-22dB measured by ARRL!
That is -16dB as ARRL numbers are inflated by 6dB.
If I'm not mistaken, that's being measured at full power output. It NEVER takes full power output of my 1500 to drive my amplifier, it's typically less than half depending on the band. But hey, let's not let more real world application of how the XCVR is actually used get in the way of a good bashing session. What fun would that be?
I wonder why Flexers think they are always under attack.
We are taking about the Flex-1500 and someone stated that ARRL measured IMD at -22dB on 40m. I cannot attest of the veracity of this statement but as no one said anything to the contrary I assume it is true.
I also assume that whatever they measured -22dB is accurate.
I also assume that when they found -22dB they double, triple checked the result as -22dB is not that good.
It could be that the unit they tested was below the norm or that Flex improved the rig after the review.
It is not the point, I just used -22dB as it was what was posted.
Or may be you think that when I say "inflated by 6dB" it is a form of bashing.
You are free to Google "Transmit IMD". May be you will find a link to National Instruments for example:
If F1 and F2 are the frequencies of the two tones, then the third-order distortion products occur on both sides of these tones at 2F2 – F1 and 2F1 – F2. Assuming that the power levels of the two tones are equal, IMD3 is the difference between the power of the fundamental signals and the third-order products, as defined in the following equation:
IMD3 = Po -Po3
where o refers to the output of the UUT, Po3 is the power level of one of the output third-order products, and Po is the power level of one of the fundamental tones.
I placed the emphasis on one
, it is not in the original text.
Wherever you look, only ARRL uses this 2 tone PEP stuff.
Yes, IMD is measured at full power, that's the way ARRL does and not specifically for Flex radios but for any radio. Do you think ARRL is bashing all the rig manufacturers? That is a way to compare different rigs, you compare bananas with bananas (2 tone PEP at full power is still a valid comparison).
You said that you never (need to) drive your amp with 5W, I never said you did and I never recommended to do so. You drive it at around 2W and it is a good thing, it will improve things but until someone measure the IMD at 2W you cannot tell by how much.
Now imagine the guy who want to drive an amp to get 100W and does not have an idea of what this IMD stuff is and buys a 100W amp. If it is FCC approved it cannot have more than 15dB gain if I am not mistaken. If it is 15dB gain he can drive it with a little more than 3W, if it has less than 15dB gain he will drive it at 5W.
What I was trying to do was to show the guy who think it is Chinese, it is not. It is not rocket science: if it is a linear scale - like I double my power or I halve my power - you use multiplication and division. If it is a log scale like when using dB you use addition and subtraction. You don't know what is 100dB? I don't, I just use a conversion table or a dB calculator. Just remember to use the correct table depending if it is relative to voltage or power. For the transmit IMD just do a little reading, nothing complicated. And when you read the review of the Flex-1500 and it says 3rd order products IMD -22dB on 40m you have an idea of what it means and what will happen when you drive your 1kW amp with the Flex at full power (the 6dB difference is just a factor of 2 difference and it won't make much of a difference for the station on the adjacent frequency).
You can even use the ARRL handbook as a reference, there is some valuable information in there.Oh my Gosh!
ARRL Handbook 2002 page 17.5
If a pair of equal-amplitude signals create IMD products, the IMD ratios (IMR) are the difference, in dB, between each of of the two tones and each of the IMD products (see Fig 17.6).
Fig 17.6 - Top: IMD ratio (as displayed on a spectrum analyzer).
It looks like they had to call it IMR in order to use their 2 tone PEP magic formula.
Now if you think that my previous post was a personal attack on you or Flex you have serious problems.
May be the Flexer syndrome