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Build Your Own Antenna - Discuss topics for building your own antenna.

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Old 01-15-2018, 6:55 AM
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Default antenna analyzer

so i'm looking to see what others use, I'm gonna be building afew different ones for my scanner. 115-137 150-160 224-400.. I'm not looking for people to tell me just by a wide band.. this is not for Tx on just Rx only..
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Old 01-15-2018, 7:28 AM
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I have the MFJ-249 analyzer. It's over 20 years old, but still does a good job.
Do you have the formulas for sizing the elements for your experiments?
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Old 01-15-2018, 7:54 AM
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Quote:
Originally Posted by KC4RAF View Post
I have the MFJ-249 analyzer. It's over 20 years old, but still does a good job.
Do you have the formulas for sizing the elements for your experiments?
I also have this analyzer. Has worked well for everything I've wanted to do.
But I believe you said you want to get up to 440. The 249 will not go that high.
Take a look at the MFJ-269 (which I've never owned). It will go up to 512.

Last edited by Golay; 01-15-2018 at 8:06 AM..
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Old 01-15-2018, 8:14 AM
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I've been doing radio since 1978 - I got my first analyser in 2015, and while it's good for telling me where the thing resonates for receive, it still 'suggests' an antenna is good that is, in fact pretty useless. All I have ever done is get to know what permanent sources exist in my area in each band - airfields, coastguards, telemetry, repeaters and even interference sources - These give me a far better result in any new antenna installation I do at home. I can tell if I've got a bit more at UHF, but have lost airband, or improved marine band at the expense of UHF. A coax switch to select between two antennas is also a great way to check a new one. The analyser did tell me that one design of antenna I'd been building for years I had always been cutting too long, and they all were resonant below the frequency I'd made them for - but the VSWR seemed fine, and they worked.

They're very good devices - myChinese one seems very revealing in what it displays - but it's not a vital piece of test gear.
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Old 01-15-2018, 10:46 AM
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I wouldn't bother with an antenna analyzer for receive only antennas. Impedance and SWR aren't near as critical for receiving as they are for transmitting.

For instance a one inch difference in a VHF quarter wave antenna will make a very noticeable difference in the SWR, but when it comes to receiving, the difference in length will be next to meaningless.
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Old 01-15-2018, 12:12 PM
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I do a lot of antenna work and an analyzer is a vital piece of equipment for me. I've owned an MFJ-259B analyzer and it was complete junk, it was plagued with intermittent problems and a band selector switch that failed early on.

I moved on to a Comet CAA-500 analog only version and have been thrilled with it. its one of the few that will do continuous from 1.5 to 512MHz getting the VHF and UHF mil air bands for testing receive antennas.

Then I got a pair of Chinese analyzers that I now use for everything. The AAI N1201SA covers 137MHz to 2.7GHZ with color graphical screen that reads out in SWR, return loss in dB and impedance from .1 to 1000 ohms. Its not a cheap piece of junk but a very accurate and reliable Vector Network Analyzer. This meter costs around $165 and you have to spend several times more $$ to equal the quality and accuracy of this meter.

I supplement the N1201SA with its low frequency brother, the AAI N2021BA which covers 1MHz to 200MHz and is a 2-port device. It not only gives you all the measurements of the of the N1201SA, it also allows you to generate a signal or sweep through a device like a filter or or length of coax or you can even tune a complete duplexer using its generate port and the S21 through loss measurement. This meter ran me about $240 and is worth every penny.

There was a comment about not needing to use an analyzer on receive only antennas. That is true if you dont care about loosing a bunch of receive signal. I used the Comet CAA-500 to do final testing on the very popular Monitoring Times X-Wing UHF satcom antenna and without those final measurements and trimming, the antenna would have never worked as well as it does.
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Old 01-15-2018, 12:40 PM
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My setup for testing relative receive-only performance:

Measuring Relative Antenna Receive Performance - Massively Uninformed

The results are relative performance. So, the exemplar antenna is measured first. The results for each antenna under test are all relative to the measurements made using th exemplar antenna. (In other words, it shows how much better or worse the test antenna is as compared to the exemplar antenna.)
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Old 01-16-2018, 5:23 AM
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ok thanks everyone for the input.... now i got some research to do on make/ models..looks like i will be going with the comet CAA-500 that prcguy talked about..
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Old 01-16-2018, 5:31 AM
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My MFJ-259B has always been an integral part of the shack test equipment. While it does not cover the UHF ham bands it is still valuable when testing and troubleshooting antennas. Also is a frequency counter and a basic signal generator. Nothing not to like about it.

