Xeigu x6100 RF issues

At some point before I acquire a KX2, i was going to do a write up of the Xeigu x6100 if anyone cares. Is a good cheap SDR, which I like it so much I may even keep it - such as the waterfall which really helps on a packed 40m band.

But the main gremlin for SOTA is RF breakthrough or worse common mode RF back up in the Mic, causing havoc. After another bout of whinging about my RF feedback issues, @MW0SAW pointed me in the direction of a YouTube clip he found which is a hack for a Mic choke:

I recon this will do the trick, but i need to put together a random wire without a choke to test ! Plan is to try a W3EDP random wire without permanent choke (that I needed for the Xeigu.)

Question: for any Xeigu and KX2 users out there. Do I really need a 9:1 ? I can test without, but why cant the KX2 or Xeigu’s tuners handle a W3EDP ? I have some vague memory that @MM0EFI might have tried this or mentioned the reason why somewhere, but i cant find it.


Hi Tim,
To be clear, are you saying there is so much RF around the operating position that the microphone picks it up? I would have thought a common mode choke (dirty balun) in the antenna feed would be where the RF should be stopped, not letting it flow around the operating position and only stopping it on the microphone lead.
If you currently have a 9:1 UNUN in the antenna lead I’m surprised that it is not acting like a choke as well as an impedance transformer. You mention testing without it, is that the state where you are getting the RF-Ingres? If so add the UNUN back in and you probably wont need the ferrite ring in the mic lead.

I was loaned an X6100 a couple of months ago so that I could proofread/verify a new book on it and I did not get any RF Ingress but I was not using it with a random wire antenna.

73 Ed DD5LP.


hello Tim nice to meet you.
I can say the 51ft EFRW with 12 ft of counterpoise tunes nicely on my KX3 with no 9T1. I used it on several SOTA activations before the last down turn in propagation when I had to use 80m to work my local chasers. Since those times I have been using resonate link dipoles and now sometimes a 49T1 EFHW. I found the kx3 also tunes 41ft with 17ft CP ok too no 9T1 but did not make any QSO with it. These EF wires are straight on the KX3 antenna socket too no feed lines involved same way as SB’s EFRW. Where as the EFHW 49T1 has 2m of feedline just enough to drop down to where I am sitting on a summit. I must say the EFHW I made with a bigger toroid for VKFF and FT891 50 odd watts needed a line choke on the coax RF would shut down BMS in my bigger LiFe PO4 and shut the radio down. Tricky things sometimes getting the right combo so wish you luck.
Ian vk5cz …


Yes, this exactly what happens with an unchoked antenna such as a random wire.

This works and basically I have to choke everything right now, except maybe good resonant antennas such as a dipole but I have not tested that for a while.

Unfortunately it doesn’t🥲. I also added a 1:1 with 7 turns and this didn’t work well. Only a common mode choke on a short section of coax did the trick.

I just would like to use a random wire direct to radio tuner or with a 9:1. Maybe I am being too ambitious with this radio ?

My theory is that current is reflected back onto the metal casing of the radio and up into the Mic.

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ATUs come in several flavours. Line flatteners and wet noodle tuners. Many integrated ATUs, like my TS570, can only cope with mild mismatches. It can cope with 3:1 mismatch. So it is ideal at tweaking antennas where the match is the wrong side of acceptable, it can flatten out the mismatch of say a 40m dipole cut for the CW end being used at the top of the band. The KX2 tuner is a different kettle of fish. I’ve experimented with mine by mistuning my EFHW match so the reading is something like 18:1, hit ATU and watch as the ATU gets that to 1.0:1 and then I have used the system for QSOs with no problem. It’s designed as a wide range tuner so will tune “a wet noodle”.

Radios designed for portable use with a range of antennas deployed as and how and thus affected by their environment should really come with a wide range ATU. Otherwise it’s not going to that much use or will constrain which antennas you can use…


Possibly at 7.50s into this video. My kx2 ATU won’t tune a W3EDP on 40m without the use of a 9:1.


I do need to investigafe this further. A half wave on 40m is 67’ or 20m. The W3EDP is 84’ or 25.6m, so the impedance shouldn’t be that high.


Hi Tim,
The problem you have clarified is most likely going to happen on all radios (so I would expect similar problems on KX-2, IC-705 etc). Perhaps you will have to settle for having a common mode choke of some kind in the antenna lead. It’s a shame that the UNUN doesn’t cover this but it makes sense as the problem is on the outer of the feeder sheath - either the CMC you have made or one of the kind linked below should work.

73 Ed.

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I have a similar experience with the ATU in the Xiegu G90 (which is the same as the one in the X6100) - so I think the RF Ingres rather than the antenna matching is going to be a problem for Time with either the X-6100 that he has or the KX-2 that he is considering getting.
I have used the SOTABeams “Bandspringer Midi” random-length wire with the G90 just to test it (it’s my second backup antenna) and the tuner in the G90 matched it fine. I don’t think I got any RF Ingres into the audio but I didn’t do a full (longer time) test.
The KX-2 is a very good radio but I think it may still need a common mode choke in the feed-line.

73 Ed.

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Nah, they’re bullet proof. Surprisingly so. There again so was the FT-817. I’m not someone who only sees Elecraft gear as 110% perfect. KX2 speaker is pants but the RF side is really rather good.

