[Elecraft] KX3 Amp

[Dave B]

With all the banter about KX3's and amp's, on batteries for "Emergency" 
use.

Please remember, that battery makers specify the AH figure, for a typical 
C/20 rate, (1/20th the nominal AH current value.)   Some may quote it at 
C/10, check the data sheets for the battery of interest, they will often 
have example of typical discharge voltage curves, for various discharge 
rates too.  That can be *Very* enlightening!

Without going into specifics, 20A from a 7AH battery may on the face of 
it give you some 20 minutes operating (7 / 20 * 60) but in practice you'd 
be lucky to get even near half that of actual "Practical Use" of your 
amp'.   Probably no more than 5 mins TX time at most before it all starts 
to collapse.

The charge/discharge efficiency of SLA (and most other batteries) falls 
like a stone with high discharge currents, also, also the voltage is 
lower at high currents as the battery nears "empty", but many high 
current loads (Amp's etc) don't work well (if at all) at those lower 
voltages, so in practice you get even less usable run time..

Try your intended battery with something else that is a similar load, 
while monitoring the voltage...


For Lithium family cell's, they (should) have a monitor circuit that will 
simply cut off the load to prevent over discharge (and resulting thermal 
"instability") leaving you totally dead in the water as it were.

As others have said, if you don't already have the needed techniques, opt 
for some narrow band mode (the built in PSK31 if your CW is not good 
enough?) to get a message out if needed via as resonant as you can get it 
antenna..   Even 3W of that can be reliably decoded many 100's of miles 
away, on the right frequencies.   Don't forget the counterpoise if using 
a wire.  However, farmers fences can make good grounds, also antennas at 
times!  :)   (Avoid "Electric" fences of course!!!)

A repeated short distress message (SOS or PanPan Medico?) including an 
international grid reference, sent on one of the QRP frequencies, I 
suspect would possibly result in some action, but I wouldnt garrantee it 
on HAM bands sadly..

Remember too, what is said somewhere in all mobile phone handbooks that I 
have ever seen (that no one ever reads) "this device uses radio signals, 
that are by their nature unreliable, you should therefore not rely on 
this or other radio service for emergency call's."   But what do most 
people cite for their ownership of a mobile 'phone?  "Use in an 
emergency"!

If you **NEED** such comm's, perhaps a satellite 'phone is more 
appropriate, and even they are not without issues.   Or carry an EPIRB 
with you if you're hiking well away from anywhere.   Activate one of 
them, even on land, and all heck will come your way in very short order!.   
Even a sat'phone and EPIRB are lighter and smaller to carry than a KX3, 
amp and battery...

But best of all, tell people you trust more or less where you are going, 
and your planned route + intended return date/time, and whatever late 
tollerance figure you think, just in case of delays.  Then, if you don't 
appear, or contact them from elsewhere by any means, they can call the 
cavelry out.  Of course, if your plans change "on the fly" get a message 
back to them, to that effect...

Enjoy the outdoors, but stay safe.   If you have known medical issues 
(type one Diabeties for example) talk to your doctor before planning any 
extended trip out "into the sticks", just in case.

Given the choice, I'd prefer to ensure I can cary/find enough water & 
food, also perhaps a simple bivoac shelter kit for any significant hike 
out, also any needed indiginous venom antidotes etc, than carrying any 
Ham Radio gear I think.

Regards.

Dave G0WBX.