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[Cliff Fuller]

I have two IEM systems and I have done an FFT scan of the radio outputs. There is no audio to the inputs of the transmitters. What is the difference that I am seeing? What is the cause of the apparent distortion?

Thanks...

[Henry Cohen]

I have two IEM systems and I have done an FFT scan of the radio outputs. There is no audio to the inputs of the transmitters. What is the difference that I am seeing? What is the cause of the apparent distortion?

Concerning the second image of 486MHz: What is the span?

Concerning both images, please specify measurement parameters for each:
RBW
VBW
Window type
Detector
Averaging

[Cliff Fuller]

Concerning the second image of 486MHz: What is the span?

Concerning both images, please specify measurement parameters for each:
RBW
VBW
Window type
Detector
Averaging

Good evening, Henry.
I'll do my best to answer your questions. Prefacing those answers, I'm using an RTL-SDR USB dongle to do the scans and using an application called "GQRX" as the tuner. I will apologize that I'm not an RF engineer so I'm having a bit of a challenge translating your questions.

Both images were grabbed under the same circumstances. No other transmitters were powered on at the time of measurement. I think the answers are as follows:

span: 2.5 MHz
RBW: 293.0 Hz
VBW: 2.5 Mhz
Window type: hamming
Detector: ?
Averaging: 85%

Thanks for the look and any insight given.

[Jerome Malsack]

roughly guessing   that one might be a digital transmitter and the other could be  old school FM ??   upper and lower side bands and the noise floor. 

[Cliff Fuller]

roughly guessing   that one might be a digital transmitter and the other could be  old school FM ??   upper and lower side bands and the noise floor.

The transmitters are a pair of PSM 900s. There are a total of 6, the 504 MHz seems to be the only one without the added "noise". They have been in service for about 10 years. There doesn't seem to be any audible degradation.

[Don Boomer]

When you are measuring is only one radio turned on or multiple radios active?

[Cliff Fuller]

When you are measuring is only one radio turned on or multiple radios active?

Only one. I don't believe IM is a factor, although there are numerous video displays and other assorted devices in the environment - a gambling casino.

I don't notice any audio issues but thought it looked strange especially with one system (504 MHz) displaying what I think I should be seeing. There have been a couple of receivers that will not pass audio, nothing heard nor does the blue light indicator come up on the receiver (if you are familiar with the PSM 900 systems). I've checked the receivers against different transmitters and vice-versa, they just don't function. They are on the way to the "doctor".

Thanks for reading and offering assistance!    :-)

[Russell Ault]

Only one. I don't believe IM is a factor, although there are numerous video displays and other assorted devices in the environment - a gambling casino. {...}

Given the possibility for non-IEM RF noise, have you tried running a scan with none of the transmitters on, just to see what your baseline noise levels look like?

-Russ

[Henry Cohen]

Good evening, Henry.
I'll do my best to answer your questions. Prefacing those answers, I'm using an RTL-SDR USB dongle to do the scans and using an application called "GQRX" as the tuner. I will apologize that I'm not an RF engineer so I'm having a bit of a challenge translating your questions.

Both images were grabbed under the same circumstances. No other transmitters were powered on at the time of measurement. I think the answers are as follows:

span: 2.5 MHz
RBW: 293.0 Hz
VBW: 2.5 Mhz
Window type: hamming
Detector: ?
Averaging: 85%

Thanks for the look and any insight given.

Detector is usually peak or average. Whereas I might quibble with some of the parameters, the fact that both measurements used identical parameters makes that issue almost inconsequential. With that said:
- Are you measuring over the air, or direct out of the transmitters?
- Have you done a baseline scan to see the environmental RF noise floor (or at least the two TV channels 16 & 19)?
- If you swap frequencies on the two transmitters, do the resultant spectral displays on the SA stay with the transmitter or the frequencies?

[Cliff Fuller]

Detector is usually peak or average. Whereas I might quibble with some of the parameters, the fact that both measurements used identical parameters makes that issue almost inconsequential. With that said:
- Are you measuring over the air, or direct out of the transmitters?
- Have you done a baseline scan to see the environmental RF noise floor (or at least the two TV channels 16 & 19)?
- If you swap frequencies on the two transmitters, do the resultant spectral displays on the SA stay with the transmitter or the frequencies?

I am measuring over the air, I have measured using the antennas separated from the transmitters and I see no anomalies. I have not measured the outputs directly.

I have done a baseline, in this locality neither 16 nor 19 are of concern (channel 18 is however).

I have not measured a swap of the transmitters, however, 4 of the 6 transmitters show similar "noise". Any one transmitter (except 504 MHz) throws similar noise throughout the spectrum.

Attached are images of pre-transmitter and post. I have imported the scans into WWB to give us something a little more familiar to look at.  :-)





Thanks, Henry...

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