XPost: rec.radio.amateur.moderated

IW5EDI Simone - Ham-Radio

///////////////////////////////////////////
1:4 Current Balun

Posted: 09 Mar 2022 03:05 PM PST http://www.iw5edi.com/ham-radio/5506/14-current-balun







Article by N5ESE




Heres yet another handy little Altoids QRP project. This makes a great
travel companion to the 1:1 current balun and is intended to aid in tuning
a balanced antenna or feedline that has a high impedance (100-600 ohms).
Ive even used it successfully to tune a 20 meter, 1/2-wave vertical with 4 radials, placing it directly at the bottom feedpoint of the vertical,
feeding it with 50-ohm line (RG-58), and letting my Elecraft K1s automatic antenna tuner do the rest.




The classic 1:4 current baluns circuit looks like so:








This version, shown below, is wound with 10 turns of RG-174 mini-coax on
each of two FT114-43 ferrite cores.













Measurements using my MFJ Antenna Analyzer showed that the SWR rose
gradually from 1.1:1 at 21 MHz to 1.25:1 at 30 MHz (into a 200-ohm dummy
load).




Construction-wise, an isolated BNC is used at the input (Amphenol 31-010), though a garden variety BNC connector (non-isolated) mounted directly to
the Altoids box could as easily been used. I grabbed a piece of 3/32 thick
PC board that I had laying around as scrap, peeled off most of the copper,
but left some copper traces to ease wiring. The PCB would also serve as the mounting plate, mounting the completed toroids with hot glue. To preserve balance, attention is given to keeping all lead lengths symmetrical; that
is, all the leads on toroid 1 are identical to toroid 2, and the length of
the wire from any junction to the input and the output connectors, is
identical for both toroids. Standard banana plug binding posts were used
for connecting the feedline to the baluns output. It is assumed that the transceiver or antenna tuner will be earth-grounded, to provide a path for bleeding static charges on the antenna.




In operation, a female-to-female BNC adapter is mounted on the BNC jack of
the balun, and the balun is then mounted directly onto the BNC jack on the
rear of the transceiver or antenna tuner. Alternatively, mount the balun at
the feedpoint (assuming the feedpoint is 100-400 ohms), and feed using a half-wavelength of coax. While throughput losses were not measured, it can
be assumed that the balun will be lossy for impedances much above or below
the intended matching range (100-600 ohms), or outside the intended
frequency range (1-30 MHz). Also, I believe the balun is readily usable at
10 watts applied power, but that it may be good to somewhat higher levels.
Use at higher levels has not been analyzed nor tested.




I used this balun between my K1 and 1/2-wave vertical to help match the antenna. Without it, the K1s automatic antenna tuner could not find a match below 5:1. With the 1:4 step-up balun, the K1 managed a 1:1 match, and 30
QRP contacts were made in dreadful band conditions during the 2002 Flight-of-the-Bumblebees contest, with contacts up and down both coasts. Needless to say, this balun is a keeper.

The post 1:4 Current Balun appeared first on IW5EDI Simone - Ham-Radio.


///////////////////////////////////////////
1:1 Current Balun

Posted: 09 Mar 2022 02:56 PM PST http://www.iw5edi.com/ham-radio/5497/11-current-balun







Article by N5ESE




Heres another handy little Altoids QRP project. For Field Day 2002, I
wanted to use my new Elecraft K1 (which has an automatic antenna tuner built-in) to feed a full-wave loop on 40 meters, to use on all bands 40
15. To preserve the feedline balance (I used 300-ohm ladder line), I needed
a balun at the output of the K1s antenna tuner. This 1:1 balun did the
trick quite nicely.




