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Product Review – The MFJ-209 Antenna Analyzer

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Review of the MFJ-209 Antenna Analyzer

Introduction

We have been on HF for a long time over here at frrl.net Southern Command. We never saw the need for an Antenna Analyzer. Certainly, no need when they first came out and were very expensive. But now, Antenna Analyzers have reached a sort of maturity, there are many models to choose from, and they have significantly come down in price. So one could ask again, do you really need an Antenna Analyzer?

A (very) basic Antenna Analyzer

The MFJ Model MFJ-209 at $140 is about as basic as you can get. It generates a unmodulated RF signal from 1.7 MHz to 175 MHz continuously in 6 bands. So that means it will cover all the HF bands plus 2m.
Connected to an antenna it will read the SWR continuously from 1:1 to infinity. The SWR scale is marked off in increments of .2 (SWR is a ratio and is dimensionless) from 1:1 to 3:1. SWR of 3 to infinity is just a red band with no scale graduations.

The MFJ-209 has connections for external power (12 volts) and a RCA jack to connect directly to an external frequency counter. The MFJ can also be powered internally by AA cells – alkaline cells recommended. The MFJ-209 is about as basic as you can get – no frills – no bells and whistles.

Maybe you already have an analyzer – but don’t know it?

Folks that have modern radios that can read SWR on a transmitted RF signal already have the basic function that an external self-contained antenna analyzer can provide. Even if you dont have a radio that reads SWR directly, if you have a modern commercially-made tuner with a SWR meter along with a radio, you have the basic capability of an external Antenna Analyzer.

An Antenna Analyzer is nothing more than an RF generator and circuitry that can read SWR. You already have that – its your radio and the built in SWR meter or external tuner that reads SWR. So, for many people, an external Antenna Analyzer is pretty much superfluous – a duplication of what you already have.

Tuning your antenna

Tuning a dipole or vertical for HF is direct and straight forward. Using your radio and low power (10 watts or less) measure the SWR at various points on the band. Suppose you want to center the lowest SWR at 14.225 MHz. If the actual measured SWR is lowest above 14.225 then your antenna is too short – make it longer. If the actual measured SWR is lowest below 14.225 then your antenna is too long – make it shorter. Its as simple as that. How much longer or shorter? You can make a few simple measurements and zero in quite easily on the optimal length for your desired operating frequency.

You will find that in actual practice there is a near linear relationship between the length of the antenna (simple dipole or mono-band vertical) and the resonant frequency. You can save some tuning time by calculating this relationship for your particular antenna in your particular environment.

If you calculate the KHz per inch you should easily be able to go to the optimal length for a particular resonant frequency for a particular antenna. Here is how to do it. At some length where you can read the SWR find the frequency where the SWR is lowest. Write that frequency down (F1). Now change the length by one (or two) inches – both sides equally for a dipole. Now find the new resonant frequency (F2). Calculate the frequency per inch (F2-F1)/(inch change).

For our 40m loaded dipole we got .04 KHz per inch. So, at a particular length, if the lowest resonance is 7.15 MHz and we want to move the resonant frequency up we have to shorten the antenna. So the inch by inch progression would be 7.19 MHz (7.15+.04=7.19), 7.23 MHz, 7.27 MHz, 7.31 MHz, and so on. You can see that 1 inch makes a lot of difference on 40 meters. To start tuning a home made dipole you need to initially get “close”. If you get close, calculate the resonance move per inch. It’s just basic grammar school math.

Finally, the real value of the antenna analyzer

Note the last point. On the HF bands using a full size home made dipole one or two inches of length (keep both side equal lengths) make a big difference in the resonant frequency. So, what happens when you use the basic (theoretical) calculation for antenna length and your radio reads SWR off the scale? You are way off. How do you determine if your antenna is too long or too short?

Here is the real value of the Antenna Analyzer. It is a RF generator with continuous coverage from 1.7 MHz to 175 MHz. It will go outside the Ham Bands and transmit a signal where your HF rig may not transmit. Most, if not all Ham Radio rigs, will stop transmitting once you get outside the Ham bands. Too bad for you if your antenna resonance is outside the Ham bands. You cant use your rig to find the resonance.

Grab the antenna analyzer and hook it up and see where the resonance point has landed. Easy. Maybe it ended up on 13.6 MHz or maybe it ended up on 15.5 MHz. That is something the antenna analyzer can tell you that your rig may not be able to tell you. Once you found the resonance landing point you can run through the same strategy above and calculate the KHz per inch and change the length of the antenna accordingly to get close to your desired operating frequency. Use your rig once you get in the ham bands.

Maybe you still dont need an antenna analyzer

Again, the antenna analyzer is just an RF generator with an SWR meter. You already have this with your rig. We dont recommend this but if you did the mod on your radio to open it up for the new 60 meter band then it probably has collateral damage of “transmits everywhere”. You now have essentially the external antenna analyzer that you just bought for $140 – an RF generator with the built-in SWR meter. So, in practical terms your modified rig and $140 antenna analyzer provide identical functionality.
You should realize that it is not legal to tansmit on your ham radio outside the ham bands.  But also realize this – that this is excatly what your MFJ antenna analyzer is doing – transmitting from 1.7 MHz to 175 MHz continuously in 6 bands and this includes portions outside the ham bands.

The MFJ-209 – how to help it out.

Again, the MFJ-209 is about as basic as you can get. After using it two things will become obvious. First, the RF generator tuning is very gross and touchy. Second, you will not be able to read the frequency off the scales with any degree of precision. In general, you dont really need to.

Your rig can help out your MFJ-209 with these weaknesses. The MFJ-209 can’t tell you exactly what the frequency of the RF generated signal is based on its gross analog dial but your rig can. If you want to get an exact frequency reading set your radio to AM mode and tune near the frequency that you read on the MFJ-209 scale. At the frequency that the Analyzer is generating you will hear a silence on AM and a peak on the S Meter. If you set your rig to CW mode you will hear a tone at the RF generated signal frequency. Once you get this far you will discover just how touchy the tune control is on the MFJ-209.

Of course, if you have that frequency counter that you bought many years ago now you have a use for it. You can directly connect the frequency counter to the MFJ “Frequency Out” RCA connector and read the frequency digitally. As you can see, my Optoelectronics 2810 has a new friend – the MFJ 209. Now I have direct digital frequency readout.

Conclusion

All in all, you may not need an antenna analyzer. It is a convenience, not a necessity. The MFJ-209 is $140 and the lowest you can go in functionality. All of this functionally you probably already have if you have a rig modified for the 60 meter band with the collateral damage (feature) of “transmit everywhere”.  Please read again above our couple of sentances of legality of transmitting outside the ham bands.

You can discover some interesting properties of antennas with your analyzer.  For example, An analyzer like the MFJ-209 can sweep large segments of the RF frequency space (1.7 MHz to 175 MHz) very quickly and show the response of an antenna.

You can easily observe the antenna response on odd harmonics. For example, you can sweep the 40 meter (7 MHz) dipole antenna and watch the SWR response as the frequency approaches 15 meters (21 MHz) – an odd harmonic. Even better, sweep one of those discone antennas with a vertical element and adjustable loaded spokes from 25 MHz to 175 MHz and be amazed at the resonance points. You can use the analyzer for discover the response of your house gutter, long wire. or improvised antenna across the entire HF and VHF frequency space.  Things that would would not think are resonant may be resonant – check them out

The MFJ-209 can “get you there” – to show you a ball park region of where your antenna is resonant. But for detailed tuning your rig with built-in SWR meter or external tuner with SWR meter is better.

Its all about convenience and the amount of money you are willing to throw to ham radio toys. Its about opportunity cost – if you didn’t spend $140 on the MFJ-209 what would you have done with that money and does that expenditure provide you more ultimate value – however you measure value to yourself.

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Written by frrl

August 3, 2008 at 10:14 pm

2 Responses

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  1. Sometimes the cheap meters are fine, but other times you need something more beefy. At the other end of the spectrum you have instruments such as this swr analyzer that are more costly but also more accurate and have better shielding from RF interference.

    Michael

    January 31, 2011 at 8:28 pm

  2. thanks for this very usefull info..!

    michel

    November 24, 2008 at 9:45 pm


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