Xeigu x6100 RF issues

Hi James,
Let me suggest if looking at radios around that price - take a look at the Xiegu G90 as well. Yes it’s heavier and needs an external battery and has a smaller screen but it puts out 20 watts rather than just 5 or 10w and that small jump in power can make the difference of a contact or no contact. Now that foundation licence holders are allowed up to 25 watts, why not go for the cheaper than the X6100, G90 HF radio. It’s a solid good performer and (rare on modern radios) the speech processor works well to give that extra punch without over doing it. The built-in tuner is also better than most.
Keep an eye on Radioddity and other Xiegu dealers as they have special pricing from time to time.
For example at the moment Radioddity are bundling the G90 with a mini and larger stand and the digital (audio and data) interface for just about the normal price of the radio alone.

73 Ed.


James, I managed 17 years of SOTA, activated 3 continents and 20 associations, achieved MG, Sloth and numerous 1st activations of summits and associations with an 817 and no ATU.

You may want an ATU but you don’t need an ATU. Just like I want a 330GTC in Pino Verde, but I don’t need one. You simply use antennas that are already a good match, can be adjusted by hand or make a simple manual tuner. A decent 817 and softcase can be had for £300-£350 and you can be on the air and activating on HF to UHF.

And if you want to know why I stopped using one, I was offered a KX2+ATU+accs new for about £1000 and then a 9 month old unused 705 for £599 off the new price and couldn’t say no. I sold the 817 and CW filter for £470 :wink:


That’s a great tip. I too have experienced RF issues with my QCX mini and EFHW. Thanks Andy


Not forgetting that a match on your lovely grassy green damp lawn may not be the same as on a rocky summit. I got some nice RF burns off my key the first time I activated in Portugal using an 817 and a simple 20m “upper and outer” vertical dipole. For my second visit I built a simple choke. No problem the next time I visited with same simple antenna. :grinning:


Hi Gerald,
I like that solution - the choke also serves to contain the coax during transport I presume?
Is that a cable spool you have built it on?

73 Ed.

Talking of ATUs (when needed) - I should receive one of these simple (and cheap) manual Z-Match units this afternoon:

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No, it’s the bottom 4cm of a plastic 2.5 litre emulsion paint can - Dulux. The can is manufactured with a top ring into which the lid fits. This ring can be carefully removed and glued into the top of the shortened can to strengthen the top. As you say, the RG-174 sits in the can for transport. I took it through airport security in my hand luggage with the 817 - no issues.


That’s a nice reuse of what would be plastic waste. It may have been recycled or not but this way it gets used for some time to come.

Isn’t that a little large for your needs Gerald? Ten turns of coax round a suitable ferrite core would be a bit easier to carry and pack away.


Weight, ferrite availability, cost and power handling.

Weight: the weight of RG-174 in an air-cored choke vs a few turns on a typical ferrite is about the same.

Availability: you need to have or buy a suitable ferrite. You need about 2-3m of coax for an air-cored choke and you probably do have that already. Or if buying coax, you buy a longer length.

Ferrites cost a few quid each and 3m of RG-174 doesn’t!

Power is a little moot as most SOTA activators are around the 5-10W level, but air-cored can handle much more power. So if sometimes you want to use your FT-857 or add on brick for special SOTA events, you know you can turn the wick up and not worry about saturating the core and it getting a bit hot.

But it’s normally because you can just make one without having to buy anything. I do think Gerald’s is rather neat. I used a 2cm offcut from a piece of tumble drier vent pipe (100mm diameter I think). You need to keep the windings ordered and not random as the rule of thumb says de-rate impedance by 40% for scramble wound.

Other than that it doesn’t matter much.


Interestingly adding a longer coax length (as in forming the choke) can also help the SWR at the transceiver end. Rob DM1CM has just added some more features to his simplified antenna modelling site sota-antennas.com and one of those additions is the ability to graphically see the effect that different coax types and lengths have on the SWR seen at the radio rather than at the antenna.



I can’t remember where I got the design from… must be somewhere on the Web. It was built specifically for my second trip to Portugal a decade ago. With RG-174 coax it weighs 245g and handles 100W no problem. As I usually use a link dipole for the lower bands and now a Slidewinder based vertical for the higher bands, it is now just part of my diminutive array of test kit. I’ve a 400W 4:1 balun somewhere, similarly collecting cobwebs. Oh the things you make and then don’t need… :joy:


Update: Ferrite core on the Mic cable solves the RF issues. I activated yesterday without chokes on the antennas and no problem.

So I suspect the Xeigu x6100’s issue is basically RF ingress in the mic which is being re-amplified and causing havoc. At least that’s my assumption.

I’d like to try this. Is the theory that this provides a low impedance route for RF to ground, but not audio frequencies ?

The Xeigu has a RJ45 connector for the mic, so I could make a patch cable as a test.:

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To provide an update on RF issues on the Xeigu after further testing. Both issues need consideration for some SOTA operating conditions

  1. RF breakthrough near AM or low frequency transmitters. You need a High pass filter to solve this. I struggled on 80m and 40m on G/CE-002 because of this.

  2. RF feedback into the Mic on unbalanced and un-chocked antennas. Current theory is RF feedback getting into the mic amp (via ground/counterpoise ?). I’ve only ever had this problem using random wires connected directly to the radio. Like this:

You need to choke the Mic cable to stop this, with a high enough impedance for 40m:

I needed more turns, so "hacked’ an ethernet cable as a test

I need a longer term solution for the RF getting into the mic cable, if anyone has ideas !

