Emergency Power and the VX-170 HT

I picked up a 5AH battery and a charge controller from All Electronics to assemble an emergency backup power supply for my VX-170 HT, and when I tested it was surprised at what happened...

According to the manual for the HT, standby current was 20.5 ma (in saver mode), so I figured a drain of 20.5 maH on a 5AH battery should last about 11 days.  So after I charged up the battery and put the HT on it (just on saver mode), imagine my surprise when it drained the battery in a day.

Turns out that with the battery pack installed, and even with the battery pack fully charged, having the battery pack in the HT increased the current drain to nearly 200 ma, giving me my 25 hour life!

I've now pulled the battery pack and just run the HT off the SLA (Sealed Lead Acid) battery, and so far the voltage on the battery is holding up much, much better.

In an actual emergency, I expect the the drain to go faster, and have budgeted 20 minutes per hour of standby, 30 minutes of reception, and 10 minutes of transmission, 12 hours a day, for a life of about 6 days on the SLA (with then about 2 more days on the internal battery).  That gives me 8 days, which should be enough to get some sort of power back online...

Random Hacks of Kindness

If you go to http://www.rhok.org, you'll see an event that took place with software developers and groups involved with disaster relief.

Here's an article on the event: http://news.cnet.com/8301-27080_3-10398073-245.html

Other than some comments by readers of the article, there is no mention of amateur radio. Which is kind of interesting, because first place went to an application that relies on cellular phones to work. Well, I guess we'll see how that works out in the next disaster.

Wide AF SSB Radio for Digital

Doing digital over SSB HF is pretty nifty. Your computer essentially processes several channels of data at once, and allows you to monitor several QSOs. When you transmit, even though the radio is capable of transmitting a 2.5khz wide signal you only send a few hertz, allowing you to drop in your signal inbetween everyone else's.

In many ways, it's a software defined radio -- the real radio is just dropping a 2.5khz wide band of HF down to audio frequencies to make it easy for the computer to deal with.

But 2.5khz isn't really optimal for digital, it's optimal for voice. And as far as making do with existing technology, it's great.

But why not build a digital-oriented, low cost (!), SSB transceiver that passes through 10khz of bandwidth instead of 2.5? It would be useless for voice, for sure, but since sound cards can digitize at 44khz they'd have no problem with 10khz of spectrum all at once. Even 5khz of AF bandwidth would be twice as useful!

HF Email, Winmor, and AMPS, TDMA, CDMA, etc.

A small thread on the Winmor beta-test group on Yahoo groups arose around the subject of needing more Pactor (and eventually Winmor) stations because accessing email over HF is single threaded. Only one user can access a station at a time, and because the baud rate is so low for HF a station can be tied up for an extended period of time.

This kind of problem has been solved many times before. In the first generation of cellular phones (AMPS), an analog phone connection would tie up a channel (pair of frequencies) at the cell node for the duration of the call, much like the current HF approach does.

This first generation approach offers us some ideas for ham radio. The first is to use multiple channels to talk to multiple stations. In AMPS the channels were full duplex (using a pair of frequencies), but the same approach could be done with half-duplex.

This would probably require some custom, and very non-standard, radio equipment at the server end to handle multiple channels at once. It would be an interesting SDR project. Or one could just install multiple radios. In AMPS, there were two different bands for transmitting and receiving at the cell node, so duplexers are used to share antennas. This works well for a full duplex connection.

Even for a single radio, the Winmor channels work in 500hz bandwidths (and 1600 hz as well, but let's ignore that). You could easily put three of these in a standard SSB signal with spacing and have three "channels" for a single, normal radio. This gives a lot more capacity, albeit with more complexity. Issues around synchronizing the transmit and receive cycles on each channel arise, but that can be solved...

2G cellular moved to CDMA and TDMA digital, allowing sharing of channels. For HF email, this moves us into the realm of things like Aloha and Slotted Aloha, which are known, although not terrible efficient, means of coordinating multiple stations on a single frequency. But if the goal is to provide service to all and not allow a single user to "hog" a relay station, that would work.

Clearly, using an off-the-shelf radio is limiting (but not totally limiting), but custom hardware would really open this up to some sophisticated usage!

ARRL Radiogram from 1928

Here's a radiogram my grandmother received from my grandfather in 1928 ...

Click on image to see full size

Pretty neat!!

LDG AT200Pro antenna tuner, initial impressions

I just got the LDG AT200Pro and have some initial impressions...

• It's great.
• It's louder than I expected.  It uses relays (yay, I love relays :-) ), and cycles them on and off very quickly.  My wife thought it was broken, and I had to assure her that was normal behavior.  You would not want to try to sleep near it when it decided to retune.
• When I switch bands, reception is muted until I do a quick transmit to let it know the new band I'm on. Didn't expect that, although in hindsight it's obvious.
• None of there online documentation makes it sound like it comes with a power cable (which it does, unterminated).  I thought I was going to have to visit "The Shack" to get the right connector to build my own!
• Although I added its power connectors tapping off the main supply, this is going to push me to get the Power Pole distribution system working.
• It has a "rebate" of a 1:1 or 4:1 balun.  I don't have a need for one right now, so I have to guess what I'll need in the future.
• The bar graph display of power and SWR is a lot more usable than I expected.  Still, it seems to me for a similar cost they could have put in a few 7-segment LEDs instead (or the n-segment ones that display letters).
• The user-interface is modal and complicated once you get past basic tuning (basic tuning is trivial, but all the features are going to take a while to figure out).  Is there a rule in ham design that says everything has to be very modal?
• It seems to re-tune more often than I expected.  I guess I thought there'd be a tuning for a band, but any movement off a frequency to a nearby one seems to be a cause for re-tuning.  Again, not a complaint, just an observation...

So far, I love it.  What an improvement over my MFJ-871 that had some "factory defects" and was very touchy about tuning...