I finally got around to making a series of measurements of the harmonic output of the FX-4CR on all bands.
I say "series" because I was trying to see if my method, rather than the equipment/radio, was the cause of the reported level on 30 meters.
From the FCC regs:
§97.307 Emission standards.
For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission. For a transmitter of mean power less than 5 W installed on or before January 1, 2003, the attenuation must be at least 30 dB.
No matter how I measured it, the FX-4CR appears to fall 10dB short of compliance on 30 meters, unless the rig is operated at 5W output or less.
But on all other bands, it is fantastic.
Other rigs have had similar issues; the uBitx and the Ultimate 3S come to mind. The (tr)uSDX has unacceptably high levels of IMD. There are similar issues with other radios as well, so the FX-4CR is not alone by any means.
What this means, real-world, is that if operating on 30m with a 20W output, you are putting out a 9mW signal on 20.2 MHz. Additional attenuation will occur since you are using a 30m antenna, rather than one for 15-ish meters.
And, for what it's worth, FCC standards prior to 2003 only required 30dB of harmonic attenuation.
I'd be curious what they are in other countries.
On all other bands, the FX-4CR easily meets compliance. For bands not listed below, the harmonic content was less than -60dB below the fundamental and can not be measured with the tinySA Ultra.
The FX-4CR easily meets FCC standards on all bands except 30m.
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Jim AC9YY shares his results, showing the 2nd harmonic to be at -48dB on 30 meters (click for larger image):
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| 6 meters |
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| 10 meters |
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| 12 meters |
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| 15 meters |
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| 17 meters |
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| 20 meters |
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| 30 meters |
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| 40 meters |
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| 60 meters |
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| 80 meters |
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For context, these rigs fail on the following bands:
ReplyDeletemcHF: 17, 30, 60, 80 meters
(tr)uSDX: 80 meters
QRP+: 12, 17, 30 meters
The QRP+ was manufactured before 2003 but it still fails the more relaxed threshold. If held to today's standards it would also fail on 10 and 15m.
And regarding the 60dB dynamic range of the tinySA Ultra...
I could have increased this by selecting a narrower RBW but this would have greatly increased the scan time (to 20 seconds or more); unnecessary since I only needed to look down to -43dB to measure if FCC compliance was met.
Nice work John. All in all it sound like the FX-4CR has improved significantly since its original release and, except to 30m, is a nice addition for the portable operator.
ReplyDeleteHi Brad - yes, it has improved but still has its quirks. For what it offers though, I can overlook them!
Delete73,
John
ReplyDeleteHi John,
I noticed my harmonics on 30 meters looks quite a bit different than yours. How do I post a picture here? My harmonics on 30 meters are 48 dB down.
Jim AC9YY
Hi Jim, you can email it to me and I'll post it. My email address is on QRZ.com. How do the other bands look?
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