Seductive serendipity / Verleidende serendipiteit

March 25th, 2014

Beverage transformers for 7QNL

To fight very likely QRN in Africa for 80, 40 and 30m (open) Beverages are envisaged.
Targeted length is 2λ @80m. I plan to roll out four (open) Beverages to obtain 8 ‘directions’.

A Beverage antenna is actually a transmission line above ground. Its impedance
depends on the wire diameter and wire height above ground.

With heights around 1 – 2m and wire diameters of 1 – 2mm the impedance amounts ~500Ω.
When using 50Ω feedline the transformation ratio has to be 10, but 9 is also ok.
It’s not that critical. For 75Ω feedline transformation ratio is around 6.7.

What is more critical is that the received EMF is not dissipated in the transformer itself!

A general rule of thumb is that the reactance of the windings has to be 5x the connected
impedance. I always use 10x, thus XlBev = ~5000Ω, XlRX = ~500Ω for the lowest
frequency, i.e. 3.5 MHz.

I had some binocular cores lying around, with a measured Al = ~0.8 μH.
Stacking three of these cores results in an Al of ~2.4 μH. Rumours tell that stacking
cores improves S/N as relatively ‘more’ copper is ‘shielded’ inside the (binocular) cores.

Since Xl = ωL = 2πfL -> L = Xl/2πf = 5000/(2π*3.5E6) = 227 μH

Further, μH = Al*N² -> N = √227/2.4 = 9.7  ->  9 turns will do for the
secondary (Bev) side, 3 turns for the primary (RX) side.

For 75Ω feedlines 10 turns secondary (Bev side) and 4 turns primary (RX side) suffices.

I used this transformer in conjunction with a 100m long West Beverage during the 2014
CQ160 CW contest, and it delivered me quite a few Caribbean stations/multipliers, which
were barely/not audible on my reversible NW/SE and NE/SW 200m long Bevs.

However, my ‘biggest discovery’ was during the PACC 2014 contest where this
‘West Beverage’ was left open at the far end. It received amazingly well on 40m, and
outperformed the TX-deltaloop (of course) and ’160/80m’ reversible Beverages
in more than a few cases. During the contest it became my default 40m RX-antenna.
Nice contact was with ZL1BVB on 40m. Listen here.

Pictures of the transformers are depicted below (click on images to enlarge in a new tab).

The ‘West’ Beverage (feed point)  itself is shown below (click on images to enlarge in a new tab).


March 16th, 2014

CW ‘Plan B’ (CAT) for 7QNL

For my planned DXpedition to Malawi (7QNL, May/June 2014) I made an Artisan (Win)Keyer
to be used in conjunction with N1MM-logger. This contrapsion works very well (at home/on the bench).

However, when abroad, what happens if the Arduino ‘resets’/stops/<fill in another issue> ?

Of course the Arduino IDE is present on my laptops, and issues may be ‘programmed away
on the fly’.

But…  what if the hardware (e.g. on the Arduino board itself) malfunctions?

OK, take/bring another Arduino (of course). But what if this one fails too (for whatever (same) reason)?

A priori, ‘Plan B’ is mandatory. Actually, ‘plan B’ nowadays equals ‘plan A’ in Madagascar (5R8NL) 2007:
Use the same (serial) port for both CAT (‘frequency administration’) and (CW) keying the transceiver,
in conjunction with a separate (hardware Boolean OR’ed) keyer (I have envisaged)

In 2007 (5R) a default laptop owned a ‘decent’ RS232 interface, and I designed a RS232-compatible
CAT + CW interface (using two transistors as levellers and inverters) for my rig. It performed well.

Nowadays USB rules.

A few months ago I ordered some ‘FT232RL’ USB-interfaces (from Ebay) to program Arduino Pico’s.
The FT232RL chipset is interfaced to my rig in an utterly simple manner: just connect the wires.
No MAX232′s, no inverters, no levellers, no optocouplers, no PCB designs, etc..

Repeat, connect the proper (RX/TX/DTR) wires …  (provided your rig has TTL-inputs/-outputs).

For whatever reason I cannot not get ‘CTS’ (= ‘PTT’) working (perhaps one of the 3.3 / 5V pads have to
be shortened on the USB-FT232RL interface board?) and DTR keys the rig, and when I send the software
‘PTT command’ in N1MM-logger to my rig everything works well, also sequencing (the amplifier) <– most important!

DTR of the FT232RL chip is configured as ‘CW’ in N1MM-logger, and is ‘interfaced’ through a diode (BAT86).

That’s all (for ‘Plan B’) from 7QNL/ PA3FYM

Below a picture of ‘Plan B’ (no…, no casing –> casing = weight. Cable tie is  … handy ; -)
(click on image to enlarge in a new tab)

March 4th, 2014

Artisan Keyer

During my upcoming planned DXpedition (target to be revealed later) my prime focus will be CW.
Of course, phone contacts are indispensible, don’t worry ; -)

Although having successfully contested with N1MM-logger, in conjunction with its serial port interface,
I was thinking about eliminating of SPOFs  (single point of failures) while abroad.

What if there is no power supply, other than some car batteries and/or my laptop fails?

Although my rig has an internal keyer, this feature has to be disabled when using e.g. N1MM-logger.
My first project was to assemble my low power K1EL K12 CW-keyer kit I bought a year ago.

This keyer was also a nice candidate to house a paddle I bought a while ago at a flea market for 1 euro.
Contrary to my Bencher this paddle is light weight (cf. travelling by airplane!).

My initial idea was to logical ‘OR’ the keyer and N1MM-logger with diodes with my rig.
This allows me to use the paddle when convenient, and also let the K12-keyer provide e.g. serial numbers
in contesting mode in case my laptop might fail.

After I showed the result of the keyer to one of my friends he advised me to get a ‘WinKeyer’,
for my convenience and let this WinKeyer do the CW-timing, instead. He also offered me one of his WinKeyers.
Despite the nice gesture I want to be as independent as possible, and decided to dig into the ‘WinKey’ matter.

A ‘WinKeyer’ is a stand alone CW-keyer which interfaces (through USB) logging software (e.g. N1MM-logger).
The logging software does not have to perform the CW-timing (I am told that this uses significant
amounts of CPU power in N1MM (???) ) and focuses on what it has to do: log contacts.
Preprogrammed function buttons (F1 – F12) now send a string through the serial/USB port towards the Winkeyer.

During my research I quickly found some Winkeyer alternatives, of which the Arduino CW keyer of K3NG
was the most elegant: simple, cheap, and … open source. More than perfect!!
Anthony reverse engineered the K1EL Winkeyer protocol (apparently the de facto standard in Winkeying).

Within no time I built the keyer with an Arduino Nano on a piece of breadboard
It worked very promising after disabling the auto reset (ASR) facility of the Arduino with a jumper.
There were some other operational issues, but these can be resolved in the (open) source code.

Contrary to the ‘well known’ commercial guys into CW-keying, Anthony K3NG is very co-operative.
Concerning his code he has an open and constructive mind towards requests, ideas, bugs etc.
After I mailed him some observations/suggestions he proposed solutions very quickly : -)

Below two pictures of my Artisan Keyer (how I call it). Note: the casings are home brew and have to be finished.