Mullard QY4-400 (4-400) x 2 Class C AM plate and screen

Valve datasheets often give one to few suggested sets of operating parameters for a valve in one several modes, and designers are left to sort of interpolate or extrapolate to their own set of parameters, eg loaded power supply voltage.

This article is a walk through and comparison of RF Power Amplifier Tube Performance Computer applied to the subject scenario.

Let’s extract from the Mullard datasheet.

We will use the Va=3kV scenario for this comparison. Continue reading Mullard QY4-400 (4-400) x 2 Class C AM plate and screen

4:1 voltage balun vs 1:1 current balun on the MFJ-949E @ 1.8MHz

A question of often asked is whether the ‘best’ balun on a T match ATU is:

  1. a Ruthroff 4:1 voltage balun (as it often fitted internally);
  2. a Guanella 1:1 current balun; or
  3. a Guanella 4:1 current balun.

The subtext of the question is often that the OM has switched from (a) to (b) in pursuit of improved common mode current rejection, and found they cannot match their existing antenna which matches ‘just fine’ using the (a).

This article explores (a) and (b) using a configuration similar to the popular MFJ-949E @ 1.8MHz, and comments on (c).

Let’s declare that although the MFJ-949E is specified for 1.8MHz, it is disadvantaged… which will exaggerate the problem to some extent… but in so doing make the problem easier to see.

We will use a SimNEC model of the ATU and a purely resistive load, as large as the ATU will match. The Smith charts shown are normalised to Zref=400+j0Ω as it is a better context for visualising loads on 400Ω transmission line typical of the use with two wire lines.

1. The bare MFJ-949E T match to a coax output jack

Above is the model. The coloured squares a sample points in a sweep of values of the matching components C1, L1, and C2. Green is loss less than 3dB, Yellow 3-6dB, and red greater than 3dB. Continue reading 4:1 voltage balun vs 1:1 current balun on the MFJ-949E @ 1.8MHz

Evaluation of Aliexpress sourced EBM315 battery packs (for DB3DL2)

In Repack of Hikoki / Hitachi EBM315 battery pack (DB3DL2) I discussed the repack of a battery pack. At the same time I also ordered a no-name replacement 1.5Ah battery on Aliexpress for $25 incl shipping… with some reservation as most batteries I have purchased on Aliexpress have failed to deliver half of the rated capacity.

So, the battery arrived and I tested it, the purple trace above, and I was pleased to see that it exceeded the rated capacity a little.

So, I purchased another from the same seller, and it duly arrived, and to my surprise, it exceeded rated capacity by 30%.

Both batteries recharge properly on the Hitachi / Hikoki charger.

Time will tell whether they are good value. In any event, they use screws to hold the cap on so they can probably be repacked with good cells.

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…

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

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

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

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)

Paralleling two synchronous AC generators – phasor diagram with AVRs

This article Paralleling two synchronous AC generators presented phasor diagrams for two synchronous generators in parallel, and Paralleling two synchronous AC generators – simple AVR discussion discussed a simple automatic voltage regulator system that can be used to share two identical machines.

To recap, the first configuration presented follows.

Above is a phasor diagram of two machines of the type discussed in parallel. This is just after ACB closure, and they are not well adjusted in this case to allow visibility of the various phasors. Continue reading Paralleling two synchronous AC generators – phasor diagram with AVRs

K3EUI’s MyAntennas EFHW on 80m

Barry, K3EUI, posted some interesting measurements of his MyAntennas EFHW which he described with some useful detail:

I have been experimenting with a “MYANTENNA” 130 foot long “end-fed” with the 49:1 UNUN*

I replaced their 130 ft antenna wire with a heavier gauge #12 stranded insulated wire (I had a few hundred feet).*

This is classified as a ONE-HALF wavelength antenna on 80m, hence the need for the 49:1 UNUN to transform 50 ohm (coax) to a few thousand ohms*

It has resonances on the other ham bands (harmonically related) but I wanted it mostly for 80m.

One leg runs about 60 ft horizontally to a tree and then the next 70 ft makes a 90 degree bend (to fit into my yard) still horizontal.*

At this time I removed a 15 ft “counterpoise” wire on the GND side of the UNUN.

I will try it later this week (after the snow) as a “sloper” or an Inverted V up to a tall fir tree.

It is only about 20 ft above ground now (with 4 inches snow) for NVIS prop, and fed with 70 ft of RG213 coax (50 ohm) with a RF choke on the coax feed line 10 ft from UNUN (the counterpoise?) and another RF choke just as the coax enters the shack.

His VSWR curve is interesting, a minimum at source end of about 1.32 @ 3.66MHz as built and measured.

Minimum VSWR is about 1.32 @ 3.66MHz. Continue reading K3EUI’s MyAntennas EFHW on 80m