QRP Antenna Tuners; Which is the best?
Grace Cunningham
to buy? KE4QOP John
Phil Wheeler
antennas. It is a kit available from EMTECH:
http://www.emtech.steadynet.com/zmdesc.htm
If you are not into building a kit, MFJ has one that works well for
portable ops. Not exactly qrp, but it does have a 6 watt scale on the
meter.
http://www.mfjenterprises.com/tuners/mfj971.html
Phil
W5LZ
"Best" is relative. For your purposes, it would be
best not to have to use a tuner. But that isn't always
possible so, I'd find one that has the 'features' you
want, like a watt meter, SWR meter, etc. Since these
are fairly common features, I'd look for one that had
the 'best' fit in my wallet. You didn't say what kind
of feedline, so if you need a tuner with balanced output,
that will probably run the price up a bit.
Good luck....
'Doc
Den
john...@surfsouth.com wrote:
> I'm putting up a qrp station at home and need a tuner. Which is the
best
> to buy? KE4QOP John
>
For QRP, the variable caps are cheap and available (250 uf tuning caps
work well). Winding a small tapped toroid and a balun is easy. An SWR
meter from salvage (hamfest), perhaps it will need an amp (DC)(also ez)
to boost the low sigs and you are all set.
Look in old ARRL handbooks... also search around the net.
Tuners and antennas are the easiest homebrew projects that anyone can
accomplish...
Give it a try.
I used a homebrew tuner/SWR meter for years with an HW-8 and was happy
with the results.
73
Den Spiess W2DEN -.-
Sent via Deja.com http://www.deja.com/
Before you buy.
R.Wilhelm
two or three years ago there was a description for a small tuner intended
to tune endfed antennas. It consisted of a L-type-network. The cap was a
cheap variable (500 pF?) and the consisted of 8 or 9 toroid coils. Similar
to what they do in the automatic tuners, the L values for the coils
followed a 1:2:4:8...law, and each could be bypassed with a switch, so
that one could use 256 or 512 different L values, making the whole thing
very flexible. With an additonal switch you could chose to have the
capacitor at the input or the output end (low or high Z antenna).
Can look up the numbers, if someone is interested.
Vy 73
Ralf
DL 6 OAP
=============================================================================
Ralf Wilhelm
Inst. f. Quantenoptik
Universität Hannover
Welfengarten 1
30167 Hannover
Tel: +49 511 762 2232
=============================================================================
"There is no no-win scenario" (Admiral J. T. Kirk)
=============================================================================
Gary Coffman
>I'm putting up a qrp station at home and need a tuner. Which is the best
>to buy? KE4QOP John
The same one that would be best to buy if you were running a kilowatt,
the one with the lowest losses. In general, loss decreases as the physical
size of the components increases, so you want the biggest tuner you can
find.
Gary
Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
Reg Edwards
> In general, loss decreases as the physical
> size of the components increases,
> so you want the biggest tuner you can
> find.
Indeed it does. It should be more widely appreciated.
Doubling both the length and diameter of a straight piece of wire
doubles its inductance and reactance and leaves its HF resistance
unchanged. Result :- Q doubles.
If all the dimensions of a solenoidal coil are doubled, the inductance
and reactance also double and the HF resistance remains unchanged.
Result :- Q doubles. To reduce inductance to its previous value
reduce the number of turns by the factor 1 / Sqrt( 2 ). This will
allow a further increase in wire diameter and an even greater increase
in Q ( subject to proximity effect.)
In general Q increases in proportion to physical size until radiation
resistance becomes a significant fraction of the total. This soon
occurs because radiation resistance increases as the 4th power of the
linear dimensions. However, an isolated magloop Q appreciably greater
than a thousand at 1.9 MHz should not cause any surprise. It will be
much more accurate and convenient to calculate than to measure.
As a big bonus, by doubling all dimensions the heat-radiating surface
area increases by 4 times. So for the same rise in component
temperature the total internal dissipation can be increased to 4 times
the number of watts. But because Q doubles, the internal dissipation
halves. And so the through-power rating of a tuner increases by 8
times, ie., in proportion to the volume of the box which contains the
components.
Disadvantage :- Weight increases by a similar large amount.
The foregoing explains why short-sighted professors, who have
forgotten their spectacles, are inclined to over-estimate component
power ratings when wandering round flea markets and car-boot (trunk)
sales.
---
Reg, G4FGQ