what I need to do to listen to 70cm on sdrsharp

Status
Not open for further replies.

doughyi8u

Member
Joined
Sep 13, 2014
Messages
17
Location
Fostoria, OH
I've been playing with SDR# for a couple days now and can get 2 meter and FM broadcast radio but when I go to 70cm I can see a raise in frequency but I don't hear anything but noise. I have it set on NFM. I'm completely new to this so bear with me.
 

rbm

Member
Joined
Jan 25, 2005
Messages
1,395
Location
Upstate New York
Have you adjusted the RF gain?
I usually run the RF gain somewhere around 30dB.

Are you using the little antenna that comes with most of the dongles?
If you are, and you still don't hear any local activity, you may need a better antenna.

Rich
 

doughyi8u

Member
Joined
Sep 13, 2014
Messages
17
Location
Fostoria, OH
I have adjusted the gain and have a copper j-pole antenna. It looks like there's some activity but all I get is noise. Like I said, I can get some 2 meter and FM radio. Also, I'm new to this and don't know what a lot of the features do. I've tried NFM, AM, LSB, USB, etc and they all change sound but it's still just noise.

Thanks for your help.
 

rbm

Member
Joined
Jan 25, 2005
Messages
1,395
Location
Upstate New York
It sounds like you have everything you need. ;)

NFM is probably what you would want to hear there.

However, seeing activity in the display doesn't mean ham activity. (or voice activity)
If you have any switching power supplies nearby, then you will likely see some 'hash' from them.

There's no activity on that band here right at this time.
But, here's what you can look for.

It's a screen capture of NFM activity on SatCom.
You can see two voice signals.
One at 253.750 MHz and another at 253.850 MHz.
You can pretty much see each syllable and the pauses in speech at both points.

There's one or two more weak signals further up the band.
The others are of unknown modulation or random signals.

Rich

 
Last edited:

doughyi8u

Member
Joined
Sep 13, 2014
Messages
17
Location
Fostoria, OH
It looks like I'm getting a good signal but it's just noise as I've mentioned. I've attached a screenshot of SDR# running.
 

Attachments

rbm

Member
Joined
Jan 25, 2005
Messages
1,395
Location
Upstate New York
That's not a voice signal.
But..... it IS a signal and not noise.

Probably a digital mode.

Rich

Edit:
The first thing you must do is make sure that your dongle is properly calibrated.
Here's one of my earlier posts that describes how to do it.
http://forums.radioreference.com/software-defined-radio/294056-frequency-correction.html#post2213388

Then:
You can either go here and search for that frequency in your state and county, and surrounding counties.
Site / Market / Frequency Query

Or......

Go to the RR database for your county and surrounding counties and look for that frequency in the 'FCC Licenses' tab for your county and surrounding counties.
 
Last edited:

rbm

Member
Joined
Jan 25, 2005
Messages
1,395
Location
Upstate New York
That image shows just data, a 'clear' voice signal will show peaks and valleys in the modulation.
You can look at a NOAA weather broadcast to see what I mean.

Rich

Like shown in this screen capture.




By the way, when I search all of Ohio, for FCC assignments between 461.4550 and 461.4750. I get 56 hits.

All of them are on 461.4625 MHz so I do suspect that you need to calibrate (or change your 'Step Size' or both). ;)

2.5 kHz Step Size would be a good start.
 
Last edited:

doughyi8u

Member
Joined
Sep 13, 2014
Messages
17
Location
Fostoria, OH
I read the post you posted and still can't get any of the frequencies to work other than FM radio. I changed the step size to 2.5. I'm having trouble calibrating my dongle. I tried a few of the tv frequencies but none of them work.
 

br0adband

Member
Joined
Apr 8, 2005
Messages
1,570
Location
Springfield MO
Looks like a pretty strong DMR signal to me, especially given the frequency. Noise is basically anything that doesn't create an actual peak on the spectrum of any noticeable level - sure there will be times when you'll see "humps" or small rounded portions across the spectrum that can be strong enough to open the squelch depending on the setting but something that shows up as red/yellow on the waterfall is pretty much guaranteed to be an actual signal of some kind.

Digital signals like DMR have the look of the one in post #5 tend to be "static" in nature and by that I mean they present a consistent visual on the waterfall which is very easy to spot. Voice signals will have a jaggy contorted quality to them because as a person is speaking the transmission is modulated hence it's not consistent and can even change based on how loudly the person is speaking.

Rest assured you ARE getting a signal, more than likely DMR as noted and that's a digital format which means you'll need either DSD+ to decode it on a computer (or the original DSD) or a physical scanner capable of DMR reception.

If you want a great resource for learning how to identify signals based purely on visual inspection from the waterfall, this is a most excellent one:

Signal Identification Wiki
 

KE5MC

Member
Premium Subscriber
Joined
Dec 19, 2002
Messages
1,040
Location
Lewisville, TX
I've been playing with SDR# for a couple days now and can get 2 meter and FM broadcast radio but when I go to 70cm I can see a raise in frequency but I don't hear anything but noise. I have it set on NFM. I'm completely new to this so bear with me.

To fill in the gaps left by the other posts.

70cm to me references the ham frequencies 420-450 MHz.

Using Fostoria as a reference it looks like in repeaterbook only 3 repeaters listed you might hear.

444.1500 / Findlay
443.8000 / Tiffin
444.8250 / Tiffin

So it does not look like in the ham band of 70cm Fostoria is a hot bed of activity. Your best time to listen is during rush-hour traffic in the morning and afternoon. Depending on your antenna you might be able to hear further than what I listed or repeaterbook may not have all the repeater available in the database in your area.

Good Luck, Keep us posted on your findings/results.

Mike
 
Status
Not open for further replies.
Top