Test to determine if receive damaged?

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franko
Posts: 30
Joined: Mon Aug 28, 2017 9:33 pm

Test to determine if receive damaged?

Postby franko » Sat Sep 08, 2018 8:25 pm

I inadvertently left an SDRplay RSPduo running monitoring FT8 on 20m while transmitting on that band on a nearby rig. The RSPduo used a mag loop antenna about 37 feet (11 meters) away from the transmitting antenna, a Buddipole coil-loaded dipole. The transmitter used ~80 watts and transmitted for about six 15-second cycles. The sent signals showed up on the RSPduo's copy of WSJT-X as +14 dB.

The RSPduo still seems to be functioning -- it gets plenty of FT8 decodes. But are there any tests I can run with common equipment to determine if it was impacted at all? When an SDR is affected by a strong nearby signal, does the damage tend to be sudden and complete, or can it be incremental degradation?

Even if it seems unlikely that there was damage in this case, I'd be interested to know about any testing procedures to use if a situation like this ever occurs again.

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Mike2459
Posts: 86
Joined: Mon Jul 24, 2017 8:24 pm

Re: Test to determine if receive damaged?

Postby Mike2459 » Sat Sep 08, 2018 8:44 pm

Only if you had some published specs and the equipment to verify those specs.

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NK7Z
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Joined: Fri Sep 02, 2016 1:14 pm
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Re: Test to determine if receive damaged?

Postby NK7Z » Sat Sep 08, 2018 9:18 pm

Contact a 2-Way shop in your area, ask if they can use the service monitor they all have to test the rigs sensitivity. If you are in Oregon, I have one and can assist.

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franko
Posts: 30
Joined: Mon Aug 28, 2017 9:33 pm

Re: Test to determine if receive damaged?

Postby franko » Sun Sep 09, 2018 12:00 am

NK7Z wrote:Contact a 2-Way shop in your area, ask if they can use the service monitor they all have to test the rigs sensitivity.

Thanks for the suggestion. Is there a more specific name for the service monitor equipment? I bought the RSP's from a Ham Radio Outlet, so I could ask them.

Then again, it also occurred to me that I have a couple of RSPduo's, so I could do side-by-side tests by connecting them to the same antenna using a splitter (in my case, I have a Mini-Circuits ZFRSC-42). Then compare performance using the equivalent antenna ports on the two units (evaluating by looking at FT8 decodes and SNR numbers in WSJT-X). This will probably serve for what I need for my purposes. I guess I was just curious if there were any other tests at the level of multimeters and/or oscilloscopes etc to get any sense of performance.

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Test to determine if receive damaged?

Postby glovisol » Sun Sep 09, 2018 12:07 pm

A simple test using an $12 noise generator and two home made attenuators is described here:

viewtopic.php?f=5&t=3352

Cheers,

glovisol

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franko
Posts: 30
Joined: Mon Aug 28, 2017 9:33 pm

Re: Test to determine if receive damaged?

Postby franko » Sun Sep 09, 2018 4:07 pm

glovisol wrote:A simple test using an $12 noise generator and two home made attenuators is described here:

viewtopic.php?f=5&t=3352

Great post, thanks for the link. I ordered one of the noise sources and will try this out when it arrives (probably in 2-3 weeks).

What design did your use for your home-built attenuators? I have a couple of commercially made one with SMA connectors, but may need more attenuation to achieve the appropriate levels.

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Test to determine if receive damaged?

Postby glovisol » Sun Sep 09, 2018 6:28 pm

Hi Franko,

As stated in the original post, the total attenuation you need is in the order of 92 dB: if you concentrate this attenuation in one attenuator, it is very likely that you will have spurious feedthru: this is why I used two 46 dB type "Pi" attenuators in series.

Each attenuator (designed for 50 Ohm input & output) has one 50.5 Ohm resistor beween input and ground, one 4988 Ohm resistor in series and another 50.5 Ohm resistor between output and ground. For precision you will have to select the resistors with a quality ohmeter, from a batch of 50 Ohm and another batch of 5000 Ohm resistors. Construction using back to back BNC female panel connectors is illustrated in the original post.

ADDED 12/09/18: A more accurate attenuator is built using four 23 dB attenuators in series, as recently shown in the original thread.

Remember that the noise source is likely to blow up with a 12 V supply: better use 10 V maximum.

If your receiver works, test results will be similar to Table 1 of the original post.

glovisol

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