?

On May 12, 2025, at 6:08?PM, John Bennett via groups.io <jkb@...> wrote:

?

Thanks to everyone for the fast feedback. To answer questions in order:

1) Yes, I plan to release hardware and software files to this site as others have done. If there is demand, perhaps Bill can add this RF board to his stock.

2) My experience with the 74ALVC74D is much better than Bill's (my observed performance > 100 MHz; clean power is critical); I expect the '3233's to poop out before the 7474's. That said, the next version will use the SI5340 LVPECL differential output option to drive TI CDCM1802's. This is a slick part that operates up to 800MHz, divides by 1, 2, 4, or 8, and offers an LVCMOS output up to 200MHz. If the mixer could support it, this would put operation from 2200M to 2M within easy reach (see below).

3) I currently use the Out0 for Rx and Out2 for TX. Having an unused output between TX and Rx during split operation is intended to cut down on cross-talk during split operation.

4) For the TX and RX clocks, I do indeed use the inverted Si5340 output capability. These outputs are *exactly* 180 degrees out of phase (at least beyond my ability to measure any difference with a 2 GHz scope) when terminated correctly. I think the external FF's are important, because phase symmetry is critical in a Tayloe mixer (which is switching FETs on and off at both edges).

5) The SI5340 is indeed more expensive, but the performance/cost benefit is pretty good (at least to my way of thinking).

6) Soldering a 44-QFN is a bit of a challenge, but a stainless stencil is ~$10, which makes the temp-controlled hot-plate soldering technique pretty reliable.

7) As you can see, I was able to replace the 5351 (and the MF logic) with a 5340 and all of its support circuitry. It's tight, but it all fits, and it's a clean layout.

8) Yes, power consumption is higher, but dependent on output configuration. I added the required clean 3.3 to 1.8V supply to the prototype RF board in the available space with no problems.

9) The SI5340 has four main versions. Two of these, the Si5340A-D (up to ~1GHz with some holes) and Si5340B-D (up to 350MHz; perfect for this application) do support both fractional and integer divides. The fractional divide feature is what makes the part a good fit.

?

Now I have a question. While I think replacing the current RF board is a win, I have been giving serious thought to creating a separate VFO card down the road. This would free up room on the RF board to do other things (like add an optional non-Tayloe second mixer (to support 2M). There are lots of options (old-school Minicircuits mixer, or something like the AD831) I am experimenting with both. I am also experimenting with replacing the Teensy with a Raspberry Pi 5, which would give HDMI outputs, and more performance and memory than the T41"X" is ever likely to need.

73,

j

On May 13, 2025, at 12:52?AM, Jim Pruitt WA7DUY via groups.io <jpruitt67@...> wrote:

? PCBWay was still offering the Global Express a couple weeks ago when I placed an order for something else.? JLCPCB had just stopped it that day. They told me it was because their Global Express carrier had stopped delivering to USA.

Thank you.

Jim Pruitt
WA7DUY

On 5/12/2025 9:16 PM, jerry-KF6VB via groups.io wrote:

On 2025-05-12 20:36, John? P via groups.io wrote:

I checked the JLCPCB price a month or so ago. $4 for 5 boards up from
$2. Not a big deal.

*** That's not a big deal.? The big deal is that their "Global Standard Line"
$1.50 shipping went away, replaced by $22 DHL shipping.

???????????? - Jerry, KF6VB

--
Jim Pruitt
WA7DUY

Interesting points!? What I have observed with the 3253 is that degradation is noticeable at 10M.? Still good enough though.? It looks worse at 6M

What I am referring to is the 3253 in the role as a quadrature modulator.? Spurs start to creep up with increasing frequency.? Also carrier rejection

gets worse and worse.? My QSE2DC design has the capability to null the carrier, which mitigates this problem.? But I think this system will run out of

gas before it gets to 2M.? I would guess that performance as a demodulator is also falling off versus frequency.

?

Early in my experiments with the T41, I built a Gilbert cell based modulator using a very old part.? The MC1496.? This is one of the oldest semiconductor

devices still in production.? It worked, but it was already running out of gas at 10M.? I? haven't found a reasonable replacement for the MC1496 yet.

A basic Gilbert cell using modern devices at reasonable cost is what I am looking for.

?

--

73 Greg KF5N

On 2025-05-12 20:36, John? P via groups.io wrote:

I checked the JLCPCB price a month or so ago. $4 for 5 boards up from
$2. Not a big deal.

*** That's not a big deal.? The big deal is that their "Global Standard Line"
$1.50 shipping went away, replaced by $22 DHL shipping.

???????????? - Jerry, KF6VB