The classic 1:1 current baluns circuit looks like so:








Two versions were built. The first was wound with 16 turns of side-by-side
AWG 20 teflon-coated wire onto a FT114-43 core. It is shown below:








It did a marvelous job on Field day, but subsequent measurements using my
MFJ Antenna Analyzer showed that the SWR rose gradually from 1.1:1 at 21
MHz to 1.8:1 at 30 MHz (into a 50-ohm dummy load). I felt I could do
better, using small-diameter coax instead of parallel pairs, and this
proved to be true, yielding 1.05:1 at 21 MHz and only 1.15:1 at 30 MHz.
Below are the schematic and picture of the coax-wound version, using 10
turns of RG-174 mini-coax:

















Construction-wise, on both versions, an isolated BNC is used at the input (Amphenol 31-010), though a garden variety BNC connector (non-isolated)
mounted directly to the Altoids box could as easily been used. I grabbed a piece of 3/32 thick PC board that I had laying around as scrap, peeled off
the copper, and used that as the mounting plate, mounting the completed
toroid with hot glue. This gave the coil a little clearance from the
Altoids cases metal, hopefully minimizing distributed capacitance. Then, standard banana plug binding posts were used for connecting the feedline to
the balumns output. Though not shown in the schematic, two 100K resistors
are added , one on each output terminal to case ground (or just one between
the two output binding posts), to bleed static charges (it is assumed that
the transceiver or antenna tuner will be earth-grounded).




In operation, a female-to-female BNC adapter is mounted on the BNC jack of
the balun, and the balun is then mounted directly onto the BNC jack on the
rear of the transceiver or antenna tuner. Alternatively, mount the balun at
the feedpoint (assuming the feedpoint is 25-100 ohms, and feed using a half-wavelength of coax). While throughput losses were not measured, it can
be assumed that the balun will be lossy for impedances much above or below
the intended matching range (25 100 ohms), or outside the intended
frequency range (1-30 MHz). Also, I believe the balun is readily usable at
10 watts applied power, but that it may be good to somewhat higher levels.
Use at higher levels has not been analyzed nor tested.




This balun lives in my QRP travel kit, and gets lots of field use.

The post 1:1 Current Balun appeared first on IW5EDI Simone - Ham-Radio.


///////////////////////////////////////////
N5ESEs 87 ft Inverted L Portable Antenna?

Posted: 09 Mar 2022 02:43 PM PST http://www.iw5edi.com/ham-radio/5487/n5eses-87-ft-inverted-l-portable-antenna%ef%bf%bc












Heres one of my favorite antennas for QRP portable operation. It provides
easy setup in the field, is extremely compact, and provides excellent performance on all bands 80 thru 15 Meters. Its a non-resonant antenna, but dont think for a minute that you lose anything from that. Using a
field-radial system as shown, the feedpoint impedances tune readily on all bands 40-15M on my Elecraft K1s built-in automatic antenna tuner, and Ive
used it with great success with my Norcal BLT Z-match. Gain on all bands is very respectable, except on 30 Meters, where it is nevertheless quite
usable. You may want to use a 1:4 impedance transfiormer (toroidal balun)
to improve your chances of matching on 20 & 30 Meters, when using the BLT tuner.




Here are the EZNEC-calculated feedpoint impedances for each CW QRP Calling Frequency:




80 Meters (3055 KHz) : Z= 69 +j308 ohms
40 Meters (7040 KHz) : Z= 111 j232 ohms
30 Meters (10110 KHz) : Z= 1693 + j1466 ohms
20 Meters (14060 KHz) : Z= 239 + j450 ohms
15 Meters (21060 KHz) : Z= 1700 + j591 ohms




I built mine of 87 ft of AWG 22 teflon-coated wire. For a counterpoise, I
use four 31 ft radials, formed like an X, with two additional 16 ft radials
to cover 20 Meters. The radials are AWG 24 wire, also teflon insulated, and connect to a common tie-point, with a 30 inch tail for connecting to the antenna tuner or rig. I prefer the teflon-insulated wire for field
antennas, as it tends to be less susceptable to changes due to moisture.
While one could use a single counterpoise wire, I believe the extra wire radials help to establish a more consistent and stable ground system in the field, and thus more predictable performance from the antenna. Both the
antenna and the radial system fit into a sandwich-sized ziplock bag.




This antenna is very flexible in its deployment. Youll get similiar
performance whether its deployed as an inverted L or a Sloper. It will work best with the far end up about 30 ft or more, but it will give excellent performance even if only raised 15-20 ft. In the inverted L configuration,
try to get the vertical portion up at least 15 ft if possible. Lower
antennas will tend to radiate more energy upward on the lower bands, but
this is not at all a disadvantage for domestic contacts.

































