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Messages - Lamewolf

31
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.
32
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.
33
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.
34
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 !
35
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 !
36
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 !
37
Gang,

I just updated the original post to include resistors 1, 2, & 3 values that I had omitted in the schematic.
38
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
39
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/
40
Antennas / Re: PAC-12 antenna
September 20, 2016, 05:57:46 pm
A hunk of wire if its long enough will be much more efficient than the PAC12 ever could be.  The PAC12 will work but requires being tuned to frequency to work properly, but a wire of 33' to 130' fed with a tuner will work much much better.  If you want store bought, there are tons of ready made wire antennas out there and you have lots of trees to hang them from, you will be more pleased with the operation of these than you would that puny little PAC12 !  With antennas, BIGGER IS BETTER !
41
Antennas / Re: Microlight 40M OCF portable antenna
September 20, 2016, 04:21:17 pm
Must be due to the surroundings, my swr on 20 is perfect, so is 40, 17, 12, and part of 10. On 80 it starts low at 3.5 MHz and is almost 4:1 at 4 mhz.

Anyway, got time to put the microweight OCF together and hang it up long enough to sweep it on the MFJ-259B and the swr is around 2.5:1 on 40, 20,15 & 10 meters, around 3:1 on 12 and 17 meters.  The wires are presently at 13' and 54' and I may be able to get the swr lower by adjusting the wire lengths.  At any rate, its close enough that he tuner in the Icom 703 will knock it down to nothing on all bands and that includes 30 & 60 meters !
42
Antennas / Re: Microlight 40M OCF portable antenna
September 20, 2016, 01:28:38 pm
Quote from: gil on September 16, 2016, 05:53:09 pm
Mine is 44+89ft.
Gil


My 80M OCF is also 44' & 89' with a dual core guanella current balun wound on FT240-61 cores.  But I didn't get so lucky on 15M where the swr is 5:1 across the band.
43
Antennas / Re: Microlight 40M OCF portable antenna
September 16, 2016, 05:53:03 pm
What was the title of that thread Gil ?
44
Antennas / Re: Microlight 40M OCF portable antenna
September 16, 2016, 05:47:01 pm
Quote from: gil on September 16, 2016, 01:52:55 pm
It should be, but surprisingly no.. I will test more soon.. I think the SWR was high on 15 but not overly so.. I can't find my notes.. It will undoubtedly work fine with a tuner. So far the antenna seems pretty efficient. Still no contacts with the US though, depressing.. I am looking forward to Lamewolf's report..

Gil


Gil,
I looked at my graph on my 80M OCF and the SWR on 15 was around 5:1 which is fairly normal but it was a flat 5:1 across the band.
45
Antennas / Re: Microlight 40M OCF portable antenna
September 16, 2016, 05:38:11 pm
BTW, I meant to add that to get 15 meters on an 80M OCF you have a couple of options.  One is to use a voltage balun to feed a standard 45/90 split antenna and the voltage balun will allow the feedline to radiate but put a good 1:1 choke 22' below the voltage balun to make that portion of the feedline resonant on 15 meters - this is called a "Carolina Windom". I do not like a radiating feedline if I can help it but it does work.  The other option is to use a different offset, and with something like a 25' - 109' offset, 15 meters will work too but does cause and imbalance that would normally cause feedline radiation, but that can be cured with a good 1:1 guanella current balun connected between the coax and the 4:1 balun and the 4:1 and 1:1 can be built into the same box if you wish.  This will allow 15 meter operation but also assures that the antenna is radiating the signal and not your coax !  And that's what I plan on with my microlight 40 OCF.  It will use lengths around 17.4' and 55.6' and should cover 40, 20, 15, & 10 meters without a tuner plus 12, 17, & 6 meters with a tuner but 12, 17, and 6 meters should have a low enough swr to still be fairly efficient and not too much loss on it.  As long as the swr is 3:1 or under, the losses aren't really all that high and the antenna will still work well when using a tuner.  And the super thin RG316 coax (about the same diameter of RG174) is still fairly low loss and from what I've read will handle a lot of power !  But I'm using it to save weight since I will only be running around 10 watts through it.