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

   Home   Help Search  
Pages: Prev 1 [2]   Go Down
  Print  
Author Topic: 30W max on PSK31??  (Read 11756 times)
N4UM
Member

Posts: 466




Ignore
« Reply #15 on: February 06, 2010, 09:17:34 AM »

It seems to me that most of the emphasis has been placed on transmitting psk31 signals and not enough attention has been paid to receiving them.  

My feeling is that if someone insists on using a receiver bandwidth of 2 or 3 khz to receive a psk31 signal they have zero credibility when they complain about QRM.  The same thing can be said of stations operating on CW while using an SSB filter on receive.

It ain't rocket science!
Logged
N7RCF
Member

Posts: 14




Ignore
« Reply #16 on: February 06, 2010, 12:03:25 PM »

Recently I have read posts like this one and “W1AW QRMing 80m PSK” that are a little puzzling. As PSK and other narrow bandwidth modes become popular, I think we will see that a large number of amateurs really do not understand how their radio works or how to effectively use their equipment to receive weak signals in the presence of stronger ones. For those that are demanding that operators use only XX amount of power or that W1AW stop transmitting because “W1AW is killing the 80m PSK sub-band” and “my waterfall just go’s black”, I have just one question.
If you were designing a weak signal narrow band telemetry receiver for use in a noisy and crowded spectrum filled with strong adjacent signals, would you dump 3 KHz of bandwidth into the front end, and THEN be disappointed with the results? And, even angry at others because “those over powered signals are shutting down my radio”!
This would not be an effective way to design such a receiver, but it is how many OM are trying to receive PSK and other digital modes, and are very, very unhappy with the results. That strong adjacent signal that is “shutting down my waterfall” is doing so because YOU allowed it into YOUR receiver pass band, and YOUR AGC did what it was designed to do and reduced YOUR receiver’s sensitivity.
Now, I’m not talking about a station that fires up right on the frequency that you are using or a over modulated signal causing spurs to land on top of that juicy DX station you are trying to work. In those cases, there’s not much you can do but gripe.

My IC-746PRO has IF DSP filters, and this is how I use them for PSK-31.
I start by using my widest filter to survey the PSK band. I then select a narrower filter (set at 300 Hz) to survey a segment of the band and exclude stronger signals that may pump the receiver AGC.
I will then click on a signal of interest.
I then click center to tune the radio to this signal (this optimizes both receive and transmit).
I then select my narrowest filter (set at 50 Hz). Unless a station inadvertently transmits on top of us, I and the other OM are alone in the universe… HI…HI…
Using my wider filters, I can also use the adjustable notch filter to select a strong signal and attenuate it down 70dB, avoiding AGC pumping.
I also use the twin pass band tuning control to attenuate strong signals, and only view segments of the band.

Bottom line, it does not matter if that offending signal is the result of excess power, proximity or just good propagation, you MUST keep strong adjacent signals out of your pass band.  
If you have an older radio and really enjoy using the digital modes, consider upgrading to a newer radio with DSP IF filters. It’s a great excuse to buy a new radio, you can tell the XYL “well the switch from analog to digital went from cell phones to TV and now I HAVE to get a new radio” ;-)

If you already have a radio with good filtering, learn how to use it properly to minimize those strong adjacent signals that are dogging you. It’s really up to you and your own knowledge and resourcefulness to use and enjoy the newer communication modes.

73 de N7RCF
Rick
Logged
N3OX
Member

Posts: 8854


WWW

Ignore
« Reply #17 on: February 06, 2010, 03:48:27 PM »

If you were designing a weak signal narrow band telemetry receiver for use in a noisy and crowded spectrum filled with strong adjacent signals, would you dump 3 KHz of bandwidth into the front end, and THEN be disappointed with the results? And, even angry at others because “those over powered signals are shutting down my radio”!

I wouldn't, but if you look at PSK websites and "common wisdom," you'll only rarely come across someone who points out the importance of filtering and how looking at the entire "waterfall" has to be approached with care and doesn't always work well.

Panoramic tuning is great sometimes, but unfortunately  it is essentially "the way PSK31 is done" rather than an option to use when the signals on the band permit you to do so.

