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Antennas for Kenwood TH-F6A
Hi - I'm an amateur radio newbie - don't even have a license yet (taking the
Technician exam 1/15). I have a Kenwood TH-F6A and I'm looking for an antenna for use from home. This looks like a good one - and it's in my price range ;-) I'm wondering what you experts think of it for a beginner? http://www.diamondantenna.net/d130j.html Also, I thought this might make a good mobile antenna. But the instructions say don't use a magnetic mount. I'm really not interested in any kind of permanent mount. Why do they say not to use a magnetic mount? http://www.diamondantenna.net/d220.html Thanks in advance for taking the time to answer. |
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Antennas for Kenwood TH-F6A
On Mon, 3 Jan 2011 23:39:10 -0800, "Ron Hinds"
wrote: Hi - I'm an amateur radio newbie - don't even have a license yet (taking the Technician exam 1/15). I have a Kenwood TH-F6A and I'm looking for an antenna for use from home. This looks like a good one - and it's in my price range ;-) I'm wondering what you experts think of it for a beginner? http://www.diamondantenna.net/d130j.html Hi Ron, Welcome to the possibly the last vestige of Amateur Radio hardware experimentation. Insofar as your antenna goes, it presents you with a learning opportunity that far exceeds the material you will be tested for. However, it does embody the significant first principles. 1. The correlation between physical size and wavelength. 2. The discussion of match. 3. Unfortunately it says nothing of the radiation pattern which has very serious implications for use. Let's return to item 1 and examine the antenna. The overall height can be rounded to 2 meters for simplicity's sake (there is no reason to be exact and this is sufficiently accurate enough for the moment). Your coax connection goes somewhere near the middle of the structure to make it a dipole - a vertical dipole of unusual shape, but still within the terms of first principles, a dipole. This makes it suitable for use on the 4M band by simple correlation between size and wavelength. However, there is no 4M amateur band, and the vendor claims down to 10M and below. The paragraph above marks our transition in the discussion towards match. By virtue of its shape (its unusual shape), it benefits from being a match at frequencies that are outside of its 4M native band. This is true for the frequencies on BOTH sides of this band. The long and short of it is that YES, the antenna is a suitable load over the entire range of frequencies, and this is of high interest to any Ham. However, being a suitable load to your transmitter (the antenna matching the transmitter's requirement for a particular size value, often 50 Ohms resistive with little or no reactance) is only half of what interests any Ham. The other half is how well does it radiate towards my intended listener? This brings us to item 3 listed above. At the lower frequencies (below 2M band), you can well allow that you will obtain a lack-luster performance. This antenna design is suited for multiband operation which sacrifices gain opportunity to achieve it. This is the see-saw of antenna design - and you choose what is most important at the cost to the other issues. Further to item 3 is the fact that above the 2M band this antenna might well seriously disappoint. This is a first-pass observation, but on close examination, you have selected an antenna that is actually two in one. Look closely at the two distinct sets of spoking elements. The lower flaring down are chosen for the lower band, the upper, more horizontal are chosen for higher bands - such as 2M and 440. The antenna has been optimized to recover from the see-saw of conflicting choice (we ALL want an antenna with universal coverage and maximum gain knowing we can not have both, and worse, we can barely expect half than less). Still, even with this hail Mary pass, above 440 the antenna is going to be a very poor performer in getting signal out towards the horizon (where your listener might be), and instead put it up into the air (where no one is, except satellites, model rockets, and airplanes). So, this being a brief discussion (some might argue otherwise), more is left to be said in response to all the questions it might provoke. Also, I thought this might make a good mobile antenna. But the instructions say don't use a magnetic mount. I'm really not interested in any kind of permanent mount. Why do they say not to use a magnetic mount? http://www.diamondantenna.net/d220.html Wind force and moment arm. It is a LOT of wire in the air for highway speeds. Trust the instructions. 73's Richard Clark, KB7QHC |
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Antennas for Kenwood TH-F6A