The post N5ESEs 87 ft Inverted L Portable Antenna? appeared first on IW5EDI Simone - Ham-Radio.


///////////////////////////////////////////
N5ESEs Shielded-Loop Receiving Antenna

Posted: 09 Mar 2022 02:26 PM PST http://www.iw5edi.com/ham-radio/5476/n5eses-shielded-loop-receiving-antenna







Right from the top of this page, Im going to say that Im an antenna experimenter, not an antenna expert. Purely seat-of-the-pants. In fact, you might even say Im an antenna cynic. I know how to use antenna analysis
tools, and I often do, but I take them with a serious grain of salt. Ive
found, in my 35 years of experimenting, that some antennas work much better than predicted, and some work much worse (and that theyre more likely to
work worse than better HI HI ). Still, I find experimenting to be one of
those true joys of amateur radio, and I encourage all of you to just try it
out for yourself, and for Petes sake, dont take my word for it (nor my explanations).




I find that most technical people do this (and I am no exception): upon observing a phenomenon, we make up an explanation for why we got our
observed results. We base this explanation on the current subset of
knowledge that weve gained from education and experimentation and folklore,
and were not likely to look for another explanation until we have another experience which forces us to expand or revise our previous explanation.
Please realize this is the case with me, also, and then enjoy the web page.




If you really want to know how it works without my ignorant rantings
getting in the way of a thorough understanding




Refer to the links following the narratives for schematics, layout
drawings, and pictures.




When I travel on business (which is way more often than I like), I like to
take along a little bit of HF ham radio for those evenings when Im stuck in
the hotel room. In 1998 I built the Jade Products SLR-40 receiver kit, so
that I could have something that fit easily in my suitcase. The SLR-40 is a 40-Meter direct-conversion receiver with balanced antenna inputs, and was specifically designed for use with a shielded loop antenna.




Shielded-Loop antennas have some nice properties that make them desirable
as portable receiving antennas. Because the E-field is electrostatically shielded, it tends to pick up less man-made noise than wire antennas. The difference in hash noise can be quite significant in metropolitan areas
(and hotels have lots of hash noise). Also, (and I think this is because of
its small size), it tends to pick up less local storm-related noise. An additional feature is that noise can be nulled to some extent, by turning
the antenna (its null is perpendicular to the plane of the loop). Lastly,
its small size lends itself to portability. (My version fits nicely in a
small suitcase, along with the receiver).




Of course, the small size is a disadvantage also. Because the profile is so low, it intercepts less energy than a larger antenna. The receiver,
therefore, must have adequate excess sensitivity and noise figure to compensate, or a preamp needs to be added. The SLR-40 receiver had more
than adequate gain for this purpose, and most receivers on the 160, 80 and
40 meter bands will, because the natural and manmade noise on those bands
is fairly high anyway. Another complication with small loop antennas is impedance matching, although because we are using this in a receiving application, the losses resulting can usually be ignored (i.e., overcome by receiver gain). Small loop antennas have very low feedpoint impedances, typically 5 ohms or less. For best efficiency, then, an impedance
transformer is warranted (although I find it completely unnecessary with
the SLR-40 receiver).




The antenna described here was an attempt to replace the antenna provided
with the SLR-40, which had rather mediocre noise performance (in spite of
Jade Electronics claims), and was somewhat flimsy. One day while following
my wife around Hobby Lobby (a crafts store), I noticed the wood embroidery rings, usually available in 12, 15, 18, and 24 diameters. These consist of
an inner hoop of wood about 1/2-inch wide and 1/4-inch thick, perfectly circular, and an outer hoop that is cut at one point, but still circular.
The outer hoop fits over the inner hoop, and a screw-fastener arrangement
on the outer hoop allows it to be tightened down on the inner hoop. This
looked an awful lot like a loop antenna to my eyes, and so I bought two, a
15 and 18 version. (Cost, <$12). In the same crafts store, I also found a supply of adhesive-backed copper tape, and I bought one pack of 1/4-inch
wide, and one of 3/8-inch wide tape. (Cost, <$6/roll). The copper tape
turned out to be a few mils thick, very strong, easy to work with, and
readily solderable.




