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ANTENNA
EI3GUB
EI3GUB
EI3GUB
EI3GUB
EI3GUB
ei3gub
My new text...
EI3GUB
WINDOM ANTENNA
I'm using homebrew Windom-Antenna recently.
In the total length of this antenna is 41m, height is about 11m, and diameter of element is 2mm.
However, it is up only about 4m height from a metallic roof.
I modified this antenna originally used as Inverted-V type of 80m band Dipole a little.
The feeding point of this antenna is located 13.6m from the edge of Element. Yes, it is Off-Centered.
BALUN of making which uses two cores, converts impedance into 1/4. The core is the one of about 4cm in the diameter. so there's no problem in the input power 100W at all. Because two cores are used, I think as much as 500W safe in power.
The diameter of the wire rolled in the core is about 1mm.
The VSWR to frequency is shown as follows.
Freq. VSWR Freq. VSWR Freq. VSWR Freq. VSWR
3.525 1.1 14.050 1.8 18.070 3 28.150 2.5
3.570 1.4 14.100 1.7 18.160 3 28.500 2.0
3.795 1.6 14.150 1.6 21.050 >3 29.000 1.3
7.030 1.4 14.200 1.3 21.449 >3 29.300 1.1
7.060 1.3 14.349 1.2 - - 29.600 1.2
7.099 1.2 - - - - 29.699 1.3
In 21MHz, VSWR exceeds 3. However it is likely to QSO with the domestic area, if Antenna-Tuner is used. I did not obtain good results though I measured its VSWR with 10MHz and 24MHz besides.
I think this easy structural wire antenna is Very FB. Because I can QRV on multi BANDs without switching some antennas.
I'm using homebrew Windom-Antenna recently.
In the total length of this antenna is 41m, height is about 11m, and diameter of element is 2mm.
However, it is up only about 4m height from a metallic roof.
I modified this antenna originally used as Inverted-V type of 80m band Dipole a little.
The feeding point of this antenna is located 13.6m from the edge of Element. Yes, it is Off-Centered.
BALUN of making which uses two cores, converts impedance into 1/4. The core is the one of about 4cm in the diameter. so there's no problem in the input power 100W at all. Because two cores are used, I think as much as 500W safe in power.
The diameter of the wire rolled in the core is about 1mm.
The VSWR to frequency is shown as follows.
Freq. VSWR Freq. VSWR Freq. VSWR Freq. VSWR
3.525 1.1 14.050 1.8 18.070 3 28.150 2.5
3.570 1.4 14.100 1.7 18.160 3 28.500 2.0
3.795 1.6 14.150 1.6 21.050 >3 29.000 1.3
7.030 1.4 14.200 1.3 21.449 >3 29.300 1.1
7.060 1.3 14.349 1.2 - - 29.600 1.2
7.099 1.2 - - - - 29.699 1.3
In 21MHz, VSWR exceeds 3. However it is likely to QSO with the domestic area, if Antenna-Tuner is used. I did not obtain good results though I measured its VSWR with 10MHz and 24MHz besides
I think this easy structural wire antenna is Very FB. Because I can QRV on multi BANDs without switching some antennas.
This aerial can be manufactured in two versions:
1) Full size with an overall length (L) of 41 m. In this case the "L1" is 27.5 m and the "L2" is 13.5 m.
2) Half size with an overall length of 20.5 meters. L1= 13.75 & L2 = 6.75 m
ATTENTION: the small version works only for 10, 20 & 40 meter Bands.
Actually, this antenna is compromise but in practice works very well ! On the other hand is a simple-wire multiband antenna, it can be manufactured very easily from anyone and that is a great advantage. I have on my QTH the small version for a couple of years and the results are very good. On 40 m band the antenna is about -6 Db (1 S) lower of a full size dipole but in practice it has the same behavior on locals and DX stations. On 20 meter Band the antenna is excellent. The multi lobe radiation pattern of antennas giving excellent results and its much - much better than a dipole
1) Full size with an overall length (L) of 41 m. In this case the "L1" is 27.5 m and the "L2" is 13.5 m.
2) Half size with an overall length of 20.5 meters. L1= 13.75 & L2 = 6.75 m
ATTENTION: the small version works only for 10, 20 & 40 meter Bands.
