signal strength very high in HDSDR

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bluesheep
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Joined: Wed Sep 09, 2015 1:07 am

signal strength very high in HDSDR

Postby bluesheep » Wed Sep 09, 2015 1:27 am

Hi,

I just got my SDRPlay and had no problem setting it up. I already use HDSDR with my softrocks (3X) and KX3, so I am fairly familiar with the interface. My first impressions are quite positive. One thing I find curious, the signal level coming into the HDSDR seems quite high. To get a reading on the HDSDR s-meter that approximates that on my Icom7000, I have to turn the "gain control" in the EXTio down 80 dB. If I "enable tuner AGC", the slider goes up and the spectrum display is much higher than I am accustomed to, much higher... If I tune to a quiet part of 20 meters, my icom shows a s-meter reading of 4-5 while the SDR Play will not drop below 7. I know there is a way to calibrate the HDSDR s-meter, but with my other (4) SDR rigs I have never had to use it. It is not just the s-meter, I feel I might be over driving the HDSDR input. Certainly if I "enable tuner AGC" I believe I am. The LNA is off. I am using Windows 7.

I guess I should not worry about strong signals, I've certainly spent a lot of time worrying about weak ones ;), but I thought I would post this here just in case I am missing something.

Thanks!
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wd9ewk
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Re: signal strength very high in HDSDR

Postby wd9ewk » Thu Sep 10, 2015 5:29 pm

bluesheep wrote:I just got my SDRPlay and had no problem setting it up. I already use HDSDR with my softrocks (3X) and KX3, so I am fairly familiar with the interface. My first impressions are quite positive. One thing I find curious, the signal level coming into the HDSDR seems quite high. To get a reading on the HDSDR s-meter that approximates that on my Icom7000, I have to turn the "gain control" in the EXTio down 80 dB. If I "enable tuner AGC", the slider goes up and the spectrum display is much higher than I am accustomed to, much higher... If I tune to a quiet part of 20 meters, my icom shows a s-meter reading of 4-5 while the SDR Play will not drop below 7. I know there is a way to calibrate the HDSDR s-meter, but with my other (4) SDR rigs I have never had to use it. It is not just the s-meter, I feel I might be over driving the HDSDR input. Certainly if I "enable tuner AGC" I believe I am. The LNA is off. I am using Windows 7.


I have had to disable the tuner AGC and change the Gain Reduction value to 0 dB for working amateur satellites with downlinks at 2m and 70cm, and then adjust the S-meter since it appears to read higher than what I see with a FUNcube Dongle Pro+ or several RTL-SDR dongles. I don't know if this is something with HDSDR, the SDRplay, or both - but it is a minor nit to pick with the SDRplay. I do this on my Windows 7 Pro laptop, and a pair of Windows 10 tablets with the recent update to the SDRplay Windows API. I may have to reenable the tuner AGC or add some gain reduction when using the SDRplay to hear other signals, but for now it is a great receiver for satellite work with what I have done in HDSDR.

Good luck!
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g1hbe
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Re: signal strength very high in HDSDR

Postby g1hbe » Fri Sep 11, 2015 10:52 am

I think the AGC system in the SDRPlay always tries to keep the strongest signal in the selected bandwidth at peak level (ie just under clipping level). If there are no strong signals, the whole of the noise floor will rise as the gain is increased. That's how I read it anyway.
Andy

bluesheep
Posts: 2
Joined: Wed Sep 09, 2015 1:07 am

Re: signal strength very high in HDSDR

Postby bluesheep » Fri Sep 11, 2015 7:01 pm

Thanks for the replies! I am very happy with the receiver and agree this is an observation with an easy work-around. I just wondered is I was missing something obvious. Thanks again...
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KW4CQ_Bob
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Re: signal strength very high in HDSDR

Postby KW4CQ_Bob » Tue Sep 15, 2015 7:11 pm

I have to agree with the original poster. I do a lot of weak signal DX work and I find the SDR to be VERY noisy on all bands/modes, like the system RF gain is way too high. I am using mine as an IF monitor on my FTDX-5000. On strong ssb signals for instance, and with the proper filter bandwidth adjustment, the S/N ratio on the SDR is comfortable to listen to but on weak signal ssb and cw it becomes pretty challenging to listen to as the band noise dominates the signal bandwidth. Switching back and forth listening to a signal on the SDR or the FTDX-5000 I get far quieter reception on the Yaesu even with the Yaesu RF Gain full up. I have tried making adjustments to the EXtio diagram but couldn't find an acceptable S/N performance level. By the way, I get these same results whether I use the SDR with as an IF monitor or with the HF antenna connected directly to the SDR's antenna jack. I would like to hear from anyone who may have found a solution to this problem.
Thanks and 73,
Bob KW4CQ
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Sideteacher
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Re: signal strength very high in HDSDR

Postby Sideteacher » Tue Sep 22, 2015 9:12 am

Regarding the AGC it will look to adjust the gain of the tuner to achieve a certain level at the ADC input. So yes no signal, the noise floor will rise up. The level it is looking to achieve is the setpoint value in ADC section of the controller. The default is -15dBfs which is 15dB below full scale. By lowering this number you can change the level at the ADC input. Alternatively disable the AGC and use the gain slider to set the tuner manually. Regarding the S meter in HDSDR you can calibrate it to read correctly. To do this you need to;

• Tune to a station with a known signal strength
• In HDSDR Click Options -> Misc Options -> S Meter calibration.
• You will be presented with a dialog box which outlines the instructions
• Once you click OK you will see the S meter now read S – Units calibration
• By left clicking you can set the meter to the known reference.
• One you are happy right click to finish the calibration.
• The meter will now read S-Units Squelch again
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