开云体育

To keep the price down, I think hfsignals may as well continue to use the 45mhz filter.
Perhaps claim 80m through 17m, beyond that is experimental, disable 15m,12m, and 10m
in the stock firmware.? Different transistors for more consistent gain should be considered.


However, if we can instrument drive level into the mixers, sounds like we may be able to have
a clean signal on up to 30mhz.? ?Perhaps replace transistors to get consistent gain through the 45mhz IF
and the Q90 stage, then monitor the top of RV1 with a diode RF probe into a Nano analog pin.

Better yet, add another 10dB of gain after the mixers so the IRF510's show trouble (much more obvious)
long before the mixers do.? So maybe add an extra gain stage between Q90 and RV1,
existing rigs could easily patch this in with an MMIC.?


If we do decide to go to 70mhz and beyond for that first IF, there are viable filters available.

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.

Here's the filters on Mouser that are between 70 and 90 mhz, and have a bandwidth of less than 4mhz:
? ??

The PX1002 from Murata looks good to me, center frequency of 86.85mhz.
25khz wide, 3dB insertion loss, over 60dB of rejection at 1mhz out,
datasheet shows how to use it in 50 ohm environment.
Not exactly cheap at $12 single unit, $6 if buying hundreds from Mouser.
The similar PX1004 at 82.2mhz is harder to get, especially in low quantities,
but might be preferred as it allows a lower vfo frequency.?

To operate at 30mhz with an 86.85mhz first IF, the vfo should be 86.85+30 = 116.85mhz.
The Si5351's internal vco is spec'd to a max of 900mhz, and our fractional output dividers can divide down
to a minimum of 8.0, so 900/8=112.5mhz max using the current si5351bx routines with the vco moved to 900mhz.
Hans, G0UPL, has found that the vco can be pressed to go much higher, beyond 1100mhz,
so we could just cheat on that, perhaps 935mhz for the vco giving 935/8 = 116.875mhz max.
I'd try that first.
The other possibility is to use the second Si5351 internal vco with fractional pll feedback and an
integer output divider on clk1, giving fine grained frequency control up to 200mhz (290mhz, according to Hans).
This second method would roughly double the size of the si5351bx routines, but that's not a major hit.
The other two si5351 outputs would continue to use the first vco, and be restricted to 112.5mhz max.

If using the equations of post?/g/BITX20/message/44278
the only needed change to the uBitx code outside the Si5351bx routines would be to change this
uint32_t? f45c? = 44995000;? ? ?// center of 45mhz filter
? to this:
uint32_t? f45c? = 86850000;? ? ?// center of 87mhz filter

The filter and 50 ohm matching networks could be on a very small PC board
glued to the back of the uBitx main board.
This daughterboard could include a new BiDi amp with appropriate transistors.
If the uBitx mixers are problematic at 86.85mhz, then perhaps a couple ADE-1's also,
replacing everything from T2 to T4 inclusive.? Parts cost of around $10 if building hundreds,
$15 bucks if adding the two ADE-1's.?

Then everybody will get fixated on making the uBitx work on 6 meters
and we get to do this all over again.

Jerry, KE7ER

?