"Richard Clark" wrote in message ... On Mon, 3 Jan 2011 23:39:10 -0800, "Ron Hinds" wrote: Hi - I'm an amateur radio newbie - don't even have a license yet (taking the Technician exam 1/15). I have a Kenwood TH-F6A and I'm looking for an antenna for use from home. This looks like a good one - and it's in my price range ;-) I'm wondering what you experts think of it for a beginner? http://www.diamondantenna.net/d130j.html Hi Ron, Welcome to the possibly the last vestige of Amateur Radio hardware experimentation. Insofar as your antenna goes, it presents you with a learning opportunity that far exceeds the material you will be tested for. However, it does embody the significant first principles. 1. The correlation between physical size and wavelength. 2. The discussion of match. 3. Unfortunately it says nothing of the radiation pattern which has very serious implications for use. Let's return to item 1 and examine the antenna. The overall height can be rounded to 2 meters for simplicity's sake (there is no reason to be exact and this is sufficiently accurate enough for the moment). Your coax connection goes somewhere near the middle of the structure to make it a dipole - a vertical dipole of unusual shape, but still within the terms of first principles, a dipole. This makes it suitable for use on the 4M band by simple correlation between size and wavelength. However, there is no 4M amateur band, and the vendor claims down to 10M and below. The paragraph above marks our transition in the discussion towards match. By virtue of its shape (its unusual shape), it benefits from being a match at frequencies that are outside of its 4M native band. This is true for the frequencies on BOTH sides of this band. The long and short of it is that YES, the antenna is a suitable load over the entire range of frequencies, and this is of high interest to any Ham. However, being a suitable load to your transmitter (the antenna matching the transmitter's requirement for a particular size value, often 50 Ohms resistive with little or no reactance) is only half of what interests any Ham. The other half is how well does it radiate towards my intended listener? This brings us to item 3 listed above. At the lower frequencies (below 2M band), you can well allow that you will obtain a lack-luster performance. This antenna design is suited for multiband operation which sacrifices gain opportunity to achieve it. This is the see-saw of antenna design - and you choose what is most important at the cost to the other issues. Further to item 3 is the fact that above the 2M band this antenna might well seriously disappoint. This is a first-pass observation, but on close examination, you have selected an antenna that is actually two in one. Look closely at the two distinct sets of spoking elements. The lower flaring down are chosen for the lower band, the upper, more horizontal are chosen for higher bands - such as 2M and 440. The antenna has been optimized to recover from the see-saw of conflicting choice (we ALL want an antenna with universal coverage and maximum gain knowing we can not have both, and worse, we can barely expect half than less). Still, even with this hail Mary pass, above 440 the antenna is going to be a very poor performer in getting signal out towards the horizon (where your listener might be), and instead put it up into the air (where no one is, except satellites, model rockets, and airplanes). So, this being a brief discussion (some might argue otherwise), more is left to be said in response to all the questions it might provoke. Hi Richard, Thanks for the detailed response. The Kenwood TH-F6A radio I intend to use this antenna with is a handheld with 5W max output power. It is a 2m, 1.25m and 70cm transceiver, with a separate wideband, all mode receiver built in that has a capability from 0.1 - ~1300 MHz. http://www.kenwoodusa.com/Communicat...rtables/TH-F6A With that in mind, what is your opinion of the adequacy of this antenna? Also, I thought this might make a good mobile antenna. But the instructions say don't use a magnetic mount. I'm really not interested in any kind of permanent mount. Why do they say not to use a magnetic mount? http://www.diamondantenna.net/d220.html Wind force and moment arm. It is a LOT of wire in the air for highway speeds. Trust the instructions. Thanks, I thought that might be the case. Again, keeping in mind the radio I intend to use, would this antenna be a good fit? Ron Hinds 73's Richard Clark, KB7QHC |
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Antennas for Kenwood TH-F6A
On Tue, 4 Jan 2011 19:38:17 -0800, "Ron Hinds"
wrote: Hi Richard, Thanks for the detailed response. The Kenwood TH-F6A radio I intend to use this antenna with is a handheld with 5W max output power. It is a 2m, 1.25m and 70cm transceiver, with a separate wideband, all mode receiver built in that has a capability from 0.1 - ~1300 MHz. http://www.kenwoodusa.com/Communicat...rtables/TH-F6A Hi Ron, Generally speaking, the more functionality, the more tepid the utility. However, as a 2m, 1.25m and 70cm transceiver paired with the antenna you describe, you will have every opportunity to do quite well. What could improve things? Raise the antenna higher! (No matter how high it might be.) This is, after all, line-of-sight operation. I can get into my buddy's 2M repeater 10 miles away, from my basement with 125mW into an HT antenna; others that are closer have to step out onto their back porch. With that in mind, what is your opinion of the adequacy of this antenna? Above the 70cm band it is going to be deaf. As I introduced my last response, this forum's best participation comes through experimentation and construction. You could easily and cheaply build your own 2m, 1.25m and 70cm transceiver antenna(s). The difficult part may be in making them robust, or building something similar as multi-band - nevertheless, building one that is adequate takes no more than a simple SO-238 socket and five pieces of heavy copper wire. A more elaborate one would have more wire and would challenge you for insuring its robustness simply because you would have to brace the extra wire in what is called a Discone Antenna design. The antenna you are contemplating is based on the Discone which is notable for being multiband and very simple (although too many websites mystify it - ask questions here). Returning to the deafness above 70cm, this wavelength is verging on being so small, that it would be a sin NOT to build your own antenna for those high bands. This is something you can do at the kitchen table in an evening during commercial breaks. 73's Richard Clark, KB7QHC |
