| "Technical Watering Hole" for popular projects, links and |
| other reference information of interest to QRPers and Homebrewers |
Kit Building Service -- Mike WA6OUW, at Kit Builders
This service offers soldering or assembly using surface mount or thru-hole components for kits. Mike has done assembly
work for NJQRP and AmQRP so we know the quality is there! If you have a kit that you can't or don't have time to build,
Contact Mike at his Web site:
Kit Builders
Club Project: Frequency Counter -- Mark Phillips G7LTT
Here is the link to my website for the NJQRP club project we have going ...NJQRP Frequency Counter
Club Project: 10MHz Frequency Standard -- Mark Phillips G7LTT
Here is the link to my website for another NJQRP club project we have starting up ...10 MHz Frequency Standard
Lithium Iron and Paper Batteries -- Ron McConnell W2IOL
HFPack currently has a discussion on Lithium Iron Nano-Phosphate (LiFePo4) batteries that is very interesting. The batteries seem to have all the advantages of other lithium based batteries with size and weight, but are safer. They are being used by the radio controlled model folks. Hams are repackaging DeWalt 36V battery packs. I plan to check those out. See ...
Reference Links for GPS+GSM/GPRS+A/D+GIO+Python Interpretter -- Joe Jesson, KB9LZB
Jackite fiberglass Extension Pole -- Vince WA2ECP
Vince won a Jackite 28 foot telescoping fiberglas pole at the FDIM dinner in Dayton this year. It looks like it will be a nice portable antenna mount. It is quite sturdy but, like most poles of this type, the top section is thin and can't support too much weight.Pulling the frequency of a crystal VFO --
Joe Jesson, KB9LZB
Interesting book on the history of the crystal oscillator and the issues getting suitable quartz blanks and crystals on-frequency during WW II... "Crystal Clear", Richard J. Thompson, Jr, 2007, IEEE Publishing
Wireless tools in the Auditor/backtrack CD -- Joe Jesson, KB9LZB
Cool & Capable Embedded Computers for Less Than $100 --
Mark Phillips G7LTT
The AMD Personal Internet Communicator has recently (2006) ceased production and outstanding inventory has been bought out by
Data Evolution Inc whom have renamed it as the "decTOP". There seems to be two variations of this device. The PIC itself ran
WINCE and in turn had a web browser/email client/etc allowing access to the Internet and appears to be locked in some fashion
to the WINCE OS by way of the BIOS. The models currently shipping (June 2007) from Data Evolution Inc have no OS installed and
can use bootable USB devices as well as the HDD. I have been sucessfull in getting AstLinux to install and run on this machine.
This page will attempt to explain how I did it.
Buyer Beware: Making this unit into a working computer takes more than average computer skills. As with most surplus equipment, you are mostly on your own. Some have reported that Data Evolution Inc. is not responsive to problems or service requests beyond the initial purchase of the unit.
TAK-tenna
Compact electrical half-wave dipole antenna --
Steve Tetorka, WA2TAK
Steve makes and sells the "TAK-tenna" a compact "rotable, portable, stealth, perfect backup antenna. It is an
electrical half-wave with radiating spiral end elements direct fed with 50 ohm coax on a resonant band. The
user selects the resonant frequency during the tuning process. It can use coax+tuner or twin lead+tuner and has
been power tested to 1000 CW watts, key down for 30 seconds (and 1400 Watts PEP) with no heat sensed on the
antenna wire or coax feedpoint when touched by hand after tesing. There are no lossy matching components
anyplace in system. Users report a 10 to 14 dB signal increase in transmit with a 90 degree rotation of the 30
inch boom. It has a low SWR across the band"
Cutting holes in mint tins -- Ron,
WB3AAL
Here is a way you can cut a clean hole in a mint tin (like Altoids) without deforming the metal
or ending up with burrs. Fill the tin with water. Place in the freezer over night. Check it out
the next morning, if it is frozen top off with more water. Let it sit for one day in the freezer.
In the meantime make a template up where you want the holes. Take the tin out of the freezer and
tape the template to the time. Use a sharp bit and drill your holes. With a sharp bit you will
only need to apply small amount of pressure, should not have to de-burr the holes.
Q-Dope
You used to be able to buy Q-Dope at Radio Shack many years ago. It's basically a liquid solution
of polystyrene. Here's a link that talks
about making your own. The author mentions buying toluene (toxic!) and using that for the solvent,
but also says that acetone is a safer alternative. So acetone from Home Depot and some polysyrene
peanuts from your latest package to arrive and you have some low loss dip for toroids.
