Cascadia Antenna Solutions

but the problem is you plan on having them electrically connected to each other

 

The SWR Myth

There are several inexpensive ways to measure an antenna's input impedance with a fair degree of accuracy, typically ±5%. The MFJ-259B is one. If you have, and know how to use, antenna modeling software like EZNEC, you can get fairly close to an antenna's real-world efficiency by comparing the measured parameters against calculated ones.

If you have the acreage, the right kind of test equipment, a fair knowledge of antenna theory, some cash liquidity, and a whole lot of time on your hands, you can even measure the signal strength at any given angle of radiation within a few percentage points. Alas, most amateurs don't have these facilities, so they resort to the SWR myth.

Measuring the SWR is an easy task, so I suspect this is why neophytes often use SWR as a means of quantifying and qualifying their antennas. The truth is, a low SWR means nothing other than your transceiver will be happy! Maybe!

One thing is for sure, it will not give you the true resonant point, unless the antenna's input impedance (at resonance) is exactly R50 +jØ; a very rare occurrence indeed! Fact is, it is possible to damage some transceivers even though the SWR appears to be low.


Thats a paste from k0bg.com

 

It takes a bit to sink it but i see the error of my ways.....I seem to shoot 1st and ask questions later kinda thing...Then i get mad at myself for not doin just that..Its the stubborn pig headed butt hole in me..

Tks for saveing me my radio and anger of my failure..Ill just put the pole idea on hold till somethin better comes along..

 

Sorry but I'll still take a 1:1 or 1:2 over a 1:5 or 1:7 any day but that's just me....

 

The difference in a 1:1 to a 1:5 is 3 watts per hundred..You wouldnt notice 12 watts dude on that xxx

 

A very common belief is that the lowest VSWR point is always the exact resonant point. This is a myth! For example, an unmatched, HF mobile antenna, of decent quality, will have an average input impedance of ≈25 ohms at resonance. This represents an VSWR of 2:1. This fact can be easily demonstrated by measuring the input impedance with an antenna analyzer.

By definition, an antenna's resonant point will be when the reactive component (j) is equal to zero (X=Ø, or +jØ). At that point in our example shown at left, the R value reads 23 ohms, and the SWR readout will be 2.1:1 (actually 2.17:1). If we raise the analyzer's frequency slightly, the reactive component will increase (inductively) along with an increase in the resistive component, hence the VSWR will decrease, perhaps to 1.4:1. In this case, the MFJ-259B is connected to an unmatched, screwdriver antenna mounted on the left quarter panel, and measured through a 12 inch long piece of coax. This fact is shown graphically in the image at right.

Depending on the transceiver in question, the resulting reactance may or may not cause any major problems, but it is still advisable to properly match your antenna. It should be noted, however, if your antenna doesn't require matching (input impedance ≈50 ohms), you need a better antenna and/or mounting scheme!

Looking at this another way. You measure your antenna's SWR with an SWR bridge, and it's 2:1. If there is no reactance present, then the input impedance of the measured antenna could be 25Ω (typical for a short HF mobile antenna), or it could be 100Ω. It could also be 50Ω ±35j. The only way you would know if there was reactance present, would be to use an antenna analyzer instead of the SWR bridge. Because of this issue, the SWR readout of any antenna analyzer should be ignored while attempting to match a mobile antenna!

If the input impedance of an antenna is other than 50 ohms non reactive (50R +Øj), any length of coax inserted between the antenna, and the antenna analyzer (or VSWR bridge), will skew the readout results. The amount of skew depends on the magnitude of the mismatch, and the length of the coax in question. For this reason, antenna analyzer measurements should be taken as close to the antenna as possible.

 

way too much emphasis is placed on achieving a low SWR. Adding insult to injury, the methodology most amateurs use to check (or set) their SWR is incorrect. A fact which will soon become glaringly evident.

At resonance, the input impedance of a decent-quality, correctly-mounted, HF mobile antenna will be about 25 ohms. By definition, the resonance point is where the reactive component equals zero (X=Ø, or +Øj if you prefer). Since the requisite impedance of our feed line is 50 ohms, the resulting SWR would be 2:1. However, if you adjust the antenna to a frequency lower than the true resonant point, the indicated SWR will decrease, perhaps to 1.5:1. For this reason, you should use an antenna analyzer with a reactance readout, when adjusting any antenna matching coil or device.

Again, you should look for the lowest reactance (X=Ø), not the lowest SWR when adjusting any matching device. Once the matching device is properly adjusted, the minimum SWR point on your transceiver (or external SWR meter) will be very close to the actual resonance point of the antenna.

Just to make sure this point is as clear as possible..... With respect to the input impedance of a mobile antenna that is lower than 50 ohms, when you adjust the antenna to a frequency lower than the true resonant point, the resistive component will increases faster than the reactive component, which causes the indicated SWR to decrease!

You can demonstrate this for yourself by adjusting your antenna analyzer to the lowest reactance (X=Ø, or as close as you can get to it), and noting the SWR. Then, adjust the analyzer's frequency until the SWR is at its lowest, and note the reactance. It will mimic the chart shown upper right (the reactance is shown in red, and the SWR in blue).

The two photos depict a 40 meter resonant antenna before (left), and after (right) proper matching. Please note that the right photo shows a few ohms of reactance. This is due to basic accuracy of the instrument in question (≈±5%). Make note of the frequency shown on the 259B. This is indicative of what you'll see while you're in the process of of adjusting an antenna matching coil or device. It is included here, because (as noted above) adjusting a remotely tuned HF antenna's matching coil is the prime use for an antenna analyzer in a mobile scenario.



So basically its sayin that lowest swr is not sayin your ant is tuned,close but not exact as it can be..I would take a 1.5 swr with zero reactance over the opposite way..

 

Well I've gotten a 1:1 at 50 ohm. Before......all that mumbo jumbo where has it ever really gotten you in getting better range or receive or anything for your radio.. I mean really what has all that time and reading done for you ?????

 

If your not using the correct amphenol connectors and if the center pin does not go up into the connecter all the way. And screw on effortlessly your pissing in the wind with getting decent readings off a AA

 

You have seen my readings...You also know there is more to it than just swr/resonance..
Swr is just a way of say how happy the radio is with the connection to your ant...
Half the stuff i read is over my head so its been trial and error...I cant complain with my skip shooter but its sway is what gets in my nerves...
With all due respect bud it seems you battle everyone about darn near everything....Im sure the people that put out the arrl book and "SOME"of the site know a butt load more than 95% here so who are we to argue..
Simple bud,if you think its bs and you dont like it before you experiment to find out then dont pay attention to it..