Depends on whether your main goal is to work people easier, or it's an
intellectual pastime. Frankly modeling and EZNEC are a great pastime
: >) If you're mainly looking for improving your signal, it's all in
what you do about the dirt. 73, Guy.
On Mon, Feb 1, 2010 at 4:04 PM, Art Trampler <atrampler@att.net> wrote:
> Thanks for the reply Terry.
>
> Well I'd wondered about the effect of the losses. I modeled a smaller
> resistance in the coil, but was doing it incorrectly, based on the wire
> length and gauge.
>
> I know antenna modeling could become addictive. One of the beauties of
> WX7G's design is in its simplicity and its ability to be made. There is an
> elegance there that a newbie like me would not be able to emulate. I might
> work and work and work and come up with an interesting solution...and it
> would likely be overly complicated.
>
> Is EZNEC the place to start?
>
> Art
>
> -----Original Message-----
> From: Terry Conboy [mailto:n6ry@arrl.net]
> Sent: Monday, February 01, 2010 2:31 PM
> To: antennaware@contesting.com
> Cc: atrampler@att.net
> Subject: Re: [Antennaware] center loading versus ground loading
>
> The unloaded Q of the inductor should have a very minor effect on the
> bandwidth and efficiency of WX7G's 67 foot antenna on 160m. The series
> resistance of a 70uH coil with Q=400 is only about 2 ohms. If the coil
> Q was 600, the Rs would drop to about 1.34 ohms. The sum of the
> radiation resistance and ground loss resistance would probably be much
> higher and swamp such a small change in coil Rs. In addition, the
> current in the coil is less than the current at the feedpoint, so this
> transforms the coil loss Rs to a smaller value at the feedpoint.
>
> My EZNEC model shows the feed Z goes from 23.74 ohms down to 23.38 ohms
> if the top load Q rises from 400 to 600. The gain at 24 degree
> elevation rises from 0.18 dBi to 0.25 dBi. The 2:1 bandwidth drops from
> 43 to 42 kHz. The top coil dissipation drops from 69 watts to 46 watts
> (with 1500 watts drive). This assumes a fairly good ground system with
> 5 ohms of equivalent loss resistance (which appears in series with the
> radiation resistance at the feedpoint) which burns up about 300 watts of RF.
>
> A lot of commercial ham antenna manufacturers depend on high coil losses
> to provide a match to 50 ohms at the feedpoint, especially in mobile
> antennas. Of course, you pay for this in poor signals. Some mobile
> loading coils are near self-resonance at the operating frequency, which
> can really burn up RF due to circulating currents.
>
> 73, Terry N6RY
>
> PS - Art, thanks for the link to the nice inductance calculator. Since
> this is the Antennaware list, you need to get your feet wet with antenna
> modeling, too. It's disgustingly addictive!
>
> On 2010-01-31 7:34 PM, Art Trampler wrote:
>> Dave,
>>
>> Sounds promising...and making more sense than my idea of using irrigation
>> pipe.
>>
>> First off, since you obviously understand more about this than I do, thank
>> you. Second, you might enjoy this calculator and discussion:
>>
>> http://hamwaves.com/antennas/inductance.html
>>
>> In order to minimize coil losses, would a more square design (length to
>> diameter) be preferable? Or are you concerned about the coil having too
>> great a Q and therefore limited bandwidth?
>>
>> In my "envisioning" of using the coil to choke the radiator around 65 feet
>> or so, I was thinking of a large coil, perhaps 4 or 5 inch diameter. I
> run
>> the Hy-Gain AV640 and notice the coils do warm up, so assume that such
> heat
>> is loss.
>>
>> The 2" diameter coil would be about 8 inches long, right? This program
>> shows a Q of about 400 ohms at 1.8mhz, which surprised me. Is there any
>> advantage or disadvantage, electrically, to a coil that was similarly
> wound
>> but 3.5" x 5"?
>>
>> Thank you for working this through...it sounds great and do-able. I am
>> curious as to your thoughts on different coil design methodologies.
>>
>> Art
>>
>>
>> -----Original Message-----
>> From: antennaware-bounces@contesting.com
>> [mailto:antennaware-bounces@contesting.com] On Behalf Of DAVID CUTHBERT
>> Sent: Sunday, January 31, 2010 7:56 PM
>> To: aa4nn
>> Cc: antennaware@contesting.com
>> Subject: Re: [Antennaware] center loading versus ground loading
>>
>> Gary,
>>
>> The Battlecreek is a good antenna. However, It looks like a lot of work
>> though to get the tubing lengths correct before and after the 40 meter
> trap
>> as well as to tune the 160 meter wire.
>>
>> Here is two band vertical that is easier to tune up. It is for 80 and 160
>> meters and it tuned from the base. Put up the antenna one time and tune at
>> the base. No relays. Direct feed with coax.
>>
>> We can write an article on the antenna for QST, CQ, or AntenneX if you'd
>> like. Here is the antenna:
>>
>> *160 meters:*
>> A 67' mast. This can be the long vertical kit from DX Engineering (about
>> $200). On top is a top hat consisting of six 0.5" aluminum tubes 6' long.