RS232 Serial Wiring and Specs
http://www.arcelect.com/rs232.htm More than
anyone might ever need to know about RS232 serial wiring and specs, but it's very complete indeed.
"RF Circuit Design" --
A very useful book that Ted Groke obtained from Amazon, authored by Chris Bowick. N2CX mentioned
that this is a classic instructional book that he's used in the past to teach RF concepts and
principles to his team at work, and it truly looks like a good one for the shack.
"DSP Signal Processing"
A hard copy of the increasingly-popular book that guys have seen before in full PDF format online
and useful for starting to experiment with the KK7P DSPx card. Dave Gwillim picked it up from
Amazon (ISBN 978-0-7506-7444-7, by Steven W. Smith).
Islander Pad Cutter (replacements)
Here's a possible replacement for the Island Pad Cutter
http://www.dadsrockshop.com/diamond_drills.html.
They have quite a variety of sizes, including some small ones that would work for SM components
and .05" pin spacing MPUs. Prices are fairly reasonable.
Battery holder with the integrated DC to DC voltage converter
This link (http://store.bodhilabs.com/) is for a line of
1.5 volt/3.0 volt to 5 volt (100mA/200mA @ 80% efficiency) converters that have a nice low profile
(no large toroid). Available with AAA or AA cell holders. They normally are available from SparkFun
but they were out of stock. I checked the BodhiLabs web page and they are selling direct for the
same price but with FREE USPS shipping. Great for small MPU projects. "You will never
look at a battery pack the same way again! It looks like a normal battery holder, but on its back,
there is a DC-DC switch converter circuit to generate a regulated 5.0V (3.3V) supply. And best of
all, this regulated output voltage is maintained throughout the normal life of the battery, and at
more than 80% efficiency. Now you don't have to design the voltage converter on your board, just
grab our VPack and off you go."
Semiconductor Analyzer Kit
http://www.m3electronix.com/sa.html.
Similar to the Peak version we've talked about and shown many times at the NJQRP meetings.
It's a very handy thng to have at arm's length on the bench.
Digital LCR Meter
http://www.m3electronix.com/featureslcr.html.
It has a lot of great measurement features.
AA-1 Enclosure from American Morse
Here's a very cool little aluminum box for projects designed for the popular Altoids mint in boxes,
like the KD1JV ATS-3A transceiver. Much more durable than the Altoids tin. As W6AME
writes ... "Pull your nice rig/accessory out of that flimsy Altoids tin & plug it into
a super durable, high-quality CNC hogout enclosure! Made from 6061-T6 Aircraft Grade aluminum, the
AA-1 has a top cover easily rotated open or removed entirely in seconds. The AA-1 is naked and
undrilled, ready for your application. Slightly taller and with tighter corner radii than the Altoids
tin, the AA-1 will hold anything an Altoids tin will hold & more." The box can be purchased
for $24 online at
http://www.americanmorse.com/aa1.htm.
USB-to-RS232 Adapter
Here's an inexpensive adapter available from Parallax, Inc
(
http://www.parallax.com/detail.asp?product_id=28030)
that allows you to connect a project that only has an RS-232 serial port connector (e.g., the Micro908)
when using a computer that has only a USB port. Lots of people had been looking for such an adapter in
the past to use in control of their serial projects, but few suitable ones worked. This one works
fine.
Mini Keyboard
Another very cool find on Parallax is a mini keyboard with a standard PS2 connector ... great for use
with the Micro908, since we no longer have the Dauphin keyboards available. This one from
Parallax is so much better, thinner and sleeker, and for the same low price of about $20.
http://www.parallax.com/detail.asp?product_id=32351
(The keyboard George received was nicer than the one pictured on the site ... thinner, shiny aluminum.)
Small, Amplified Speakers
N2CX found a cool little battery-powered amplified dual speaker assembly found at Walgreen's and the Five
Below store. With a standard 1/8" plug on the end, it's great for a portable speaker on the QRP
rig ... not great fidelity with those tiny speakers, but works pretty well for CW when you need to have
generally audible reception. See photo here.
"Practical RF Design", by Doug DeMaw
This book is very informative with lots of circuits and description of operation, yet in typical DeMaw
fashion being really easy to understand and usable on the bench. It struck me as being a simpler
version of the very popular "Experimental Methods in RF Design" by Hayward, Campbell and
Larkin. The book can be purchased online for $19.95 from MFJ by going to
http://www.mfjenterprises.com/products.php?prodid=MFJ-3507.