Shop around as there are a number of different manufacturers, hope you find what you are looking for.
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Old 01-16-2018, 7:53 AM
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I had a MFJ-259 (don't remember what letter) back about 15 years ago. It died after it was out of warranty. A few years ago I got a RigExpert AA-1000. It's way better than the MFJ. One thing I like about it is it has a TDR function.
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Old 01-19-2018, 4:47 PM
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I've been building antennas for over 40 years and never once needed
an antenna analyzer.
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Old 01-20-2018, 9:57 AM
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So how do you check antennas that have BW extending outside the ham bands? How would you check a receive antenna for VHF air or UHF mil air or public service bands without transmitting?
Do you have a scalar or vector network analyzer?

A scalar or vector network analyzer and a return loss bridge will do the trick and give the best results. I was just playing with a new Keysight N9952A that a friend of mine just got. In addition to an antenna analyzer its a spectrum analyzer, full 2 port vector network analyzer, power meter and some other stuff in a hand held package that goes to 50GHz. Only problem is it cost $110k. Ouch.
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I've been building antennas for over 40 years and never once needed
an antenna analyzer.
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Old 02-09-2018, 3:36 PM
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Some individuals can build an antenna once that can last for 40 years. That endeavor would probably use an analyzer.
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Old 03-05-2018, 8:18 PM
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Hi Guy's

Well, I took the plunge and bought a Surecom SA-250 Antenna Analyzer.

I'm not a Ham, but I bought it to help best tune up my J-Pole scanner antenna cut for the RailRoad Frequencies.

VSWR is 1.09:1 ( it just shows 1.09, but I know it's supposed to be a Ratio).

This nifty lil critter shows me Zx, Rs and Jx as well.

I also know Zx is the characteristic impedance, Rs is the total resistance. and jX is inductive reactance (either Capacitive or Inductive).

What I would like to know is (without having to study the ARRL Hand book), what am I looking for with these other Characteristics?

Like should Rs be as close to 50 ohm's as possible?

Should Zx be like the above...as close to 50 ohm's as possible?

What about Jx ? where should that parameter fall?

I'm just trying to understand better what I'm reading!

Yes I use a Balun at the Radio connector end to eliminate common what-cha-call-it...(can't remember the term right now).

Any help Much appreciated.
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Old 03-06-2018, 2:51 AM
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You use a balun at the radio connector? Are you using flat twin feeder right back to the radio?

I~f you are using a J-Pole - just for receive, they work surprisingly well when the thing is badly tuned on receive, but the transmission tuning is much more typical. Using your meter, the most useful feature is simply to see the VSWR curve, because this shows you where it's resonant, and where it isn't, the gain suffers. With a J-Pole, you have to cut the long out and back element, but then tune the matching stub where it attaches to the vertical - so in effect, the length of the radiating (or receiving) component has to be right, and then when it is, the matching section enables as much as possible to flow down the cable. I think most people cut the radiator with maths, and tune the matching section for minimum VSWR. Zx is the one that I pay attention to - Impedance gets messed up by the phase errors that capacitive and inductive reactance contribute - but the practical upshot for my level of antenna work is that if the impedance is as close to 50 as you can get, the other parameters fall into place.

VSWR - as close to 1:1 as I can get - frankly the one measurement that really seems to matter.

There's no need for the balun if you are feeding it with ordinary unbalanced coax. It's presence in the circuit will distort your readings - so you could cut the antenna WRONG. What you need is to dump the balun and fit a common mode choke - a ferrite ring, or a few of them just to stop your feeder becoming part of the antenna - these I would put at the top, near to then antenna - because otherwise, the antenna cable could (not always will) radiate, and all your choke will do is stop the last few feet! There's no need for a balun - because the balanced part is the 1/4 wave at the top, and the feed point sorts this out.

