[RF induction problem - Solved] Hotspot mode failing after 2/10/2020 updated

[kd2lh]

Yes. I'm testing this with the Radioddity supplied antenna right on the radio, but at 1 watt of radiation.

I'm actually experimenting with this to see how well this can be addressed with various torroids on the cable or shielding on the Pi.

One step at a time.

If we really do need external remotely mounted antennas, I'd like to verify that - otherwise be able to give some guidelines.

So right now, it's running on a heat sink shielded Pi4B and two torroids on the USB cable (one at each end).

[VK3KYY]

Did you also put a ferrite on the power cable to the RPi?

If you are transmitting power indoors, any wire will get induced RF if it’s not shielded, including the traces on the RPi PCB.

DMR seems to be especially prone to causing noticeable RF induction because of the pulse nature of the transmission.

Even my LED ceiling lights flicker badly, in my shed / workshop, if transmit in the shed.

[kd2lh]

Yes - I had a ferrite on the power cable of the PiZeroW as well as both ends of the USB to GD77 cable. The Pi itself was not shielded in any way, and it did fail after a period of time.

I don't have a ferrite on the Pi4B power cable (which is the power adapter sold by Raspberry Pi themselves).

So far, the Pi4b that is more shielded with metal heat sinks plus ferrites on both ends of the GD77 USB cable has not failed in the past 32 hours.

It's likely that just shielding the Pi and ferrite filters on the cables will suppress the problem.

I have been running at one watt. I'll now experimentally move up to 2 watts next. Testing that shows that higher power can desense the WiFi channel, leading to a BER rate on incoming signals from Brandmeister (Parrot test).

[VK3KYY]

Well,

I guess you could try 5W or 5W++ as if you get it working with that, then it will be ultra reliable when you switch back to your normal 1W

But you may find that 5W starts to interfere with all sorts of other devices around the house

[kd2lh]

So far, 2 watt has been running for over a full day on active talkgroups. I'll look at upping power again tomorrow.

[kd2lh]

I purchased a milled aluminum case for the Raspberry Pi Zero W in order to try and give the computer board itself better isolation from the UHF coming out of the nearby GD77 or DM-1801.

Search for "Aluminum Alloy Metal Case Protective Shell Cover Box for Raspberry Pi Zero Black/Sliver" on Alibaba or Amazon for something similar.

Here are photos of the one in silver finish:

IMG_0181s.jpg (87.52 KiB) Viewed 4255 times

IMG_0182s.jpg (54.54 KiB) Viewed 4255 times

So far, this is operating at 2 watts without interference with the USB line. Note that I have RF Chokes installed on both ends of the USB cable.

[VK3KYY]

All of my duplex MMDVM Hotspots are in metal boxes already.

I just cut some holes for the antennas.

It also helps when I'm using the GD-77 as a hotspot, but I always use an external antenna, which greatly reduces the RF field in the shack

[kd2lh]

These are setup on my lab workbench for testing.

My main UHF antenna here is up in the attic, and connected to a XPR-8300 repeater.

I need to figure out a configuration for an event hotspot that would be easy to deploy, and even operate on batteries for several hours.

Marc KD2LH