LTSpice
A free download of LTSpice is available from
http://www.linear.com/designtools/softwareRegistration.jsp and there is an active Yahoo group for it
at
http://tech.groups.yahoo.com/group/LTspice. It uses a capacitor model for fast simulation of quartz
crystals. KB2TQX found it a bit fiddly to hand calculate the motional inductance and capacitance
values, so he wrote a small utility to do the calculations. This led to a more general resonant LCR
calculator. We have them available here.
WSJT Program for Meteor Scatter & EME Communications
WSJT is a computer program for VHF/UHF communication using state of the art digital techniques.
It can decode fraction-of-a-second signals reflected from ionized meteor trails, as well as steady signals
more than 10 dB weaker than those required for conventional CW. One of its operating modes is particularly
well optimized for amateur EME (Earth-Moon-Earth) communications. WSJT is open source software and
is licensed under the GNU General Public License. See full details at
http://pulsar.princeton.edu/~joe/K1JT/)
Boy Scout Radio Merit Badge web site
Gary K2GW recently conducted the 3rd annual Boy Scout Radio Merit Badge Day at Sarnoff Labs, where 49
scouts got their merit badge. He developed a new Radio Merit Badge Web site to assist Boy Scouts
in meeting the Radio Merit Badge requirements, also providing free instructional materials for Radio
Merit Badge counselors. According to Gary, "The best way to learn about radio is by doing, but
this site will help you learn a bit beforehand, so you can get on the air even faster! And you'll be
able to pass your requirements easily when you do meet with your counselor." Gary's 30 years of
experience as a Radio Merit Badge Counselor for a few hundred Scouts is the foundation of this Web site.
You can see the nice write-up on the ARRL web page
(
http://www.arrl.org/news/features/2007/01/26/1/?nc=1)
and the full description of the program on Gary's web site at
http://k2gw.tripod.com/radiomeritbadge/.
MPS430 Microcontroller Development- Great for QRP applications!
Dave KB2TQX tells about the TI MSP430 homebrewing capabilities and inexpensive tools available. You can
check out all the TI MSP430xxx development information at the popular SparkFun site
http://www.sparkfun.com/commerce/categories.php?cPath=2_11, as well as other MPU development stuff
there. The TI ez430 Development Stick is about the same size as a USB thumb drive. Contains programmer
and a tiny MSPF2013 target board (14-pin TSSOP package). The '2013 is a 16 MIPS MPU with a 16 bit Sigma
Delta A/D converter, 2K Flash, 128 bytes of RAM, 10 GPIO ports, SPI and I2C and UART. Cost $20 , comes in
a DVD case with CD containing IAR Kickstart C Compiler, Assembler, IDE, Debugger (single-step etc.), USB
drivers etc. The spec sheet is here and online here:
http://focus.ti.com/mcu/docs/mcuprodmsptoolsw.tsp?sectionId=95&tabId=1203&familyId=342&toolTypeId=1
(scroll down)
http://focus.ti.com/docs/toolsw/folders/print/ez430-f2013.html#description. For another $10 you
can get 3 additional target boards that carry the MSP430F2012, which has a 10-Bit, 200-ksps A/D Converter
with Autoscan instead of the 16-bit SD A/D that the '2013 has.
http://focus.ti.com/docs/toolsw/folders/print/ez430-t2012.html. If you want to be able to do embedded
programming while you are airplane bound this is perfect. No wires, no JTAG plugs etc. The MSP430 series
are really low power. Active mode at 1 MHz 2.2v just 250 microamps. They will run down to 1.8v and up
to 3.6v. I have attached the PDF of the specs for the MPUs used in the ez430. Oh yes, EFFICIENTLY
programmable in standard C!
3.3v/5v plug-in power supply
Here is that nifty little 3.3v/5v plug-in power supply from SparkFun that works with the solderless
breadboards:
http://www.sparkfun.com/commerce/product_info.php?products_id=114. It's only about $9.