Actually, this antenna is compromise but in practice works very well ! On the other hand is a simple-wire multiband antenna, it can be manufactured very easily from anyone and that is a great advantage. I have on my QTH the small version for a couple of years and the results are very good. On 40 m band the antenna is about -6 Db (1 S) lower of a full size dipole but in practice it has the same behavior on locals and DX stations. On 20 meter Band the antenna is excellent. The multi lobe radiation pattern of antennas giving excellent results and its much - much better than a dipole
Can You Say "SATURATION"?
The antenna, as originally installed, had two wires (the top two in the image below). In this configuration, the Windom is advertised to work on all bands but NOT on 15 meters. But it heard GREAT on 15 meters, and I have a tuner, so a little SWR's not a problem, right? Wrong. Most Baluns that I saw advertised on the Internet warn about power limits. They are rated at whatever limit on SSB - and generally tell you to forget about AM and RTTY. But I figured that a Balun that's rated at 1KW on SSB should play fine with 100 watts on CW, even with a little SWR, right? Wrong. The antenna loaded up fine on 15 meters with the tuner, but after about 15 minutes of CW operation I noticed the SWR meter going nuts, and retuning wouldn't work. Whoppie. Now we've melted the 1KW Balun with 100 watts, and the contest is over. Not so. After about 10 or 15 minutes, the Balun cooled off again and I was back in business, but staying away from 15 meters.
I remembered seeing an old 40 meter dipole out in the garage, which was just about the right length for the additional two wires that were advertised to make 15 meters one of "ALL" the bands again, so a quick trip to the back yard with a tape measure, a ball of string, and the old 40 meter dipole produced the second set of necessary wires on the feedpoint to enable 15 (and supposedly 30) meter operation. Here's the final configuration:
It doesn't take a brain surgeon to figure out that since the feed point of the antenna is only 25 feet high, the ends of the two shorter wires are a lot closer to the ground than what they probably should be - maybe 2 feet higher than my six foot fence. Which may account for the high SWR on 30 meters. But with the addition of the second set of wires, 15 had become very usable, and the SWR on 15 and 20 was low enuff so I could pop back and forth between those two bands without even bothering with the tuner.
The antenna is obviously too low, but even at this height it's very usable on all bands but 30 meters. SWR on the bands as it's installed now:
3.800 - 1.5:1
7.000 - 2.2:1
10.125 - 3.4:1
14.000 - 1.9:1
18.110 - 1.5:1
21.100 - 1.5:1
24.900 - 1.4:1
28.500 - 2.1:1
The antenna, as originally installed, had two wires (the top two in the image below). In this configuration, the Windom is advertised to work on all bands but NOT on 15 meters. But it heard GREAT on 15 meters, and I have a tuner, so a little SWR's not a problem, right? Wrong. Most Baluns that I saw advertised on the Internet warn about power limits. They are rated at whatever limit on SSB - and generally tell you to forget about AM and RTTY. But I figured that a Balun that's rated at 1KW on SSB should play fine with 100 watts on CW, even with a little SWR, right? Wrong. The antenna loaded up fine on 15 meters with the tuner, but after about 15 minutes of CW operation I noticed the SWR meter going nuts, and retuning wouldn't work. Whoppie. Now we've melted the 1KW Balun with 100 watts, and the contest is over. Not so. After about 10 or 15 minutes, the Balun cooled off again and I was back in business, but staying away from 15 meters.
I remembered seeing an old 40 meter dipole out in the garage, which was just about the right length for the additional two wires that were advertised to make 15 meters one of "ALL" the bands again, so a quick trip to the back yard with a tape measure, a ball of string, and the old 40 meter dipole produced the second set of necessary wires on the feedpoint to enable 15 (and supposedly 30) meter operation. Here's the final configuration:
It doesn't take a brain surgeon to figure out that since the feed point of the antenna is only 25 feet high, the ends of the two shorter wires are a lot closer to the ground than what they probably should be - maybe 2 feet higher than my six foot fence. Which may account for the high SWR on 30 meters. But with the addition of the second set of wires, 15 had become very usable, and the SWR on 15 and 20 was low enuff so I could pop back and forth between those two bands without even bothering with the tuner.