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Right, brain dump on the reflector in case anyone else has this issue with the x6100 and for help/validation :rofl: :rofl:

Concerning 2) the issue of RF back into Mic.

I have isolated the problem: Situation is that RF is reflected back to GND when using an unbalanced, un-choked antenna, in effect I believe that the metal radio case and GND becomes part of the counterpoise. I only see this with a Random Wire fed directly from the radio, because all my other antennas are choked.

Random wire fed directly…

This RF is travelling from the antenna, along the metal casing and feeding into the Ground GND cable of the microphone and then being amplified/mixed by the mic causing RF issues when TX’ing.

Now if I choke only the GND feeding the mic cable the problem is resolved. (Thanks to Allan @GW4VPX for the testing !!!):

Blue and green are ground for PTT and mic…

So long term solution is to place a choke/filter on microphone GND to prevent any RF above say 5Mhz entering the microphone like this. Essentially a Low pass filter on GND, like this:

Would a cap in Parallel work ? Also a low pass filter, but i’m not sure as the RF ingress is coming from ground:

Thoughts ?

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Good morning Tim,
We take some huge liberties and can get away with a lot when working QRP. I suspect that if you tried replicating this set-up with 100w the microphone would bite your lips.

My thoughts: The Xiegue X6100 has an amazing ATU, but it is expecting to be connected to an unbalanced antenna without excessive common mode current on the coax sleeve. The BNC connector is bonded to the case which is fine for an unbalanced feed if the outer of the coax/ case is at or near RF ground potential. If we connect a balanced feed, or an unbalanced feed with common mode current on the sleeve, and do not earth the radio,the microphone cable and our body provides a route to ground.

Some suggestions:

  • Try connecting the case of the radio to ground a short wire from the BNC outer to a metal object or peg/ stake in wet ground. If you are not able to provide this, putting the radio directly on the ground may improve the RF earth path from the case.
  • Try using a choke on a short length of coax even if you are using a 1:1, 4:1, 9:1 or 49:1 impedance transformer.

I don’t think that these problems are specific to the Xiegu X6100. Many CW keyers behave erratically when using a paddle in similar circumstances. When we experience RF on the audio, the radio is telling us that there is something wrong with our antenna setup.

I am an ‘amateur’, I am happy to be corrected and I am keen to hear other people’s thoughts. Thanks for starting an interesting thread Tim.


Absolutely right… :rofl: :rofl: :rofl:

I tried this and it does work - effectively stops RF ingressing to the radio case and ground. But the section of coax and Torriod makes the tuner work harder and the SWR doesn’t always match as good on 40m. Plus its extra weight. But it IS a solution.

Why am i considering a fix to the mic? and not just choking every antenna - because i look over my shoulder at the KX2/iCOM 705 users just using random wires and getting away with it… i would like to do the same :slight_smile:

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I’ll put my hat on as a former EMC engineer responsible for getting assorted medical equipment through CE testing.

The experiments suggest that the problem is RF pickup on the microphone cable. But you should prove that by putting the radio into TX in AM/FM mode so that it is trasmitting but with no microphone cable connected. (You figure out how to do this.) If the radio is stable in this condition (listen to the radiated signal, check for power fluctuations and displays are not misbehaving) then you can be pretty sure the issue is external pickup not internal pickup.

I don’t know what the supplied mic cable is like but it always strikes me that using UTP type ethernet cables is asking for trouble. Despite having fixed an FT817 type cable once I cannot remember how it was shielded. The next thing I would try is a piece of STP cable for the mic lead. You will need to connect the shields to the ground and I would do this only at the radio end. First try without, then try stripping the insulation back and adding a short wire to connect the cable shield to ground.

The other thing I would try and have suggested this is to get 10nF surface mount caps and solder them to the back of the mic connector on the radio so the are soldered to the up/down/ic/ptt etc. and mount them vertically. You should have a row of 7 standing up. Then use a piece of wire connect all the other ends together and connect to ground. Keep wires short. That will provide a path for RF induced on the cable to pass straight to earth.

EMC problems can be solved but in most of the jobs I did when working on this, it was an iterative process.

That should tell you an awful lot of info about your setup. You mission Jim, should you decide to accept it, is why does taking the the mic cable out of the circuit alter how the tuner works? The answer to that should take you down a path of enlightenment. .-)


I have tried that, using the PTT microphone on the radio. There is NO RF feedback issues if an external mic is not connected. So RF feedback into an external mic is the issue and I am pretty much 99% sure that this is pickup of RF on the case ground of the radio & hence mic - probably via reflections from the antenna counterpoise. If the antenna is choked it is not an issue, so this is unlikely radiated pickup.

But its the ground (Radio casing, and GND feed to the mic) that is carrying the unwanted RF and with a portable operation, the radio (or antenna) is not truly grounded (unless i purposefully work out a way to do this - and thats faff).

I really hope so and thanks for advice. Trying caps and mini inductors from RS components on the GND wire of microphone is my current thinking for next steps.

The mic cable in/out does not meaningfully affect tuning or swr. Its adding a section of 50 Ohm coax to the antenna presenting more like 3500 Ohms and the tuners is now working harder i assume ?

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Really. How do you know this?

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If I choke only the microphone GND cables (attached to case of Xeigu) … problem solved. Also if i choke the counterpoise/GND of the antenna … problem solved.

Incidentally when I choked the GND cables of the microphone with a too-low Impedance i had the problem on 40m,. Up the impedance so the cuttoff frequency includes 40m, problem is solved.

Why else would i see these results if the ground is not receiving unwanted RF… i cannot come up with another plausible solution other than attaching an oscilloscope to the GND.

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