Toroidal inductors are highly variable

Subtitle: But Using Dope is Just Fine!

Part of the tune-up procedure for many QRP transceiver kits suggests manipulation of the windings on LP filter toroids in order to maximize RF output.

I was curious just how much of a change in value could be accomplished without changing the number of windings.

The readings below were identical on both the nanoVNA and the DE-5000. The differing values represent a 45% change - quite significant!

The inductor shown is for the LP filter in the 20m QCX-mini, spec'ed to be 0.9 uH, which it is when wound correctly.

 

 

VA3RR pointed me to much more info on this topic.

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UPDATE:

After making the measurements above, I put a light coating of clear fingernail polish on the coil to "lock it in".

I remember stern warnings against doing this from Norcal and others who stated that this would change the inductance of the coil and that there would then be no way to correct it.

So I never bothered to use any kind of dope on any of the kits I built, including a number of them designed for outdoor use (the dope can also be used to fix the coil to the chassis).

My measurements echo those who do use dope (coil dope, that is!) - that it causes no change to a coil's L value once it dries.

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"Decomissioned"

 SuitSat returns...

 

DECOMMISSIONED | Sci-Fi Horror Short Film from Perception Pictures on Vimeo.

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Video: Using nanoVNA to determine unknown L or C values

Thanks to cloudy skies and a nearly full moon, I was able to put aside my new obsession hobby, plug in the soldering iron and begin the assembly of G0UPL's newest offering - the QCX-mini.

Rather than plunging into the project with the idea of having a completed transceiver as soon as possible, I wanted to spend a little time along the way with my nanoVNA (and later, with the tinySA).

I'll probably be the slowest builder of the QCX-mini in the history of the human race.

First off: Measuring the inductance of the toroids used in the kit.

Enter the nanoVNA:

 

HB9AMO's spreadsheet can be downloaded here.

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$80 Signal Generator - video review by OM0ET

 

Available here.

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The Andromeda Strain

The inexpensive star tracker I bought last month continues to amaze me. And so do the capabilities of an ordinary camera with telephoto lens when used with it.

A cool front passed through south Texas yesterday, removing all traces of haze & humidity, leaving us with uncommon transparency of atmosphere. I took advantage of the opportunity to set up the items - once a 30 minute process, now honed down to a third of that time.

I wasted valuable time photographing the Pleiades, which were high overhead and therefore available for photography for hours. Meanwhile, Andromeda was low and setting. By the time I realized this, the galaxy was only 40 degrees up and trees took up a good portion of the horizon.

The next opportunity to photograph Andromeda with multiple long exposures won't come until October when it will once again be high overhead and visible for hours.

But for now, I managed to shoot thirty 30-second exposures (Nikon Z6, 300mm/f4 lens at f4, ISO 2500, stacked in Sequator. And twenty 30-sec dark frames for noise elimination suppression) before both galaxy and camera were down at treeline:

M31 with its companion galaxies (M32, fuzzy blob to the left. M110 lower right).

 

Fun Andromeda facts:

• It is 2,500,000 light years away.
• M110 and M32 are in orbit around Andromeda (M31)
  
• Like our Milky Way, it is a spiral galaxy.
• Contains 1 trillion stars, twice that of the Milky Way.
• Until the 1930's Andromeda was thought to be a nebula within our own galaxy.
  
• It is the only naked-eye non-Milky Way object we can see. All else is merely foreground.
• We are approaching the Andromeda at the rate of 50 miles (80 km) per second.
• The Milky Way and Andromeda will collide in 4.5 billion years. Stock up on canned goods.

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Update:

A mesa blocked my view of Andromeda while I was in west Texas last week; trees and light pollution obscure it from home. For this image I drove to a location an hour north of home that was indicated on this map to be significantly darker. It was. My specific QTH was in the parking lot of a cemetery at the end of a dirt road in the Davy Crockett National Forest. Spooky, eh!

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