The AM Forum
May 23, 2024, 06:00:44 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Bandscans ... activity displays ...  (Read 18298 times)
0 Members and 1 Guest are viewing this topic.
W8ER
Guest
« on: January 28, 2005, 10:20:10 PM »

As all of you know I have long been an advocate of opening up the bands to all modes everywhere .. sort of a "here's the band edges, stay between them. 160 is like that and it appears to work quite well.

I have looked for a long time for the right hardware/software to substantiate my claim that half of the HF spectrum is being wasted from non use. I have often said that the lower half of 75 meters is dead and the upper half is crowded and a lot of the problems we experience on 75 is due to crowding.

Earlier this evening I did a scan of 80/75 meters and would like your comments on how best to evaluate the display, possible things to look out for in setting up and evaluating the results and, of course, how will they be best used.

Most of the display is obvious. I have the AGC set to fast and the bandwidth filter set to 600 hz. The receiver is centered at 3750. The activity you see just below 3750 was Canadian SSB and AM, verified by listening to the activity.

All comments are welcome.



--Larry W8ER
Logged
Steve - WB3HUZ
Guest
« Reply #1 on: January 29, 2005, 12:12:53 AM »

Not much else needs to be said. I've seen similar on spec an looks.
Logged
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 8094


CQ CQ CONTEST


WWW
« Reply #2 on: January 29, 2005, 12:47:58 AM »

You probably would have to take into consideration that Friday evening was the start of the CQ 160 Meter CW contest. Maybe a number of the 80 Meter CW "regulars" were not here but down on 160 CW doing their thing.

How many times are you going to sample the data? Once, twice, 100 times and over what span of time. What about propagation conditions during the sample period? What about antenna orientation? And, in the end, it's only what you see at your location. In order to create an analysis of overall band activity and usage, sampling with similar equipment, should be done at a number of locations around the country. It's an interesting exercise, and probably would make great water cooler discussions and fodder for bandwidth petition bashings, but I'm not sure you could do much more than that with the results.
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
Steve - WB3HUZ
Guest
« Reply #3 on: January 29, 2005, 03:14:02 AM »

"What about propagation conditions during the sample period? What about antenna orientation?"


These apply to both CW and phone sigs. I don't see how they are relevant.
Logged
W8ER
Guest
« Reply #4 on: January 29, 2005, 04:09:13 AM »

Pete said:
Quote
You probably would have to take into consideration that Friday evening was the start of the CQ 160 Meter CW contest. Maybe a number of the 80 Meter CW "regulars" were not here but down on 160 CW doing their thing

Contesting schedules would certainly be relevant!

Samples on different days and different times would iron out any propogation worries.

Pete said:
Quote
It's an interesting exercise, and probably would make great water cooler discussions and fodder for bandwidth petition bashings, but I'm not sure you could do much more than that with the results.

When the FCC is petitioned for a rule change, I have been told that data speaks volumes. Assuming that I would have gathered such data and would present it to further the premise that half of the allocation is underutilized and likely to be under a new proposal, I would think it more valuable than water cooler discussions!

My fear is that I would be gathering this data and overlooking something that might invalidate my position. My request goes in that direction. What should I be doing and what part of my display raises questions as to what is shown. A good example is since CW is either on or off when the receiver scans that particular frequency, is the display of the CW portion of the band valid? After all I might be scanning a signal during key up?  

It's a larger question than it might seem on the surface Pete. I don't want to go to all of the trouble and in the presentation phase be shot down because I overlooked something, such as the contest schedules which is a good point!

Ed Hare has offered some good suggestions but since he is a damn CW person  :oops:  I am hoping to get some additional guidance from the boyz here!

--Larry
Logged
w3jn
Johnny Novice
Administrator
Member

Offline Offline

Posts: 4611



« Reply #5 on: January 29, 2005, 09:37:41 AM »

A single scan on a single night doesn't mean much.  As your receiver sweeps by it is very possible to miss a CW signal, which by its very nature has a low duty cycle.  You need to repeatedly revisit the same freq to make sure you catch this activity.

Also, the resolution bandwidth and/or display resolution doesn't give as stark a representation as I've seen.  A spectrum analyzer with <500hz RBW (and NO AGC) gives a mich better representation of what's going on.

I've done this (perhaps you saw my post in the ARRL Forum) with a spectrum analyzer using max hold and multiple sweeps over an extended period, and I've been doing this every once in a while for a month or so.  WHile my measurements closely agree with yours, a noise pulse will cause the display to apparently see the whole band as active!

