Month: March 2024

My ATU is soooo good, it will give a perfect match on anything, even…

I was reading the mail on a net on 40m one day many years ago, and one of the participants asked people for their recommendation on his intended ATU purchase. This was pretty technical for this net where the qualification to join is that you tell all what you are going to have for dinner.

So, one of the guys tells ’em “mine will tune the proverbial wet string.”

Gotta do better than that? Next guy says “mine is so good… I tuned up the other day for a perfect match then thought the band was a bit dead until I realised I did not have an antenna connected!”

Let’s work a real example

MFJ claimed that the MFJ-949E is the most popular tuner purchased… so lets use it as an example.

We will use 160m as I measured the magnetising impedance of the internal balun a few days ago and used in the a recent article. This article uses the same basic model… but no antenna connected.

Above is the test setup, NanoVNA connected to the transmitter jack, mode switch set to Tuned / Balanced… and there is no antenna on the balanced line terminals (the balun link is in place). Continue reading My ATU is soooo good, it will give a perfect match on anything, even…

Last update: 13th March, 2024, 6:45 AM

Lewallyn’s meaning of Radiation Resistance

Hams tend to not share a common meaning for terms, and in defence will say that anything is ok so long as the author makes their meaning clear. The latter is a huge burden in online discussions where a post may be less than 50 words.

Tom Rauch states:

Radiation resistance is both the most useful and the least useful antenna-related term. Radiation resistance can easily be misused and rendered useless. This is because radiation resistance has multiple poorly-defined meanings. When a term has several nebulous meanings or uses, it is only natural that misuse or mixing of terms appear. Lack of a firm, single, well-accepted, definition allows the term “radiation resistance” to slip from one definition into another. This often results in well-intentioned, but totally erroneous conclusions, that seem to follow accurate, logical, thought!

Continue reading Lewallyn’s meaning of Radiation Resistance

Last update: 13th March, 2024, 8:43 AM

Analysis of a practical non resonant dipole scenario on 160m

Non-resonant dipole with two wire feed line and T match ATU discussed some of the issues with the common multi band configuration with emphasis on the lower bands where ATU losses can be sufficient to cause internal damage.

This article explores a scenario that came up in discussion with another ham.

His scenario is a moderately long dipole (just under λ/2) fed with a moderately long length of nominal 450Ω windowed ladder line… I am being obscure, but I don’t want to dwell on the details from that angle. This is not a case of someone loading up the roof rain gutters, or window frames, it is a serious antenna.

The chap is using a MFJ-941E ATU, which appears to use the same componentry as the MFJ-949E with which I am very familiar, the 941E appears to be a version of the 949E without internal dummy load.

So, he was able to get a good match easily using the internal balun (4:1 voltage balun), and from the settings we can estimate the matching and particularly the losses.

A model

I have separately come to a view that the Q of the 949E inductor at ‘A’ switch position is about 170 @ 1.8MHz. I also measured the magnetising impedance of the balun, it was 2.8+j350Ω @ 1.8MHz.

Above is a model capturing: Continue reading Analysis of a practical non resonant dipole scenario on 160m

Last update: 10th March, 2024, 10:46 AM

Non-resonant dipole with two wire feed line and T match ATU

This article discusses a very popular HF antenna with hams, the non resonant dipole centre fed with two wire line. Some ‘experts’ call this a doublet, but their distinction is not captured in the IEEE Standard for Definitions of Terms for Antennas which considers doublet and dipole as equivalent.

Whilst these antennas can work well, remembering that all antennas “work” and “any antenna is better than no antenna”, is a deeper understanding useful?

As a basis for discussion, an NEC-4.2 model of a 60m centre fed dipole at 15m over ‘average ground’ (σ=0.005, εr=13) and 30m of lossless 400Ω VF=1 feedline was built. It is almost λ/2 at 160m, so might appeal as potentially useful down to 160m.

Above is the geometry of the example antenna.

 

Above is a Smith chart plot of Zin to the feed line from 1 to 30MHz, the cursor is at 1.9MHz, and this impedance 14.4-j181Ω will be used in the following discussion. Continue reading Non-resonant dipole with two wire feed line and T match ATU

Last update: 4th March, 2024, 11:00 AM

Repack of Hikoki / Hitachi EBM315 battery pack (DB3DL2)

I have had a Hitachi DB3DL2 ‘pencil’ type cordless screwdriver for about 12 years, and one of the supplied two batteries (EBM315 1.5Ah) has just failed. This is not the first failure, the charger failed after about five years use and the LED push button became electrically leaky flattening the battery so the push button was removed. The second battery is still working, but at about 65% capacity.

It is actually a really good tool to use, and so worth trying to extend its life. To that end:

  • I purchased a new genuine Hikoki (new name for Hitachi -Koki) charger on Aliexpress for about $80 shipped (they are more like $150 locally);
  • I purchased an after market EBM315 1.5Ah battery on Aliexpress for about $25 shipped;
  • I purchased locally two Panasonic NCR1650B unprotected 3.4AH 18650 cells to repack the two original batteries; and
  • repacked the failed battery.

Above is a capacity test of the new Aliexpress 1.5Ah battery and the working 14 year old Hitachi battery. The little squiggles are concerning, to be further investigated. It is my experience that most rechargeable batteries purchased on eBay and Aliexpress grossly fail to meet specified capacity, the one is a welcome change… though note the quite low cell voltage to achieve rated capacity. Continue reading Repack of Hikoki / Hitachi EBM315 battery pack (DB3DL2)

Last update: 21st March, 2024, 11:57 AM