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Antennas for Kenwood TH-F6A
"Richard Clark" wrote in message ... Returning to the deafness above 70cm, this wavelength is verging on being so small, that it would be a sin NOT to build your own antenna for those high bands. This is something you can do at the kitchen table in an evening during commercial breaks. That sounds like fun! Where do I go to find out more? |
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Antennas for Kenwood TH-F6A
On Tue, 4 Jan 2011 22:55:49 -0800, "Ron Hinds"
wrote: "Richard Clark" wrote in message .. . Returning to the deafness above 70cm, this wavelength is verging on being so small, that it would be a sin NOT to build your own antenna for those high bands. This is something you can do at the kitchen table in an evening during commercial breaks. That sounds like fun! Where do I go to find out more? Hi Ron, Antenna design has many variables with frequency (or its inverse with wavelength) being key among them. This means, of course, that you must first select the frequency or band of frequency you want to work (or to listen to). Second, you would want to set some goal for gain over an ordinary dipole or monopole (a misnomer as all antennas are dipoler, but this term is universally acknowledge to informally mean a vertical). Perhaps a dipole or monopole (vertical) is enough to begin with. Third, you want to select the polarization you intend to work (or listen to). This is extremely important for VHF/UHF because its line-of-sight path is very polarization sensitive. Verticals will "see" verticals. Horizontals will "see" horizontals. Verticals and Horizontals will be blind to each other. This is sort of mixing metaphors where previously I used the term "deaf," it amounts to the same thing: "cross polarized" signals will NOT WORK. In the VHF/UHF bands, casual use is vertical polarization; however, for serious DXers it is often horizontal and that activity is usually confined to DX bands within the VHF/UHF. By casual use I mean simplex between you and someone else locally, or contacts through repeaters for greater, but still local range. Fourth, height is key to "seeing." And, as you are entering into experimentation, you want to erect some pole that will be both securely fastened when erected, but also lowerable so that you can attach your design and transmission line to it. Here again is the see-saw nature of design. You will be raising and lowering this more than once, so plan on it ahead. Fifth, once you have the first four thought through (if not actually achieved) you should observe one quality about antenna design: it is scaleable. This means that if you find an antenna described on the internet that embodies all of the considerations listed above BUT it is in the wrong band, then there is a simple solution. An example will serve to illustrate. Let's suppose you run across a Discone Antenna design on the internet (it satisfies your need for multiband application, let's say). However, the author of the design reveals how it was set up for HF operation between 60M and 10M (a very do-able design, if somewhat unwieldy in construction). Your interest is not in HF (suppose), but rather in VHF. What to do? The antenna you are considering, but which is too large, is too large by 10 times. Scaleability in antenna design answers this with: change the existing design to 1/10th of all physical lengths and widths. TA DA! A broadband antenna that works 6M to 220MHz with the characteristics of the original size. What was formerly an unwieldy size is now more manageable by virtue of scaling. Just do it. The same logic applies to more complex designs (and less complex ones, certainly) that you might see touted on the internet. Finally - there is no reason to expect that anything you find on the internet actually works as the author of the page may describe. In fact, the higher the content of gushing and exhortation, accompanied with a laundry list of claims, will give every indication of someone being out to lunch. Check in here for sanity checks. This may inspire long discussions that ramble through many posters here (so far, none have been inspired to dip their oar in this thread). This is the nature of newsgroup activity that often focuses on minutia. However, from the bulk of response, you will get the general sense. 73's Richard Clark, KB7QHC |
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Antennas for Kenwood TH-F6A
On Jan 4, 2:39*am, "Ron Hinds" wrote:
