will be reduced both output and input. If you counter this by adjusting the output or the input of the soundcard to accomplish what you set out to do that is OK, but when you move back to the middle of the waterfall your signal is over-modulated crap! Readability is lousy, IMD is lousy and you will be unpopular. People then start playing with ‘mic gains’ etc and we are back to the beginning.
Don’t go to the middle of all the DX working on .070 USB to ‘tune up’. It is incomprehensible to do that, although it is a penchant for those who find someone up the band talking in SSB and they do exactly that!
Go up or down from the PSK frequency with your VFO to tune up, and then you won’t incur the wrath of other PSK operators.
Go to the SSB section and on a clear frequency, or use a dummy load. Turn all speech processing off, and all ‘TX equalization’. They are never used in PSK31. Open all filters wide, but make sure you keep the AGC in line. Someone might destroy your receiver, ‘Tuning up’!
Speak into the microphone normally and adjust the ‘mic gain’ so that ALC moves but the limit is never exceeded. Now your ‘rig’ is ready! No other adjustments to the radio, apart from the power control.
Pick a clear frequency near .070 the PSK31 Frequency, a couple of Khz either side. You may need someone to help you. They can monitor your trace as necessary.
Set the soundcard output to a low position, about 20% in your software. Set your radio’s meter to ‘ALC’ position, turn the power control on your radio to about half power, no more.
Set the TX cursor in the middle of the waterfall, and transmit a carrier, and note the ALC reading. If it moves too much reduce the soundcard output. If it doesn’t move, and the radio doesn’t produce any power, increase the sound card output, in the software.
By adjusting and testing with a carrier only you must arrive at a position where the soundcard output will make the radio transmit at the selected power without MOVING the ALC meter.
This can be confirmed by a receiving station as two thin lines. When you have achieved this, then try it again while transmitting text. You are now ‘modulating’ the ‘carrier’. You will need to make some adjustments to arrive at desired power output from your rig, without any ALC movement.
You now have a ‘clean signal’ and you can get your friend to verify that. Move to the PSK31 frequency and you are in business!
Now you are in the middle of the ‘passband’, and if you go away from the middle of the waterfall, the signals will be diminished, both output and input, because of the ‘shape’ of your band pass filters. You can go about plus and minus 500Hz only without noticeable change, but if you see a station outside these self-imposed limits, and you wish a QSO with them, then what to?
Move the VFO so that the desired trace is in the middle of your screen! It’s simple isn’t it. You have the best signal on the frequency now, in the best position!
Don’t play with your gain controls, don’t play with the power control, keep in the near middle of the waterfall by moving your VFO.
That’s exactly why I get to work all this ‘rare DX’, get good scores in contests, because my 50 watts is concentrated into 31HZ. A thin bright line. Easy to read signal.
Similarly on receive, if you choose to use your receiver filtering to reduce interference from unwanted lousy traces, you will need to have the station you want in the middle of you screen. You can even block out an offending signal by shifting your own VFO and introducing your IF shift. Be careful and move the VFO in exact increments, so you can find him again. The ‘markers’ in some software are useful for this. With my TS870 I can receive on the other VFO in CW mode and use a receive bandwidth of just 50Hz! That gets rid of all lousy signals on the frequency! But I need to operate with split VFOs to transmit in SSB, receive in CW.
Personally, I have the PSK frequencies in memory channels, and I normally operate on the memory channel. In contesting I set one VFO 500Hz up and the other 500Hz down exactly, and I can keep track of stations over a wide range without going outside my bandpass, by switching VFOs. I always use dual channel mode to keep an eye on my fellow contestants, between calls.
Some do send their text in the upper case, (Capital letters), and this is an error. If you send text like this it is more prone to errors, is slower, and is akin to ‘SHOUTING!’ When you type on the keyboard it is unnecessary to stay ahead of the buffer. You are the one in control. The computer can’t anticipate what you are typing. Remember that it takes longer to encrypt a capital letter, and longer for the other computer to decipher the letter. Combined with poor signals and band conditions, sending in the lower case could mean making that difficult contact. Of course you should use capitals where appropriate to make your text easier to read. Punctuation is not important either, nor should ‘yore’ spelling bother too much, as long as the message is passed.

I leave the audio slightly up so that I can ‘hear’ the other action on the frequency, while watching the print on the screen. I know if someone else starts up or down the band by the audio created, and a lousy signal is audibly lousy too!

Antenna height above ground will affect your transmission and reception. A low antenna, relative to earth, will have a higher angle of radiation, so that the majority of your RF may be lost in space. If it is reflected at all and the station you want is a long way away, there may be too many ‘hops’ between you and the DX. This is why some stations work DX with lower power and you don’t even see the trace! A vertical works better than a low dipole in a lot of cases, purely because of the ground affecting the angle of radiation. The reverse can happen as well, depending on the state of the ionosphere. This angle of radiation is particularly important on the 6M band, in that for VHF to reflect, it must strike the reflecting layer at a very shallow angle. The basic rule is the skip distance varies directly in proportion to the frequency in Mhz. But there are too many variables to describe here!

Last but not least, make sure you radio station has the best ‘earth’ possible. Make sure every device in your shack is connected to that ‘earth’, with the fat, short cables or braid. Digital modes play merry hell with your signal if you don’t!

Good luck and see you in PSK31!

Duncan ZL3JT (Jungle Telegraph)