73
Dan
Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W3DCB
Member

Posts: 30




Ignore
« Reply #18 on: February 11, 2010, 10:20:32 AM »

"I've seen some stations mention they use 100 watts, one even that he was pushing 300 watts. Why ? When conditions are bad high power is of no use, its only making it difficult for others. Today I was being affected by a Russian station about 1,300 miles away, so I changed bands. There's just no need for excessive power using PSK"

Other than anecdotal evidence, is there any radio theory or objective evidence to suggest or confirm such a proposal?  Sloppy signals are sloppy signals.  It makes no difference what the wattage is.  If someone is spattering, then the issue is a dirty signal.  Don't be afraid to let someone know that they may need to clean up their act.  When I first started using PSK (at low wattage I may add), I had a sloppy signal and was told by several operators who helped  me clean it up.  I was thankful for the assistance.  I was using a new radio, an FT-2000, which I was not used to in a mode which I was not used to, using computer driven algorithms which I was not used to.  I had run RTTY in the 70s with a model 28 and a model 15 TTY using a homwbrew TU with Kenwood Twins, an SB-102, and a Tempo-1, among others, and had to re-orient myself to new procedures and the new DSP solid state radios.  Within a week or so, I got the hang of it, but I might have continued to have sloppy x-missions if I had not been told right off by some very helpful hams.  Sometimes because of a high noise floor or other conditions, higher wattage is called for just like in any other mode.  Well, take care...just my 2 cents!

Daniel C. Baral W3DCB
Logged
G0GQK
Member

Posts: 634




Ignore
« Reply #19 on: February 11, 2010, 12:51:56 PM »

Its quite entertaining reading all these comments about the intricacies of transmitting PSK.
The originator of the medium, an Englishman, for his sins, tested his invention for a long time in the period 1998-1999 and wrote that 10 watts was sufficient, at the time, to be able to reach all corners of the world. This chap also invented Amtor and being a damn sight more clever than most people, he also knew what he was talking about.

He designed it as a narrow band form of transmission and he probably never expected that there would be power mad loonies using 200 watts. I've noticed since the bands have improved slightly that the same people who wind up the power on contest days are now doing this with PSK. Traces as wide as roads, with bright red lines running down the centre. And some still call it a narrow band transmission. Ha !

G0GQK
Logged
DF7DQ
Member

Posts: 8




Ignore
« Reply #20 on: February 11, 2010, 01:03:46 PM »

....If someone is spattering, then the issue is a dirty signal....

I also think it is like this. Why first excepting a dirty signal that the half of the world has to reduce bandwide in receiving clear other signals?
The problem is, that everybody gives 599 instead of 595 and if you criticize the signal, the fault is almost always shifted to the receiver side.

Well, but the topic still is ... why more than 30W
Have fun with PSK.........

Peter
Logged
N3OX
Member

Posts: 8854


WWW

Ignore
« Reply #21 on: February 11, 2010, 01:16:24 PM »

He designed it as a narrow band form of transmission

Then why does everyone insist on wide-band reception?
Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
G0GQK
Member

Posts: 634




Ignore
« Reply #22 on: February 11, 2010, 01:40:02 PM »

This is a re-print of a personal testimonial by WB8IMY

Using my Icom IC-706 and an end fed wire, the results have been impressive. Despite my high noise levels and using only 25 watts and a G5RV, K8SRB was transmitting error free text. The software will copy text which cannot be heard, and had this been RTTY there would have been no contact. the mode is becoming popular in Europe, Australia and Japan, and contacts have been made on 160 metres. The mode seems more suitable for HF than RTTY

Many may recognise WB8IMY as a contributor to QST and this was in an article in QST about 2001

Advice from the Zakanaka help sheet also about 2001

1  Make sure that your speech processor is off
2  set the radio AGC to slow
3  Keep your power output low, try around 30 watts,  this is a lot of power for PSK
   
   30 WATTS IS A LOT OF POWER FOR PSK
 
4  Make sure your sound card audio is not over  driving        

G0GQK
Logged
N3OX
Member

Posts: 8854


WWW

Ignore
« Reply #23 on: February 13, 2010, 03:41:54 PM »

This is a re-print of a personal testimonial by WB8IMY

3  Keep your power output low, try around 30 watts,  this is a lot of power for PSK

You can quote whoever you want. My respect for WB8IMY's contributions to ham radio is not really a sound argument why 10dB extra clean power output, say 300W instead of 30W, would be a problem on bands where QSB might be 30dB and differences in propagation could mean that a really far-off DX signal could easily come in 40dB or 50dB less on average than that from somewhere with better, stronger propagation.

It's pretty typical that on a given afternoon, I may hear some parts of the USA at 59 or 59+10dB, possibly even just with 100W and a good, high dipole... and other USA stations in different places or DX stations will be S4 or S5.  Let's say we've got 40dB difference on 20m.

Why is 10dB such a fundamentally big deal when a guy from Texas could come in here a thousand times louder than a 300W DX station while the Texas guy is running 30W? 
 
