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Messages - Lamewolf

#31
Antennas / Re: Windom Antenna Analysis With The MR100.
January 10, 2017, 04:55:22 PM
Gil,

How do you interface the MR100 with a computer to get those nice looking graphs and what program do you use to do it with ?
#32
Antennas / Re: Interesting mod for off center fed dipole
December 29, 2016, 03:12:08 PM
Quote from: madsb on December 17, 2016, 10:02:41 AM
Remember that a low SWR does not indicate an efficient antenna. Otherwise I would immediately swap my dipole for a 50 ohms resistor since the resistor is both compact, lightweight , easy to set up and has a consistent low SWR across all the HF bands :)

Sendt fra min S60 med Tapatalk

True, but the resistor in  this application is not for any loading purpose since it is one million ohms, it only purpose is to protect the capacitor from static damage.
#33
Antennas / Re: Interesting mod for off center fed dipole
December 17, 2016, 09:37:17 AM
Quote from: gil on December 13, 2016, 06:01:50 PM
Interesting, I have never heard of this... Mine is working better now that I slipped ten ferrites over the coax, close to the middle, about 11m from the BALUN. I had to change the BNC connector so it was the perfect opportunity. Now the SWR is lower on all bands.

Gil

Thinking of experimenting with this myself.  I have a jumper with ferrite beads on it between the balun and feed line on mine, but been thinking of turning it into a Carolina Windom by moving it down the feedline enough to give me 15 meters.
#34
Antennas / Re: Interesting mod for off center fed dipole
December 13, 2016, 05:57:12 PM
Quote from: gil on December 13, 2016, 09:17:19 AM
Do you mean in parallel with the BALUN?

Gil

No, in series with the longer wire at the exact center of the antenna.  If the total length of the antenna is 134' then the cap and resistor goes 67' from the long end.

Rick
#35
Antennas / Re: Interesting mod for off center fed dipole
December 13, 2016, 08:08:53 AM
UPDATE !  When I first read about adding the capacitor, I thought it said to add it between the longer wire and the balun which did work well for 80 meters but raised the 40 meter swr.  The cap is supposed to go in the middle of the antenna, so if your antenna has a total length of 134' the cap would go 67' from the end of the longer wire.  Value of the cap can be anywhere from 100pf to 230pf depending on where you want resonance to fall on the 80 meter band - the higher the cap value, the higher the resonance is and most folks are getting good results using 200 to 220 pf.
#36
Antennas / Re: Interesting mod for off center fed dipole
December 05, 2016, 03:27:47 PM
Well, I took the cap back off my windom this weekend because it actually raised the swr on 40 meters  - back to the drawing board !
#37
Antennas / Re: Windom Antenna Analysis With The MR100.
December 01, 2016, 01:30:20 PM
3.5 to 3.8 ?  I doubt it would help as it moves the resonant frequency up the band which would probably put it out of your privileges.  Didn't realize you could only cover the lower end of the band.
#38
Antennas / Re: Windom Antenna Analysis With The MR100.
December 01, 2016, 09:46:09 AM
Gil,

Looking at your 80 meter swr curve here and it looks like your antenna could benefit from adding the capacitor between the balun and longer wire, but if you do be sure and put the 1 meg 3 watt non inductive resistor across the cap to protect it from static damage.
#39
Antennas / Interesting mod for off center fed dipole
December 01, 2016, 08:19:28 AM
My homebrew off center fed dipole has always needed a tuner on 80 meters, but I discovered that by adding a 80pf to 130pf high voltage capacitor between the balun and the longer wire it lowers the swr and moves the lower swr up the band somewhat.  My best swr on 80 was 2.4:1 at 3.5 MHz and quickly rose as I tuned up the band.  I operate around 3.810 to 3.830 where the swr was around 3:1.  I found a 120pf 5KV disc cap in my junkbox and decided to try it and it moved the useable swr up to 3.850 and dropped it to 1.5:1 with a <2:1 swr from 3.750 to around 3.950.  The value of the cap determines the resonant point, so by varying the value, you can move the resonant point around within the band.  Also, put a 1 megohm 3 watt non inductive resistor across the cap to protect it from static charges.  Anyway, I can now operate 80 meters on some of my favorite frequencies without a tuner.
#40
Quote from: cockpitbob on August 24, 2016, 09:02:43 AM
I built one but never used it much.  I need to dust it off.  My house has become ridiculously noisy (like S-7 to S-8 on 20m).

After I told a friend of mine about building mine, he started reading about them on the web and built one himself.  Then with it hanging from the rafters in his basement (underground) workshop, he worked a bunch of DX with it running only 50 watts !  He calls me on the phone and tells me he is working DX with his newly built toy, and I tell him I didn't doubt it and that's when he tells me that it was underground when he did it - that blew me away !
#41
Antennas / Re: Coax Length and SWR.
October 08, 2016, 10:13:19 AM
Quote from: gil on October 06, 2016, 04:03:56 AM
I agree. Lots of transmitters today are also protected against high SWR. It surprised me to observe that a "random" end-fed wire is practically, if not quite, as good as a resonant half wave. You can load up anything with a good tuner.. Antenna size seems to be much more important. A good counterpoise for anything other than a half wave helps a lot too.. I happily transmit with a SWR up to 2.5:1. I'd rather not have tuner losses when using QRP. With the RT-320 I don't even care.. When using digital modes I'm a bit more careful, but CW or SSB, nah..

Gil

Gil and gang,

Even though the radio may be protected does not exclude losses in the system.  The system being feed line, connectors, tuners, antenna etc.  All of these components can introduce losses, and so does a mismatch.  To figure efficiency, you have to take all of this into account.  For example, if you have 3db of loss in the feedline, you lose about half the power you put into it in the form of heat in the feed line, so again - 100 watts in, 50 watts effective radiated power (ERP).  Now couple that to an antenna that has 3db of gain which effectively doubles the power, and you are back to 100 watts ERP, but if the antenna is an isotropic radiator (no gain), your ERP is still 50 watts.  So even thought the radio is protected doesn't mean you are operating into an efficient load.  So with your RG174 coax, you could see a big improvement by using cheap RG58 coax which only has about 28% loss in 100' at 14 MHz compared to 50% in the RG174 !
#42
Antennas / Re: Coax Length and SWR.
October 08, 2016, 09:52:09 AM
About 3db of loss (half power) in 100 feet of RG174 at 14 MHz, so at that frequency you are looking at 100 watts in with about 50 watts to the antenna - not very efficient !  But ice may not form on your coax in winter when transmitting !  ;D

PS: That is in a matched condition, as swr rises so does loss !
#43
Gang,

I just updated the original post to include resistors 1, 2, & 3 values that I had omitted in the schematic.
#44
Antennas / A different take on the off center fed
September 29, 2016, 10:06:12 AM
Wondering if anyone here has ever used one of these ?
If so, let us know how it worked out and how well the match was.

http://www.g7fek.co.uk/software/G7FEK%20antenna.pdf



Rick - KC8AON
#45
Antennas / Re: PAC-12 antenna
September 21, 2016, 01:31:38 PM
HERE'S ONE ANTENNA I WOULD RECOMMEND ! http://www.aerial-51.com/model-807-ul/