开云体育

The High band spectrum analyser topic prompted me to post similar measurements I made with a low band QMX using an apparently good spectrum analyser.
I've attached the data and my analysis. It should describe what I did.
What strikes me is that the first harmonic may be a bit high, -40 dB on 80m.? The power also seems to be a bit low.
What do people think, do I have anything to worry about?

I did get the feeling that something changed after using it with a vertical antenna, the power seemed to decrease.? I've some spectrum analyser traces before that where the harmonics were lower but they were running at a lower supply voltage.

I know that power levels isn't an exact science but are the harmonics OK?

Chris, G5CTH

Thanks Ron,
I reckoned that if the manufacturer wrote the maximum limit on the front of the analyser that was what it would cope with. I'm running about half that power.
I've got a home made attenuator attached to my home made 8W dummy load which is about 38.7 dB attenuation, I'll give that a go.
Well you may have a point, using my home made attenuator puts the second harmonic at about -52 dB.That's relative to the primary that's about -2.5dBm

My home made dummy load consists of 4x 2W 50R thick film SMD resistors, then a 2k2 through hole resistor with the output across 2x100R SMD resistors.? My NanoVNA suggests that it's quite linear. I wouldn't trust it for absolute power measurements but maybe it's better for relative power.

dBc? Ah, relative to carrier.

Must look for more attenuators at the next radio boot sale...

Thanks,

Chris, G5CTH

On Thu, Feb 29, 2024 at 06:52 PM, Chris wrote:

I reckoned that if the manufacturer wrote the maximum limit on the front of the analyser that was what it would cope with.

"Cope with" and "make accurate measurements with" are different things.??
73, Don N2VGU

On Thu, Feb 29, 2024 at 08:20 PM, Ronald Taylor wrote:

Chris, you technically don't meet the -43 dBc requirement

Yes he does.

You clearly didn't bother reading his non US callsign which is quite clearly
written at the end of his post.

HINT - next time try reading the UK regs instead, there are no requirements
other than making sure your tx doesn't cause undue intereference to others.

Technically speaking, he can have a harmonic greater than a fundamental,
and if it's not causing "undue intererence" then no rules are broken.

OK, so that's an extreme example, but true. Reality is diferent, and most ops
will take pride in suppressing unwanted emissions so that they don't cause problems.

However, the point here is that many of us get just a bit pissed off with posts that
assume the world has the same US rules.

Now leave the rest of us alone to enjoy OUR regs, not yours.

--
- 73 de Andy -