The reason it's a big deal if I'm thinking about the Texan running 300W and being 59+20dB instead of 59+10dB (and you're probably thinking the same of an EU location to which you have excellent propagation).

Of course the 300W station with fantastic propagation doesn't ever need to run 300W *to reach you,*  but maybe they don't want to work you.  Maybe they want to work over the pole to some far off DX.  And yeah, they mess up your waterfall to do it... because your waterfall includes dozens of stations who aren't actually the weak one you want to listen to.

You can't expect everyone to be equally weak in your waterfall when there's 40dB or 50dB difference between the loudest and weakest stations even if they all ran the same low power output.

73
Dan


Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
Member

Posts: 12770




Ignore
« Reply #24 on: February 13, 2010, 06:11:10 PM »

Peter didn't originally design PSK31 with a waterfall. I was on PSK31 pretty early on when there was no waterfall and we tuned the signals using the VFO on the radio just like any other mode. Most probably used narrow CW filters at the time when they were available. It wasn't to later when the waterfall was added that people insisted on using wide SSB filters and the problems with AGC pumping began.

Bottom line is that 30W is NOT a magic number for clean output. With a properly designed system you can output a clean signal at any power level. If your experience is like mine then even if everybody on the band is running 30W, some signals will be S1 and some will be 20dB over S9 because of the difference in propagation. The answer to the problem: use a narrow IF filter once you establish contact.

In he past I've had the same issue with RTTY. I was accused of not listening before calling CQ on a crowded band. As it turns out the QSO was going on over 2KHz away but the station was using his 3KHz wide SSB filter to operated RTTY which is only about 500Hz wide. There was plenty of separation had the station been using the proper filter. I had plenty of space between us with my 500Hz filter selected and I had to tune considerably off my frequency before I could even tell they were there.

The newer digital ops need to gain a better understanding of IF filters and learn how to use them. Otherwise they have no case against QRM. It doesn't matter if you are running PSK31, CW, RTTY, or any other mode. What would we say to a SSB operator who complained about all the strong signals on the band and then said he had a 350KHz wide IF so he could "take in" the whole 20M band at one time? What do we say to CW ops who complain about QRM when using a SSB filter in the IF?

Logged
AD6KA
Member

Posts: 2236




Ignore
« Reply #25 on: February 17, 2010, 04:23:25 AM »

" As it turns out the QSO was going on over 2KHz away but the station was using his 3KHz wide SSB filter to operated RTTY which is only about 500Hz wide."

The other station was probably running AFSK instead of FSK, which is why he had his wde SSB filter on.
Logged
AA4PB
Member

Posts: 12770




Ignore
« Reply #26 on: February 17, 2010, 05:12:49 AM »

It's quite possible that he either didn't have a narrow filter or didn't have a radio that permitted him to select the narrow filter while running SSB. The issue is however, that on a crowded band when running a mode that is 500Hz wide you can't expect everyone to give you 3KHz of "clear air" just in case you have a wide receiver. Like on CW, if you use SSB filters you can't legitimately complain about some guy calling CQ 2KHz away.
Logged
N5XTR
Member

Posts: 108




Ignore
« Reply #27 on: February 17, 2010, 08:26:15 AM »

Well, I didn't realize that my stray would cause such an arguement.  For those who got bent out of shape, I apologize to each of you.  I have been operating PSK for 3 years, but it is time to move on.  CW has become my mode of choice now, thanks to the SKCC.  I suppose my Signalink interface will be used for an Echolink node to try and bring activity back to this town.  
--... ...--

Joel - N5XTR
Logged
AA4PB
Member

Posts: 12770




Ignore
« Reply #28 on: February 17, 2010, 10:03:41 AM »

Joel, the stray is no problem as far as I'm concerned. Certainly many hold that opinion. My intent was to point out that technically a strong signal doesn't necessary indicate excessive power and that more power does not necessarily mean your transmitter is distorting the signal.

With the sun spots coming back people are also going to run across the issue of the ionosphere causing phase distortion in the signals, especially over the poles. A perfectly clean transmit PSK31 signal can be distorted to the point of zero copy by the ionosphere. Odd when you run across a nice steady S9 PSK31 signal but can't print anything.

Bottom line, in my opinion, is that water falls are convenient but filters can provide the ability to copy weak signals with strong signals on the band. The receiving operator needs to take some responsibility for the QRM if he's running an IF many times wider than required to receive the desired signal. That applies regardless of the mode.

73,
Bob


Logged
Pages: Prev 1 [2]   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!