Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Lower power output when using PSK31??  (Read 6848 times)
WB0AXN
Member

Posts: 90




Ignore
« on: May 05, 2008, 06:02:58 PM »

Hi,

I notice when I'm using PSK31, the maximum power output I get is between 25 and 30 watts....even tho I have the rig's power output on maximum...which is 100watts.  I'm using an Icom 746Pro...on 40 & 20 mtrs.

Although I've only made a few contacts, I do notice some of those contacts report power at 30 to 50 watts.
I make sure I'm not over-driving and my ALC does not move off zero.  
If I increase the drive, the power output remains the same, but the ALC shows movement, which, of course, I don't want.  
So far, all of my contacts say I have a good clean signal...with a minus 25 to 30 IMD.  
What do I need to do to increase my power output and keep my clean signal??
Roland
Logged
KG9NZ
Member

Posts: 28




Ignore
« Reply #1 on: May 05, 2008, 06:57:12 PM »

25 to 30 watts is probably about right for a 100 watt rig on PSK31.  PSK31, like other digital modes including RTTY, is 100% duty cycle, so you have to keep the power down to keep from possibly overheating the rig.  And PSK31, because its signal has such a narrow bandwidth, does well at low powers.  

So I wouldn't worry too much about running only 25 or 30 watts.  Since your IMD is so low, you could try increasing the gain just slightly (even allowing a small amount of ALC to kick in).  You might still have an acceptable IMD even with a small amount of ALC.  Of course, you should confirm this with an IMD report after you make your adjustments.

73,
Frank KG9NZ
Logged
WB0AXN
Member

Posts: 90




Ignore
« Reply #2 on: May 05, 2008, 07:07:42 PM »

Thanks, Frank....for your reply to my post.

I think it's best for me to not worry about the output and continue having fun with PSK31....my first effort at digial modes.  
With the bands being in poor shape lately, it's a wonder anyone makes any contacts...but they do quite well with PSK.

Roland
Logged
AA4PB
Member

Posts: 15066




Ignore
« Reply #3 on: May 06, 2008, 06:41:10 AM »

Actually your PRO is rated for 100% duty cycle at 100W and it will run 100W on FSK modes like RTTY. PSK31 however (like some of the other digital modes) has amplitude variations therefore it requires that the transmitter operate in a very linear mode. This means that you need to keep the power output fairly low to ensure a good quality signal (good IMD).

You should run your rigs power output control at maximum power and then decrease the audio drive (via the mike gain control and/or the sound card levels) to obtain the proper power output. Normally, 30 watts is fine.
Logged

Bob  AA4PB
Garrisonville, VA
KE4DRN
Member

Posts: 3746




Ignore
« Reply #4 on: May 06, 2008, 02:32:55 PM »

hi roland,

here is a nice video from k7age on
setting up transmit levels for psk31

http://www.youtube.com/watch?v=I3CwHaX7t5M&feature=related

73 james
Logged
WB0AXN
Member

Posts: 90




Ignore
« Reply #5 on: May 06, 2008, 05:35:00 PM »

Thank you AA4PB....for the info on how my power output should be adjusted for good signals.  
And, thanks to KE4DRN for posting the link to the PSK video.  It's a sixteen minute video and will take an hour or more to view it without pausing every few seconds.  
I wish I hadn't cancelled my high speed internet I had for eight years.  Our cable company penalizes you if you don't subscribe to their TV service too.  
I hope they're happy to lose another customer.  

73 to all,
Roland
Logged
KB9CRY
Member

Posts: 4283


WWW

Ignore
« Reply #6 on: May 06, 2008, 06:55:36 PM »

Yes, very low on PSK is good.
Logged
W6ONV
Member

Posts: 98


WWW

Ignore
« Reply #7 on: May 07, 2008, 12:13:56 AM »

I have seen similar issues with my ICOM IC-718, currently running it at 100w and was seeing output in the 30-40w range, but very good IMD/signal reports in my QSOs. Initially I thought it was a problem, but further reading I found out that not to be the case.
Logged
WB0AXN
Member

Posts: 90




Ignore
« Reply #8 on: May 07, 2008, 05:11:50 AM »

Greetings!