The antenna is obviously too low, but even at this height it's very usable on all bands but 30 meters. SWR on the bands as it's installed now:
3.800 - 1.5:1
7.000 - 2.2:1
10.125 - 3.4:1
14.000 - 1.9:1
18.110 - 1.5:1
21.100 - 1.5:1
24.900 - 1.4:1
28.500 - 2.1:1
The page describes a Windom antenna with a 4:1 homebrew transformer. The feed-point of this type of antennas (off center) has an impedance of about 300 Ohms. With a 4:1 Balun transformer is possible to feed easily by using a coaxial cable of 75 Ohms (300/4=75), like RG59 or RG11. In practice, under this condition we have an SWR ratio of 1:1,5, but that is no problem if your transceiver has an internal Antenna Tuner. The SWR 1:1,5 it can be easily minimized by using the antenna tuner.
The antenna works on all bands between 3.5 - 28 MHZ including WARC bands other than 10.1 MHZ. The accepted power with this balun is 300 W and the SWR is quite low, not more than 2:1 at the band edges. FIG. 2 shows the Balun transformer.
The antenna works on all bands between 3.5 - 28 MHZ including WARC bands other than 10.1 MHZ. The accepted power with this balun is 300 W and the SWR is quite low, not more than 2:1 at the band edges. FIG. 2 shows the Balun transformer.
NEW Carolina Windom shown cut for 40, 20, 15 and 10 meters.
It will operate on 80, 30, and 17 meters but
will require a tuner for these bands.
This more recent, New Carolina Windom, version has some very interesting characteristics as seen in the drawing above.
For one, the 4:1 Balun has been moved to the antenna radiator and is built into the center insulator. The other interesting feature is that the 10 feet of coax from the Balun is terminated in a choke or line isolator. I have fitted the 10 foot stub with PL-259 UHF connectors on each end. This allows the coax vertical radiator to be easily removed if desired. It is designed to hang vertically which is one reason why this antenna is so effective. The radiation pattern when using the vertical radiator combines both horizontal and vertical radiation components and lowers the effective angle of radiation getting more of your signal near the horizon.
It will operate on 80, 30, and 17 meters but
will require a tuner for these bands.
This more recent, New Carolina Windom, version has some very interesting characteristics as seen in the drawing above.
For one, the 4:1 Balun has been moved to the antenna radiator and is built into the center insulator. The other interesting feature is that the 10 feet of coax from the Balun is terminated in a choke or line isolator. I have fitted the 10 foot stub with PL-259 UHF connectors on each end. This allows the coax vertical radiator to be easily removed if desired. It is designed to hang vertically which is one reason why this antenna is so effective. The radiation pattern when using the vertical radiator combines both horizontal and vertical radiation components and lowers the effective angle of radiation getting more of your signal near the horizon.
EI-3-GUB
ei3gub
Padraigh
Padraigh
EI3GUB
SLIM JIM ANTENNA PROJECT
Several designs rolled into one
Edited and condensed from various designs
Page updated with new information
The Slim Jim Antenna
The Slim Jim is a vertically polarized omnidirectional end-fed antenna having considerable "gain" and this is concentrated almost parallel to ground toward the horizon rather than skyward making it more efficient than a ground plane type antenna by about 50 percent better. It can be built for almost any frequency!
( Below 10 meters it gets VERY tall )
Due to it's SLIM design, there is very little wind loading.
It is fed with 50 ohm coax.
It uses a 'J ' type matching stub (J Integrated Matching = JIM), hense the name SLIM JIM. Credit for the original design goes to F.C. Judd, G2BCX. Since the vertical angle of radiation is so narrow, about 8 degrees toward the horizon, it usually out performs 5/8 wave or groundplane type construction due to their much higher angle of radiation. It is estimated that the Slim Jim appears to have about 6dB gain over a 5/8 wave antenna due to the extreme low angle of radiation.
(Most of the radiation is directed toward the horizion making the "gain" appear much greater than other vertical type antennas it has been compared to with A/B testing)
Editor's note: There are many gain figures quoted for this antenna and also various descriptions of the actual type of antenna on various websites.
Some have even stated that, "In fact I found it outperformed a 1/2wave over 1/2wave over 1/2wave colinear!"
No matter what you call it, it seems to do an excellent job according to most reports. What have you got to loose?
Please let us know your results.....email us!
n4ujw AT hamuniverse.com
Using heavy duty construction would make this a good omni repeater antenna. When correctly matched for lowest swr, it has wide bandwidth.
Drawing on right shown with antenna mounted on PVC pipe
Construction details:
NOTE: NO PART OF THIS ANTENNA SHOULD BE GROUNDED!
