Optical system going NLOS

Thanks to the interest of a colleague in my optical experiments, I sped up the work on my MCW light receiver.

Using a 10mm red LED at ca. 30mA and the OPT201 without any lens or post-amplification I could make some spectrograms with Spectrum Laboratory.


First of all I studied the environment: the incandescent bulb produced a clear set of harmonics every 50 Hz, with those at n*100 Hz being stronger ("1"). Then the 520 Hz line is definately the laptop TFT dimmed backlight ("4"), since at full brightness the signal disappears. Notice the result of a mixing between 488 Hz MCW signal and the strongest 100 Hz harmonic ("2"): this certainly occurs at electrical levels, not optical.

Next was a ca. 4.5m LOS test, with the LED light overloading the sensor. Even the cameraphone could see it:


I used my CW memory keyer to send a meaningful message (pre-recorded holiday CQ) at the lowest possible speed, about QRSS0.5 (0.5 seconds per dot).

In total darkness except the laptop screen, the spectrogram looked like this:

A quick test at 15 WPM revealed a perfectly readable signal. The shade effect of a hand obstructing the light beam is surprisingly strong. A wav recording is available, if anybody wants to hear it.

Then I moved the TX further away in another room, for a total of 11.5 metres Non Line Of Sight (NLOS). Only after my eye had adjusted to darkness I could see some weak red reflections on objects in the intermediate room, but the spectrogram was faster:


There it is! My QRSS CQ was on the screen, fortunately not masked by the laptop backlight. Remember the receiver had no focusing lens whatsoever.

I forgot to measure the response of OPT201 with a 3.3 Mohm series feedback resistor. Next test could be 300m LOS still without lens on the receiving side.

Stay tuned! Or better.... watch out! :-)

NiMH constant current charger

I started working on this circuit long ago, and never used it thoroughly.

Given that NiMH cells can be slow-charged at a constant current rate for a given amount of time, I built this circuit. Provided the timed slow-charge condition is verified, you can live without end-of-charge algorithms.

Some charging facts (if I remembered where I read this, I'd credit the author).
A NiMH cell, if charged at C/10, in 10 hours will reach approx. 66% of the fully charged state. You achieve the remaining 33% with 5 more hours. That's where the magic 15 hours come from.

My constant current circuit required a PNP transistor. I picked a BD646 from the junk box in a TO220 package. Since the transistor had to be floating from ground, I needed a way to attach it to the metallic enclosure for thermal dissipation without electrical contact.
Forgot about nylon screws, a search through the electronic junk showed this solution: wrap the transistor in what I believe to be a mica foil and then press it against the heatsink/box.

This is how it looks like:




I recharged a 9.6V pack while watching the temperature and the current. The transistor runs barely warm, while the power resistor heats up considerably.

The pack under charge will increase its voltage, thus effectively reducing the charge current, in a auto-stop fashion. But since this occurred quite early in my charge cycle, I had to increase the input voltage to more than 14V.

One word of caution about the plugging sequence.

Charge start: connect the power supply and then the battery pack
Charge end: disconnect the battery pack and then the power supply

Otherwise the pack will discharge into the power supply. Probably a 1N400x diode on the +Vcc line blocks the process and allows to use a timed AC socket.

The Amateur's Code

I'm copying and pasting this text here for future personal reference. A Good Reading anyway!

The Radio Amateur is

CONSIDERATE...never knowingly operates in such a way as to lessen the pleasure of others.

LOYAL...offers loyalty, encouragement and support to other amateurs, local clubs, and the American Radio Relay League, through which Amateur Radio in the United States is represented nationally and internationally.

PROGRESSIVE...with knowledge abreast of science, a well-built and efficient station and operation above reproach.

FRIENDLY...slow and patient operating when requested; friendly advice and counsel to the beginner; kindly assistance, cooperation and consideration for the interests of others. These are the hallmarks of the amateur spirit.

BALANCED...radio is an avocation, never interfering with duties owed to family, job, school or community.

PATRIOTIC...station and skill always ready for service to country and community.

--The original Amateur's Code was written by Paul M. Segal, W9EEA, in 1928.


[...meanwhile in the lab a constant current NiMH battery pack charger has been completed and tested...]

18 km per liter = 42 miles per gallon

I've read on CNN.com a long article about hypermilers. I've read on WIRED (April 2008) about a fake company that promised electric cars and, to go with them, a Smart Fortwo that scored an eco-friendly 37 mpg (15.7 km/l).

Yesterday I filled the tank on my FIAT Seicento (1100cc unleaded fuel engine) with 31,61 liters. I had driven 575km (357 mi), on highway, countryside (80%) and suburban, with an average 70 km/h (44 mph) speed limit. With some easy math it turns out to be 18,19 km/l (42.78 mpg). Cool!

