Want to Buy KBPF3 or KBPF3A

Chuck ke9uw

I would like to buy a KBPF3 or KBPF3A

Thank you,

EDIT: Elecraft put me on the list for the KBPF3A, so I think I will amend my request for just the KBPF3A. Which ever comes first, Elecraft or a forum member.
Thank you,

Amy Rotenberg

What is the difference between them?

Chuck ke9uw

I think the A version already has the low frequency higher sensitivity mods installed. The KBPF3 would need the three surface mt caps installed and the L1 and L2 removed.

Amy Rotenberg

What would be that frequency threshold?

Thank you 


As Chuck says to convert a KBPF3 to KBPF3A needs only to remove 2 surface mount inductors L1 and L2, plus adding 3 0603 size surface mount capacitors (0.1uF), one each on top of the existing C3 C4 and C5.
Also a 220uF capacitor needs to be added to the motherboard of each RX.
Elecraft make a mod kit KBPF3MDKT_KBPF3
As explained in Elecraft document  https://ftp.elecraft.com/K3/Manuals%20Downloads/E740264%20KBPF3%20Modification%20Kit%20Instructions%20Rev%20A2.pdf

This modification should extend the frequency range down to 100kHz when using the KSYN3A, but not with the older KSYN3 which only goes down to 490kHz, unfortunately just above the 630m. amateur band. Please see my recent thread discussing if this lower limit can be extended. It appears to be Firmware limited, and no suggestions have been made yet for any workarounds.
If KSYN3 could cover, say, down to 450kHz, this is hardly a fundamental change and would help many K3 owners who cannot now obtain or afford the KSYN3A and want to at least listen on 630m..
73, John

Chuck ke9uw

There are errors in the posting and Elecraft instructions where KBPF3 should be written instead of KBPF3A. Note above where it says:
"This modification should extend the frequency range down to 100kHz when using the KSYN3A". It should say "This modification should extend the frequency range down to 100kHz when using the KBPF3".

Elecraft also states: "If you have two KBPF3As (one for the main receiver and one for the sub receiver), and you wish to use both for 100-500 kHz reception, then you will need two of the mod kits." Actually, if you have two KBPF3As, you won't need any mod kits. 

Am I correct on this?


The KSYN3"A" is required to allow the brain to go below 490 KHZ. You also need the KXV3 (AorB) and put the antenna on the RX antenna BNC to bypass the LPF (or for the Sub, come in the rear AUX connector).
You need to put the big capacitor on the 9V line as it is noisy on those low freqs.
Keith WE6R Elecraft K3/K4 Tech