Since this thread has been about power output and the proper drive settings to obtain a good-clean signal, I have discovered each digital software varies and I need to re-adjust my sound card levels for each program...at least on PSK31...which is the only digital program I've used thus far.
My first venture in digital modes was PSK31....about three months ago.  Digipan was recommended, so I installed it and soon got hooked on this new mode for me.  Soon, others suggested I try other software, so I installed PSK31 Deluxe, Airlink, MultiPSK and HRD+DM780.  I soon noticed I had to change my sound card putput levels for each program.  Some a little and some more....and each program has it's own audio sliders.  Thru trial and error, I found DM780 to work the best with adjusting the levels.  When I built my homebrew interface two weeks ago, I added two pots...one for receive and one for transmit.  Using DM780, I found out I don't need to fool with the interface pots, since the software does an easier/  better job.  
Has any of you tried other programs and found the same thing?  
I haven't used each program enough to choose a favorite.
Since the 40 and 20 meter bands have been in poor shape lately, I've had a chance to do more testing my levels, without interferring with other stations.  I soon found out the "transmit" pot on my interface causes me the most problems, when it comes to setting my drive levels properly.  Before I added the pots to the interface, I used a resistor attenuator and everything worked great.  I should remove the pot or figure out a better way for the interface to adjust the power level, rather than the software.  
I'm curious how many of you digital fans have pots on your interface??

Roland
Logged
AA4PB
Member

Posts: 15066




Ignore
« Reply #9 on: May 07, 2008, 09:49:20 AM »

I find the pot on the interface to be much easier to use than the digital sliders. In addition, I find that the audio level required changes with the band. In addition, on some transmitters (depending on filter ripple) it can even change with the transmit position on the waterfall. This is another good reason to keep the power output low so that you don't hit a "hot spot" in the waterfall and overdrive.
Logged

Bob  AA4PB
Garrisonville, VA
SV1ENS
Member

Posts: 129


WWW

Ignore
« Reply #10 on: May 07, 2008, 12:02:58 PM »

I've been operating DIGI since 2000, and I never found it necessary to operate with more than 10-15 watts. My old IC-706 MKIIG and my new FT-857 was/is set to 10% power.  PSK, 15 watts & a moderate antenna will work the globe !

Although my homebrewed sound interface can be set to different levels, I never change the level between modes, I set to the mode that requires the lowest drive and work all modes with that. Works well and keeps my signal free of interference :-)

A very good S/W for DIGI is MixW...

73
Demetre - SV1ENS

------------------------------------------------
Yaesu:
http://groups.yahoo.com/group/yaesu-radio/join
Kenwood:
http://groups.yahoo.com/group/Kenwood-Radio/join
Icom:
http://groups.yahoo.com/group/IcomRadio/join
Logged
KE4DRN
Member

Posts: 3746




Ignore
« Reply #11 on: May 07, 2008, 02:38:48 PM »

Hi Rowland,

you can watch the video at the local
library or a family member will share ??

Here is a freeware utility that will save your
soundcard settings to a file so you don't have to
configure the settings to use digipan, etc.

Getting QuickMix

QuickMix is freeware. You can download VERSION 1.06 by clicking on this link:

http://www.msaxon.com/quickmix/QuickMixIn.EXE

73 james
Logged
K7RNV
Member

Posts: 98


WWW

Ignore
« Reply #12 on: May 10, 2008, 03:55:32 PM »

Hello from Reno Nv. If you computer has speakers that need to be plugged in you have to turn up the alc to get full power, but you do not want to do that as the signal will be splattering. If you just have the speakere on the computer that just plug in no power, and you do not want them on anyways, turn up the volume a bit and as you turn up the volume, the power will go up.. Just my two cents worth.......73 Bob
Logged
WA0LYK
Member

Posts: 0




Ignore
« Reply #13 on: May 17, 2008, 06:04:59 AM »

30 watts of AVERAGE power output is about right for a PEP of 100 watts with psk31.  If you had a power meter that read PEP, you would find that you are hitting 100 watts PEP output.

You need to do some research on how the average value of sine wave and speech waveforms relate to the peak value.  The commonly used reference is that the average value of a sine wave is 0.707 (square root of two) of the peak.  In other words, you should see 70 watts of average output on your power meter if you put a pure sine wave into your microphone input.

PSK31's waveform is such that I believe 35 watts of average power is about what should be observed.  Don't hold me to the exact value, I would need to go back and calculate the actual value.

Jim
WA0LYK
Logged
AA4PB
Member

Posts: 15066




Ignore
« Reply #14 on: May 17, 2008, 04:18:27 PM »

I believe that with a PSK31 idle signal (i.e. you are not typing characters) the average power is 50% of the PEP. When you start typing the average power will go up a little.

You do not want to run PSK31 at 100W PEP on a transmitter rated for 100W PEP output. You need to keep the PEP well below the maximum in order to ensure that you maintain a good clean signal. 30-35W is a good place to be. One of the issues is that the total gain of many transmitters varies with the acutal input frequency because of ripple in the filters. If you set your radio to the upper limit at one spot on the waterfall and then move to another spot on the waterfall the transmitter output may increase beyond the limit. It is best to keep it low enough that you can operate anywhere in the waterfall without overdriving the transmitter.

Logged

Bob  AA4PB
Garrisonville, VA
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!