TTL to RS-232 level adjuster boards
Pre-built surface mount:
http://www.sparkfun.com/commerce/product_info.php?products_id=449, or discrete through-hole parts kit:
http://www.sparkfun.com/commerce/product_info.php?products_id=133
"Pain free" USB interface kit
http://www.sparkfun.com/commerce/product_info.php?products_id=199
Tri-color LEDs
SparkFun offers surface mount tri-color LEDs that are simply BEGGING to be included in our homebrewing
projects! You can find them at
http://www.sparkfun.com/commerce/product_info.php?products_id=7844
DRM Radio
Mark Phillips, G7LTT provides a glimpse into the latest "engineering miracle" that he's found. As
some of you know he's heavily into digital broadcast radio (his degree is in RF Data Networking) and he's
been working as a test site for the DRM Consortium. In very much the same way as the SoftRock, the current
method of decoding DRM is to feed a 12KHz IF from your radio to your PC's sound card and then attack it with
software. Take a look at http://www.g7ltt.com/drm/. He
converted his FT-847 over the weekend and it's working just dandy. The DReaM software (available for
Linux/Mac/Winblow$) also allows him to decode analogue transmissions as well as DRM. Anyone wishing to try
DRM can drop him a line.
Lithium Polymer (LiPo) Batteries -- Great for Portable QRP Use
... but be careful!
Here's some great information recently posted on our NJQRP reflector concerning a quite compact power source
for portable operations.
Dave, KB2TQX overviews the technology & sources:
I have recently become interested in using the high power density LiPo (Lithium Poly) battery packs that are used by the electric powered model community. For those not familiar with them, these battery packs are very small and lightweight and have amazing power densities and peak current capability. They also have an amazing voltage discharge curve. They tend to be a bit more hazardous than other power sources if they are not properly treated, so don't abuse them, and follow all the cautions with respectful thoroughness.
Anyway, I was interested in using one of these packs for a small QRP Tx/Rx. Initially this will be my Small Wonder Labs DSW-20, but I am also getting a KD1JV (Mr. Melt Solder) AT Sprint III for Christmas, courtesy of my lovely daughter Christine. She was very happy to find out what her Dad would like for a present, as I am terribly hard to buy for - forget the socks, shirts, sweaters (jumpers/pullovers for the GQRP folk) and other assorted wearable presents, if it's not a new tool, piece of test gear or neat new amateur radio kit, I'm afraid it doesn't engage "rapture mode".
I wanted to get a battery pack that gave me decent operating time and output power but one that also didn't cost way too much. Here in the USA one of the best places that I've found, and one that has been recommended to me as having good stock and prices, is AeroMicro (http://www.aeromicro.com). I settled on buying an 11.1 volt (nominal) 3-cell, 1300 mAH LiPo battery pack, and the one I picked was their "GWS 3-cell 1300mAh Li-Poly Pack" at $30.75. In these days of NiMH capacities over 2500 mAH that didn't seem like much capacity for the money, but I was also interested in the weight and physical size factors. It would take 9 NiMH AA cells to match the power capacity, which would be a whole lot bigger and quite a bit heavier than the LiPo pack.
My next step was to look at a charger for the pack, since LiPo batteries have to be carefully charged to avoid fire or explosion. There were quite a number available that were dedicated LiPo chargers ranging from $25 to over $100. But on further perusal I found that Ripmax (actually a UK company) manufacturer a very reasonably priced Universal charger - the "Pro-Peak Prodigy II Digital Charger and Discharger", which handles not only LiPo batteries, but also NiMH/NiCd, LiIo (lithium ion) and even Lead Acid, and what reviews I found for it on the Internet said it worked very well.
For all that capability it wasn't that much more expensive than a decent high tech LiPo charger. If you look at the specs on AeroMicro (http://www.aeromicro.com) you see that it runs off 12 volts DC and has a voltage booster in its circuitry so it can charge/discharge 1-5 cell LiPo/LiIo packs, 1-14 cell NiMH/NiCd cells or 1-6 cell Lead Acid cell batteries at between 100mA and 5 amps, in 100mA increments. At $69.99 I thought it was not a bad price for such a capable charger.
I ordered the LiPo pack, the charger along with a matching charger adapter cable for the LiPo pack which uses a JST connector - one of the modeller's world standard connectors. I placed the order on Saturday 25 Nov, and AeroMicro, bless 'em, shipped it out the same day, so I should have the order sometime this week. I'll post my experiences using this new (to me anyway) power source for those interested as I gain some experience. For those in the UK, the charger is available online from http://www.ripmax.com for about 60 pounds.
First off, the LiPo battery pack. It's made in Taiwan judging from the URL on the packaging (http://www.gws.com.tw) and is designated GW/BP3S1P1300. It also states on the battery pack itself "Material from Japan under USA technology. Assembled in Taiwan". It weighs in at exactly 3 ounces (85 grams) and physical dimensions of 2.5"x1.375"x0.75" (6.5x3.5x1.8 cm).