It should be totally insulated from it's mount, mast, tower, etc with at least 1/4 wavelength of "freespace" distance. Formulas are provided below for all the measurements including the freespace distance.
The Slim Jim should be constructed from 1/2" copper pipe. Also old tv antenna elements or aluminum tubing could be used with some ingenuity and would be lighter. Experimentation with heavy guage wire supported inside PVC tubing or attached to insulated material such as wood could also be tried and would probally be successful with some ingenuity. 300 ohm twinlead versions also work great!
Using copper pipe, bends are made with soldered 90 degree copper elbows. An adjustable slip sleave made from copper can be added to the element on top above the gap for tuning purposes or possibly some sort of nut, bolt arrangement soldered into the upper end to adjust spacing if needed. (See the 2 meter SSB loop project on this site for better details and pictures of the nut, bolt arrangement.)
Depending on the frequency or band, the average length of the gap and spacing between the elements is 3" at 72MHz and 1" at 220MHz. (See updates below) For 2 meter work this would be around 1 1/2 to 2 inches.
Some experimenters report about 1 inch or less works well. Experiment with the adjustment for best results. The recommended mount is the use of PVC pipe and PVC pipe "T's."
Testing and tuneup:
Support the antenna as high as possible from the ground and other nearby objects especially metal, and fit the coaxial cable to the antenna with some crocodile (alligator) clips. It is suggested that the center conductor be attached to the longest element, shield to the shortest. See diagram above. Attach about 2 to 4 inches up from the bottom and check the VSWR at the design frequency.
USE LOW POWER!
Adjust the clips up or down to get the best match, mark where they are to be finally installed, remove the clips, and solder the coax directly or use clamps, screws, etc. Waterproof or seal all connections and the end of the coax. Use the copper sleeve or nut bolt arrangement, if added, for any necessary tuning.
FORMULAS
(For results in inches)
NOTE: Air gap and element spacing may have to be determined by some experimentation for various frequencies.
See new info about gap spacing below.
(Divide results by 12 for feet)
3/4 wave (longest section = 8415 / fMHz = inches
1/2 wave section = 5610 / fMHz = inches
1/4 wave section = 2805 / fMHz = inches
* 1/4 wave freespace = 2953 / fMHz = inches
* This is the distance that antenna should be
from mounting boom, mast or tower.
Note: These formulas are believed to be accurate.
Some trimming or tweaking of lengths may be needed with YOUR construction!
Slim Jim Metric Formulas:
(For results in meters)
Updated June, 2006
(For results in Centimeters, multiply results by 100)
213.74 / fmhz = 3/4 wave overall length
142.496 / fmhz = 1/2 wave length
71.248 / fmhz = 1/4 wave length
Feed point = About 10 to 20% of 1/4 wavelength (+ - tuning)
75 / fmhz = 1/4 wave "freespace" in Meters
Note: These formulas are believed to be accurate. Some trimming
or tweaking of lengths may be needed with YOUR construction!
Some Examples
2 Meters 146.00mhz
3/4 wave section 8415 divided by 146 = 57.63 inches
1/2 wave section 5610 divided by 146.00 = 38.42 inches
1/4 wave section 2805 divided by 146.00 = 19.21 inches
1/4 wave freespace 2953 divided by 146.00 = 20.22 inches
Feed point about 10 to 20% of 1/4 wave = 1.9 to 3.84 inches (+ - tuning)
The gap would be a guestimate at about 1 1/2 to 2 inches (+ - tuning)
Remember, the 1/4 wave freespace is the distance from the mount
as a minumum.
6 Meters 50.150mhz
8415 / 50.150mhz = 167.79 inches
5610 / 50.150mhz = 111.8 inches
2805 / 50.150 = 55.93 inches
Gap spacing 10 to 20% of 1/4 wave = 8 inches (15%)
Freespace mounting distance 58.8 inches
10 Meters 28.400mhz
8415 / 28.4mhz = 296.30 inches (24.69 feet)
5610 / 28.4 = 197.5 inches (16.45 feet)
2805 / 28.4 = 98.76 inches (8.23 feet)
Freespace mounting distance 103.97 inches (8.66 feet)
17 Meters!
A 52 foot vertical including minimun distance from ground!
Hay don't laugh! It might be worth a try for about 6 db more!
