I anticipate getting my general cert this coming week, and the used TS-440SAT just showed up in the mail so I am itching to get some wire (I have a 100ft roll of 16AWG kicking around) up in the air and ready to go. Based on the constraints below, I know I will not be able to get a world-class antenna, but I would like to be able to at least make some contacts on a variety of bands.
I am very limited on space as I live in a ground floor apartment which is right on the corner of an intersection. There are two trees outside of the window that my "station" will be set up at. They run parallel to the wall and are 10-15ft away from the building. The trunks are ~35 feet apart and the trees themselves are not very tall. They are also near a busy sidewalk so all components will have to be out of reach (i.e. no inverted-vee or radials). Likewise, I do not think my landlord would appreciate it if I attach anything to the building itself.
At this point, If I go for maximum antenna length, I can probably anchor to a couple of sturdy branches and get a span of 45-50ft but only around 20ft off the ground. I may be able to get up to 30ft above ground, but likely with reduced length.
The reading that I have done has basically assured me that this is too short and too low for any sort of serious antenna. I have also been somewhat overwhelmed with the different applications of baluns and traps, ladder line vs coax vs twin-lead, etc. However I have also heard the stories of simply loading up a rain-gutter and working DX contacts, so I know that things could be worse.
To at least offer a little bit of my own effort before simply begging for someone to come to my house and design an antenna for me: I am wondering if I can cut a dipole with ~35ft to a side, hang it at the best compromise of height vs. length (call it 45ft horizontal at just over 20ft above ground) and dangling the rest to create an inverted-U. Then hoping the built in tuner can at least get some signal out on the currently active bands (the longer range the better).
Is this a feasible option, or is there something that you would suggest? In either case, what would be the best way to feed it (type and length of line)? As I stated before, this will be a get-on-the-air-fast-and-cheap antenna that I can use to have some fun while I do more research and get to the point that I can competently design something better.
Many thanks for 1) reading my long post and 2) offering any feedback!
At this point, If I go for maximum antenna length, I can probably anchor to a couple of sturdy branches and get a span of 45-50ft but only around 20ft off the ground. I may be able to get up to 30ft above ground, but likely with reduced length.
That would be sufficient for a dipole for 20 meters or up. Or a "fan dipole" for multiple bands. Or a dipole fed with window line which could work on multiple bands. You could do worse.
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To at least offer a little bit of my own effort before simply begging for someone to come to my house and design an antenna for me: I am wondering if I can cut a dipole with ~35ft to a side, hang it at the best compromise of height vs. length (call it 45ft horizontal at just over 20ft above ground) and dangling the rest to create an inverted-U. Then hoping the built in tuner can at least get some signal out on the currently active bands (the longer range the better).
Is this a feasible option, or is there something that you would suggest? In either case, what would be the best way to feed it (type and length of line)?
That should work for 40 meters. You make it a bit too long to start with, then after checking the SWR, trim the length down to minimize the SWR in the part of the band you want to work in. You should be able to get it down to the range of 3:1 or better, where a typical in-rig auto-tuner would be able to work.
Other options for simple & quick wire antennas include an inverted-V, where you get the center of the antenna up as high as you can and the ends lower, or a sloping dipole, or if you have three or four supports you can make a loop antenna. There are lots of things you can do with wire. But a single band dipole is the simples and quickest.
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As I stated before, this will be a get-on-the-air-fast-and-cheap antenna that I can use to have some fun while I do more research and get to the point that I can competently design something better.
That's the right atitude in my opinion. Get on the air the best way you can do so quickly, and start making contacts. At first, you won't realize your limitations, so why worry about it and lose air time overintellectualizing the antenna issue!
i believe in KISS
try a loop of wire
20m should fit your situation
it doesnt have to be square but you want to get as much space in the middle as possible
loops will do multiple bands and with a tuner you should be fine
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. . . I am wondering if I can cut a dipole with ~35ft to a side, hang it at the best compromise of height vs. length (call it 45ft horizontal at just over 20ft above ground) and dangling the rest to create an inverted-U. Then hoping the built in tuner can at least get some signal out on the currently active bands (the longer range the better).