Does your RX panadapter have a max hold function (ie can it hold the peak over repeated band scans)?  If so, then let it go for 15 minutes, take a pic, reset it, then rest for 15 min, then repeat.  Do this for an hour, then take an hour off and repeat the exercise.  Do this for an extended length of time.  *Then* you'll get some statistically valid results.  Finally, I recommend using a more suitable measurement system: a ham receiver with a digitized "band scope" just doesn't cut the mustard here, IMHO.

All in all, this is a very worthwhile exercise.  It's fine to state anecdotally that there isn't much CW activity; it's yet another to provide valid measurements (preferably from different parts of the country) that vividly illustrate the dearth of occupancy below 3750.  One could say the same for 40 (the novice band seems to be empty during the day, and occupied only by foreign BC at night) and parts of 20 as well.

73 John
Logged

FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 8094


CQ CQ CONTEST


WWW
« Reply #6 on: January 29, 2005, 01:28:55 PM »

Here's my unscientific study taken around 2 AM EST Sat. morning. Used the 756 PRO II and inverted vee, apex at 55 feet, directed East/West. From 3800 to 3900 heard 7 SSB QSO's, 2 AM QSO's, 3810 beacon, and some buzzy's. From 3900 to 4000 heard 8 SSB QSO's, 2 foreign broadcasts, and some buzzy's. From 3500 to 3675. heard 52 CW signals, 1 SSB signal, and 4 RTTY signals. From 3675 to 3800 heard 12 foreign speaking and English speaking QSO's.

Note: the majority of the CW signals were weak; many not even moving the S-meter and some difficult to see on the 756 PRO II spectrum monitor. Even with the scope range set to +/- 12 KHz, many of the CW signals were masked the noise floor yet they were audible in the headphones.

Again, not very scientific, and only one small slice of time. An hour later or an hour earlier, the mix could be very different.
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
w3jn
Johnny Novice
Administrator
Member

Offline Offline

Posts: 4611



« Reply #7 on: January 29, 2005, 01:45:04 PM »

Quote
and some buzzy's

Quote
2 foreign broadcasts, and some buzzy's


Sounds like the buzzies need their own sub-band.

You are correct in pointing out that some of the CW sigs are VERY weak, and it's easy to miss them when doing a band scan as they can show up as noise.

52 CW signals don't need nearly the bandwidth as a couple dozen or so phone signals.  Also, as Larry pointed out, CW ops have 100% of the HF amateur spectrum.  Phone has < 50%.

73 John
Logged

FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
Steve - WB3HUZ
Guest
« Reply #8 on: January 29, 2005, 07:00:01 PM »

The fact that the CW signals were so weak means they would hardly, if at all, interfere with each other. All the more reason to put all of them in a 20 kHz segment and have the rest for phone.
Logged
Jim, W5JO
Member

Offline Offline

Posts: 2503


« Reply #9 on: January 29, 2005, 07:48:18 PM »

In previous decades there were two methods of obtaining a VHF or UHF FM license.  An applicant could apply through the approved coordinating agency for a frequency (which could be wrong in it's allocation) or they could monitor a frequency for a specified period of time (I forget the period, but it was comparatively short).

What the applicant was supposedly looking for was stations within a 10 mile radius of the location where the antenna was to be located.  While this does not work well on a band that has long distance propogation, this group might establish teams with this particular goal in mind.  

Sort of the same principal as the moderator team of this board performs.  All members should agree on a method, determine time lines, and equipment to be used.  Who better to ask than Ed, W1RFI?  If that method was followed and there was not much activity logged around the country, would proponents of the proposal have a very good case and data to back up the proposal?

I listen around the 75/80 meter band quite frequently and do not hear much activity here in central Oklahoma.  Having people in the NE, SE, South Central, North Central, North West, and South West would cover all those bases.

I, personally, do not see what impact a contest should have on these measurments.  After all, they are short duration and infrequent.  Given  a portion of the CW band was allocated to phone, then it would be no worse than chasing DX on CW.  Many stations near each other would  require the use of those fancy DSP filters and band pass filters they so love.  Should such a large portion of the 75/80 meter band be reserved for infrequent contests?  I don't think so.  In fact, I don't believe much consideration should be given contests at all.  

I think you guys are close to a method to determine an answer and when you find it, things could change if several filed a proposal to the ARRL and the FCC directly.
Logged
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 8094


CQ CQ CONTEST


WWW
« Reply #10 on: January 29, 2005, 09:07:33 PM »

Quote from: Steve - WB3HUZ
The fact that the CW signals were so weak means they would hardly, if at all, interfere with each other. All the more reason to put all of them in a 20 kHz segment and have the rest for phone.


They were weak at my location. Doesn't mean they were weak to each other or weak at other locations around the country.