The lengths will have to be adjusted slightly for the addition of the top and bottom connection points.
See Construction and Testing tips below.
CONSTRUCTION and TESTING TIPS
CONSTRUCTION:
=============
The Slim Jim should be constructed from 1/2" copper pipe OR near this size of any conductive material but this is not an absolute! The bends are made with soldered 90 degree copper elbows if your using copper tubing.
A slip sleave or other arrangement can be added to the upper or lower part of the gap made from copper, brass or aluminum for adjustment of the gap measurement for swr tuning, although the average length of the gap and spacing between the elements is 3" at 72MHz and 1" at 220MHz. Some experimentation may be needed for gap distance.
For 2 meters, this would be about 1 1/2 to 2 inches. Here again, this measurement is not extremly critical and the gap, element spacing and element length all interact.
The total distance from the top of the gap around the entire length and back to the bottom of the gap should equal about 1.5 wavelengths or in the case of the 2 meter example above about 115.26 inches.
No part of the antenna should be grounded to the tower or mast. The
recommended mount is the use of PVC pipe and PVC pipe "T's."
Make sure the space between the tower or mast and the antenna is one "freespace" 1/4 wavelength.
TESTING:
========
Stand upright (on a railing or non-conductive object, clear of metal surfaces,
drain pipes, etc.) and fit the coaxial cable to the antenna with some crocodile (alligator) clips. Attach about 2 to 4 inches up from the bottom (at 2 meters). It is suggested that the center conductor be attached to the longest element, shield to the shortest and using just enough power to get an swr reading, check the VSWR. Adjust the clips up or down to get the best match, mark where they are attached, remove the clips, and solder the coax directly. Seal connections and end of coax!
Use the copper sleeve, or other spacing adjustment if added, for any necessary tuning. You may not get that perfect 1:1! The air gap, total length and element spacing all interac,
I was looking for a simple omni-directional antenna. Then happend to see ur slimjim design and tech details.
Immediately brewed one as follows:
Freq: 145 Mhz ( being our center freq. in VHF )
PVC Pipe support: 32 MM Dia.
Ant. Eliment : 15 SWG Copper Enamilled.
Gaps and spacings used : 152, 98.3 , 49.2 CM
Gaps: 1.1/2" Feed Point: 2" Gr . Clearance:
Several designs rolled into one
Edited and condensed from various designs
Page updated with new information
The Slim Jim Antenna
The Slim Jim is a vertically polarized omnidirectional end-fed antenna having considerable "gain" and this is concentrated almost parallel to ground toward the horizon rather than skyward making it more efficient than a ground plane type antenna by about 50 percent better. It can be built for almost any frequency!
( Below 10 meters it gets VERY tall )
Due to it's SLIM design, there is very little wind loading.
It is fed with 50 ohm coax.
It uses a 'J ' type matching stub (J Integrated Matching = JIM), hense the name SLIM JIM. Credit for the original design goes to F.C. Judd, G2BCX. Since the vertical angle of radiation is so narrow, about 8 degrees toward the horizon, it usually out performs 5/8 wave or groundplane type construction due to their much higher angle of radiation. It is estimated that the Slim Jim appears to have about 6dB gain over a 5/8 wave antenna due to the extreme low angle of radiation.
(Most of the radiation is directed toward the horizion making the "gain" appear much greater than other vertical type antennas it has been compared to with A/B testing)
Editor's note: There are many gain figures quoted for this antenna and also various descriptions of the actual type of antenna on various websites.
Some have even stated that, "In fact I found it outperformed a 1/2wave over 1/2wave over 1/2wave colinear!"
No matter what you call it, it seems to do an excellent job according to most reports. What have you got to loose?
Please let us know your results.....email us!
n4ujw AT hamuniverse.com
Using heavy duty construction would make this a good omni repeater antenna. When correctly matched for lowest swr, it has wide bandwidth.
Drawing on right shown with antenna mounted on PVC pipe
Construction details:
NOTE: NO PART OF THIS ANTENNA SHOULD BE GROUNDED!
It should be totally insulated from it's mount, mast, tower, etc with at least 1/4 wavelength of "freespace" distance. Formulas are provided below for all the measurements including the freespace distance.
The Slim Jim should be constructed from 1/2" copper pipe. Also old tv antenna elements or aluminum tubing could be used with some ingenuity and would be lighter. Experimentation with heavy guage wire supported inside PVC tubing or attached to insulated material such as wood could also be tried and would probally be successful with some ingenuity. 300 ohm twinlead versions also work great!
