Top Band Antennae?
What is the recommended practice these days for Top Band antennae for
restricted spaces? Many years ago (50?) it was to adapt a mobile area for fised station use. |
Top Band Antennae?
gareth wrote:
What is the recommended practice these days for Top Band antennae for restricted spaces? That kind of depends on what you mean by "restricted spaces", but in general you put up the tallest radiator you can assuming the ground in your area is at least half way decent. Unless you are in a high wind area, it is pretty trivial to get up to around 10 to 15 meters tall with decent aluminum and no guys. Many years ago (50?) it was to adapt a mobile area for fised station use. I assume you meant mobile antenna, which is very short; a radiator that is 4 meters tall, or about the height of a single story house, will easily outperform a mobile whip in the same place. In addition, since a fixed antenna can be made much sturdier, you can have more top loading than on a mobile which further improves performance. -- Jim Pennino |
Top Band Antennae?
"gareth" wrote in message ... What is the recommended practice these days for Top Band antennae for restricted spaces? Many years ago (50?) it was to adapt a mobile area for fised station use. Move. If you can't move, put up the tallest vertical you can. Put a capaticive hat on the top and coil just under that. Then put down as many radials as you can. Unless you provide for tuning at the anenna, the short ones will have a very narrow bandwidth. Not much more than the frequency it is cut for. |
Top Band Antennae?
gareth wrote:
What is the recommended practice these days for Top Band antennae for restricted spaces? Many years ago (50?) it was to adapt a mobile area for fised station use. Magnetic loop antennas require very little space. If you Google VK3YE you will find he has a design for a homebrew loop that covers 1.8 to 21 mhz. It will not be very efficient, but you can always build a loop of greater diameter which will raise the efficiency. There are a number of loop designs on the net. There are an increasing number of loops being manufactured as well. Size-wise, a magloop will outperform many full sized antennas. de Irv VE6BP |
Top Band Antennae?
"Irv Finkleman VE6BP" wrote in message
... gareth wrote: What is the recommended practice these days for Top Band antennae for restricted spaces? Many years ago (50?) it was to adapt a mobile area for fised station use. Magnetic loop antennas require very little space. If you Google VK3YE you will find he has a design for a homebrew loop that covers 1.8 to 21 mhz. It will not be very efficient, but you can always build a loop of greater diameter which will raise the efficiency. There are a number of loop designs on the net. There are an increasing number of loops being manufactured as well. Size-wise, a magloop will outperform many full sized antennas. Thanks, I'll pass it on to my mate who is recently licensed and is intent on do-it-yourself including resurecting an old Codar AT5 TX. |
Top Band Antennae?
On Friday, February 20, 2015 at 4:16:04 PM UTC-6, wrote:
gareth wrote: What is the recommended practice these days for Top Band antennae for restricted spaces? That kind of depends on what you mean by "restricted spaces", but in general you put up the tallest radiator you can assuming the ground in your area is at least half way decent. Unless you are in a high wind area, it is pretty trivial to get up to around 10 to 15 meters tall with decent aluminum and no guys. Many years ago (50?) it was to adapt a mobile area for fised station use. I assume you meant mobile antenna, which is very short; a radiator that is 4 meters tall, or about the height of a single story house, will easily outperform a mobile whip in the same place. In addition, since a fixed antenna can be made much sturdier, you can have more top loading than on a mobile which further improves performance. -- Jim Pennino You can also use top guy wires as top loading, which can easily be longer than most conventional capacity hats. As a bonus, they keep the antenna from blowing down if the wind huffs and puffs and tries to blow his antenna down. Also one good thing about large top loading is the much improved current distribution through the whip, which can let one place the loading coil at the base, with little degradation of the current distribution through the whip, being as you are not depending solely on coil location to improve current distribution. That allows one to easily get to the coil to change taps, or one can use a large roller coil as the inductor. As mentioned, the bandwidth will be pretty narrow, so one really would want a way to adjust the coil, unless they don't mind being on the same frequency all the time. I couldn't live like that, being I often work CW around the bottom of the band, and phone usually between 1870- 1900 khz or so.. |
Top Band Antennae?
