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Author Topic: Do I need an antenna analyser?  (Read 2822 times)
M5AEO
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Posts: 273




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« on: August 21, 2012, 12:26:59 PM »

I enjoy building antennas for HF and 2m and was wondering if an 'antenna analyser' would be a good investment.  They are quite expensive, and because I don't really know how to use one I'm a bit hesitant to buy one.  Also they only seem to be made by MFJ, which is slightly worrying re: quality.

Jonathan, M5AEO.
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W5FYI
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« Reply #1 on: August 21, 2012, 12:36:34 PM »

I've been happy with this one: http://www.autekresearch.com/va1.htm.  The links on the web site tell more.  I like it because it is shirt-pocket sized, operates from a single 9V battery, and has an auto-off feature. GL
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AA4PB
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« Reply #2 on: August 21, 2012, 12:37:45 PM »

Try a google search - there are a number of others like Palstar and RigExpert to name a couple.
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W5DXP
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« Reply #3 on: August 21, 2012, 12:51:05 PM »

They are quite expensive, and because I don't really know how to use one I'm a bit hesitant to buy one.

I experiment a lot with antennas, my favorite ham radio subject. I have saved myself hundreds of hours using EZNEC and my MFJ-249B antenna analyzer. How much is your time worth and how much of it do you spend on antenna systems?
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W5LZ
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« Reply #4 on: August 21, 2012, 12:57:58 PM »

If you enjoy messing with antennas, and if you do more than just a little bit of that 'messing', then an analyzer would be very handy.  If it's just an occasional thing, it probably wouldn't be very 'frugal'.  I think they are just handier than any thing and I like playing with antennas.  It's worth it to me, can't speak for anyone else.
 - Paul
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WB6BYU
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« Reply #5 on: August 21, 2012, 01:05:33 PM »

Do you need one?  No.  Many of us experimented for years without one.

Does it make life easier?  Yes, in many cases.  It is easier for taking measurements up on the
roof than my initial approach of hauling my tube rig (with 60 pound power supply) up the ladder
to check the SWR as I made adjustments.  The later Argonaut 505 with a small gel cell battery
was much more convenient, and the hand-held devices take that a step further.

I have one of the older ones - analog dial that isn't necessarily very accurate (so I calibrate
it against my receiver if needed) and it only reads SWR on a meter, nothing else.  It certainly
doesn't give me a digital readout of impedance in R and X, but I find it useful for most
purposes:  It makes it easy to tune across the band to find the point of minimum SWR, for
example, even if it is outside the ham bands.  If I want to know the actual feedpoint
impedance, then I can calculate it by adding series / shunt elements and measuring the
shift, or grabbing a simple L network tuner, adjusting for 50 ohms, and calculating the load
impedance from the tuner component values.

If I wasn't used to working with simpler equipment, then I'd probably be more concerned
about having an SWR analyzer that does everything.  It isn't all that often that I really need
to know the input impedance of an antenna without having a computer model that gives me
a pretty good starting guess.


There are a number of problems that users can encounter from having more data available
than they know what to do with.  Probably the biggest one is assuming that X=0 at
resonance with out taking the coax length into account (including the length inside a balun.)
If you don't, then you can end up with an antenna tuned far outside the band.  I've seen
some spectacular misadjustments of gamma matches achieved by tuning it based on the
frequency of lowest SWR, rather than the lowest SWR at the desired frequency.
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M5AEO
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« Reply #6 on: August 21, 2012, 01:35:02 PM »

Thank you for the advice.  That last answer from Dale is what terrifies me about antenna science!  I don't understand very much of it!

M5AEO
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STAYVERTICAL
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Posts: 875




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« Reply #7 on: August 21, 2012, 01:36:02 PM »

Hi Jonathon,

If it is going to give you financial stress, then I would not buy one - you have to get your priorities right.
As others have said, there are more options than MFJ, so investigate them if you are in the market for one.

I have an MFJ269 and a VK5JST (HF only kit built) analyser, and I use the MFJ one most of the time.
As regards quality, MFJ gear I have bought has been mainly positive, but with some quality issues certainly.
If you do buy an analyser, make sure you have an easy warranty repair/replacement path.
You don't want to have to take it personally back to the manufacturer.

As regards how much you will use one, this is something which varies with the user.
I also experiment a lot with antennas.
I must say that the analyser, in my case as a layman - not an engineer, only comes out at the end of the process.
I use it for final matching to 50 ohms or whatever the case is.
Most of the time is spent making the antenna.
But you can certainly use your rig on low power to do the final swr tweaking.

If you think what the analyser is, and how it works, it will be helpful.

It is a low power transmitter, which is fed to a bridge where the unknown leg is the antenna.
By measuring phase and amplitude across some bridge components, a microprocessor calculates impedance.
Since impedance is a combination of resistive and reactive components (R and X), other things can also be measured.

For example, if you measure reactance of a capacitor or inductor, then you can calculate its value in Farads or Henry's.
In addition, if you short one end of transmission line, and progressively change frequency until you read another short, you can calculate velocity factor and loss of that line section.

These are only two additional things for which an antenna analyser is useful.

I would suggest you do a lot more research on the uses of analysers.
You can download the manual for the MFJ269 and it has a lot of interesting information on how to use it.
But just because it can do these things does not mean you are going to use it a lot.
So, only you know how much use it will actually get.

In my case it sits in the cupboard for 95 percent of the time, but it's 5 percent of application is certainly very useful.

73 - Rob
« Last Edit: August 21, 2012, 01:43:31 PM by STAYVERTICAL » Logged
N4NYY
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Posts: 4821




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« Reply #8 on: August 21, 2012, 02:59:39 PM »

I enjoy building antennas for HF and 2m and was wondering if an 'antenna analyser' would be a good investment.  They are quite expensive, and because I don't really know how to use one I'm a bit hesitant to buy one.  Also they only seem to be made by MFJ, which is slightly worrying re: quality.

Jonathan, M5AEO.

They are a very good investment. Better investment than a Bird meter from someone running 100W. It is amazing how many people spend $500 on a Bird meter, even though they are running 100 watts.
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N6AJR
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Posts: 9927




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« Reply #9 on: August 23, 2012, 12:17:57 PM »

pick up a used MFJ 259b, and you will be able to play antennas much easier.  also only use alkaline batteries in it, they last a long time.  if you use rechargeable batteries (1.2 volts each)  they star at a lower voltage and when it gets to about 11.5 volts it quits.  a set of alkaline will start at 15 volts ( 1.5 volts per battery) and they last a long time before the voltage drops too low.
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