Why screw terminals?

[Brent DeWitt]

Full disclosure:

I am a degreed EE with about 50 years as a ham (now AB1LF).  The MRF101 amp is another fling at QRO.

I like this design, but have a couple of questions/criticism/comments:

- Why are the RF in/out laid out as screw terminals, rather that BNC/SMA edge mounts?

- Has anyone documented the assembly process to thermally couple the 1N4148 bias compensation diode to the MRF?  If not, I would be happy to contribute some mechanical build notes!

73 all,

Brent, AB1LF

[jcve...@gmail.com]

Why screw terminals?

1. >1/10th the price RF connector; >1/20th if you also count the mating connector
2. Smaller size/weight
3. Shorter projection off the PCB
4. @50 MHz the difference between the TB and a RA BNC is >-0.2dB.

Thermal coupling of the 1N4148:

It doesn't really matter, you could probably get away with no thermal compensation on the bias; we aren't running closed-loop trying to keep the bias within 5% of the target value.

The amp works fine from 75mA to 150 mA even higher with a good heatsink.

73,

Jim WA2EUJ

[Christopher Zeman]

I completely agree with you regarding the screw terminals. I hate them, too.

Chris, N9XCR

[jcve...@gmail.com]

I have a test fixture where the coax jumpers need to be inserted and removed repeatedly making the TB's a bit of a pain. In this case I solder a 2-pin 0.1" header onto the coax which makes it easy to insert and remove the jumpers multiple times.

Jim.

[Andy Aagaard]

I kind of like SMAs myself. I just used one of the corner pins and removed the others. At HF frequencies I don’t think my mod will make any difference and it tested fine on the VNA. 

[Nick Kennedy]

I vote for the screw terminals. I don't think the benefit of RF connectors is enough to justify the bulk, expense and difficulty of installation.  I think if I wanted to use coax, I'd consider RCA connectors.

73

Nick, WA5BDU

[jcve...@gmail.com]

Whenever I make a decision, there's bound to be other who would have made a different decision. Given that these PCBs were introduced in the fall of 2019, and we're only having this discussion 3.5 years later, means it was a pretty good decision.

Jim.