Central Machinery 8" Press and WEN Vise (that fits)

Recently bought a Central Machinery 8" drill press from Harbor Freight ($79) for a project.

But I had trouble finding a vise that would fit, I found this WEN DPA423 3" drill press vise ($29) fits.

Annoyingly HF dont sell these vises, the ones they sell don't fit - as noted in many reviews. Fortunately the reviews are searchable which is how I found this vise after a bit of frustration - as most product listings don't specify the center to center spacing of the slots on their vises.

The drill press for what it is seems pretty reasonable, I got it for an upcoming antenna upgrade project.

40m 1/3 Wave Elevated Vertical 50 Ohm

40m elevated vertical (1/3 wave) using 40ft / 12m Spiderbeam pole, 3 x 16ft / 4.9m radials, 50 ohm feed.

We can feed a vertical off-set by extending the vertical element and shortening the radials to raise the feed-point impedance while maintaining resonance.

The radials must be electrically isolated from a metallic mast (if used), and a high quality 1:1 current balun to isolate the coax shield from the antenna system, I'm using a Balun Designs 1115t.

Elevation Plot:

SWR Plot:

In this case making use of a 40 ft / 12 meter Spiderbeam pole mounted 10 ft / 3 m above ground on the 2nd level deck at the back of the house.

Modeling this using bare 12 AWG wire, the radial length to achieve resonance was 23 ft / 7 m. At least part of the reason my radials ended up shorter will be because I used plastic coated wire, and the vertical wire is attached to a fiberglass pole, but there may be something else having an effect..

However after trimming the radials for resonance the analyzer showed a perfect match:

The analyzer hung off the balun with a 6" jumper, since the SWR didn't change after connecting the feed-line is an indication the balun is doing its job.

The SWR response turned out to be more broad-banded than predicted according to the IC-7300, it covers the whole 40m band only rising to 1.5:1 at 7.3 MHz (feed with 70 ft of LMR-400):

Photo of the antenna:

The longer radiator moves the current maximum slightly higher above surrounding clutter.

One radial runs out near the end corner of the house, one out to a tree in the back yard, and one along the under side of the deck, this also allowed mounting the balun out of the weather. With the shorter radials I was easily able to maintain ideal symmetry.

Compared to a 1/4 wave ground plane model same height above average around with four radials, the 1/3 wave vertical peak gain is 0.2 dB less but one degree lower at 22 degrees.

Some or more of that 0.2 dB might be gained back with the higher current maximum in the real world environment with ground clutter, and broader 1:1 SWR vs 1.3:1 or higher with a ~36 ohm 1/4 wave. Either way a negligible trade off (if any) for a much more convenient radial configuration and 50 ohm feed. Field strength readings would be the next step.

Noise floor is not too bad at S4 to S5, compared to S3 to S4 on my 130 ft doublet at 55 ft height.

We'll see how it works out :-)

Model file: GP-40m-40ft.

40m 2 Element Delta Loop

Parasitic (driver + reflector), reversible, direct 50 ohm feed, equal length 75 ohm sections for matching and the open stub long enough to reach a common switching point.

Recently during the middle of the day I noticed a local station here on the US west coast spotting EU stations on 40m FT8 via psk reporter. This is fairly unusual due to day time D layer absorption, but not impossible. I emailed asking for more info about the antenna they were using, they replied saying they had built a two element delta loop array based on 40 Meter Parasitic Delta Loop Array by W8WWV.

Trying to model this by hand in EZNEC the results were not great, especially trying to get a 50 ohm match. Since there are interactions with element spacing, resonance, etc - change one thing it throws off several others.

Decided to give this problem to the optimizer in AutoEZ. Optimizing for gain and direct 50 ohm feed, I let the optimizer adjust the length of the bottom wire, the height of both loops, and the feed positions symmetrically, and vary two equal lengths of 75 ohm coax for the open stub and matching section to keep it simple.

I was pleasantly surprised when AutoEZ found a perfect solution using two equal length sections of 75 ohm coax that will easily reach a common point, and provide a direct 50 ohm feed!

