Mal, last time I checked "full size" for 40m
really was about 66 feet, so ... ah ... B->
While you can build your antennas any way you
want to, most others have found that the use
of a properly designed balun does have benefits.
I predict you and Jim are about to have an ah
eeerrrr ... "interesting conversation" as to
the topic of baluns and if they are needed. B->
73 de Billy, AA4NU
-----Original Message-----
>From: N7mal <n7mal@citlink.net>
>Sent: Jun 19, 2008 6:52 PM
>To: William Moore <whmoore@sympatico.ca>, towertalk@contesting.com
>Subject: Re: [TowerTalk] Trapped in antenna trap confusion
>
>Bill here is what I've used for many years very/extremely successfully and
>more important why.....
>I've used the reyco traps. The keyword is traps. They really are traps, not
>dipole shorteners like those ugly bulky high-gain things. An 80/40 meter
>reyco trap dipole is only about 12 feet short but not where it counts. If
>you use the KW40 traps the 40 meter portion of the antenna is full sized(33
>feet). That 33 feet is also the full current portion for 80 meters. That is
>why the term trap fits them and not so many other products.
>I also have never used, and will never us, a balun on a dipole. I will stack
>the performance of my dipole up against anyone using baluns and I guarantee
>I will equal or beat them every single time.
>I know there are a lot of engineers etc here who will provide all manner of
>documentation but I'm an (cranky) 'old-fart' who relies wholly and solely on
>practical/real world experience. I've tried baluns and for me all they add
>is weight and expense.
>Good Luck with your project
>Again just my -2cents worth
>73
>
>
>MAL
>N7MAL
>BULLHEAD CITY, AZ
>http://www.n7mal.com
>Everyone in the world is
>entitled to be burdened
>by my opinion
>
>
>----- Original Message -----
>From: William Moore
>To: towertalk@contesting.com
>Sent: Wednesday, June 18, 2008 20:12
>Subject: [TowerTalk] Trapped in antenna trap confusion
>
>
>Hello,
>
>I seek help in resolving some confusion with respect to antenna traps.
>
>I am an Old Timer, who has been passively active in Amateur Radio since
>first licensed in my early teen years. Now retired, I want to pick up from
>my all too short youth and recapture the awe, glory, excitement and
>satisfaction of radio magic that comes from kit builds and home brew station
>set-ups. Winter is now over, my K2 is complete, the J-38 key cleaned, and
>my code speed is approaching a respectable 15 wpm. So, with spring in the
>air, an OT's fancy turns to ............well, ummm, thoughts of
>constructing some simple home brew antennas.
>
>My bands of interest (until higher band conditions improve) are 75, 40 and
>20 metres. Open wire feeders to my antenna garden are not at all possible.
>Access to the antennas will be 100 foot conduit runs of RG-8 coax to the
>antenna locations. I also live on a rock pile which is well covered in a
>dense forest making ground mounted vertical installations impractical. Trees
>for dipole supports are limited to about 30 feet likely resulting in NVIS
>like dipoles for 40 and 80. What I have in mind from my literature review
>are to construct a horizontal 80/40 trap dipole and an elevated 40/20 trap
>vertical. The dipole design would be a classic W3DZZ type or perhaps the
>newer style W8NX type using coaxial traps. These two dipole antennas are
>described in the 19th Edition ARRL Antenna Book or at
>http://www.arrl.org/tis/info/Trapped.html
><http://www.arrl.org/tis/info/Trapped.html.> . My proposed vertical is
>based on an article "Four Bands on a Pole" by W4DWK/W1CQS which appeared in
>the September 1972, QST, or at
>http://www.arrl.org/tis/info/Vertical-H.html. This vertical antenna is
>essentially a 1/4 wave 20 metre element terminated into a 14.150 Mhz trap,
>which is followed by a 10.5 foot element extension beyond the trap to
>provide a reasonable match at 40 metres.
>
>However, questions and confusion conflict my decisions
>
>1. Should I forget using coaxial traps in favour of the W3DZZ classic coil
>and capacitor traps? W8JI offers some compelling arguments against coaxial
>type traps in his speaking notes on this subject located at
>http://www.w8ji.com/traps.htm. I draw the conclusion that coaxial traps are
>too low in Q, lossy and inefficient for an effective trap. However, are they
>sufficiently poor that they should be removed from consideration?.
>
>2. What should be the design frequency trap of antenna traps? W8JI
>recommends in his notes that the trap resonant frequency should NOT be at
>mid-band. For instance, he suggests 6.5 Mhz for a 40 metre trap. On the
>other hand, the ARRL Antenna book recommends that a 40 metre trap should be
>designed for 7.150 Mhz. Also, how would one ever calculate the correct
>frequency for other bands using W8JI's trap frequency recommendation?
>
>3. Trap capacitor selection? To build a conventional (High Q) trap would
>require a good HV mica transmitting capacitor. However, I can't find a
>reasonably priced source for these old mica transmitting capacitors that
>used to be so prevalent. One could use ceramic capacitors, I suppose.
>However, according the ARRL Antenna Book ceramic capacitors are subject to
>changes in capacitance when subjected temperature fluctuations. I live in
>north-eastern Quebec where the temperature throughout the year can vary
>between +/- 33 degrees C from zero. So, I don't know if I could use these
>caps because so far, I can't find any charts showing the temperature affects
>on ceramic capacitors.
>
>4. Trap element lengths? None of the articles I have read provide a
>formula or a rule of thumb for determining the estimated element length(s)
>of the next lower band following the trap.
>
>As my background is in the field of business and economics, any layman's
>answers, suggestions or recommendations will be very much appreciated. Thank
>you.
>
>Bill VE2WMA
>
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|