Help with SDR and POCSAG im so close

I have been trying to decode POCSAG for almost a year now with a pro-2055 and no luck, I think do to the system being simulcast and me being in between 3 tower locations, I can decode on different frequencies just not the one I need to.

Anyway SDR Sharp maybe the answer, I think I am so close right now, I can decode on 149.7625 ALLLL DAY long no problem, I switch to 154.430 which is our Fire paging frequencies and I cant get anything, well tonight I was finally home for a page and captured it on SDR, I just need to know what I need to do to fine tune this thing now from here to pickup the POCSAG 512 traffic.

I have attached a couple screen shots of what I picked up but PDW didn't decode it, so im assuming maybe because im not in the exact "center" of the pocsag signal? The frequency is 154.430 but the center seems to be 154.433 I am going to try it there and see if that helps at all. I have to use the antenna t hat came with the NooElec because like I said any other antenna is WAY to much antenna, even the stock retractable antenna on my Pro 2055 is to much for this frequency.

Any suggestions are appreciated.

In SDR Sharp put you cursor on the wheel beside the speaker and you should see the word configure, click on that. Now go the the bottom of the screen to the Frequency correction (ppm) adjust it up or down and it will peak the frequency that you are after.

Moonbounce

What moonbounce said. Make sure you calibrate your ppm correctly.

Your RF gain is WAY too high to use it with any 'real' antenna.

You can attach a better antenna and adjust the RF Gain slider somewhere in the middle of it's range until you have a clean signal.

'Snap to Grid' with a frequency step of 12.5 khz for that band is wrong.
It will tune to 154.425 OR 154.4375. But NOT 154.430.

Set it to 2.5khz and it will properly tune to 154.430

Rich

I would say set the step to 2.5KHz and leave it. Then you don't have to worry about changed offsets due to rebanding, etc.

The step should be 7.5 on VHF high band.

What decoder are you trying to use?

I'm using PDW Pocsag decoder, and like I said in can decode a couple other frequencies no problem with the same antenna but 154.430 seems finicky I will try what you guys have said so far though. Thanks

DaveNF2G said:

The step should be 7.5 on VHF high band.

What decoder are you trying to use?

Click to expand...

Shouldn't stepping be 5 khz? I don't know anything about POCSAG maybe they are on different stepping, but as far as i know 138 Mhz to 174 Mhz is 5 khz.

Moonbounce

moonbounce said:

Shouldn't stepping be 5 khz? I don't know anything about POCSAG maybe they are on different stepping, but as far as i know 138 Mhz to 174 Mhz is 5 khz.

Moonbounce

Click to expand...

Times have changed.

The 2.5 kHz step allows you to tune most frequencies in most bands.

The 7.5 kHz step will not work in some VHF bands. (NYSEG in New York State is one example)

5 kHz won't give you the split frequencies.

There are a few other step sizes that are useful but if you're jumping from band to band, it can be helpful to select 2.5 kHz steps to start with.

Then change for specific needs.
For example, in the Military air band 25 kHz steps are normal.
So it takes ten steps to make it to the next 'normal' frequency. If you're tuning around there, you'll want to select 25 kHz steps to start.

I do most of my tuning by looking at the signal and clicking on it.
With the 2.5 kHz step, I always land on the frequency I want to tune to. So I just leave it there except for special cases.

Rich

More from the RR Wiki:

"VHF private land mobile narrowband uses 7.5 kHz spacing. Existing VHF channels will remain, with new ones - already in use in some areas since the late 1990s - created between existing channels; for example, 160.230 and 160.245 remain, with 160.2375 created between them."

"This creates significant problems for many users of programmable radios and scanners, since nearly all are based on 5 or 6.25 kHz channel step size, and few of the designated 7.5 kHz channels in Part 90 can be reached with such channel steps. "

"Makers responding to this challenge have found it necessary to implement 2.5 kHz channel steps to reach all of the defined channels in the allocation table. "

Narrowbanding - The RadioReference Wiki

This video is pretty good on getting your software dialed in.

https://www.youtube.com/watch?v=IaKEYEyrRgk

OK the 2.5 kHz step work WAY better, even for my 149.770 frequency.

