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

Jack Brabham - KZ5A
 

Tom,

The 4302 or the newer 4312 (which seems hard to find) are the modules I'm thinking of.    I think the 4302 was mentioned in ZL1AXG's article.

The placement between the LPF and the pre-driver puts the ATTN in the antenna path on RX which is presumably 50 ohm and I assume is also 50 ohm on TX considering the by-directional LPF.

This placement, to non-engineer me, looks like the ideal "effector" location for an RX AGC scheme, ahead of any active devices.    Or it could just be setup as a manual RF gain control on RX.   It is also looks like a very straight forward way to control drive levels per band on TX, either via pre-sets or an ALC setup.

I'm also thinking that this approach should be largely free of "unintended consequences".

In any case it looks like an enjoyable experiment.

73 Jack KZ5A




On 4/19/2019 5:10 AM, Tom, wb6b wrote:
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


 


Join BITX20@groups.io to automatically receive all group messages.