Category: Amateur Radio

A desk review of the MiniPa100 kit – #1: characterise the output transformer

This article is one in a series of a desk review, a pre-purchase study if you like, of the MiniPa100 kit widely sold on eBay and elsewhere online.

One of the first questions to mind is whether it is likely to deliver the rated power, so let’s review the MOSFET output circuit design from that perspective.

Sellers mostly seem to need to obscure the MOSFET type in their pics, so essentially you buy this with no assurance as to what is supplied, no comeback if the supplied MOSFET is not up to the task. Online experts suggest the MOSFET is probably a MRF9120 (or 2x IRF640 in a 70W build). The amplifier claims 100W from 12-16V DC supply.

Note that this module does not include the necessary output filter which will lose 5-10% of the power from this module.

In this case Carlos, VK1EA, connected a sample output transformer (T2) core from a recently purchased MiniPa100 kit to a EU1KY antenna analyser. The fixture is critically important, it is at my specification. Continue reading A desk review of the MiniPa100 kit – #1: characterise the output transformer

Last update: 11th June, 2021, 7:41 AM

(How) does this balun work? A variation on the theme …

My article (How) does this balun work analysed a balun configuration sent to me by a correspondent, apparently published on Youtube channel TrxBench.

Essentially, my analysis was that it comprises two 12t winds of two wire transmission line in parallel on the ferrite ring. The potential benefit was that the characteristic impedance Zo of each transmission line is probably close to 100Ω, and the parallel combination is probably close to 50Ω.

Online experts following fashion are opining that a low Insertion VSWR balun is better made with two wire line(s) than winding a single 50Ω coax line. They make these claims without evidence, I am not convinced.

In that vein, here is a variation on the TrxBench balun above.

The designer describes it: Continue reading (How) does this balun work? A variation on the theme …

Last update: 8th May, 2021, 9:14 AM

Some pretty woolly thinking on measuring Thevenin equivalent source impedance of a ham transmitter

A ham seeking to optimise his station based on some measurements with a VNA and some modelling of a matching network posted the results of a test in the process.

The radio is an Icom IC-7300. I bypassed the built in tuner, transmitted a tone into my external tuner, adjusted it for SWR=1. I then disconnected the tuner from the radio, and measured the impedance looking into the tuner with a VNA. Surprisingly, (to me anyway) the result was a pretty good 53-j3 Ohms at 14 MHz.

What should we / have expected? It is an interesting case to study. Continue reading Some pretty woolly thinking on measuring Thevenin equivalent source impedance of a ham transmitter

Last update: 3rd May, 2021, 6:37 PM

Collins 30-L1 on FT-8

After a lot of grief with Excel trying to open and fix some 10 year old spreadsheets… finally…

I was recently asked about FT-8 on the Colling 30-L1 linear amplifier considering my article Collins 30L-1 and AM.

The first thing to note is the Colling 30-L1 manual cautions against AM and FSK:

That said, what are the reasons for such a prohibition? Continue reading Collins 30-L1 on FT-8

Last update: 2nd May, 2021, 9:37 AM

N6THN’s novel balun – flux leakage

N6THN’s novel balun presented measurement of the Insertion VSWR of the subject balun, and N6THN’s novel balun – an explanation gave explanation that included mention of flux leakage as a contributor to the quite high inductance per unit length of the transmission line formed by the two windings.

A correspondent suggested that with a ferrite core, flux leakage is insignificant. This article calculates the coupled coils scenario.

The balun as described

Above is the ‘schematic’ of the balun. Note the entire path from rig to dipole. Continue reading N6THN’s novel balun – flux leakage

Last update: 21st April, 2021, 11:03 AM

N6THN’s novel balun

One sees lots of articles and videos on how to make a current balun suited to a low VSWR antenna. This one was recommended in an online discussion on QRZ.com. N6THN might not have invented this balun, but he made a video of it.

In this case, it is described in the referenced video as part of a half wave dipole antenna where you might expect the minimum feed point VSWR to be less than 2.

Apologies for the images, some are taken from the video and they are not good… but bear with me.

The balun as described

Above is the ‘schematic’ of the balun.Note the entire path from rig to dipole. Continue reading N6THN’s novel balun

Last update: 21st April, 2021, 6:03 AM