Doping toroids

Back in the olden days, when kits were plentiful and freshly-made products from Small Wonder Labs, OHR, Norcal and KD1JV filled the air, a common question was "Should I dope the toroids?"

By which they mean, should the coils be secured to the board - and/or the windings to the core - with a small dab of clear fingernail polish?

Even then, before POTA, many QRPers enjoyed taking their rigs on hikes or backpacking trips and were concerned about the possiblity of jostling a toroid out of whack (a technical term). After all, they are a fairly significant mass to be held in place with two tiny (at times) 26g connections.

Answers varied but were mostly in favor of not doping them. I don't blame the kit vendors for offering this advice - can you imagine the headache of a kit builder, doping a coil into place and then learning that it contained one winding too many? Better to not dope them and retain the ease of removal/adjustment.

The stated reason for not doping them was that the fingernail polish would change the characteristic of the coil?

Some of my commercial gear does have doped toroids - the FT-891, for example. Meant to be used in a mobile environment, it makes sense. Of course, Yaesu is certainly compensating for any possible change in a coil's inductance by taking the effect into account with the coil's initial construction.

With a few redundant LP filters on hand - and a possible bicycle ride over bumpy terrain this spring, QRP rig stowed - I decided to see what the effect would be.

1 to 4 GHz: nanoVNA 2 Plus4 vs. Keysight FieldFox

After a three week transit, my nanoVNA 2 Plus4 arrived in my mailbox. It was around $170 and I would not have spent that if the prior nanoVNA's hadn't given me the confidence to do so. But their performance has been incredibly accurate, so I ordered and had high expectations of the new VNA.

Today I finally had the opportunity to put the diminutive piece of test equipment on the bench to get a real idea of its performance.

The nanoVNA 2 Plus4 differs from the previous versions in several ways. It has:

• A metal case
• An internal 18650 Li-Ion battery (not included due to shipping restrictions)
• A charge status indicator for the battery & charging from a computer's USB jack
• Beefier controls for slewing the cursor and markers
• A 4.4 GHz upper freq limit
• 20dB more dynamic range than earlier nanoVNA's

It is primarily due to the increased dynamic range that I bought this VNA. Like most hams, I don't need to measure anything at 4 GHz but I do want the increased accuracy (hopefully!) that comes from increased dynamic range.

Measuring MDS with TinySA, RMS multimeter and attenuators

The popularity and low price of the nanoVNA and TinySA devices allow hams and other radio hobbyists to make measurements that were out of reach just a few years ago due to the expensive equipment required.

For those who have a TinySA, you not only have a spectrum analyzer - you also have a surprisingly accurate signal generator.

With a series of attenuators, a TinySA, RMS multimeter and some cabling, I had all I needed to make an uncalibrated MDS measurement of my radios. Maybe you do too. Here's how to do it.