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Re: Building homebrew ubitx: Need pre-v3 schematic PDF. Also, source for 45M15 (45 MHz IF) filter?

 

I believe this is the original uBitx schematic:? ?

In this post:??/g/BITX20/message/33203
Farhan explains that the 45mhz filter must be narrow enough to reject signals 2 mhz away from center.
I believe he is using the 45m15a, which is probably 15 khz wide with two poles.
But most anything 45mhz with 2 or 4 poles will work.
Bandwidth of available filters varies from 7.5 khz to 30khz, this shouldn't matter much either.?

A search for "45 mhz crystal filter two pole" finds this throughole part, in stock at Mouser:
? ??ECS ECS-45K20A
I'd guess that will work fine.

Most such crystal filters are now surface mount.
Those would work too, but may be harder to hack into an existing PC board.
I don't think I would bother with creating a new board.
? ??

Perhaps a more serious issue for you is that the old uBitx schematic only shows
two low pass filters after the IRF510's.? These did not sufficiently attenuate the second harmonic.
The current design has four low pass filters there.??
If all you have is two LPF's, I suggest you stuff them for your favorite two bands.
Lower bands could be supported by adding an appropriate LPF stolen from the current uBitx design
in line with your antenna coax.? Of course, whichever of the two LPF's inside the rig that you select,
nothing higher than that will get out to the antenna port.? ?
I suggest stuffing LPF's for 20 and 40 meters (also covering 17m and 30m, respectively),
use an external LPF for 80m.

Give anything above 17m a pass for now, as those bands are a bit problematic.
Power out can be down under a watt on those high bands, and we can have an out of band spur
when transmitting.? Those issues are still being resolved.

Jerry, KE7ER



?

On Mon, Jun 4, 2018 at 11:32 am, David Feldman wrote:
This posting contains two questions:

I am building a homebrew version of ubitx (on PCB layout I created myself). PCB was manufactured a year ago, but did not start bringing up circuit at that time.

Since about 2 weeks ago, I have been bringing up the receive path first (along with necessary microcontroller and synthesizer stages), one stage at a time, beginning with the loudspeaker, and so far having good results and fun experience.

I realize now (that I am at the 45 MHz IF filter, heading towards the first mixer) that I did not save schematic I used to create PCB, and v3 schematic (more recent) includes a part (the 45 MHz crystal filter) I did not find in the version I based my PCB layout on. I understand the benefit of the filter, however, I wish to continue progress on my PCB based on older design, as I will gather changes (including use of the newer IF filter design) for a future PCB rev.

My PCB layout assumed multi-pole LC filter from the schematic I had available at the time (original or maybe v2, but not v3 or later). In this version, the 45M15(A? B? F?) filter was not included, and it is not present on my PCB layout.

So, I have two questions:

1. What is URL or other way to find version of ubitx based on LC filter in 45 MHz path?

2. Where is current source for the 45M15 (A? B? F?) filter used in V3 and later designs? I did not find it in search on US distributors nor on ebay; I understand these should be low cost part with good availability, so I think I am not looking in right place?

Thank you, and this is very enjoyable project!

73 Dave WB0GAZ wb0gaz@...
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