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Greetings All,

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? ? ? ? ?I am considering the procurement of a ZK05-BM LNA but prior to taking the plunge I am wondering if the amplifier will survive OK if accidentally exposed to a close proximity high level signal. For example a 3 foot separated RubberDucky-to-RubberDucky signal from a 5W handheld.

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? ? ? ? I wonder if anyone in this group has encountered ZK05 failures related to accidental input overload?

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73

Tom

VA7TA

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Hi VA7TA, the ZK05-BM saturates when the input exceeds 0dBm and the intermodulation distortion worsens rapidly. Inputs above +20dBm will damage the ZK05-BM.

There are other factors in play, how much power do you intend running, and at what frequency. There are free space calculators that will calculate the path attenuation.? Handheld antennas are not that efficient, I would expect at least 2 to 4 dB loss through the antennas in the same plane, if one is vertical and the other horizontal then the attenuation will be a lot more, but it wouldn't hurt to use 20 to 40dB attenuation before the LNA. If you are performing measurements with a tinySA then aim for at least -20dBm.?

Greetings,

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Thanks for the responses! Good to know +20dBm (ie 100mW) is the danger zone limit. As 5W is roughly +37dBm the minimum aggregate path loss with a 3dB safety factor should be at least 20dB.

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I am thinking of an EMI tracking scenario where there could be close proximity HT transmissions whilst tracking down a noise source in the field involving LNA usage. I am having trouble establishing a feel for the close proximity path losses associated with the signal spreading and antenna inefficiencies that might be encountered.?

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I hope some day to find the time to make some swept frequency measurements with my tracking generator.?

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73 & Thanks Again!

Tom

VA7TA

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I would start with much more attenuation than you think you need and then back it off. Signals are cleaner when they come out around -40dbm.

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When I experiment with an HT and using the SA antenna I have a 10db attenuator on the SA and 30db between the radio and its antenna. Transmitting from less than or about 1 wavelength I get a good clean signal with the HT on low power, 1 watt...?

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1 watt minus 40db is 0.0001 watt. When I cable connect the radio to the SA I put 80db of attenuation between them, again for 1 watt. The SA is a VERY sensitive device?

Hello,
this may not be the right place but oh well!
I fried the input of my tinysa ultra, a few microseconds switching.
Is it possible to buy a replacement motherboard and where?

Thanks, Daniel F5BUD

On Sun, Dec 15, 2024 at 11:21 AM, F5BUD wrote:

I fried the input of my tinysa ultra, a few microseconds switching.
Is it possible to buy a replacement motherboard and where?

Unfortunately no.? The manufacturer does not sell replacement boards or parts.? You can order parts from electronics vendors and replace them if you are able to do SMD repair.? The part numbers are listed in other posts in this group.

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Roger

Thanks Roger,

Input RF switch U22:AS179-92LF
LNA U14:BGA2817

Attenuator U38:PE4312C-Z
You can try replacing them.

Please be careful with external pre amplifiers. Remember, if it is directly connected to the input of the SA and the input of the pre-amp sees a signal of 0dbm, the spectrum analyzer sees +20dbm. Way outside its input specifications. The pre amp might survive a +10dbm signal in close proximity, but am not sure your SA will. Also remember, any signal lost because of attenuators before the amplifier are NOT recoverable. it is better only to use an external amplifier when the signals are very low and there are no other signals in the area. One way to protect the analyzer is to use a limiter between the pre-amplifier and the SA. Unfortunately, a good wide band limiter cost several times the price of a TinySA unless one finds one at an auction place.

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John