unwanted images

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Sdrlistener
Posts: 6
Joined: Thu Nov 19, 2015 6:54 pm

unwanted images

Postby Sdrlistener » Thu Nov 19, 2015 7:15 pm

Hello,

i have my sdrplay for a week now,
and enjoy it together with a Bonito megactiv 305 active antenna.
however on the 80meter band i get images every 60 khz or so,
changing the gain reduction lessen these but does not solve it.
this happens on other bands also (40meter, 20 meter)
if i disconnect the antenna, these images does not go away.
is there a solution for this, or a test that pinpoints the source?
thanks for any help

3616mhz@-5db.JPG
3616mhz@-5db.JPG (237.64 KiB) Viewed 2797 times
Attachments
3616mhz@-40db.JPG
3616mhz@-40db.JPG (249.17 KiB) Viewed 2797 times
Last edited by Sdrlistener on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Tech_Support
Posts: 240
Joined: Mon Jun 01, 2015 7:00 pm

Re: unwanted images

Postby Tech_Support » Thu Nov 19, 2015 7:57 pm

Hello SDrlistener,
These almost certainly result from external interference pickup from things like switched mode power supplies and other sources of electrical interference. There are two main routes that these can get to the RSP. The first and most common is via the USB ground. The second possible source is via the antenna feed (the shield if you are using coax). The most effective way to reduce this is loop your USB cable through a clip-on ferrite (up to 3 loops if possible) and also do the same with your antenna feed cable. People have generally found that this substantially reduces the amount so electrical interference that couples to the RSP.

Sincerely

SDRplay Tech_Support
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Sdrlistener
Posts: 6
Joined: Thu Nov 19, 2015 6:54 pm

Re: unwanted images

Postby Sdrlistener » Thu Nov 19, 2015 9:04 pm

thanks for the advice, time to order some ferrit i guess 8-)
would it help if i build the sdr in a metal casing?
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NN4F
Posts: 128
Joined: Fri Apr 03, 2015 1:54 pm
Location: Ridgeville, SC
Contact:

Re: unwanted images

Postby NN4F » Thu Nov 19, 2015 10:04 pm

Sdrlistner,

on SDR -Console on HF (80m) I run my gain reduction at 75-80 remember this is gain reduction not +gain, so 0 is fully open, and 80 is less, and then you can drop the visual gain also, try running the gain way down 65-80 and see if that removes them...?

Paul - NN4F
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--
Paul Jones - NN4F, Charleston SC
http://www.facebook.com/groups/SDRPlay

Sdrlistener
Posts: 6
Joined: Thu Nov 19, 2015 6:54 pm

Re: unwanted images

Postby Sdrlistener » Fri Nov 20, 2015 9:40 am

Hello NN4F,

i will try it this evening,
thanks for the tip :^)
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Sdrlistener
Posts: 6
Joined: Thu Nov 19, 2015 6:54 pm

Re: unwanted images

Postby Sdrlistener » Fri Nov 20, 2015 5:31 pm

i just connected 4 ferrit rings on the antenna cable , near the receiver.
i also wove the coax trough a ferrit ring is this;
cm-choke.jpg
cm-choke.jpg (15.38 KiB) Viewed 2690 times


this is the result, gain @-80 dbm:
gaindown.JPG
gaindown.JPG (250.79 KiB) Viewed 2690 times


this is with gain at -20dbm:
3709mhz@ferrit.JPG
3709mhz@ferrit.JPG (231.78 KiB) Viewed 2690 times


it shows some improvement , but the images still are very present.
tomorrow i try to make a balun out of coax and insert it directly at the antenna.
Last edited by Sdrlistener on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Sdrlistener
Posts: 6
Joined: Thu Nov 19, 2015 6:54 pm

Re: unwanted images

Postby Sdrlistener » Sat Nov 21, 2015 5:12 pm

i solved the problem today,
turned outto be a noisy router downstairs.
founded it by shutdown the surch protectors from the electric installation one by one till the images where away.
i disconnected it alltogether and use a less noisy, but also less powerfull one.
just to be shure i added 4 clip-on ferrits on the incoming antenna cable and used a usb cable without earth connection to the laptop.
i also put the sdrplay in an empty iron cookie drum and connected this box to the radiator for earth connection.
thanks for the tips all
this is the result:

solved.JPG
solved.JPG (214.02 KiB) Viewed 2649 times
Last edited by Sdrlistener on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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