Author Topic: Unexplained increase in SWR  (Read 6388 times)

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spacecase0

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Re: Unexplained increase in SWR
« Reply #15 on: February 09, 2014, 10:00:12 AM »
is it cold there ?
is maybe previously conductive water now non conductive ice ?

you can get rid of the copper grounding issue pointing your signal with an antenna that does not use the ground much, like a 1.25 wave vertical, or 5/8 wave

BTPost

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Re: Unexplained increase in SWR
« Reply #16 on: February 09, 2014, 01:51:11 PM »
PLA... If you need to build an RF Ground for your chosen Antenna System, then you need to understand that it is relatively easy to build it for ONE Frequency. HOWEVER, It is a Totally different proposition to build an RF Ground that has a Low Impedance, across the HF Spectrum. We have situation's here in Alaska, where there is NO Ground conductivity, Period. It is like siting a HF Station on a Piece of Glass. In these situations, and needing a Low Impedance RF Ground that will work across the whole HF Spectrum, One needs to think like a Broadcast Engineer, and think MANY Dozens of Ground Radials, or a complete Grid of Ground Wires. Surface Area covered is What you are looking for. The more Surface Area, the Lower the Impedance across the spectrum. Many Hams up here use the Steel Roofs on their Cabins as their RF Ground. This works well, IF and ONLY IF, all the Pieces of Steel Roofing are Electrically Bonded together to make a significant surface Area. I use this type of RG Ground, for my 5BTV Trapped Vertical.  I used a 40 ft Chunk of 1" Battery Braid, run along under the Ridge Cap and Bolted into each of the Sections of Steel Roofing to do the Bonding. The other thing that you need to understand is that the Antenna Pattern will be skewed  toward the RF Ground, if the Radiator is not Centered in the RF Ground. Most of the Radiated RF Power will be in the Direction that has the Best, and Lowest Impedance RF Ground. MultiFrequency RF Grounds are NOT easy to build or design, and understanding this has been the downfall of many a Ham, and their Antenna Systems.

http://www.99850.net/Images/House.JPG
http://www.99850.net/Images/Hf.JPG

The labeled HF Antenna in the first Picture, is the 5BTV, and the RF Ground, Favors the Lower 48 states.

The Tower in the Second Picture is used so that the Lack of Ground conductivity isn't an Issue. This is for a 1Kw Marine Coast Station, and a 150 Watt Alaska Private Fixed Station.
The Top dipole is a custom Morad Electronics Trapped Dipole for 3.2 and 5.1 Mhz.
The Middle dipole is a Standard Morad Trapped Dipole for 4, 6, 8, 12, and 16 Mhz Marine Bands.
The Bottom dipole is a Pair of Morad Electronics 1.6 Mhz Loaded Whip Antennas, mounted in a dipole configuration, and feed with a Custom SEA1612B AutoTuner with a 4:1 Balun on the Output of the Tuner to feed the dipole. If you look real close you can see the Feed Lines that go from the Tuner, mounted on the Base of the Tower, to the dipoles, just inside the Loading Coils. This Antenna System will tune ANYWHERE in the HF spectrum from 1.6Mhz to 30 Mhz, Except at the Electrical 1/2 Wave Point of the natural Resonance of the Whip Antennas, and 200 Khz on either side of that, frequency.
The Vertical Antenna at the Top, is a Super StationMaster VHF Antenna that is for the VHF Marine Coast Station.

I designed, and Installed, this Antenna System, 2 decades ago, and it is still in operation Today. Just say'en..... YMMV......

« Last Edit: February 09, 2014, 01:56:20 PM by BTPost »
Bruce in alaska AL7AQ

PLA

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Re: Unexplained increase in SWR
« Reply #17 on: February 09, 2014, 05:44:06 PM »
BT, Ive considered a blanket of hardware cloth over the whole yard, but only until I considered expense.

Ill find something that works, just have to play with it

But Ill look at your inks, I read your thread in SM on roof tuning and it was enlightening

Lamewolf

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Re: Unexplained increase in SWR
« Reply #18 on: October 18, 2014, 10:49:34 AM »
I have an offcenter Windom which has been acting up, so I put up a long wire last night thinking it would be a quick fix for the issue.

Now either antenna will not tune at all, so outside I went, analyzer in hand to see wtf is the problem. <9.9 in all bands except 80m on both antennas.

The long wire is a piece of wire and a 1:1 balun!!!!!!  Why is is jumping to <9.9 and why is the windom doing the same. I figured it had to be a connector or coax, but I swapped cables and everything I could, with each antenna running autonomous from the other, no conection between the two.


Ok experts, why?  What is going on here and why ?  Because its making me nuts

Well, for one thing you don't mention the length of the "longwire" ?  I would not expect to put up a random length of wire fed by a 1:1 balun and expect it to be resonant just anywhere - it will only be resonant at its 1/4 wave length verses frequency and then close on odd multiples of that.  But you should be able to match it on all bands with a tuner which you stated you were using but didn't mention what brand/type of tuner.  Also, on the Windom, check that balun to make sure there are no problems there.  I have seen cases with Windoms where the balun was burnt up even with only 100 watts by force feeding it on non resonant bands which can lead to very high RF voltages and arching that does all sorts of nasty things to a balun.  Even saw one balun catch on fire !