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PostPosted: Fri Jun 23, 2017 5:42 pm 
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Joined: Tue Jun 13, 2017 2:42 pm
Posts: 2
I recently received an rs-hfiq. I'm a new ham and just getting into working with HF. I was testing my antenna and rs-hfiq yesterday and noticed that there was a signal peak at the center of whichever freq I tuned to. It s sounds like a continuous tone. There is a local 40m net I was tuning into on 7.088. There has a peak at the center, but using LSB cut it out and I can't hear the constant tone at 7.088. Unfortunately, I was rushing and forgot to test the mic input level. Before the net started, I noticed if I lowered the mic gain to the very lowest (-16db), the tone disappeared. As soon as I increase the gain (-15.5db) the tone comes back and I can see it in the waterfall and spectrum display.

Can anyone give any insight into what is happening? Is the lowest mic gain the correct setting? Just posting this question because I won't have time to test for a few weeks and want some insight to take with me to the field when I can test. I am using the built in sound card on my laptop, it provides 96khz sampling.


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PostPosted: Sat Jun 24, 2017 8:03 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 881
Hi,

If you are using the StarTech USB sound card, you should set the mic gain to 0. That gives the best dynamic range. On some sound cards, like the X-FI, you have to use the line input because the mic input isn't stereo. Using the line in generally means that you need a little gain. The rule of thumb for setting the input channel gain is turn it all the way down then increase it until the noise floor starts to come up. That's the point where the external noise is about equal to the internal noise so increasing the gain further doesn't buy you any sensitivity but it does cut down on the large signal handling capability.

As for the noise bump in the center of the spectrum, it shouldn't be there no matter what setting you have the Mic Gain on. With the RS-HFIQ a bump in the center of the spectrum is generally caused by dirty USB power, which is something that you don't have a lot of control over. I have one computer which must have a very noisy 5V supply because running RS-HFIQ's from the USB makes a bump that extends into the SSB passband. The work around here is to get an external powered hub. This will bypass the power supply in your computer and provide cleaner power for the RS-HFIQ.

73,
Jim WA2EUJ


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PostPosted: Wed Nov 08, 2017 12:51 am 
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Joined: Wed Nov 08, 2017 12:20 am
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I'm currently having the same problem with peak at the center of the tuned frequency. I believe my problem was self induce. I was working on another radio an left the RS-HfiQ on the same frequency while I was transmitting on the other radio, about 5 watts. Now the clip light comes on as soon as I plug up the antenna along with a spike at the center of the tuned frequency. All other operations seem to be normal.

Could this possible be a problem with the Rf input?


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PostPosted: Wed Nov 08, 2017 6:34 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 881
I've noticed that the Clip LED flashes sometimes until Omni-Rig starts and initializes the RS-HFIQ. Do you still see the Clip LED after you start HDSDR? If so there may be some damage in one of the RF stages.

Noise 'humps' in the in the center of the spectrum are generally caused by issues with the sound card and/or the USB powering the RS-HGIQ's Nano. If you unplug the IQ RX from the soundcard and the hump is still there, there's something wrong with the sound card, driver or cable. If the 'hump' goes away there's something wrong with the RS-HFIQ, generally a noisy 5V source on the USB. Try using a USB hub that's powered by and external (clean) source.

Here is a shot of what the spectrum should look like with a Sound Blaster SB1090 receiving a signal from a signal generator at -60 dBm:


Image

You may need to go here to see it:

https://www.dropbox.com/s/upl188wtd2gpc ... -60dBm.png


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PostPosted: Thu Nov 09, 2017 4:14 pm 
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Joined: Wed Nov 08, 2017 12:20 am
Posts: 2
I Try using a USB hub that's powered by and external (clean) source, an that seems to have corrected the problem. Planning on picking up a new mother board today. Again thanks a lot to all who responded.

Eugene
Kb7myo


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