Can a Matched pair of MOSFETs Produce these results? - Page 1
Forum section: electronics / rf-microwave

author: steele
author_rank: Newbie
timestamp: March 25, 2020, 10:47:59 pm
content: This shop I see online, in his videos replaces the transistors.I was wondering if you Can replace the MOSFETs in a radio to produce these Results as pictured below?Or is there something else going on? Is it just this simple to put in new transistors to get these resultsin the first picture he says the radio is dirty and in the after picture he states the radio is now all cleaned up.

author: TheMG
author_rank: Frequent Contributor
timestamp: March 26, 2020, 01:25:24 am
content: It is theoretically possible. If the transistors are in a push-pull linear amplifier and they are severely mis-matched, the resulting non-linearities can create excessive IMD (inter-modulation distortion), which I believe is what we're seeing in rather significant quantity in the before picture.That being said, the two images were taken with slightly different settings, particularly the resolution bandwidth, so that accounts for some of the difference, though it does certainly look like the amplitude of IMD products is lesser in the second picture.

author: wraper
author_rank: Unknown
timestamp: March 26, 2020, 01:37:46 am
content: Yep, direct comparison of those measurements is misleading since measurements have different span / RBW. Also MAX-MOD they are selling is complete BS. Not that it does not work as replacement of original part but their wild claims.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 26, 2020, 05:27:29 am
content: Quote from: steele on March 25, 2020, 10:47:59 pmIf it is who I think it is, he lies in his teeth!

author: steele
author_rank: Newbie
timestamp: March 26, 2020, 09:49:36 am
content: So, as I thought in most of his after videos you don’t see even the sideband showing I see he’s using setting changes to hide something.Kinda figured there was no magic part.

author: Mark19960
author_rank: Regular Contributor
timestamp: March 26, 2020, 12:01:34 pm
content: This fella again....Some fairly important things here...1. The DUT in image #1 is at 30.66dBm whereas the DUT in image #2 is at 44.42dBm2. Resolution Bandwidth is different.3. Span is differentValid comparison?NO.Very misleading comparison.AM CB radio modulated with 1K tone. Can see that in the first image but not the second.Assuming it's the same.In image #1 the same radio is running at around 1 watt and probably being modulated pretty hard.Image #2 has a much higher carrier level.*all settings and conditions must be the same* and I doubt you will see him do that.If he did that then these devices he has on offer would not look near as good.The devices in question like maxmod belong in the snake oil section of the forum.I found one thread on maxmod in there already so it's right where it ought to be.Simple answer? snake oil + misleading marketing.

author: Mark19960
author_rank: Regular Contributor
timestamp: March 26, 2020, 02:30:33 pm
content: Yeah... I did that because radio chaps would not accept the maths.The maths disprove the maxmod but maths were somehow wrong to this lot.The maths to disprove maxmod are pretty trivial.It's not that it doesn't work. It just doesn't cause you to have more power or run cooler.Just a custom labeled part.Oh well.

author: steele
author_rank: Newbie
timestamp: March 27, 2020, 11:45:26 am
content: It looks like the gentleman was forced to show another measurement because of this post, Here is the new result and measurement after he changed the MOSFETsI still see distortion as it was in the first before image..The video is laced with vulgarity and ethnic slurs where he posted this new information. hence why I will not link to it right now..How much better does it look then the first image?

author: wraper
author_rank: Unknown
timestamp: March 27, 2020, 11:55:15 am
content: Quote from: steele on March 27, 2020, 11:45:26 amIt's still 42 vs 30 dbm, not comparable.

author: Mark19960
author_rank: Regular Contributor
timestamp: March 27, 2020, 01:35:33 pm
content: Not surprised about the slurs and vulgarity. That's his thing.That said, if I compare my radio to the above posted today......I adjusted my power level to closely match the image above.All I did here was adjust the RF deck idle current.The radio has IRF520 MOSFETs..... Nothing fancy. Whatever they had in Shenzen at the time I am sure.No special devices with imbued powers.This isn't a hard concept. Do they both have some IMD? Sure. Good luck eliminiating it.Is it a problem? No?Doesn't warrant replacing anything. Just adjust it and move on.Buy nothing. Leave it alone. It's real easy.Edit: had to add the image.. :x