The fella who invented the Slim-Jim, the variant of the J-Pole lived near me back in the 70s, when I was the young one - and all the older hams had one. I tried one and hated it. The J-Pole has hardly any measurable gain over a simple wave ground plane, which is so much easier to make - and apart from trimming the length, they just work. J-poles need two sections to be adjusted, 3 if you include moving the feed point. So three adjustments that can restore VSWR to 1:1 or close. However - as they interact, how can you be sure that the theoretical gain (which isn't anything special) is being achieved. You could have a wrong length, and therefore inefficient radiator electrically tuned back to 1:1 but with gain less than a dipole - I'm guessing this would be shown in the other test results the meter show - but as for interpreting them? Not sure I could use them to categorically say the top section is too short, or too long.

J-pole have a tiny amount of gain and it's made up from a bit more in one direction and a bit less in another. The polar pattern in the E plane is not symmetrical, and again, this impacts on dimples in the Omni-directional pattern too. Dipoles are fully omni, and symmetrical in the E plane.
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Old 03-06-2018, 6:29 AM
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My bad, actually I did not mean "Balun" It was a snap on ferrite bead.

Well, my question still hasn't been answered. What are acceptable parameters for ZX, Rs, and JX ?

Like I said, what am I looking to see? ZX as close to 50 ohms as possible? RS as close to 50 Ohm's as possible? JX...?

What really am I shooting for here other than the SWR of 1:1?

I need to know what the ideal for these parameters are. so I can judge whether I am close or far away from what is actually good.
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Old 03-06-2018, 7:40 AM
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Quote:
Originally Posted by Mikejo View Post

What I would like to know is (without having to study the ARRL Hand book), what am I looking for with these other Characteristics?

Like should Rs be as close to 50 ohm's as possible?

Should Zx be like the above...as close to 50 ohm's as possible?

What about Jx ? where should that parameter fall?
I have seen those questions asked before, but have yet to read a clear explanation.

Since we know what they are, we just need the next half of the information as to where those values SHOULD be .
Also, and just as important, which values are too far out of range to be acceptable?
What is too high, and what is too low?

Very, very, good questions. If we had answers to these in a concise manner, I think we could bring some discussion to a higher level as far as antenna building and installation is concerned.

Anybody willing to take a shot at it?
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Old 03-06-2018, 7:47 AM
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MFJ 259-B had mine long time works great...
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Old 03-06-2018, 11:50 AM
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I thought we had answered it?

There is very little information on these devices, but I think we should assume the resistance measurement is radiation resistance, rather then something very simple like DC resistance. Radiation resistance for a simple antenna like a wave vertical on a ground plane should read about 72Ohms. The analyser just uses the results of the sweep to implement the maths required. At resonance, the impedance is mostly resistive - so your impedance measurement indicates the impedance pretty accurately. At resonance, the reactive component should be 0 Ohms - but this would also mean that it wouldn't actually be much use as an antenna as the energy injected wouldn't be going anywhere.

So I suppose the aim is for VSWR to be 1:1, Impedance to be 50 Ohms, radiation resistance 72 Ohms and reactance 0. These will be mutually impossible to get, each having impact on the others.

If you have a 50Ohm dummy load, run this past your analyser. Then try to make all the results you get fit and produce conclusions. Sometimes weird results will make sense, once you figure out what is happening.
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Old 03-06-2018, 12:33 PM
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OK. This is what I have so far:

SWR: Standing Wave Ratio, ideal is 1.0:1, Acceptable Range is1:1 to 2.5:1
Zx: Characteristic Impedence, Ideal is 50, Acceptable Range is (40 to 65?)
Rs: Resistance of System, Ideal is 72, Acceptable Range is ??? to ???
jX: (Reactance?), Ideal is (-64?), Acceptable Range is ??? to ???

Can anyone fill in the ?? and make any necessary corrections?
I think if the answer is in this format, it will be much more readily understandable without getting too wordy or sidetracked.
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