[Antennas] QRP rig and Mini Antenna; Mini Tin Questions

Mon Jul 6 16:13:26 EDT 2009

Nick,

I have responded to some of your questions below with my thoughts in 
CAPITAL LETTERS. Others have responded and all have made good suggestions 
regarding wire type etc. One point that you have to clarify is the frequency of 
operation - 40 meters as the transmitter implies, or 20m which you mention 
as a band of interest. It may not do both.

Good luck
Norm W4QN
===============================================================
Subject: [Antennas] a few portable antenna questions
excerpts-
Background:
I bought a 40m RockMite from SmallWonders Laboratories to experiment with 
and I'm really excited by the possibility that I might be able to store a 
whole 20m *station* into an Altoids tin. Sounds crazy maybe, but I would 
then be able to take it backpacking with me. That, and I'll never turn down a 
good project.
==============================
Questions:
(1) The RockMite is solid-state. Does this mean that the RF output is 
balanced or unbalanced? 
===>IT IS MOST LIKELY UNBALANCED, THE ANTENNA CONNECTION POINT WILL TELL 
YOU WHICH.==== 
(2) Is a (small diameter) coax-fed dipole a good antenna system to use, or 
will anyone suggest something better/simpler/smaller?
====> IN YOUR CASE AND BASED ON YOUR REQUIREMENTS I WOULD NOT RECOMMEND 
IT. TOO FRAGILE, YOU WON'T HAVE IT HIGH ENOUGH. IF YOU ARE WILLING TO CARRY 
A COLLAPSIBLE SUPPORT IT MAY BE ABLE TO WORK (SEE BUDIPOLE FOR AN IDEA). I 
WOULD CONSIDER A QUARTER WAVE LENGTH OF COPPER WIRE, A STAINLESS SKEWER AS 
A ANCHOR, GROUND AND FEED POINT FOR MINI TEFLON COAX. ADD TO THE OPPOSITE 
END OF THE WIRE A MONO-FILIMENT EXTENSION TO TOSS OVER A TREE OR A ROCK 
OUTCROPPING ABOVE YOUR CAMP SITE. YOU MAY HAVE TO BUILD A SIMPLE "L" MATCHING 
NETWORK. ===> 
(3) My tent is about 4.5 feet high and has aluminum support rods so I'm 
thinking that 3m of feedline ought to get my wire far enough away from those? 
(It's tempting to use the support rods as a counterpoise for a vertical, 
but I still would like to be able to use this setup if I'm without the tent. 
Two interchangeable antennas maybe?)
===> SAME AS ABOVE SHOULD SATISFY THIS REQUIREMENT====
(3) Are dipoles best driven by a balanced or an unbalanced signal? And if 
I need to drive it with a balanced signal can I do that with something like 
miniature ladder-line?
====> IT MAKES LITTLE REAL DIFFERENCE, AND IN YOUR SITUATION IT MIGHT BE 
BETTER UNBALANCED AND ALLOW THE COAX TO BE PART OF THE ANTENNA. =====
(4) Would it help if the station were tied to ground? If so, I have six 
eight-inch aluminum tent stakes at my disposal. 
===> ONE PROBLEM WILL BE RF GETTING INTO THE CIRCUITS, A GROUND WILL HELP, 
AS WILL A RF CHOKE IN THE FEED LINE. ABOUT 10 OR 15 FERRITE BEADS SLIPPED 
ONTO RG-174 COAX WOULD BE EFFECTIVE.=====
(5) All other things being equal, the shorter the wavelength, the happier 
I will be, because the antenna will be less of a hassle to put up and take 
down. Is 20m a good band? I will have only one crystal.
===> 20M IS A GOOD BAND, BUT IN YOUR OPENING STATEMENT YOU SAID YOU BOUGHT 
A 40M ROCKMITE - IF THAT IS THE ONLY BAND, THEN YOU ARE COMMITTED TO THE 
40M BAND.===
(6) Do they make really tiny straight keys?
===> YES, AND YOU CAN MAKE YOU OWN FROM A MICRO SWITCH
.
(7) Has anyone tried anything like this before?
====> I HAVEN'T COMMON, BUT THERE IS NOTHING TOO UNUSUAL IN WHAT YOU ARE 
TRYING TO DO. YOUR CHOICE OF MATERIALS, AND THE CONFIGURATION WILL BE KEY 
TO YOUR SUCCESS. A STRANDED, JACKETED WIRE IS MORE DURABLE THEN SOLID AND 
UN INSULATED WIRE, (PENALTY IS A LITTLE SIZE AND WEIGHT). ===== 
Sorry for all the questions, but I'm trying to plan this out as much as 
possible. I admit that allowing myself even one extra Altoids tin would make 
this much easier, but I like the challenge and even though this might not be 
the most practical setup, I'm hooked on the idea of simplicity and think 
it would be lot of fun to build and tweak. Now, if I could only finish 
learning CW... :-)
====> A SECOND TIN MAY BE NECESSARY TO HOUSE A TUNING UNIT TO GIVE YOU 
MORE FLEXIBILITY IN MATCHING A VARIETY OF ANTENNAS. FOR THE ANTENNA AND COAX, 
USE A ZIP LOCK BAG TO CARRY THOSE PARTS. ===== 

REMEMBER YOU ARE QRP TO START WITH, SO THE BETTER THE ANTENNA PERFORMANCE 
THE BETTER YOU CAN EXPECT TO HEAR AND BE HEARD. 

ANOTHER ANTENNA THOUGHT, I WOULD CARRY AS MUCH LIGHT GAGE WIRE AS POSSIBLE, 
 END FEED IT (NEEDS A MATCHING CIRCUIT) AND STRETCH THE WIRE AS FAR AND 
HIGH AS YOU CAN GET. BRING A SLING SHOT OR A "TOSSING" WEIGHT TO GET AN END 
UP IN THE AIR.
Answers, questions, concerns, and comments are all very welcome.
Thanks for the bandwidth,
Nick Hecker (KI4YSP)
------------------------------
Message: 3
From: "Richard (Rick) Karlquist" <richard at karlquist.com>
Subject: Re: [Antennas] a few portable antenna questions
fourninefour at yahoo.com wrote:
> I think that a dipole made from thin steel "thread" will be strong,
small, quick, lightweight, and a good performer.
> Nick Hecker (KI4YSP)

At 10 MHz, 30 gauge copper wire has 1/3 ohm of resistance
per foot. Steel has many times that loss, especially if
it is "music wire", which I suspect is what you are
thinking about. Stick with copper.
Rick N6RK
------------------------------
From: iam at pmug.org (DavidE Benedict)
Subject: [Antennas] Mint Tin Questions Answers
Basic dipoles are naturally balanced and need a transformer inserted to be
fed w/ coax.
Basic verticals are naturally unbalanced.
Transistorized equipment can be designed as balanced or unbalanced.
Simplest circuitry is usually unbalanced.
Some have used zip cord as balanced line. There is very light/small zip
cord available.
Use 30ga copper wire, not steel.
There are a few miniature straight-key designs.
David
W7DBH
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