I'm picking up the signal on 154.430 as you can see i attached another screen shot, but still no luck decoding in PDW. I dial into 149.770 and boom as you can see there picking that up as well and its decoding in PDW I attached a PDW screenshot as well so you can see what it transfers to.

When I set the PPM setting should that stay the same for the entire frequency range? I set it to a NOAA station and just kept adjusting PPM until the voice came in the clearest and red line was at the highest peak point in the IF Spectrum box.

I dunno what im missing here to decode that 154.430 funny thing is im really close to the towers for that frequency - like were talking 10km line of sight close - and who knows where that 149.770 is broadcasting from.

The images I attached are as follows
1. 154.430 is 512 POCSAG TEXT
2. PDW window of decoded pages on 149.770
3. POCSAG 1200 Numeric on 149.770
4. POCSAG 1200 Text on 149.770

Im just not understanding why its not decoding the 154,530 , anyone have any other suggestions? The POCSAG 512 TEXT seems really long compared to the POCSAG 1200 Text not sure if this is normal or what?

If you're trying to decode a weak signal, you MUST be properly calibrated.

You can use one of the two procedures below.

And yes, it will stay 'relatively' accurate from band to band.
But, only after the dongle was warmed up before you did the calibration.

In addition, I've found that in many cases I get better decode in WFM mode with the same bandwidth setting.

By the way, I see your volume is maxed out.
That may be causing some distortion. Backing off a little sometimes will help.

Rich

My preferred method is using the pilot frequency of an ATSC TV signal. (Preferably more than just one.)

http://forums.radioreference.com/software-defined-radio/294056-frequency-correction.html#post2213388


An alternate method using a GSM signal. (Preferably more than just one.)

http://forums.radioreference.com/so...quency-calibration-reference.html#post2262579

Rich

rbm said:

Times have changed.

The 2.5 kHz step allows you to tune most frequencies in most bands.

The 7.5 kHz step will not work in some VHF bands. (NYSEG in New York State is one example)

Click to expand...

Times have not changed that much at all. The VHF band is broken into several segments. 7.5 kHz steps are required across the band (in the United States), but to land on allocated frequencies, one must use the correct "frequency 0" for the band segment in question.

NYSEG's frequencies are irrelevant to this discussion as they are building a statewide P25 trunked system on frequencies that used to be allocated for paging. However, their channels are at 15 kHz intervals in most cases, which is twice 7.5 kHz.

I see at least one participant in this thread is in Canada. Subband allocations and other parameters are slightly different there.

DaveNF2G said:

NYSEG's frequencies are irrelevant to this discussion as they are building a statewide P25 trunked system on frequencies that used to be allocated for paging. However, their channels are at 15 kHz intervals in most cases, which is twice 7.5 kHz.
.

Click to expand...

Dave, you're playing word games.

If you pay attention to what I wrote, you would understand that you can select a step size of 2.5 kHz and leave it there most times.

It you would rather be constantly changing your step size, have at it.

Rich

2.5 k is a nice "one size fits (almost) all" setting for easy mouse wheel tuning.

I've found PDW an odd tool. I sometimes find that it struggles at first, but if I leave it decoding, it seems to improve with time.

Winflex was much better, but it is difficult to find nowadays, especially if you want it without viruses and droppers inserted.

Hey
I have the huge Problem that PWD decode just 50% of the messages.
So i turn the noise reduction on and PWD decode more.
So what can i do to get more messages?

You need a good, strong, and clean signal to get solid decodes.

These are the settings that work 100% for me.

A marginal signal will put garbage (or nothing at all) on the screen.

That is shown in the second screen capture.
Same signal, almost the same SDR# and PDW settings but on a GHz antenna system.

Edit: I wasn't able to find a 512 POCSAG signal here.

Rich

Normal:



Weak signal:

I was just testing decoding POCSAG-4 using PDW v3.12 and changing the sample rate from 2.8 to 2.4 seemed to provide better decoding, from 79% to over 90% with no change to antenna or frequency... For what it's worth.

My sample rate is at 2.04