[time-nuts] Re: RCB-F9T Adapter PCB with USB and 50 Ohm Timepulse SMA Connectors

[Carsten Andrich]

On 22.08.22 00:24, John Sloan via time-nuts wrote:
> I’ve been using this SparkFun ZED-F9T board with pretty good luck for a while now. It has an SMA for the active
> antenna, two SMAs for TP1 and TP2, a micro-USB for power and serial port, and SparkFun’s “Qwiic” I2C connector
> (which I’ve never used on any of their boards). I’m currently running this board flashed with TP1 set for 1PPS and
> TP2 set for 10MHz. However, I don’t really have any instruments good enough to render an opinion on how well this
> works.
>
> https://www.sparkfun.com/products/18774 <https://www.sparkfun.com/products/18774>

Sparkfun's ZED-F9T breakout board interfaces look like a step up from 
u-blox' RCB-F9T. However, my reason to use the RCB-F9T is simple: I've 
had a bunch of these for years and don't want to throw them away. Also, 
I need to feed the timepulse signals into a 50 Ohm load and the ZED-F9T 
output pins are only rated for max. 5 mA [1]. Except for a 33 Ohm 
resistor, the Sparkfun board routes both timepulse pins directly to the 
SMA connectors [2]. I doubt that results in 50 Ohm source impedance 
required to properly drive a high impedance load via a 50 Ohm 
transmission line.

Have you had any issues with unmatched transmission line effects?

Best regards,
Carsten

[1] 
https://content.u-blox.com/sites/default/files/ZED-F9T-00B_DataSheet_UBX-18053713.pdf#page=13
[2] 
https://cdn.sparkfun.com/assets/6/c/2/5/b/SparkFun_GNSS_Timing-ZED-F9T_Schematic.pdf