I am using my RPi4 with HDMI and GPS.
I have used both a USB dongle GPS and a USB cabled GPS - with no problems.

I AM using a metal case for my RPi.
I am using a FLIRC case: https://www.amazon.com/gp/product/B07WG4DW52/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
With the RPi at "idle" it is 43C.  I did add a few stick-on heat sinks inside the Flirc case, in addition to the CPU that the case sinks...

This "should" work too;
https://www.amazon.com/gp/product/B07ZX4NTCN/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I have one, but haven't tried it yet.  I think it will run cooler (the way it is built) than the Flirc.

73, steve WB3LGC

On 2/23/20 11:47 AM, Chris Weiss KJ7GST wrote:

>From what little info I can find, the Raspberry Pi 4 output is always active. On previous boards, there was a configuration option to disable it, but that's not (yet) implemented on the Pi 4. (Reference: https://www.raspberrypi.org/documentation/configuration/config-txt/video.md)

Since it's basically acting like an antenna, keeping the GPS as far away from the HDMI ports as possible would be helpful, and of course, don't plug any HDMI cables in.

If your Pi4 is in a case, you could try getting some adhesive copper foil and putting it on the part of the case near the HDMI ports. I'd be curious to know if that makes a difference, assuming that interference from the HDMI port is what's causing the sporadic GPS issues for you).