There is no protection circuit board on the battery pack, just a small PCB that electrically connects the cells in series. So there is no limitation on short circuit current or control of the lower voltage limit when discharging the cells - you shouldn't ever discharge below 3.0 volts per cell. Exceeding the maximum discharge rate (6C = 6 x 1300mA in the case of my pack) can cause over heating and mucho problems including reduced capacity and over heating. Also there is no protection against too high a charging rate (1.5C is the maximum for my pack). Here we are dealing with fire/explosion potential if the charging rate is too high. You mustn't ever be in a hurry to charge these LiPo battery packs.
Here is the blurb from the information card enclosed with the battery pack, exactly as printed:"Lithium-Polymer (abbreviation LiPo) batteries require particularly careful handling. Mishandling these batteries may lead to explosions, fire, smoke and risk of poisoning. Don't series or parallel connect battery packs since the cell capacities and charging condition may be too different. Therefore, the battery packs we supply are selected."
"Charging
1. These batteries should be charged with a charger that is specifically designed for LiPo cells.
2. The GWS LiPo batteries can be charged at a maximum rate of max. 1.5C. (1C corresponds to the cell capacity).
3. These batteries shall be charged within a range of temperature 0 degrees C to 50 degrees C.
4. Reverse charging is prohibited. These batteries shall be connected correctly. The polarity has to be confirmed before you make the wiring."
"Discharging
1. The GWS LiPo can be discharged at continuous currents of around 6C (with 85-95% capacity). High discharging current may reduce the discharging capacity remarkably or cause overheats.
2. These batteries shall be discharged within a range of -10 degrees C to 60 degrees C. The battery temperature during discharging should not exceed 70 degrees C.
3. Normally, LiPo batteries start to discharge at 4.2V and terminate at a cut-off oltage of 3.0V."
"Shipment
For transport of lithium cells and batteries, the battery shall be shipped in 30% charged state for th safety reason. All GWS LiPo are charged in 30% charged state at the original manufacturer."Secondly, the charger. This is a sweet looking unit in a metal case. It weighs in at 7.6 ounces (215.5 grams). Add another 0.8 ounces (22.7 grams) for the bulldog battery clamps that banana plug onto the 30" (138 cm) long 12 volt DC supply leads. Dimensions on the charger are 4.5"x3.0"x1.0" (11.3x7.6x2.5 cm), the little rubber feet on the bottom of the charger add another 3/16" (0.5 cm) to the 1.0" (2.5 cm) dimension.
Applying power lights up the backlit LCD a nice bright blue. The LCD display could be a little higher contrast, but it's perfectly easy to read. I read the instructions carefully and set up the charger to charge my new LiPo battery pack. When I started charging the battery pack was at about 11.3 volts, and current was 1300 mA. After 40 minutes the battery pack voltage was at 12.2 volts and the current was down to 850 mA. After 60 minutes the battery voltage of the pack had stabilized at 12.6 volts and the charge current was down to 240 mA and the charger said that it had put 1003 mAH into the pack. Charging finally halted at 72 minutes 44 seconds with a total of 1040 mAH delivered into the battery pack.
During the whole charging cycle I felt the battery pack at least once every 5 minutes and it remained completely cool to the touch. The charger got just barely warm. The manual for the charger says that for LiPo chemistry packs it charges by constant current until a cell voltage of 4.0 volts is achieved, and then switches over to a constant voltage charging scheme, then when the current into the pack drops to 100 mA, the cell is considered charged and the unit halts the charging cycle.
Next step is an output power check with my Small Wonder Labs DSW-20 with the LiPo battery pack hooked to my KD1JV Digital RMS RF Power Meter. Power was hooked up to the DSW-20 and pack voltage right off the charger was 12.53 volts and the current into the DSW-20 in Rx mode was 30 mA. Key-down and the DSW-20 was pulling 300 mA the battery pack voltage right off the charger was 12.44 volt and the output from the DSW-20 is 1,844 mW.
Surfing around, I came across this website that has some very useful files (PDFs, a .XLS and a .DOC) all covering usage of Lithium-Poly batteries. Essential reading for those planning on using this powerful energy source. http://www.fmadirect.com/tech_data/techdocs/
The protection circuits can be purchased separately - they have to be matched to the cells characteristics. The chief functions of the circuit are:
1) Limiting current that can be drained - use a fuse as a replacement if you like. Most Li-Poly cells can handle a 3C discharge rate safely (C=mAH capacity, some cells for a higher price can handle up to 16C or 20C).
