Why use the SR105U vs the DRA818U transceiver module?

[trevor229]

I was looking over the project and noticed the high shipping cost for one of the sources for the SR105 module. I have also seen a few sources claim that it is legacy/discontinued. It seems harder to find a reliable source compared to the DRA818U (or V for VHF) module. It has nearly the exact same scpecifications and is much more ubiquitous and usually below $10. The only reason I could think of is AMSAT utilizing this module on actual space hardware? I am really curious.

[njsat]

https://a.co/d/ammAf4A Rogers E. Campbell, IV RECMedia, LLC Cell: (973) 202-9384 Pager: (201) 237-0581 <https://aka.ms/AAb9ysg>

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________________________________ From: Alan Johnston ***@***.***> Sent: Monday, January 27, 2025 8:06:51 AM To: alanbjohnston/CubeSatSim ***@***.***> Cc: Subscribed ***@***.***> Subject: Re: [alanbjohnston/CubeSatSim] Why use the SR105U vs the DRA818U transceiver module? (Discussion #355) Hi, No, AMSAT isn’t flying this module, our FM transceivers are custom designs. This module was chosen because of its low power 0.5 W output. The 1 W DRA818U would drain the batteries faster. Also, the attenuator circuit already gets warm with this module, and having a high transmit power when the receiver is inches away isn’t great. If this module was discontinued in the future, I would look at the SR110U module as it is pin selectable 0.5 W output/ 1 W. This would be useful if flown as a high altitude balloon payload. — Reply to this email directly, view it on GitHub<#355 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/BNRFN43ZZE3224MWBPZA3DT2MYVOXAVCNFSM6AAAAABV4EEFV6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTCOJWHE2TEMQ>. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[alanbjohnston]

I’m looking into it. It is always a good idea to have more than one part in case of supply interruptions, and this module looks promising.

[alanbjohnston]

So I have done some investigation experimentation.

I wasn't able to find anything saying the SR105U is being discontinued, but this could happen at any time with any part. I also wasn't able to find a DRA818U or SA818U at a cheaper price or without the same hefty shipping charge to the USA (e.g. DHL).

I got a few SA818U and did a Main board adding the footprint. I just added it to the bottom of the PCB to leave the rest unchanged. You can see the Gerbers and schematic if you look at the 818 branch.

Here's the pros and cons:

Pros:

• It has a 1W high power mode which is useful for a balloon payload
• It is available from multiple sources
• It might draw a lower current in low power mode

Cons:

• It is not software compatible with SR105U. I got it to work with changes (see the transmit.py file in the 818 branch). It also reverts back to factory defaults everytime it powers off or the PD pin goes low. The SR105U saves its previous configuration.
• Its footprint is bigger with more pins

I'll keep testing it, but at this point I think I will stay with the SR105U. I might leave it as an optional part on the PCB bottom, but I haven't fully decided yet.

If anyone gives it a try or has a strong opinion, let me know.

Alan