>> Right below the top hat is a 70 uH inductor. It is made of 2 inch PVC pipe
>> with close wound #14 THHN wire (from the hardware store). To adjust it to
>> resonance on 160 meters a 10 uH base coil is adjusted.
>>
>> The top hat mass can be reduced by using the DX Engineering top hat with
> the
>> long spokes. The inductor will need to be sized for this. I can do this in
>> EZNEC.
>>
>> *80 meters:*
>> A 64' wire spaced 2' from the mast. It is base tuned with a loading coil.
>> About 2 uH. The bottom of this coil connects to the bottom of the 160
> meter
>> tuning coil. The coax attaches there.
>>
>> Put up the vertical. Tune 160 meters. Tune 80 meters. Done.
>>
>> Dave WX7G
>>
>>
>>
>>
>> On Sun, Jan 31, 2010 at 1:23 PM, aa4nn<aa4nn@earthlink.net> wrote:
>>
>>
>>> HI Gary,
>>> All you need do is emulate the Battle Creek Special.
>>> You can google to get specifics. The BCS uses only
>>> one wire to top load for 160m and only one wire to top
>>> load for 80m. Excellent antenna...no switches, no tuning,
>>> just change bands and go. If you are unable to find
>>> specs, let me know.
>>> 73& all the best.
>>> de Joe, aa4nn
>>> Lake Wylie, SC
>>>
>>> ----- Original Message -----
>>> From: "Gary K9GS"<garyk9gs@wi.rr.com>
>>> To:<antennaware@contesting.com>
>>> Sent: Sunday, January 31, 2010 2:41 PM
>>> Subject: Re: [Antennaware] center loading versus ground loading
>>>
>>>
>>> I have been contemplating an antenna design to cover 40, 80, 160M.
>>> Basically ~32 ft of aluminum tubing/mast, a trap, then more tubing/mast
> to
>>> ~60 ft (possibly using a capacity hat to tune on 80M) and then a second
>>> trap
>>> above the capacity hat with a T-top loading wire to tune on 160M. My
> goal
>>> would be no switching/control lines at the antenna. I work almost
>>> exclusively CW so I don't need to cover the entire 80/160M band.
>>>
>>> Thoughts??
>>>
>>> 73,
>>>
>>> Gary K9GS
>>> ++++++++++++++++++++++++++++++++++++++++++++++++
>>> K9GS
>>> Gary Schwartz email: k9gs (at) arrl.net
>>> Check out K9NS on the web: http://www.k9ns.com
>>> Society of Midwest Contesters (SMC) http://www.w9smc.com/
>>> GMDXA http://www.GMDXA.org<http://www.gmdxa.org/>
>>> ++++++++++++++++++++++++++++++++++++++++++++++++
>>>
>>> ----- Original Message -----
>>> From: "Art Trampler"<atrampler@att.net>
>>> To:<antennaware@contesting.com>
>>> Sent: Friday, January 29, 2010 10:48 PM
>>> Subject: [Antennaware] center loading versus ground loading
>>>
>>>
>>> I live on a fairly small lot and use a Hy-Gain AV640 for 40 through 10
> and
>>> currently have no antenna for 80 or 160.
>>>
>>>
>>>
>>> My backyard is about 90 x 70 but has some ill-placed and ill-shaped trees
>>> for either wire antennas or a tower.
>>>
>>>
>>>
>>> So I am thinking of another vertical, but this one ¼ wave with a radial
>>> field. I would like to get 80 and 160 out of it. I don't mind having to
>>> guy it, or even having to pour a concrete base for it.
>>>
>>>
>>>
>>> My first thought is to use aluminum irrigation pipe as others have, and
>>> have
>>> about 60 to 65 feet of it, an insulator and inductor and high voltage
>>> relay,
>>> and then perhaps 15 to 20 of much smaller aluminum tubing, with a sloping
>>> capacity hat of four wires going partially down the four top guys. I
>>>
>> don't
>>
>>> know if I could get away from the relay, and put up a trap instead but am
>>> wary of using a true trap (coil& capacitor) rather than just a large,
>>>
>> high
>>
>>> Q coil.
>>>
>>>
>>>
>>> As you can see this idea is full of possibilities and mechanical
>>>
>> drawbacks,
>>
>>> so the question is, is there that much to gain from the center-loaded
>>> design
>>> with capacity hat, versus a switchable tuning network at the base of the
>>> antenna?
>>>
>>>
>>>
>>> Your input is appreciated. I am hoping to make this a summer project and
>>> reward myself with 80 and 160 in the winter.
>>>
>>>
>>>
>>> 73,
>>>
>>> Art
>>>
>>>
>>>
>>> Art Trampler, KØRO
>>>
>>>
>>>
>>> _______________________________________________
>>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 8.5.432 / Virus Database: 271.1.1/2662 - Release Date: 02/01/10
> 12:37:00
>
> _______________________________________________
> Antennaware mailing list
> Antennaware@contesting.com
> http://lists.contesting.com/mailman/listinfo/antennaware
>
_______________________________________________
Antennaware mailing list
Antennaware@contesting.com
http://lists.contesting.com/mailman/listinfo/antennaware
|