I think 250 KHz for phone operation is more than enough on 75/80M but I'll take more. I'm not sure it would help many AM'ers who seem to be stuck between 3870 and 3890.
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
Steve - WB3HUZ
Guest
« Reply #11 on: January 29, 2005, 09:22:39 PM »

That's great if they aren't weak to each other but weak to everyone else. That means they won't interfere with anyone else and can easily fit into a 20 kHz segement.

This is sounding better all the time.
Logged
W8ER
Guest
« Reply #12 on: January 30, 2005, 12:45:29 AM »

Johnny Novice (like hell) said:
Quote
You are correct in pointing out that some of the CW sigs are VERY weak, and it's easy to miss them when doing a band scan as they can show up as noise.

It has been pointed out to me by W1RFI that a chink in the armor of using a spectrum analyzer to do these scans is that they are incapable of the sensitivity necessary to see the weaker CW signals that are actually there (nearer the noise level). In my setup, I am using a receiver and scanning software to move the tuning up the band, in small steps, and check for activity. Since I have the bandwidth narrowed to 600 hz, I would suspect that missing a weak CW signal would be more difficult. I would assume that I might actually favor the showing for weak CW signals.

Comments?

HUZ said with great sarcasm:
Quote
That's great if they aren't weak to each other but weak to everyone else. That means they won't interfere with anyone else and can easily fit into a 20 kHz segement.


:lol:  :lol:  :lol:



--Larry
Logged
Art
Guest
« Reply #13 on: January 30, 2005, 08:53:38 AM »

I used an SDR-1000 to repeat the experiment at around 7PM last (Sat) night and the same result was observed. The upper end of the band was significantly more crowded than the lower.
Unlike a spectrum analyzer the SDR is capable of displaying signals into the ambient noise due to its low noise figure.
I operate some CW and some phone and still can't understand why a mode is given preference over a much more prevalent and popular one.

-ap
Logged
w3jn
Johnny Novice
Administrator
Member

Offline Offline

Posts: 4611



« Reply #14 on: January 30, 2005, 10:17:06 AM »

Quote
Unlike a spectrum analyzer the SDR is capable of displaying signals into the ambient noise due to its low noise figure


The noise figure of my spectrum analyzer isn't an issue, due to the high atmospheric and manmade noise level on 75.   In fact, I had about 10 dB of attenuation in line so as to prevent overload and to protect the mixer in the analyzer (ask my why I know to do this!).  This particular analyzer has a very low noise figure (for a spectrum analyzer) as it is.  If I can copy it on the R-3030 I can see it on the spectrum analyzer except for very weak signals that just don't appear as peaks out of the noise.  However, using the max hold will also hold noise peaks, which tends to further drown out weak signals.

Probably the best instrument for this sort of work would be an Agilent vector signal analyzer with the color spectrogram option.  If set up correctly you can see signals buried in the noise.  Yuo can also max hold the spectrogram on these wonderful instruments, and obtain microhertz of resolution bandwidth (if you're willing to wait forever for a meaningful display!).

73 John
Logged

FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
w3jn
Johnny Novice
Administrator
Member

Offline Offline

Posts: 4611



« Reply #15 on: January 30, 2005, 10:17:27 AM »

Quote
Unlike a spectrum analyzer the SDR is capable of displaying signals into the ambient noise due to its low noise figure


The noise figure of my spectrum analyzer isn't an issue, due to the high atmospheric and manmade noise level on 75.   In fact, I had about 10 dB of attenuation in line so as to prevent overload and to protect the mixer in the analyzer (ask my why I know to do this!).  This particular analyzer has a very low noise figure (for a spectrum analyzer) as it is.  If I can copy it on the R-3030 I can see it on the spectrum analyzer except for very weak signals that just don't appear as peaks out of the noise.  However, using the max hold will also hold noise peaks, which tends to further drown out weak signals.

Probably the best instrument for this sort of work would be an Agilent vector signal analyzer with the color spectrogram option.  If set up correctly you can see signals buried in the noise.  Yuo can also max hold the spectrogram on these wonderful instruments, and obtain microhertz of resolution bandwidth (if you're willing to wait forever for a meaningful display!).

73 John
Logged

FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
Art
Guest
« Reply #16 on: January 30, 2005, 11:44:53 AM »

Yeah, that's right. . . atmospherics and man made noise is probably greater than 20dB on 80M. . .
The SDRs got a spectrogram too . . . will check it out . . . toys and little time to figure out how to operate them . . .

-ap
Logged
Steve - WB3HUZ
Guest
« Reply #17 on: January 30, 2005, 02:20:51 PM »

John brings up a good point. A rolling spectogram or falling raster spectral display would probably be a better way to monitor activity over a period of time. These approaches are better than using max hold on a 2-D spectrum display because time is displayed and the overall display not corrupted by static and other noise bursts.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.24 seconds with 19 queries.