Paul Butzi |||

Xiegu G90 More Thoughts

With a little more time operating with the G90 I have some further thoughts/observations.

Power connections

I think the supplied power cable is awful. I think the choice of the JST EL2P 4.5mm connector for power is likewise awful. I suspect everyone is aware of this even if they don’t seem to mention it, as the cooling stand for the G90 sports a Anderson Powerpole input, and then daisy chains power to the G90 via the JST connector with a very short lead.

Part of the problem is the rating of the JST connector. The G90 is specified as drawing 6A at 12.8v when transmitting at full power. The max current specification for the EL2 connector with 18ga wire (which is what is in the provided cable) is 6A, so that makes me a little uneasy.

On top of that, the voltage drop across a 1 meter length of 18ga wire is going to be on the order of 0.25V at 6 amps. That also makes me uneasy. I can hear you asking But why would they make the power cable out of 18AWG wire?” They did that because 18AWG is the maximum size wire you can cram into the crimpable pins that go into the skeezy-ass JST EL connector!

(side note: crimping the contacts for APP is simple, just buy a decent crimper. If you want to put contacts on 10AWG wire, no problems, just use the 45A contact. Crimping contacts for the JST EL series connector is a process that ranks with neurosurgery by comparison, as I have to do it without a dedicated crimper. Why don’t I own a dedicated crimper for the JST EL series connector? Because no one else uses EL connectors!)

One solution would be to rip the JST connector out and replace it with Anderson Powerpoles, and simply replace the entire path with, say, 12ga or 14ga wire.

What I will probably do first is toss the Xiegu power cable into the trash and replace it with:

  • a short 16ga pigtail from the JST EL connector, through a fuse block, to a Anderson Powerpole connector.
  • use one of my many assorted 12ga Powerpole cables in some suitable length to get from the power source to the radio. This might be as simple as plugging a Bioenno battery directly into the pigtail.

I understand that many hams dislike Anderson Powerpole connectors. I don’t understand their reasons (easy to disconnect accidentally, poor performance in the face of vibration, hard to install, confusing in the field), which all seem contradicted by my actual experience using PowerPoles in my shack and in the field. But the fact remains that PowerPoles are the defacto AND dejure standard and to pretend otherwise is silly, and radio manufacturers who insist on using Molex or JST connectors seem to be engaging in Luddism, and I wish they’d stop, because I’m tired of routinely chopping Molex or JST connectors off radios and substituting PowerPoles.

Are there better power connectors than Anderson PowerPoles? Yes, there surely are, although they’re probably way more expensive and only marginally better.

Are those connectors which are superior to Anderson PowerPoles the usual multi-pin Molex connectors? Definitely not. Admit it, folks. Those Molex multi-pin arrangements are a workaround solution to getting enough amps into the damn radio through a connector series where each individual contact can carry only a fraction of the required current, all while providing some assurance that no one will plug the power in backward and let the magic smoke escape from the radio.

I have the same complaint about QRP radios using horrid 5.5/2.1mm coaxial plugs for power. They pull out at the slightest provocation. They are a great entry point for all sorts of environmental gubbage that will make them work poorly. They’re one more thing to get left on the workbench and forgotten so that you have no way to power the radio in the field.

Weird Phantom 2KHz tone

One of the things I’ve done to improve my operating in the field is get a Heil BM-17 headset to go with the G90. Using a headset makes it vastly easier to operate, as I only need to hit the switch in the PTT control to transmit, and using the headset makes it incredibly more easy to pick signals out of the noise when the signal is very weak. On the external speaker on the G90, which is actually pretty good, a signal must be pretty strong to be heard clearly. On a headset, you can pick out a signal at what can only be described as ESP levels if you have some idea of what the station on the other end is sending.

So I wanted to get the mic gain and compression settings dialed in on the G90 with this headset before taking it all out into the field. It turns out the G90 has just one setting for compression - it’s either on or off. It turns out you want it on.

Mic gain is more complicated and the supplied hand mic has a sort of funky audio spectrum response curve, so I was pretty confident the very different response of the Heil headset mic would require a different gain setting.

So I set up to test, transmitting on the G90 into a dummy load, and listening on one of my other receivers to assess the sound. This isn’t a great way to tweak audio because you also hear your speech through your skull, but it’s definitely good enough to just adjust levels

I’ll describe my test setup - I have the G90, set up with the Heil headset adaptor plugged into the mic jack. The headset adaptor breaks the contacts at the rj-45 mic jack out into a 3.5mm jack for the electret mic input, and a .25” jack for PTT. The G90 is set to a frequency in the 20m band and USB mode.

The antenna output of the G90 is running directly into a 50 ohm dummy load. Transmit power is set to 20W.

I monitor the transmission from the G90 using my main antenna some 50 feet away and either an Icom IC-7300 or an Elecraft KX3. In each case, the mode of the receiving radio is set to USB and the frequency matches that on the G90.

With a mic plugged in to the adaptor, I close the PTT switch and speak into the mic, and as expected I hear my speech on the audio output of the monitoring receiver. If I adjust the mic gain on the G90, I hear the audio change on the monitoring receiver, so this is the way I can adjust the G90 mic gain to get best performance from that mic.

With no mic plugged in, I close the PTT switch, and on the monitoring radio I hear a 2KHz tone. I would expect that with no audio input, there would be essentially zero RF output from the G90 and thus I’d hear silence on the monitoring receiver.

It took considerable head scratching and an email exchange with the support folks at RadiOddity before I realized that the power output from the G90 when it transmits this ghost 2KHz tone is very, very low. I’ve not tried to measure it, but I’m guessing it’s well below 1 watt.

It turns out this happens if a mic is plugged in, as well. I can plug the mic connection for either a Heil BM-17IC or Heil Proset 7 IC, and without speaking into the mic, the G90 transmits a very weak signal which carries the 2KHz tone. Again, the power level is very low, but it is not zero. It’s perfectly possible that the power level is only a few mW, which would put it as much as 20dB down from the power level the g90 is set to.

I can’t imagine a situation where this behavior would matter in the field, the power level of the 2KHz tone is so low. But it is a curious thing and I wonder of the Xiegu engineers are aware of it, as I expect it’s an artifact of the digital audio input chain and may well happen with every Xiegu radio that shares that audio input chain design and implementation.

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