Hi - I'm an amateur radio newbie - don't even have a license yet (taking the Technician exam 1/15). I have a Kenwood TH-F6A and I'm looking for an antenna for use from home. This looks like a good one - and it's in my price range ;-) I'm wondering what you experts think of it for a beginner? http://www.diamondantenna.net/d130j.html Also, I thought this might make a good mobile antenna. But the instructions say don't use a magnetic mount. I'm really not interested in any kind of permanent mount. Why do they say not to use a magnetic mount? http://www.diamondantenna.net/d220.html Thanks in advance for taking the time to answer. Richard is providing a lot more info than me, but the reality is this: 5 watts is not going to do all that great. Your mileage may vary, but a lot of that power will be eaten up by feedline losses. Also, bear in mind that a multi band antenna is generally a compromise on every band it works on. And finally, a hundred bucks plus shipping is a ripoff for that antenna in terms of performance. On 2 meters, 220, and 440 a jpole you could make out of old curtain rods or scrap conduit for ZERO will work as well or better. Also, if you make antennas...do not just clone something. 75% of jpole projects start with copper tubing you have to purchase. Nothing wrong with that, but the reality is anything metal you can make long enough will likely work fine. Most people who publish web how to's on Jpole antennas are copying old designs. Designs get set in the mud and dry out to the point that noobs get a mindset that nothing else can work on account of seeing so much of the same thing. A hundred bucks would go a long way toward some high quality feedline. Save the money and build an antenna. Dave |
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Antennas for Kenwood TH-F6A
"Dave Smirkenberg" wrote in message ... A hundred bucks would go a long way toward some high quality feedline. Save the money and build an antenna. Dave Hi Dave, Thanks for your comments. On the subject of feed line - which of these would be better: RG-8X RG-8/U RG-213/U Thanks again for the reply. - Ron |
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Antennas for Kenwood TH-F6A
Ron Hinds wrote:
"Dave Smirkenberg" wrote in message ... A hundred bucks would go a long way toward some high quality feedline. Save the money and build an antenna. Dave Hi Dave, Thanks for your comments. On the subject of feed line - which of these would be better: RG-8X RG-8/U RG-213/U Thanks again for the reply. - Ron RG-213 and RG-8 (both of which standards are actually obsolete, so you're buying RG-213 "type" cables) are basically the same.. roughly 0.4" in diameter, solid polyethylene dielectric, AWG13 inner conductor. RG-8X is a smaller diameter foam dielectric cable which will have higher loss (because the conductors are physically smaller, so IR losses are higher). There are tons and tons of other cables that may be better or worse for your application. Are you looking for something for VHF and up? In that case, the foam dielectrics tend to be lower loss than the solid dielectric. foam dielectric 75 ohm coax (as used in cable TV systems) is pretty good from a loss standpoint at VHF and UHF, although you need to check the exact type (there are some pretty bad 75 ohm coaxes out there, too). Do you care about exposure to the elements? Does it need to be flexible? Are you transmitting through it (e.g. is power handling important?) |
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Antennas for Kenwood TH-F6A
"Jim Lux" wrote in message ... RG-213 and RG-8 (both of which standards are actually obsolete, so you're buying RG-213 "type" cables) are basically the same.. roughly 0.4" in diameter, solid polyethylene dielectric, AWG13 inner conductor. RG-8X is a smaller diameter foam dielectric cable which will have higher loss (because the conductors are physically smaller, so IR losses are higher). Then of the three I mentioned, the RG-8/U would be best? There are tons and tons of other cables that may be better or worse for your application. Are you looking for something for VHF and up? In that case, the foam dielectrics tend to be lower loss than the solid dielectric. foam dielectric 75 ohm coax (as used in cable TV systems) is pretty good from a loss standpoint at VHF and UHF, although you need to check the exact type (there are some pretty bad 75 ohm coaxes out there, too). Yes, I am mostly interested in 2m, 1.25m, amd 70cm at the moment. Most cables I've seen - in my admittedly brief exposure - have been 50 ohm. Wouldn't 75 ohm cause more loss? Do you care about exposure to the elements? Yes, as it will be running from a roof antenna to the house. It is on the north side of the building though, so the majority of it would not be exposed to the sun. Does it need to be flexible? Somewhat. Once in place it won't be moved around much, if at all. Are you transmitting through it (e.g. is power handling important?) I hope to be ;-) I'm taking the Technician Class test Saturday! As for power handling, all I have at the moment is a 5 watt max handheld. I am interested in building a 50-100 watt power amp for it, though. You wouldn't happen to know where I could find a schematic for such an animal, would you? Thanks so much for your reply Jim! |
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