Using copper pipe, bends are made with soldered 90 degree copper elbows. An adjustable slip sleave made from copper can be added to the element on top above the gap for tuning purposes or possibly some sort of nut, bolt arrangement soldered into the upper end to adjust spacing if needed. (See the 2 meter SSB loop project on this site for better details and pictures of the nut, bolt arrangement.)
Depending on the frequency or band, the average length of the gap and spacing between the elements is 3" at 72MHz and 1" at 220MHz. (See updates below) For 2 meter work this would be around 1 1/2 to 2 inches.
Some experimenters report about 1 inch or less works well. Experiment with the adjustment for best results. The recommended mount is the use of PVC pipe and PVC pipe "T's."
Testing and tuneup:
Support the antenna as high as possible from the ground and other nearby objects especially metal, and fit the coaxial cable to the antenna with some crocodile (alligator) clips. It is suggested that the center conductor be attached to the longest element, shield to the shortest. See diagram above. Attach about 2 to 4 inches up from the bottom and check the VSWR at the design frequency.
USE LOW POWER!
Adjust the clips up or down to get the best match, mark where they are to be finally installed, remove the clips, and solder the coax directly or use clamps, screws, etc. Waterproof or seal all connections and the end of the coax. Use the copper sleeve or nut bolt arrangement, if added, for any necessary tuning.
FORMULAS
(For results in inches)
NOTE: Air gap and element spacing may have to be determined by some experimentation for various frequencies.
See new info about gap spacing below.
(Divide results by 12 for feet)
3/4 wave (longest section = 8415 / fMHz = inches
1/2 wave section = 5610 / fMHz = inches
1/4 wave section = 2805 / fMHz = inches
* 1/4 wave freespace = 2953 / fMHz = inches
* This is the distance that antenna should be
from mounting boom, mast or tower.
Note: These formulas are believed to be accurate.
Some trimming or tweaking of lengths may be needed with YOUR construction!
Slim Jim Metric Formulas:
(For results in meters)
Updated June, 2006
(For results in Centimeters, multiply results by 100)
213.74 / fmhz = 3/4 wave overall length
142.496 / fmhz = 1/2 wave length
71.248 / fmhz = 1/4 wave length
Feed point = About 10 to 20% of 1/4 wavelength (+ - tuning)
75 / fmhz = 1/4 wave "freespace" in Meters
Note: These formulas are believed to be accurate. Some trimming
or tweaking of lengths may be needed with YOUR construction!
Some Examples
2 Meters 146.00mhz
3/4 wave section 8415 divided by 146 = 57.63 inches
1/2 wave section 5610 divided by 146.00 = 38.42 inches
1/4 wave section 2805 divided by 146.00 = 19.21 inches
1/4 wave freespace 2953 divided by 146.00 = 20.22 inches
Feed point about 10 to 20% of 1/4 wave = 1.9 to 3.84 inches (+ - tuning)
The gap would be a guestimate at about 1 1/2 to 2 inches (+ - tuning)
Remember, the 1/4 wave freespace is the distance from the mount
as a minumum.
6 Meters 50.150mhz
8415 / 50.150mhz = 167.79 inches
5610 / 50.150mhz = 111.8 inches
2805 / 50.150 = 55.93 inches
Gap spacing 10 to 20% of 1/4 wave = 8 inches (15%)
Freespace mounting distance 58.8 inches
10 Meters 28.400mhz
8415 / 28.4mhz = 296.30 inches (24.69 feet)
5610 / 28.4 = 197.5 inches (16.45 feet)
2805 / 28.4 = 98.76 inches (8.23 feet)
Freespace mounting distance 103.97 inches (8.66 feet)
17 Meters!
A 52 foot vertical including minimun distance from ground!
Hay don't laugh! It might be worth a try for about 6 db more!
The lengths will have to be adjusted slightly for the addition of the top and bottom connection points.
See Construction and Testing tips below.
CONSTRUCTION and TESTING TIPS
CONSTRUCTION:
=============
The Slim Jim should be constructed from 1/2" copper pipe OR near this size of any conductive material but this is not an absolute! The bends are made with soldered 90 degree copper elbows if your using copper tubing.