In the Xeigu this is down to one or more of: poor design, poor RF susceptibility testing, variable build quality. Or something stupid like case isn’t actually grounded to the radio in this particular set. Seriously, a production radio designed for portable use and it’s susceptible to its own RF on its own microphone, that’s poor.

I’d be very tempted to slap a few 10nF caps (SMD for shortest leads) across the mic inputs to ground and see what happens. My QCXminis picked up their own RF on the paddle and headphone leads using an EFHW as I was sat right in the near field. Some 10nF cured it.


Well said.

I’ve activated alongside the KX2 and if does not suffer the same issues.

Similar, when running EFHW in parallel, the breakthrough on my Xeigu from the KX2 a short distance away is audible on every band. The KX2 does not show any breakthrough from the Xeigu providing I am not on the same band… so clearly the RF filtering on the KX2 is way superior.

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Well for nearly twice the price you’d expect the Elecraft to be better but my point remains that if you have common mode currents coming back down the feeder from a non-resonant antenna - irrespective of which radio is there, it would be better to stop the problems altogether before they get to the radio rather than to filter them out with whatever method is appropriate (decoupling capacitors, ferrites on the mic lead etc.).

When I still had my Yaesu FT-817ND (a very good radio which I regret selling) I had RF Ingres from a “bad” antenna at one point, so IMHO the key is to sort the antenna out, latest at the feeder.

73 Ed.

A non-resonant antenna does not generate common mode currents. They are caused by an unbalanced antenna (e.g. a dipole fed by coax) or by inadequate grounding on a monopole.

If you are sat next to your antenna then RF will be induced into leads and so you do need to filter it out. A common mode choke often helps because it stops RF coming down the feeder which goes right to the radio.


My non-resonant antennas are also unbalanced antennas.

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Actually I’d expect a radio sold for portable use to work in its own RF field no matter what the price. :wink:

The FT817ND was sold as a portable radio and mine suffered from RF Ingres with some antennas - I believe this is not a specific Xiegu or Yaesu problem, rather an antenna design and operation issue. I have not experienced this problem using the loaner X6100 that I had - but then I was using a known good antenna.

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My issue here is that for sota you just cannot get a perfect antenna if you have to compromise with speed of deployment and with mulitband capability. My EFHW SWR will vary on the 40m band from 1.5 to 2.5 depending on how good/bad the ground is on the summit… i guess all that reflected energy, albeit small is getting back to the rig.

I’ve had the Xiegu side by side with a KX2 and it does not suffer in same conditions. Maybe I have a dodgy Xeigu, maybe its just nowhere near as good as the KX2. IDK.

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All understood Tim (I’m also a long-time activator, MG etc) I tend to stick with dipoles or loaded verticals rather than end-fed antennas.
Your side by side comparison using the same power into the same antenna on the same activation is about as good a comparison as you can get.

I think we all know that the Elecraft is a very good radio in lots of different factors.



Common mode current and reflection (SWR > 1) are two different things.

You may have SWR = 1 AND common mode current or vice versa.

SWR > 1 affects the behaviour of the PA towards the load.

Common mode current may inject rf somewhere in the TRX. If this injected rf is to strong, it affects the function of the TRX somehow.

73, Ludwig


Hi Tim, I’d be interested to hear how you found this radio, not withstanding the issue you’ve had? I have never owned a HF radio and have been confined to listening so far on public SDRs like Hack Green and G0XBU’s great setup near Jodrell Bank to see what it’s all about - but I’m looking to take my first steps (phone obviously!) so I’m interested what you think for a beginner like me?

I like the fact that the Xiegu X6100 has an ATU built in and seems pretty portable and is also “sort of” within reach of my pocket. Whilst the Elecraft radios look amazing I just can’t justify the price at the moment. I also like the look of the venerable FT817/818 (there seem to be used ones floating around for similar sort of price as the Xiegu), but I know they don’t have a tuner, but they do have 2m/70cm… horses for courses.

Anyway, if you have time to tell me what you think I’d be really interested - PM if you prefer.


Hi James,
Short note now, I’ll do a full write up then :slight_smile:

In short I think it is a brilliant little radio for the money, circa £500. I love it and it has been solid. Have had allot of fun, made some great 10m/20m DX contacts in the current conditions (VK on 10w). I really love the waterfall feature, helping me to find space on the bands or to find stations calling CQ if I’m on the hunt.

I got ‘advised’ by a retailer that it is a Chinese mfr and that it would be buggy compared to double the money example like ICOM. Nope. I’ve not had an issue at all with the radios software functioning as it should.

Two main drawbacks compared to the KX2 for me:

  • I need to choke my EFHW and random wire, as per above. Not really a problem, it’s good practice anyway.
  • it’s slightly heavier than the KX2 (880g vs 450g) Actually I could reduce the weight to be closer to the kx2 by removing the internal battery, but i haven’t.

But then it’s 1/3 of the price and has more features.

Late night 80m activation in mid wales.

I think it outperforms the 817/818 as a SOTA radio although I don’t own one so I risk starting a debate with that comment :slight_smile:

I was skeptical at first, have grown to love it and I would defo buy one again,