Searching around for information on designs using switched open stubs, there are a few which use 3/8 λ open stub for the reflector.

Interesting to note, the starting model I had used equilateral triangles (what I happened to have), the optimizer settled on right angle triangles (very close at 89 degrees). Agrees with accepted wisdom for vertically polarized deltas, see SCV Polarized Wire Antennas: The Delta Branch - L.B. Cebik.

On to the details..

 

Item	Measurement
Horizontal wire height above ground	3 m / 9.8 ft
Horizontal wire length	18.28 m / 60 ft
Height to apex above ground	12.31 m / 40.3 ft
Side wire length	13.04 m / 42.78 ft
Element spacing	7 m / 23 ft
Feed position up side	16.3% or 2 m / 6.5 ft
75 Ω coax length from each element	13.74 m / 45 ft (VF=1)

Each 75 ohm line meets at a common point:

• 75 ohm line connected to the driver matches the system to 50 ohms.
• 75 ohm line to the other element is left open circuit resonating it as a reflector.
• Direction reversed by swapping which is open and which is connected to the driven element.

With the 75 ohm lines being equal lengths and one is open circuit, the switching network/relay wiring is kept simple.

Current chokes at each loop feed-point: With the VF of the coax used measured and taken into account, there should be enough excess length to use for a current choke (winding it around ferrite) at each loop feed-point (the choke must preserve the line impedance and electrical length), and to reach a common point for switching.

The model uses bare 12 AWG copper wire, and VF of 1 for the 75 ohm coax. The model would need to be updated if using insulated wire and re-optimized, the VF of the coax being used would need to be measured with an analyzer and length multiplied by that number (e.g. 0.8 or what ever it is) to get the electrical length.

As a test when I updated the model using RG-11 factoring in VF and loss figures, there is a small 0.3 dB or so drop in gain, this will be partly from the SWR on the matching section and the effect of the open stub causing small losses.

Elevation Plot

Azimuth Plot

SWR Plot

Coax losses would smooth this out more

Now if only I had the room to build it :-)

EZNEC and AutoEZ model files: 40m 2 Element Delta Loop.

Dec 2024, I ran across The Parasitical Right-Angle Delta towards the bottom of https://antenna2.github.io/cebik/content/wire/hsyg.html, simpler system using shorted stubs with 75 ohm coax, and 50 ohm feed.

PSK31 Fldigi Macros for Field Day

These are the PSK31 Fldigi macros I setup for Winter Field Day last year.

I came across a lot of PSK31 activity by chance (7.070, 14.070), but it took a while to figure out how to take part..

Frustratingly the information needed to simply get setup and get going is not found in one place. I like to give points to field day/contest stations but not seriously compete. Are they trying to get more people into contesting by keeping it mysterious?

Info collected from:

• Winter Field Day
• ARRL Contest Sections
• KK4DSD PSK31 Field Day Macros

I set these up on an empty macro row in Fldigi:

ANS CQ (Answer CQ):

<TX>
<CALL> <CALL> de <MYCALL> <MYCALL> k
<RX>

W/FD Exch (Send exchange for your station, e.g. 1H is single home op, WWA is western WA):

<TX>
<CALL> 1H WWA 1H WWA de <MYCALL>
<RX>

73 (Send when your exchange was copied):

<TX>
73 de <MYCALL>
<RX>

QSO @>> (Start free text message):

<TX>
<CALL> de <MYCALL> <MYCALL>

RX (Go back to receive):

de <MYCALL> k

<RX>

HamAlert Automate Telnet Login

HamAlert is a useful tool to receive alerts for when a desired station appears.

I use this with the Club Log band slots integration to alert for new countries on bands I don't yet have confirmed.

With the Telnet option I keep a window open where the alerts scroll by quietly and I can glance at to see if there is anything new.

Typing in usernames and passwords is a chore, here is a shell script that'll auto login (replace username and password stars as required):

#!/usr/bin/expect

set timeout 30

spawn telnet hamalert.org 7300
expect "login: "
send "K1LH\r"
expect "password: "
send "*****\r"
interact

Here it is in action: