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Author Topic: The MFJ analyzers look nice. They really do. I just don't have that money....  (Read 6844 times)
K8AXW
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« Reply #15 on: May 31, 2011, 09:21:04 PM »

I went the KJ4FUU route.... bought the MFJ-209, which was the original analyzer.  MFJ and I has a big row over this because they said it "was a stand alone analyzer."  I had to buy a Optoelectronics counter to go with it so I could get an accurate frequency readout.

This worked out real well because now I could use the counter for other things.  In the meantime, I found the analyzer indispensable.  I can tune up antennas faster and easier that with the SWR meter and do it without putting a signal on the air. 

If you want just a reasonant frequency SWR readout, go the cheapest MFJ you can get and buy a separate counter.  (The dial doesn't even come close and the unit is worthless without a counter!)
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N3OX
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« Reply #16 on: June 01, 2011, 05:49:00 AM »

MFJ and I has a big row over this because they said it "was a stand alone analyzer."  I had to buy a Optoelectronics counter to go with it so I could get an accurate frequency readout.

This worked out real well because now I could use the counter for other things.

How much did you end up spending on the pair?  You can just use the MFJ-259B counter when you need a frequency counter.  It's got an external input.

With the prices I found, it seems like the '209 + frequency counter would be more expensive than the '259B without the ability to read resistance and reactance (and the concurrent ability to measure inductors, capacitors, stubs, etc.)  I think trying to save $100 and just getting the '209 is probably false economy if it needs even one add-on.  There is no way to later add on the things the '259B does by spending $100.  

I suppose if you leave your radio on in the shack near a window and just listen for the '209's signal on the frequency you want then you don't need the counter, but still.  It is, IMO, much less useful than the ratio of the prices would suggest.
« Last Edit: June 01, 2011, 05:54:36 AM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W8JX
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« Reply #17 on: June 01, 2011, 07:05:39 AM »

You don't NEED an "antenna analyzer".  A decent SWR meter is really all you need. 

It is a wonder how all us "Old Timers" ever managed to radiate a signal before "antenna analyzers" came along.

HI!!

Dick  AD4U

The old timers also had tube based radios with tunable Pi L networks in final that could match a wider impedance range too. And the technology was not available to build analyzers like they make today. I played with a Rigexpert AA-54 at Hamvention and it was pretty impressive. I am considering getting one. It can scan/plot SWR on 5 separate frequency ranges at same time. Far more capable than MFJ one.
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KJ4FUU
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« Reply #18 on: June 01, 2011, 11:03:03 AM »

The 209 made sense for me because I already had a counter. If I didn't have one, I would have gone with a higher up model, possibly not an MFJ at all. I gave it 3 stars in the review I wrote for eHam, and mentioned that without the counter, it wouldn't have been helpful to me.

As it stands now, I only use it occasionally. I'm QRP, with a random wire out my window, and I use my Emtech ZM-2 tuner with that, and the tuner allows me to tune without hurting my finals, since the power goes into some resistors until the LED goes out, indicating that it is tuned. I will use the MFJ when I get around to tuning my Par EndFedZ 10-20-40, and when I use my Blue Star P1 vertical (the P1 is only used when I go portable).

-- Tom
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KG6MZS
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« Reply #19 on: June 01, 2011, 11:52:49 AM »

I think if you have a SWR meter and just need to tune a few HF antennas you probably should just stick with the SWR meter.  I think the analyzers have made people obsess a bit about true resonance, that is X=0, when the best adjustment for many antennas just needs to present low VSWR to the coax cable.

I normally agree with you Dan, but I think you are wide of the mark here.  My MFJ 259B doesn't make me "obsess" about resonance anymore than my Fluke makes me "obsess" about power consumption.  Both are great tools and really enhance the whole antenna building experience --one of my favorite parts of the hobby.
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KB1TXK
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« Reply #20 on: June 01, 2011, 12:37:21 PM »

I really appreciate all the replies. Let me start there.

I'm going to see if anyone is hocking one at the hamfest on saturday.  That will be the determining factor on how I proceed.  If I can get a 259B (or ~ equivalent) on the cheap there..so be it. Otherwise I don't know at this point. Still up in the air haha.

Also, this is probably pie-in-the-sky but I want both resonance AND low SWR.  Probably anal, and I'm sure my tuner can get around any flaws...but ideally I don't want to have to rely on the tuner for anything. I'd like to consider it a luxury...not a necessity.
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WB6BYU
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« Reply #21 on: June 01, 2011, 01:03:48 PM »

Quote from: KB1TXK
... I want both resonance AND low SWR...


If your SWR is low you must be close enough to resonance anyway.
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KB1TXK
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« Reply #22 on: June 01, 2011, 01:23:39 PM »

So my dummy load resonates? Wink
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N3OX
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« Reply #23 on: June 01, 2011, 03:36:43 PM »

I normally agree with you Dan, but I think you are wide of the mark here.  My MFJ 259B doesn't make me "obsess" about resonance

No, you're right.  It's not the fault of the tool.  It's the fault of bad advice from the "has to be resonant or it won't work" crowd.  There aren't a ton of people who think that you're going to get significantly better results if you trim your dipole or tune your vertical using a MFJ-259B than you will with a SWR meter and your transmitter.   But they exist, are vocal, and cause trouble, IMO. 

Quote
So my dummy load resonates?

No, but that's a totally different thing, because your dummy load is a lossy, NON-resonant load. 

If you have a dipole or a vertical connected to the rig with low loss coax, the goal for the sake of lowest line loss should be the lowest SWR.    Let's say you're tuning a dipole so that you can use it without your tuner.  Can you describe a way, by cutting off or adding a foot or two of wire, where you'd add a whole bunch of loss?  Can you describe a way that you could get a low SWR by detuning the dipole far, far from resonance and adding a bunch of loss?

What about the same for a multiband trap vertical that's designed to be fed directly with coax?  Can you screw up the tuning in a way that gives low SWR while adding a bunch of loss, aside from actually stripping out radials to lower your SWR by adding loss?

Resonance and low VSWR are really strongly tied together for antennas designed to be fed with coax, and there's not much point in trying to set the antenna for one or the other, except that X=0 by itself doesn't ensure low SWR. So if you have to favor a setting, you should favor low SWR, provided you're doing things like making length adjustments to the antenna.  And even if you're making more complicated adjustments, you need to know MORE than the resonant point.

It's easy to get low SWR using a tuner even if you're not radiating much power, but knowing the resonant point of the antenna or antenna system won't keep that from happening.  You need to know/calculate other things, like the loss of the mismatched feedline between the antenna and tuner.  Resonance doesn't preclude lots of line loss.  You can even have sharper, narrower resonances with MORE loss in the system if you have a complicated enough matching system.  A mistuned tuner with way too much inductance would be one example.  But being able to measure complex impedance doesn't help you out of that hole, not really.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W6EM
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« Reply #24 on: June 01, 2011, 08:23:48 PM »

Interesting dialogue.  So, for all that profess "SWR" is sufficient, let's get to talking about real world examples.  So, you've just cut what you think is a resonant dipole, and hung it up.  Now, will SWR tell you if it's too long or too short?  Nope.  Complex impedance will, though.  Do I need to add some length back or cut some more off?  Big difference.  The analyzer tells you with either -JmX , too short, or jnX, too long.

Try making stubs with an SWR meter.  Not quite sure how I'd go about doing that.  But, guessing at how long your soon-to-be shorted quarter wave stub will be is the first step.  The second, well, is simple, with a good bridge like a 259B.  Sweep the frequency while watching the impedance.  When it falls to almost zero, that is the resonant frequency, since an unshorted, open ended quarter wave length is a short at resonance.  Then, just prune till the short is where you want it in the frequency domain.  Again, how would one do that with an SWR meter?  Once the length is the right length, then short the end and voila, stub completed.

If your antennas aren't in the shack, tuning and pruning would be quite a task, running back and forth to cut and try using an SWR meter.  Oh, I guess if you have a QRPP source, and your SWR meter is really very unique and super sensitive, I guess you could just turn on the low power source and take your SWR meter outside with you.......

73.

Lee
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W7ETA
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« Reply #25 on: June 01, 2011, 08:48:34 PM »

Ssssssh

Don't tell anyone!

From 1978 to 2006 I played ham radio with out an antenna analyzer.  And, I never worried about resonance.

Best from Tucson
Bob
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N3OX
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« Reply #26 on: June 02, 2011, 04:18:47 AM »

Interesting dialogue.  So, for all that profess "SWR" is sufficient, let's get to talking about real world examples.  So, you've just cut what you think is a resonant dipole, and hung it up.  Now, will SWR tell you if it's too long or too short?  Nope. 

Lee, when I was a youngster way back in... uh... 1995, and only had a SWR meter, here's how I did it.  I cut the dipole to 468/f, maybe added a little.  I put it up.  Then I checked the SWR at the bottom, middle, and top of the band of interest.  Sometimes there was already a SWR minimum inside the band.  If there wasn't, I looked at the trend.  If the SWR was higher at the bottom of the band than the top, the antenna was too short.  If it was higher at the top than the bottom, it was too long.

If you don't correct for feedline length, the reactance you measure at the shack doesn't tell you the right thing about whether your antenna is too long or short.  If you do it right at the antenna or cut an exact  multiple of a half wavelength of coax, or do calculations to transform the impedance to that seen at the feedpoint.  But all of those are more complicated than just checking to see if the minimum SWR point is inside or outside of the ham band by looking for a local minimum inside. 

And if you are talking about the MFJ-259B, and not a more expensive analyzer, you have to move frequency and look at how the reactance changes.  It doesn't tell you the sign of reactance.   Again, I am NOT saying it's not useful to measure reactance.  I'm just saying that for basic trimming of antennas, ASIDE from the issue of convenience, a SWR meter is totally sufficient.  If you have to put up two or three antennas and are going to leave them for years, you might not want to spend the money on the analyzer.

Quote
Try making stubs with an SWR meter.  Not quite sure how I'd go about doing that. 

I could figure out a way to do it but probably wouldn't use a SWR meter.  Looking for a minimum in received noise with the stub across your receiver input is probably one possible way.  But again, this is a little beside my main point.  I would never be without my MFJ-259B.  It's a very useful general purpose impedance meter.   It's very convenient to have it sitting outside when I'm tweaking antennas.  Even more so when my yard was bigger.   But I think it's useful to think about when it's needed and when a SWR meter will do an equally good (albeit slower) job.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W5DXP
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« Reply #27 on: June 02, 2011, 05:18:56 AM »

The analyzer tells you with either -JmX , too short, or jnX, too long.

Not if the measurement is taken through a feedline of unknown length attached to the antenna. If the SWR is not 1:1, the reactance of the impedance changes sign every 1/4WL along the feedline.

I recently got an email from a new ham trying to trim his dipole to resonance after using the 468/f formula. He couldn't understand why his 80m SWR was sky high. He was feeding his resonant dipole with 60 feet (~1/4WL) of ladder-line. The impedance looking into his feedline was approximately (450/50)*450=4050 ohms, i.e. SWR(50)=81:1.
« Last Edit: June 02, 2011, 05:26:01 AM by W5DXP » Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K7RBW
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« Reply #28 on: June 02, 2011, 06:49:01 AM »

It's the old trade-off of time or money. If you're going to play with antennas, you're going to be spending some degree of both. With the analyzer, you'll spend money and save a lot of time. If you don't, you'll save some money and spend a lot more time.

With an SWR meter you'll be able to tell if an antenna is too long or too short but it can be hard to tell by how much. This (for me, anyway) means multiple trips up to the antenna to tweak a bit (not too much...) and back down to the radio to find out if you got it right or went past te mark. That got old quickly.

With an antenna analyzer you can see how much you're off and make more educated guesses which translated to fewer round trips to the antenna.

As a recent example, I used the antenna anlyzer to measure a couple of  half-wave dipoles and found the velocity factor of the wire I was using was different that what I had estimated AND that it varied slightly with frequency. Putting this variable into the formula, I was able to extrapolate and get the right length the first time, every time on each HF band. I couldn't have done this with just an SWR meter because it would have been too tedious to even try (Yes, it would have been possible, but it would have taken MUCH longer--to the point where it wouldn't have been worth the effort to me.)

If you just want to tune up one antenna, one time, on one band, the SWR meter is probably sufficient. If you want to experiment and explore, then the $250 analyzer is worth every penny!
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W6RMK
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« Reply #29 on: June 02, 2011, 07:56:07 AM »

going back to the original post...

You've basically got the classic trade between time and money.  The SWR/reflected power meter that is in your rig (I can't imagine a $800 rig that doesn't have one..) is sufficient to adjust your antenna to acceptable ranges.  It's tedious, easier with two people (one at the antenna, the other at the rig to shout..that's better or that's worse) and a royal pain if you're trying to get a perfect match on a multiband antenna.

Or, you can spend some of the cash on a measurement tool that makes it easier. Rx noise bridges (Autek, Palomar, innumerable kits and designs in the handbook) or "three voltmeter" bridges (fair number of designs out there) are at the bottom end of the scale, fancy multiport network analyzers at the top.  Probably a range from $50-$1000, all told. 

Again, a trade between time and money: spend your time scrounging at hamfests/eBay/etc or building something from parts (<$10) or spend your time at your job and pay someone else to do the building/retailing.

It also depends on what you want to do.  Do you just want to "tune up" the antenna?  Do you want to actually measure R&X? Do you want to measure coupling and mutual impedance?    Do you need to do things like measure electrical length of a transmission line?  Some tools are better than others at some of these. 

Another trade of time and money.  With a diode, a voltmeter, and a resistor and a capacitor, using the rig as your RF source, you could probably make ALL of the measurements described above, it would just take a while, and you'd be building your own cal standard and calibrating it.  This was standard practice 100 years ago.  It might even be educational (nothing like using a slotted line to understand reflections and SWR, after all)


One thing to bear in mind is that a lot of the older techniques were considered tedious and horrible not because of the difficulty making the actual measurement, but because the data reduction with slide rule and graph paper was hard.  A good example is the "three voltmeter" quasi bridge scheme to measure both R and X  A pain to reduce the data by hand, trivial on a computer.  However, I'd not want to be hanging at the top of a tower swapping my diode detector around a homemade bridge and trying to adjust element lengths.
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