Re: Attenuator function in CEC firmware #ubitx #firmware #nextion

Tom, wb6b
 

On Thu, Apr 18, 2019 at 04:26 PM, Jerry Gaffke wrote:
You could easily control that attenuation from a processor, perhaps
These may be a little overboard for the purpose but I have one of each of these digitally controlled attenuators that I bought to build up my tool set for making RF measurements. 

This one had the part number of the attenuator chip ground off. Depending on the manufacture of the part, the specified low frequency cutoff could be 9Khz, 1Mhz or 10Mhz. For HF measurements a possible 10Mhz cutoff is an issue.
https://www.ebay.com/itm/New-OLED-6G-Digital-Programmable-Attenuator-30DB-step-0-25-RF-Module-Micro-USB-/263584061842
However, the construction with the machined aluminum body is impressive.

This one specifies the part number in the description and the number on the attenuator chip matches. It is a 9Khz to 4Ghz attenuator. It doesn't have a display, so would be a better choice for installing into the uBitx. 
https://www.ebay.com/itm/PE4302-Digital-RF-Step-Attenuator-Module-High-Linearity-0-5dB-50-ohm-RF-DSA/121830578745

You can also buy the current version of the Peregrine attenuator chip from Digikey, mount it on a SMD adaptor board and add it to your uBitx IF chain. But, the modules are easier to work with.

These parts have an actual 50 ohm impedance (when the other end is 50 ohm terminated). It might be that the 50 ohms is a bit more load that the IF chain was designed for. 

Tom, wb6b


 

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