Is this a feasible option, or is there something that you would suggest? In either case, what would be the best way to feed it (type and length of line)? As I stated before, this will be a get-on-the-air-fast-and-cheap antenna that I can use to have some fun while I do more research and get to the point that I can competently design something better. . . . KB1TBR
Yes, you can configure your dipole as described. An overall length of about 65' will do just fine. The droopy "U" configuration is not uncommon; just get the horizontal portion as high as possible, and make sure those drooping ends are out of reach from the ground. My own 65' doublet works quite well at 30' high, and is just 12 feet out from the side of my house.
If center-fed with coax, a 40 meter dipole can also be used effectively on 15 meters. The coax length is critical in just one respect; it must be long enough to reach between the antenna feed point and your radio equipment. You will, however, probably need to trim the antenna elements to resonance. Once tuned, it may load on other bands as well, but with poor efficiency and much loss in the coax transmission line. There is a better way.
If center-fed with balanced line (twin lead, window line, or ladder line), your antenna can be used quite effectively on 40-10 meters. Such an antenna is generally used with an external transmatch (antenna tuner). However, that is not essential if you are willing to experiment with differing lengths of transmission line (using the feed line as an impedance transformer). This way, you lose the expensive tuner, needing only a current balun (connecting balanced line to unbalanced line) at the transceiver. This technique is effective, but not very common. Stay with me.
The trick is to find a length of feed line for each band that provides an impedance within the range of your built-in antenna tuner. This is neither complex nor magic. It does, however, require that the final segment of feed line be removable, to allow replacing it with other segments of differing length. Here, I fail you somewhat; I'm at the wrong computer to give you the link to a excellent description (with pictures) of how this can be done. I hope that someone reading this can provide that URL. (I'll look for it tomorrow.)
I can tell you that it is possible to determine the removable segment lengths experimentally, using either your radio equipment or an antenna analyzer. It is also possible to determine the lengths using a Smith Chart, if you lean that way. I favor experimentation, so I've chopped up lots of old twin lead on the way to successful multi-band doublets over the years.
I've tried to give you some assurance that your antenna situation is not hopeless. Beyond that, I've tried to offer some food for thought and further exploration. 73
Can you get permission to put a vertical on the roof?
If so, it would outperform the low dipole.
Food for thought.
I see a lot of HF verticals (for ham radio) on the roofs of apartment buildings around here; don't know if they got permission or just went ahead and did that, but obviously it's often done.
OK, back again with the link that I promised you. As I reviewed that page myself (always educational), I discovered that Cecil also describes exactly the antenna that I recommended, not just the concept. Don't ignore all the instructional material, but once you've scrolled to the middle of the page you'll find information about his No-Tuner "Shorty" HF-Band Antenna. Don't let the word "Shorty" throw you; this is a full-size 40 meter half-wave antenna. It's just short compared to the 80-10 meter HF antenna that he first describes on that page.
In case you haven't tumbled to this yet, using differing-length transmission line segments eliminates both the cost and the loss of a wide range transmatch. BTW, if you read Cecil's bio here at the zed, you'll see why we count him among those zed denizens who know what they are talking about. 73
Can you get permission to put a vertical on the roof?
If so, it would outperform the low dipole.
Steve is right. Although the high take-off angle of a low dipole doesn't mean you won't be able to work any DX, a vertical (over a good radial field) at the same height will be able to work more DX because of a lower take-off angle. Actually, it is good to have one of each, since low dipoles and verticals complement one another. In practice, a low dipole usually provides better coverage than a vertical within several hundred miles of your station.
A dipole antenna can outclass a vertical antenna if the dipole is installed a half-wave above earth. That, BTW, is a bold generalization, not a rule. Good A-B comparisons can & do reveal exceptions.
Given my own antenna restrictions, hog-heaven for me would be an 80-10 meter doublet up 30' in the back yard, and a (fir tree-cloaked) 80-10 meter vertical/inverted L over a good radial field in the front.
Thanks for all the great suggestions and encouragement. Based on what I've heard here, and some more research I've done, I am leaning in the direction of a G5RV Jr antenna (I haven't asked, but I am sure the vertical is a no-go).
I got the tape measure out and found that I can get 45ft of horizontal span at ~25ft high with more than enough room to dangle the remaining 6ft.
I went out and got some coax and 300ohm twin-lead only to realize when I got home that the site above specs 17ft of 450ohm feed line. Oops. Can I just use a longer section of twin-lead to make up the difference or should I return it and try to find the right stuff?
Much has been written, both pro and con, about the G5RV antenna. Research it to cut through hype & myth, and you'll find that it does the task it was designed for if installed as intended. Too many are not. Also, too many hams expect the G5RV to work well on all bands; some even swear that it does (contributing to the hype & myth).
