Which external BPFs improve SDR performance?

[k3rw]

I have a Anan A-10E and 200D, as well as a Yaesu FT-818. If I can get a good amount of out of band rejection over their stock specs, I'd sure like that. There is probably a point of diminishing returns, and I am not sure where that is.

I'm interested in setting up an external bandpass filter bank to act as a pre-selector, in order to improve receive performance for my Anans. I'm not looking at these for transmit performance. My understanding is the Anan 3rd order filters are merely so-so, but this could be improved perhaps by bypassing them and adding higher order filters (?). Beyond that, its more the 1) which one and the 2) implications I am less familiar with. Any exploit will not be for transmit, so a smart way to bypass this on transmit would be paramount.

I'm new to the idea and not well-versed on filters. I've been reading different electrical engineering websites about different filters. It does appear to be a tradeoff between filter performance, insertion loss, and cost.

Just generally, maybe answering this would help my understanding:

1) Does a BPF performance improve, all other things being equal, when it goes from a 3rd order, to say a 5th or 7th order?

2) Dependent on #1, what type of filter set should we look for to improve Anan performance on rx?

3) Considering tradeoffs for insertion loss, cost, etc., what may be a good direction to consider for this experiment? (I'd think a 11th order or huge multi-pole BPF bank with cascaded LNAs, etc,, might be extreme overkill).


I've seen some filter banks like the SV1AFN version, 10 bandpass filters, SMAs in and out. Here it is:

https://www.sv1afn.com/en/product-categ ... ector.html

I'm drawn to this because I do sometimes use the 60m band, and SDRs don't have great performance in this area. But in terms of 'is this a good one' I have no idea. It doesn't seem to publish insertion loss, or other specs. FYI--I noticed the 60m band hasn't been updated in the schematics.

Other filter banks I see offer 200w power handling. These seem more intended for amplifiers but may also be suited for the task. However it may be limited by the fact many are 3rd order filters, which is not substantially different from the existing Anans. Some have toroids, some have more surface mount type stuff, etc. Some have high Q, others have high insertion loss.

One group doing SO2R stuff built this for their setup, but it was primarily for transmit in a multi-op station. Maybe it functions just as well as a receive filter bank (I wouldn't know!).

https://ac0c.com/main/page_so2r_5b4agn_bpf_modules.html


Just getting the discussion rolling along. 73 de Greg, K3RW/KH7