On Fri, 20 Feb 2015 21:38:30 -0000, "gareth"
wrote: What is the recommended practice these days for Top Band antennae for restricted spaces? Either the tallest helical antenna possible, or the tallest vertical with a top hat, or a conglomeration: http://www.hamuniverse.com/k6mm160metervertical.html Also, add some ground radials. A problem with short 160m antennas is that the operating bandwidth is very small. Change frequency even slightly, and you have to retune the antenna or antenna coupler. Short antennas also exhibit low impedances, which implies high currents, which suggests that beefy low loss components are needed. Many years ago (50?) it was to adapt a mobile area for fised station use. Huh? What's a fised station? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Top Band Antennae?
On 21/02/2015 04:50, Jeff Liebermann wrote:
Huh? What's a fised station? He means fisted station. ;-) |
Top Band Antennae?
"Jeff Liebermann" wrote in message
... On Fri, 20 Feb 2015 21:38:30 -0000, "gareth" wrote: Many years ago (50?) it was to adapt a mobile area for fised station use. Huh? What's a fised station? typo - one key lateralised - fixed |
Top Band Antennae?
On Sat, 21 Feb 2015 11:09:31 -0000, "gareth"
wrote: "Jeff Liebermann" wrote in message .. . On Fri, 20 Feb 2015 21:38:30 -0000, "gareth" wrote: Many years ago (50?) it was to adapt a mobile area for fised station use. Huh? What's a fised station? typo - one key lateralised - fixed Is that because everything in the station needs fixing? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Top Band Antennae?
"Jeff Liebermann" wrote in message
... On Sat, 21 Feb 2015 11:09:31 -0000, "gareth" wrote: "Jeff Liebermann" wrote in message . .. On Fri, 20 Feb 2015 21:38:30 -0000, "gareth" wrote: Many years ago (50?) it was to adapt a mobile area for fised station use. Huh? What's a fised station? typo - one key lateralised - fixed Is that because everything in the station needs fixing? Only the photographic negatives |
Top Band Antennae?
On Fri, 20 Feb 2015 15:58:32 -0700, Irv Finkleman VE6BP
wrote: Magnetic loop antennas require very little space. If you Google VK3YE you will find he has a design for a homebrew loop that covers 1.8 to 21 mhz. It will not be very efficient, but you can always build a loop of greater diameter which will raise the efficiency. Nope. The efficiency is in the diameter of the conductor used to build the loop, not in the diameter of the loop itself. I bigger diameter loop just allows it to tune to a lower frequency. A "fatter" or larger conductor, reduces IR losses and therefore improves efficiency. There are a number of loop designs on the net. There are an increasing number of loops being manufactured as well. Size-wise, a magloop will outperform many full sized antennas. Yep, and there's a subtle reason why a loop will outperform other antennas. A loop has a very high-Q and therefore a very narrow operating bandwidth. This does nothing for the actual signal being received, but does wonders for reducing the QRM and QRN (mostly atmospheric noise) on nearby frequencies, thus improving the SNR (signal to noise ratio). If there's more noise than signal, you're not going to hear much. One might guess that such noise, which is out of the receivers IF bandpass, would not have an effect on the receive signal. Not true. The atmospheric noise mixes with other noise sources (and other signals) in the band and eventually produces noise that lands in the receiver bandpass. The loops high-Q eliminates much of this noise before the mixing occurs, thus improving the receive SNR and letting you hear signals that would buried in the noise on a wider band antenna. In transmit, the loop isn't any better than a similar size conventional HF antenna. Transmit antennas rely on their directivity to obtain usable performance. Unless you're doing spread spectrum or frequency hopping, a high-Q antenna doesn't do anything useful. Note that these are receive only loop antennas in the 300-500 KHz range: http://radiomarine.org/idbfiles/0000/0469/kgh-02a.jpg http://radiomarine.org/idbfiles/0000/1509/pioneer6.jpeg -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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