Have you ever heard TNSTAAFL (there's no such thing as a free lunch)? The G5RV avoids using a transmatch by substituting a fixed length of balanced line to provide a good impedance match for 50 ohm coax. Yes, the transmission line is an impedance transformer; however, it is a wavelength-dependent transformer. The "fixed length" is correct at the design wavelength; other wavelengths result in mismatch.
So, when the G5RV is used on ham bands away from the design wavelength, the mismatch results in high SWR on the recommended "minimum" length of coax. The result is increased loss in the coax. That not only means less power reaching the antenna, but also little (to no) reflected power reaching the SWR meter in the radio shack. Consequently, the ham glued to that meter is tickled pink about his "flat" SWR (whatever-the-heck "flat" means). Worse yet, he mindlessly accepts whatever contacts he can make as proof that the G5RV is a great multi-band antenna. Horse hockey! His contacts basically prove that QRP can produce contacts.
OK now, some folks reading the above will call it a hatchet job on the G5RV. Not so. I do not intend to disparage the G5RV; as proof, read again my earlier comment, "it does the task it was designed for if installed as intended". I don't even consider it a problem to use the G5RV as a multi-band antenna; it's actually OK so long as compromised performance is understood and accepted. The problem comes from believing and repeating the hype & myth about the G5RV being a great multi-band antenna.
Wait now, don't go away. Let's do some tweaking on that G5RV Jr and actually turn it into a great, low-loss, multi-band antenna.
First, the G5RV Jr with its 51' of wire, is minimally long enough to be effective on 40 meters. That's actually OK if you don't have room for more wire, but 65' would be better.
Now, use the balanced line section from the feed point as recommended, but scrap the coax. In its place, use still more balanced line all the way back to the radio shack and connect it to a good transmatch. There, now you have an antenna system with multi-band impedance matching capability and a low loss feed line that won't soak up power on the way to the antenna. But wait, there's still loss in that transmatch. And besides, there's no room in the budget for a good transmatch.
Right, so forget about the transmatch then. Instead, how about substituting various lengths of balanced feed line ? We could actually switch in (or plug in) a piece for each band, making a total length that would transform the impedance to match your transceiver's 50 ohm output. All we'd need then is a current balun to properly connect the balanced transmission line to the unbalanced transceiver output.
At this point, you surely realize that I've just turned that G5RV Jr into Cecil's "Shorty", but now you know exactly how each part of the "Shorty" system works to make it a low-loss, multi-band antenna. You could also backtrack and devolve a "Shorty" antenna into a much less effective G5RV Jr. Aside from the hype and the myth, however, I hope you'd wonder why anyone would want to do that! 73
Gary, K9ZMD/6
Last edited by K9ZMD; 11-09-2009 at 08:42 PM.
Reason: I'll pick my own grammatical nits, thank you.
There is some incredibly bad info in this thread about changing the length of your transmission line to enable a transmitter to tune up.
It is being insinuated, that there is a "magic" length that will provide a 1:1 VSWR to your transmitter, no matter what the antenna impedance may be.
This is incorrect.
The VSWR will NOT change no matter WHAT the length of a transmission line (Excepting VSWR changes due to line loss).
A antenna that has a 5:1 VSWR will have a 5:1 VSWR with ANY length of line.
A VERY FEW antenna impedances- resistive only, no reactance allowed- can be corrected with lengths of line to 50+j0
If the added line is a different impedance than the existing line.
For the rest of the 99.99% of antenna impedances-those with inductive or capacitive reactance- all you can hope for is you MAY transform the antenna impedance into a impedance that your transmitter is capable of loading.
To reliably transform any antenna impedance into 50+j0 will require 2 elements in the matching circuit. You will need a "stub" of the correct length, and the "stub" will have to be located the correct length from the antenna.
The "stub" can take many forms, either a open or shorted parallel stub, or a section of transmission line with a characteristic impedance greater than, or less than the rest of the transmission line. The type of stub will depend on what the original impedance is, and what you want to transform it to.
SOME antenna tuners, particularly the "L" match, have large "forbidden zones" where they CANNOT match 1/2 of the possible antenna impedances possible,Using a 1/4 wavelength of transmission line (electrical length please), will transform a antenna impedance that is in the "L" match's forbidden zone to an impedance that can be matched.
Rege
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