2) Limiting the low voltage point - Li-Poly cells should never be discharged below 3 volts, as they will be ruined and won't take a charge properly afterwards, even though they seem to be charging OK.
3) Some protection circuits may limit the cell charge rate. Li-Poly cells must be very carefully charged, most at no more than a 1C constant current rate, until the volts per cell reaches 4.0, then the charger flips over to constant voltage charging, with a voltage of 4.2 volts to finish off the cell, ending the charge when the charging falls below 100 mA.
With careful handling you can get away without a protection circuit. They are deliberately omitted from most Li-Poly batteries that are used for model planes as the discharge current limit is pushed hard to the maximum.
Anyone interested in protecting their Li-Polys without going the route of a full, matching protection circuit might want to look at using something like this, for over-current (parallel two or more as needed): http://www.allelectronics.com/cgi-bin/category.cgi?item=RXE-065 You could also add a "fuel gauge" so you can monitor your low voltage point - match the Li-Poly total cell voltage to the PCB you buy (select at the drop down box): https://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2775 Note that I HAVE NOT tried these Fuel Gauges out attached directly to the Li-Poly cell pack, BatterySpace says they have to be plugged into the protection circuit PCB, but when downloaded the Datasheets for the protection PCB and the Fuel Gauge it looks to me as though the Fuel Gauge just connects to the battery terminals. Anyone else see a complication? $3.95 for a ready-to-go battery Fuel Gauge is pretty cheap.David N4YMV offers some cautions ...
A few cautions and some background on rechargable Li batteries. These cells are quite good for QRP--they have very good capacity vs size and vs weight. They are reasonably cost effective and can withstand 1-2C discharge rates. Li-poly cells can be made in many interesting shapes--including the standard rectangular slabs. Li-ion cells are typically cyllendrical in design which means they are a bit less space efficient in most designs.
The down side is that they must be handled safely--both mechanically and electrically. Mechanically, Li-poly is pretty darn safe, but Li-ion is a bit more pickey. It can respond very poorly to mechanical stresses--dings, bumps, nails pounded through it ... Also, both Li chemestries deal poorly with extremes of temp--you shouldn't use these cells below 0C or much above 40C. On the top end, they tend to rupture and on the bottem end, they tend to produce metalic Li instead of the much safer ionic form.
The model airplane crowd has really fallen in love with Li-poly cells as they are memchanically rugged, lighter than Li-ion, and come in capacities that are useful to RC aircraft use. Unfortunately, these folk come to li batteries from NiCd which can be abused relentlessly and show few problems for it. No so for Li chemestries.
Both kinds of Li cells must be protected from over charge (both in voltage and in charge rate) and discharge (again both in voltage and in discharge rate). This is why a consumer (and all but the bravest designer) will never see a 'bare cell' but will always see them in some kind of pack with a bit of circuitry which serves to protect them. Some RC folk have chosed to forego the weight penalty of the protection circuitry. This is *very* unwise as it's often done by people who fail to realize that the circuitry is there for a very good reason. Go search google for videos of cells and planes catching on fire due to abuse.
All of that said, Li cells are great for QRP use. As we're not going to be trying to power a huge motor with them, but too just a 1-5W transmitter. If the Li cell/battery is sized correctly for the application, this will be a wonderful match. Most (which is to say all but specially designed cells you are unlikely to come across) Li cells are designed for a discharge current not to exceed twice their capacity (commonly refered to as 'C'). So, a 1.3A*h cell/battery would be good for 2.6A of current draw--nominally. There are some extended capacity cells which trade off discharge rate for raw capacity and which can only tolerate 1C rate of discharge, so this is not a hard and fast rule. Please refer to the specifications for the pack for specifics.
But, we can see that even 1C of discharge from a three cell 1.3A*h pack should handle all but the largest of QRP applications. With a 'middle of the range' terminal voltage of 11.1V (3.7V * 3) and a discharge of 1.3A (1C), this is almost 15W. That should be enough to power a reasonably efficient 5W rig, no?
If treated properly, Li chemestry rechargable cells make a great addition to the QRP toolkit. The main problem is to remember to think of them properly. Don't think of them like NiCd cells which can be abused, but more like deep cycle marine Lead/Acid batteries which need a lighter touch when being handled electrically.
Last updated: December 20, 2008
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