My transmitted signal analysed

 A quick look at a spectrograph to analyse my transmitted signal.

Setup:

Transceiver : ICOM IC-7610

Power       : 108W

Antenna     : 500W dry dummy-load with 40dB tap

Modulation  : SSB (LSB)

Audio setup : see here

Receiver    : RF-Space SDR-IQ

Software    : SpectraVue Ver.3.39

IF-Gain     : +6dB

RF-Gain     : -20dB

Lets analyse the signal.

The grey section shows the receiver audio bandwidth (BW), i.e. the SSB RX filter bw or the CHANNEL BW. 

The black area is the so called Video BW, in this case a 30kHz view of the spectrum. A frequency spectrum display from 7.160MHz to 7.190MHz .

The green line is the real-time capture and the blue line is the in-time capture, the memory of the previous capture. 

The display also shows some vertical lines with a distance (spacing) between two lines of 10dB and there are also some vertical dotted lines which are 3kHz apart. Additionally I have applied "smoothing" to quieten the real-time capture. (I'll show the same signal without smoothing further down below) 

Now let's look at the BLUE line (the Sideband envelope), as that line dipics my previous SSB transmission. The top of the signal is about -59dB (S9+14) a reasonable strong signal. We can also see that the width at the top of that line fits into the grey, the 3kHz bandwidth marker, and is about 2.9kHz wide (100-3000Hz). We can also see that the signal slowly spreads out towards the bottom, down to the about -90dB from were it then spreads between a bit more quickly to 7167.8kHz and 7182.8kHz. Since the carrier frequency is at 7175kHz, we can deduce that the signal is spreading -7.2kHz and +7.8. 

Struth, what a crappy wide signal ! 😇

BUT, wait! The WIDENING of the signal starts at approximately at -91dB (S6). Which would mean that from the peak of the transmitted channel BW the signal is "clean" for about 32dB. Now that is a pretty good NON pre-distorted signal. 

The following table shows how the signal from about the -90dB mark spread very quickly, but also drops very quickly in signal strength. 

Frequency	Signal Strength		Frequency	Signal Strength
7169kHz	-100dB	S4.5	7169kHz	-100dB	S4.5
7166kHz	-114dB	S2.2	7181kHz	-114dB	S2.2
7163kHz	-124dB	S0.5	7184kHz	-124dB	S0.5

NOTE: S-Value steps are in 6dB

This does help me to understand how wide my signal really is and when and how I would cause channel interference based on a 3kHz channel spacing. 

Below is the same signal without smoothing.

As we can see it is very easy to check our own transmitted signal. The requirements are not that strenuous. A  tap, dummy load and a SD-Receiver is all that is required to not only check our transmitted audio, but also our transmitted signal. Here are a couple of tap's that are easy to replicate, a 40dB and a 50dB tap.