A slip sleave or other arrangement can be added to the upper or lower part of the gap made from copper, brass or aluminum for adjustment of the gap measurement for swr tuning, although the average length of the gap and spacing between the elements is 3" at 72MHz and 1" at 220MHz. Some experimentation may be needed for gap distance.
For 2 meters, this would be about 1 1/2 to 2 inches. Here again, this measurement is not extremly critical and the gap, element spacing and element length all interact.
The total distance from the top of the gap around the entire length and back to the bottom of the gap should equal about 1.5 wavelengths or in the case of the 2 meter example above about 115.26 inches.
No part of the antenna should be grounded to the tower or mast. The
recommended mount is the use of PVC pipe and PVC pipe "T's."
Make sure the space between the tower or mast and the antenna is one "freespace" 1/4 wavelength.
TESTING:
========
Stand upright (on a railing or non-conductive object, clear of metal surfaces,
drain pipes, etc.) and fit the coaxial cable to the antenna with some crocodile (alligator) clips. Attach about 2 to 4 inches up from the bottom (at 2 meters). It is suggested that the center conductor be attached to the longest element, shield to the shortest and using just enough power to get an swr reading, check the VSWR. Adjust the clips up or down to get the best match, mark where they are attached, remove the clips, and solder the coax directly. Seal connections and end of coax!
Use the copper sleeve, or other spacing adjustment if added, for any necessary tuning. You may not get that perfect 1:1! The air gap, total length and element spacing all interac,
I was looking for a simple omni-directional antenna. Then happend to see ur slimjim design and tech details.
Immediately brewed one as follows:
Freq: 145 Mhz ( being our center freq. in VHF )
PVC Pipe support: 32 MM Dia.
Ant. Eliment : 15 SWG Copper Enamilled.
Gaps and spacings used : 152, 98.3 , 49.2 CM
Gaps: 1.1/2" Feed Point: 2" Gr . Clearance:
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No. of Votes: 61
Avg. Rating: 5.21
Avg. Rating: 5.21
Meter Started: Jan 10, 2007
My new text...
My new text...
How to Check SWR with the radios built in meter
**Note** Generally the built in meters are not all that accurate, however they will get you close if that's all you have.
First of all locate the switches you will need for this test.
1) The S/RF, SWR, Cal switch (A three position switch either a slide or a rotary)
2) The variable "SWR Cal" knob
Then familiarize yourself with the meter and scale.
For this procedure you will only be interested in this scale
Place S/RF, SWR, CAL switch to the "CAL" position
Key the mic on the radio and hold it keyed until noted
Slowly adjust the Variable "SWR Cal" knob until the needle is on the "CAL" mark on the meter
Now place the S/RF, SWR, CAL switch to the "SWR" position
Note the location of the needle (It helps to jot it down on a piece of paper, you may need to do this test a few times more)
Un-key the mic
Ideally you should see a reading of 1.5 or less which would be here
GOOD
A reading of 2 or less is considered "Safe", (As long as you are not running a "High Power" radio or an External amplifier) which would be here
SAFE
If your readings are higher than 2, your antenna system needs some attention and you should limit your talking until you get the SWR down
BAD
Tech Support Top
**Note** Generally the built in meters are not all that accurate, however they will get you close if that's all you have.
First of all locate the switches you will need for this test.
1) The S/RF, SWR, Cal switch (A three position switch either a slide or a rotary)
2) The variable "SWR Cal" knob
Then familiarize yourself with the meter and scale.
For this procedure you will only be interested in this scale
Place S/RF, SWR, CAL switch to the "CAL" position
Key the mic on the radio and hold it keyed until noted
Slowly adjust the Variable "SWR Cal" knob until the needle is on the "CAL" mark on the meter
Now place the S/RF, SWR, CAL switch to the "SWR" position
Note the location of the needle (It helps to jot it down on a piece of paper, you may need to do this test a few times more)
Un-key the mic
Ideally you should see a reading of 1.5 or less which would be here
GOOD
A reading of 2 or less is considered "Safe", (As long as you are not running a "High Power" radio or an External amplifier) which would be here
SAFE
If your readings are higher than 2, your antenna system needs some attention and you should limit your talking until you get the SWR down
BAD
Tech Support Top
e/mail ei3gub@hotmail.com
No. of Votes: 61
Avg. Rating: 5.21
Avg. Rating: 5.21
Meter Started: Jan 10, 2007
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