I have a different opinion on buying used heliax. Unless you scan it (TDR minimum) you will never know if what you are purchasing is a piece of good used heliax... or something hit by lightning now has carbon track shorts and/or dielectric that is saturated with water. While some lucky people have purchased used heliax with success, I would use the same common sense as when purchasing any used coax.
Dr. William J. Schmidt - K9HZ / J68HZ/ 8P6HK/ ZF2HZ Owner - Operator Big Signal Ranch Staunton, Illinois email: b...@wjschmidt.com -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Jim Miller Sent: Sunday, July 28, 2013 7:51 PM Cc: elecraft@mailman.qth.net; John Fritze Subject: Re: [Elecraft] KAT-500 and 30' Flag Pole Antenna Users? John When working through your setup consider getting some 7/8" hardline to use as feed which depending on your run length to the antenna may allow you to keep the KAT500 in the shack with acceptable loss. You'll still need some coax jumpers to get from the hardline to the rig inside the house so you'll need to calculate and add that loss along with the little bit at the antenna. Any of the online loss calculators will give you the answers. Use 10:1 as the max SWR estimate at the antenna to calculate the feedline loss since the KAT500 can't tune more than that anyway. Here's some examples: @10:1, LDF5-50, 3.5Mhz, 100ft yields a total loss of 0.32db. Same for 28Mhz yields 0.86db. http://www.arrg.us/pages/Loss-Calc.htm Such hardline is readily available at much less than new prices if you buy used. I paid a bit over $1/ft for mine if you're luck you might even find it free. Connectors are pricey but since you only need two, no big deal. The tradeoff is having the tuner in the shack where is it visible and usable without concerns for weather vs temperature and humidity issues outside. 73 jim ab3cv On Sun, Jul 28, 2013 at 8:24 PM, Javier Campos <nm6e_...@sbcglobal.net>wrote: > Thanks to all for the replies. Excellent points and real life experiences > have provided some valuable insight. > > The antenna should be her in about a week or so. > > I will use my MFJ antenna analyzer (I hope it still works) after I get it > standing up and eventually (need to let the "look" set in of just the > aluminum) for the neighbors before I attach the UNUN and the radials. > > After all, it's a "Flag Pole" to my HOA so I just need to let it sit there > and let the novelty wear off before I attach UNUN, lay the radials and dig > the trench for the coax. > > It will also give me time to freshen on on plotting the R+jx on the smith > charts, again after 24+ years from doing in it in college. > > Thanks again and you will all here from me once this is all installed and > put together and on the air. > > Javier NM6E/5 > > > ________________________________ > From: John Fritze <fritzej...@gmail.com> > To: elecraft@mailman.qth.net > Sent: Sunday, July 28, 2013 2:35 PM > Subject: Re: [Elecraft] KAT-500 and 30' Flag Pole Antenna Users? > > > Javier, > > Here's some additional info for you to my first post. > > A lot of great info can be found here regarding the antenna design you are > considering: > > http://www.sgcworld.com/technicalInfoPage.html > > If the tuner is at the radio and the output from the tuner is coax (such as > a built in tuner in the K3) the tuner is tuning the coax and not the > antenna. It will make the rig happy and isn't that what we mostly are > looking for anyway? But the main problem is how do we get the most > transfer of power between the coax and the antenna? > > A schematic circuit of any antenna is a resister, inductor and capacitor in > series. By adjusting the capacitance or the inductance we can try to > arrive at 50 Ohms to match to coax. That's what a remote tuner is trying > to do by adding capacitors and coils into the circuit. Once the match is > found, then the rig output, coax, and antenna are all 50 ohms giving us the > maximum transfer of power so it is not burnt up as heat in the coax. > > A remote tuner tunes the antenna and the coax is effectively flat SWR from > the rig to the tuner. One problem I have found is that coax should NEVER > be used at the output of a remote tuner (BUT we all do it don't we, even I > do on occasion)! From the remote tuner to the antenna it is all antenna > and it is all radiating. West Marine sells a product called high voltage > wire, it is 10 or 12 gauge, stranded and tinned, covered with a white PVC. > It is not cheap but it is a really good product. Sometimes a remote tuner > will tune with a short coax at the output, but it won't be happy and you > will find that the tuner will hunt for a solution. > > One other issue folks sometimes have is trying to tune the vertical when it > is too short for the tuner. Ideally you need to be 42-43 feet to work > 80-10 meters. If you want to sometimes get on 160, then you need to be > closer to 55 feet at a minimum, but then you are compromised at 10-6 > meters. Not because the antenna won't tune the longer vertical but because > angle of take off is too high. If you try to tune an antenna which is too > short, the voltages at the relays can be very high, causing arching and > burning of relay contacts. One way around this is to tune at a very low > output, then raise power once the relays have set where they need to be. > Be careful to not vary too far in frequency however! Another solution is > to add in inductance by jumpering in a coil when you want to work the lower > bands. There are numerous articles in QST about getting a 42 foot vertical > onto 160 meters. > > Remember: a properly grounded vertical antenna is only about 25-30 ohms. > So right off the bat you have a 2:1 mismatch. I also do not use an UNUN or > balun of any type and have not had any issues. Again, you need a VERY GOOD > GROUND. > > I know for the real antenna gurus out there everything I have stated is > kind of simplistic and there are tons of variables and best solutions per > application. I am just giving you 30 years of real world experience. > > > -- > John Fritze Jr > K2QY > AARA president 2013 > ACACES secretary 2013 > Albany County RACES Radio Officer > ARES ENY DEC Northern District > Hudson Div. Asst. Director > Twitter: @k2qy > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