Given these materials, I decided to construct the antenna as follows:
First, I carefully placed a length of 1/4-inch wide copper tape all the way around the outside of the inner hoop, centering it between the edges. The adhesive back tape stays in place easily. This will form the actual
receiving antenna loop. Rather than making it continuous, the tape was
folded out (perpendicularly) at each end, forming pigtails that would later
be connected (by soldering) to the tank circuit at the bottom of the
antenna. Second, I placed a length of the wider 3/8- inch copper tape all
the way around the inside of the inner hoop, overlapping slightly, making
it continuous (and soldering it lightly to make sure). Lastly, I placed
more 3/8-inch copper tape around the outide of the outer hoop, up to the
point where it met the screw-fastening device. Now, the hoops are
assembled, aligning the pigtails-end of the inner hoop with the fastener
end of the outer hoop, and tightening. We will not disassemble the hoops
from this point forward. At this point, the inner receiving loop should be effectively shielded by the inner and outer copper tapes, but with NO continuity to either shield.




Continuing with assembly, we now cut the inner and outer copper shields at
the top of the hoops (exactly opposite the fastener and pigtails), and wrap some copper tape all the way around, soldering it to the inner and outer shields on both sides of the gap. This gap is very important in creating a faraday shield that attenuates only the E-fields.













Refer to the photo if this is unclear. We also wrap some copper tape all
the way around, connecting the inner and outer shields, near the bottom
(feed point), just outboard of the loop antennas pigtails (and solder it).
Be very careful not to short the shield to the loop antenna or its
pigtails. There will be a gap at the outer shield at the bottom (due to the fastener arrangement, but none on the inner shield. If you want, you can
solder the outer shield to the fastener, although this is a minor point.
This can be seen in another photo..













I elected to hand-cut and hand-route a small 1 x 1-1/2-inch PCB from some
scrap double-sided material I had. This would help me mount the tank components, used to resonate the loop antenna at the band of interest. I
tack soldered a 8-80 pF air variable (Sprague-Goodman GZC80000, available
from Digikey and others) to the PCB, and added other ceramic disk
capacitors as necessary to resonate the antenna at the frequency of
interest (in this case, 40 Meters) with the variable at mid-range. The
pigtails of the loop connect in parallel with the capacitors, soldered to
the PCB. Again, be careful not to short the loop antenna to the shield, or
the antenna will not perform correctly.




We constructed a base for the antenna out of some 1/4-inch thick hobby wood (basswood, I think), purchased from the same crafts store. The pictures
will show the details of this, which are quite non-critical. The hoop
assembly and PCB were fastened to the mount using liberal amounts of
hot-glue. We placed rubber feet on the very bottom. There may be sturdier methods of assembly, although this method has survived a dozen trips or so
(so far) in a small suitcase transported through the airlines.




The antenna is balanced, and this balance must be maintained in order for
the low-noise performance to be realized. This means that the receiver
should have balanced inputs (as does the SLR-40 receiver), or that it be link-coupled, or that a balun/tranformer be used at the antenna. As a
result of this requirement, the antenna must either be fed with two equal-length pieces of coax (shield common), or fed with
shielded-twisted-pair cable. I had access to some scrap teflon-coated shielded-twisted pair, so I used that. ( I tried it earlier with two
sections of coax, with equal results). In either case, the inner conductors should connect across the tank circuit/feedpoint, and the feedline
shield(s) should connect to the loop antenna shields on one end, and the receiver chassis/electrical ground at the other. In our case (for use with
the SLR-40 receiver), the feedline was terminated with two RCA-type phono plugs, one for each center conductor.




In the future, I plan to try other arrangements. One will be for unbalanced receivers, using a broadband RF transformer or balun mounted at the antenna
to provide the balance-to-unbalanced conversion, and to provide better impedance matching (step-up-step-down). Another arrangement will insert an
FET preamp at the feedpoint, powered by a 9-Volt battery, to boost the
signal for use with unbalanced receivers or higher-frequency bands where
the sensitivity is required. Both concepts are shown schematically below,
as are other drawings and photographs of the antenna.
































The post N5ESEs Shielded-Loop Receiving Antenna appeared first on IW5EDI
Simone - Ham-Radio.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)