29 November 2011

UV-3R VHF second harmonic

Definition: a second harmonic is a spurious emission of a transmitter located at twice the fundamental frequency (or first harmonic or "dial"). In most cases the second harmonic is not produced on purpose.

UV-3R, especially the single-line display, exhibits too little suppression of the second harmonic of the VHF transmitter. This occurs when the RTX is used on the VHF HAM band (144-146/148 MHz). Suppression gets better and within required limits when the VHF transmitter is used above 150 MHz.

This means un-modified UV-3R is not certified for VHF amateur radio operations. Transmitting, say, at 145.500 MHz, will result in a parallel transmission on 291.000 MHz, which is probably allocated to a Defence Ministry. In the Files area of the Yahoo! group some LPF modifications have been measured and described in detail. Unfortunately they are not for everyone.

So, what options do I have?
  • use unmodified UV-3R on VHF only if strictly needed, being aware you might be disturbing communications around 290 MHz. On UHF the little "R" is spurious emissions compliant.
  • insert a VHF band/low-pass filter between UV-3R and the antenna
  • have someone apply the LPF modification
Why is it so? No one has figured out why the VHF signal is so dirty. It might be a driver/final wrong bias current. UV-3R Mark II is apparently performing better, but still above the required suppression level.

28 November 2011

Back up pictures during long trips

I have had an interesting chat about methods for preserving your digital pictures (movies) while being out on an important and long trip. In other words, how to make sure you precious shots come back home with you.

Assumption: you have a way to read memory cards through a computer (not necessarily yours) or use a stand-alone card copier.

Memory cards are pretty cheap. So, why not bringing along an additional extra set, making a copy of a full card and sending it to your home address? You may even prepare addressed envelopes with a thin cardboard reinforce inside. Stamp can be bought as if you were shopping for postcards and you don’t even need a trip to a post office unless you want a Registered letter. Better to send one card per envelope. Once you have safely backed up your picutres (at home), extra cards can be reused for the following adventure.

If you know a trustworthy local, leave her/him your backup copies, either an external HDD or extra memory cards. This will minimize the risk of loss/damage on the journey back home too. If nothing bad happens to your "originals", she/he will keep the hardware afterwards as a reward for the service offered.

Online storage populated overnight is another option, if your hotel has a fast and cheap Internet connection. (If you carry your own laptop consider using Dropbox through my referral link.) But if you shoot a lot (and in RAW ;-) ), it might not be practical.

Worried about someone stealing your shots? Either the postman or your local contact person? Encrypt the backup card content with a tool like TrueCrypt. Format the card/disk to resume full, unencrypted, functionality.

21 November 2011

Fast knob rotation solved

Good news: I have solved the puzzle of missing steps with fast rotary encoder rotations. It was a piece of inefficient code, which has now been rearranged using AVR's Pin Change INTerrupts ("PCINT").

The 96 states / 24 cycles per rotation encoder is now read properly: it doesn't miss a step.

Now the FR/IFR firmware has to be adapted to a new form of interaction...

09 November 2011

Hey! Isn't that a knob?

It is a knob indeed. I have started tests of a quadrature rotary encoder connected to my (Interactive) Frequency Reader development board. This extension will allow to tune the FT817 as if we were rotating the main knob on the front panel.

The firmware is able to read the rotation direction and increase (decrease) the VFO frequency accordingly. I am having troubles with fast rotations, something that should be mitigated with the use of a larger knob or a less sensitive encoder. I would like to avoid the addition of a binary divider between the encoder and MCU.

03 November 2011

Broken AF on Canon 18-55 IS lens, what about IS? - part 2

Previous blog post ended with a question: "if the AF is lost, how about the IS? How to find out?"

Many people say that you can hear the Image Stabilyzer in action as soon as the shutter button is half-pressed. Honestly, on the 18-55 IS lens, I didn't feel/hear anything. Other references online tend to confirm that the lens is "quiet" and you can't tell the IS is in action.

Another test is to shoot two pictures, with and without IS, freehand, and look at the difference. You need the proper subject and light too, and perhaps more than just a couple of shots (and maybe 10 coffees...).

Then it occurred to me once that if I hold the camera lens against my ear (grab the camera with the right hand, so the bottom side of the lens touches the right ear) and half-press the shutter button ... I can hear a faint ringing, like a few small bells at the other end of a tunnel. When the IS switch is turned off, no ringing can be heard.

What does this mean?

Well, in my case it means that probably the IS is still working despite the AF being out of order. If you have doubts, listen closely to your lens whispers.