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rabbit73 30-Jun-2015 3:50 PM

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What can be done:

The strength of WSOC is -15.9 dBm, and WXII is -79.3 dBm, for a dynamic range of 63.4 dB, and for a required SFDR of 79.4 dB. That's a big dynamic range to deal with, especially since WXII is a 2Edge signal.

If you don't have enough gain for your weak desired signals without a preamp, and you have too much gain with a preamp, you can insert an attenuator between the antenna and the amp input to try for a happy medium. The cable between the antenna and the amp is providing some attenuation, but it is not enough. The attenuator will not only optimize your SFDR, if possible, but also reduce the strength of your strongest signals. You can use a variable attenuator before your amp for testing and then replace it with fixed attenuators of equivalent value.
•Attenuation values 1, 3, 6, 8, 10, 12, 16, 20dB (FAM)
The up and down arrow for different values is faint; you can click on 1 dB to see other values.

As you increase the attenuation it will tame your strongest signals that are causing overload, but it will also make your weak signals even weaker. You might think it is counterintuitive to add an amp to make the signals stronger, and then insert an attenuator to make them weaker. The advantage is that for every 1 dB of attenuation, the IMD spurious signals are made 3 dB weaker, so there is a net payoff of 2 dB SNR (Signal to Noise Ratio) improvement for every dB of attenuation. If you insert a 6 dB attenuator, you get a 12 dB improvement in SNR.

If you want to read more about my preamp overload tests and the attenuator technique:

Preamp Overload Test 3

I have received a lot of positive feedback from people who have tried the attenuator technique and it worked for them; I have received negative feedback from people who thought it wouldn't work but never tried it.:)

If you are unable to tame your strongest signals without damaging your weakest desired signals, it means the required SFDR is too great for the attenuator technique. You are then left with exotic (expensive) solutions like a separate antenna, preamp, and single channel custom bandpass filter for the required real channel number of the weak signal from Tin Lee. If you only have one strong signal causing trouble, you can order a custom single channel bandstop filter to tame that single channel, so you will only need one antenna.


Please let us know the results of your tests on this same thread.

Best regards,

nkirkley 1-Jul-2015 7:24 PM

Thanks for all your suggestions! I will definitely try the FM filter first!

nkirkley 25-Jul-2015 4:24 PM

Hello Rabbit! I have finally ordered an FM trap and the attenuator. I would have done it sooner, but, went on vacation. Anyhow, once I receive these I assume the plug in would be this. Coax from antenna to FM Trap, then coax to attenuator, then coax from attenuator to amp (splitter). Is this a correct guess? Thanks.

rabbit73 25-Jul-2015 6:35 PM

That is correct. Good luck!

nkirkley 25-Jul-2015 7:58 PM

Thanks! I will let you know what happens!

nkirkley 6-Aug-2015 9:10 PM

FM Filter
Just a follow-up. Neither the FM filter nor the attenuator helped me pull in any more channels. Oh well, it was worth playing around with.

However, with the attenuator, like a splitter, it has two ends to connect coax. Does it matter which connector comes from the antenna and which goes to the amp?

ADTech 6-Aug-2015 9:18 PM


Does it matter which connector comes from the antenna and which goes to the amp?
Nope. The attenuator doesn't care.

rabbit73 7-Aug-2015 12:05 AM


Just a follow-up. Neither the FM filter nor the attenuator helped me pull in any more channels. Oh well, it was worth playing around with.
Sorry that they didn't help; it was worth a try. You need the attenuator AND the FM filter at the same time.

What attenuator did you use? How much attenuation did you try?

If you keep adding attenuation up to the point that the weak signal is gone, then the dynamic range (the difference between the strongest and weakest signal) is too great for this technique.

Was the coax grounded? If yes, how? If not, the test isn't valid.

nkirkley 10-Aug-2015 4:39 PM

Ging to try again
I didn't realize you could fine tune the attenuator. I will give it another shot and get back with you.

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