My urban average is between 14 and 15 km/l (33-35 mpg) driving 20-25 km per day.

Field Day Logging and the Dupe Sheet (on paper)

If you've browsed through my past posts, you probably know I like to do outdoor VHF contesting. Since I usually carry my station on my shoulders (from battery to antenna), there's no way I would take a laptop with me. Therefore all the logging is done on paper, using a homemade logbook.

I have produced and published two PDFs with either A4 or A5 size pages (scroll down my website to HAM Travel section), the latter being much more convenient when there is no chair and table at the operating position.

Each page obviously stores a limited number of contacts so soon the list of worked stations gets out of sight. In the old days without real-time computer logging, how did contesters avoid duplicated QSOs? Here's a tip I have not seen mentioned in the last years: use a dupe sheet!

What is it? The dupe sheet is a separate page where you copy all worked callsigns, sorted by the first suffix letter, after each QSO. If you turn page on the main log, the dupe sheet will stay under your nose for a quick lookup. During the post-contest log typing, the dupe sheet provides a callsign cross-check to minimize bad/quick handwriting errors.

The dupe sheet from my Alpe Adria VHF 2008 Contest.

From the picture you may also spot another field day tip: you need a sure-write mean of writing. Something that works below 0C/32F and upside down (as well as in absence of gravity). While a scalpel or a chisel might do, they're not fast enough for contest logging. A pencil does the job. I also carry a felt-tip marker (OK for low temperatures).

Open project of keypad for FT-817?

I posted this request on the GQRP reflector.

I am looking for an external keypad to match my FT-817 that can be built at home. Has it ever been published on SPRAT?

I've seen a couple of commercial products whose cost is equivalent to setting up my own development station, since I can master both software and hardware programming.

Yesterday I operated 6 hours /P in the Alpe Adria VHF contest and noticed that I'd like to have direct access to, in descending order:
- VFO A/B control
- Power setting
- Direct frequency dial
- Metering control (Pwr, Mod, Alc, Swr)
- VOX on/off
- Operating Mode (but this control has dedicated buttons anyway)

If there is no known open (= free circuit diagram and microprocessor code) design, I will develop my own external keypad and share it.

I received no feedback, so either everyone is on holidays or the world doesn't need an(other) FT817 external keypad.


Update 2008-11-24: the IK1ZYW keypad is now real! See newer blog posts or its homepage.

My QSL for 9A/IK1ZYW, Summer 2008

I had a little more than 50 QSOs from Rab, nevertheless I wanted to design a nice QSL front.



This originates from a digital picture I shot, some work on the computer and printed at the photo shop around the corner. I printed it in 10x13cm format, and will cut the excess bottom band to fall within QSL bureau 9x14cm limits.

The bottom band also carried an experiment: how small can the text be to stay readable (with magnifying glass, if needed)?

Using a pro service for printing is both cheaper (30 eurocents/pic in small quantities) and guarantees a longer lasting product than home printing.

I will honor all QSL requests for my contacts from 9A of July 2008. I am not sending out first.

Some radio-activity from Rab, IOTA EU-136, IOCA CI-096

2008/June/29 to 2008/July/12: 9A/IK1ZYW on Rab Island, Croatia. References IOTA EU-136 and IOCA CI-096.

Equipment:

• 12V 7AH SLA battery
• FT-817 at 5W
  
• homebrew CW paddle and memory keyer
• homebrew switched L tuner
• 12m vertical wire radiator + counterpoises
• pencil on block notes for logging
  

Being on a family holiday rather than a DX-pedition, time and energies for radio were limited. HAMming time was confined at night, after 23 local time, or during afternoon baby naps, when the operator didn't prefer to take a nap as well...

One HAM-dream finally came true: operating from the sea shore. The 24th OQRP Contest and the visit of XYL's friend allowed me for a little outdoor activity in the bushes of Gozinka cove.



Even though a couple of contests were around, 20m and 40m bands were quite dead for a Saturday afternoon. Was the propagation on holidays too?! I didn't feel any salty-water effect/improvement!

I continued the OQRP contest from the apartment terrace, close to downtown Rab. The antenna was ca. 12m of wire held vertical with a 9m fiberglass fishing pole and one counterpoise of ca 8m tied to the metallic terrace fence. With a switched L tuner I could get a proper match from 80 to 10m.


In the OQRP Contest I worked 38 stations in 15 DXCC entities. I worked everyone I could hear, but did not look for non-contest stations to increase the QSO count.

Overall I had more than 50 QSOs in two weeks. Every time I could be on the air I did manage at least a QSO. 30m was the most prolific band during non-contest periods.

A big thank to all the operators I worked, both in and out the contest. I will reply to all QSLs received with a photographic card I'm assembling with the pictures I took on the island.

72!