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Author Topic: MFJ-207 Antenna Analyzer with Buddipole and FT817  (Read 6189 times)
M0GYY
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Posts: 1




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« on: October 02, 2010, 07:05:50 AM »

I am soon to have my first trip onto the moors with the ft 817 and my new Buddipole deluxe set, as a lot of suggestions say an Antenna Analyzer is easier to set the antenna up with does anyone know if the MFJ-207 Antenna Analyzer would do the job. I have a limited budget and would probably only be on 20 and 40mtr bands.

Any suggestions please

Kind thanks

Gary
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WB6BYU
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Posts: 17277




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« Reply #1 on: October 02, 2010, 09:54:30 AM »

The MFJ-207 should be perfectly adequate - I regularly use mine for tuning antennas.

The one limitation is that the tuning rate is rather fast for a narrow-band antenna such as the Buddi-Pole,
and the frequency readout isn't very accurate.  But  by listening for the Analyzer signal on your rig
you can tell whether the antenna is resonant above or below the desired frequency.

A couple of techniques I've used:

(1) to find the resonant frequency, locate the dip on the Antenna Analyzer then tune the rig through the
band until you find the signal and read the frequency on the dial.  (I use the AM filter in my TS-450 and
CW or SSB mode, which allows me to step through the band 10 kHz at a time and still find the signal.)

(2) To check the SWR at the desired frequency, set the rig to that frequency and adjust the Analyzer
until you hear the signal, then read the SWR off the analyzer.

(3) To see if the antenna is resonant too high or too low, set the rig to the desired frequency and tune
the analyzer through the band.  You should hear it the signal as it passes the receiver frequency.  If you
are tuning up in frequency and you reach the SWR dip before you hear the signal, the antenna is resonant
too low and needs to be shortened (or the loading inductance decreased.)

Takes a bit of practice, but works well enough.

You can also tune the antenna with just the rig and an SWR meter:  I use the inexpensive type designed for
CB radios, but some of them may require too much power to drive them to full scale on 40m.  Fortunately
it often isn't too difficult to rebuild the insides of such a meter for HF QRP use.
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STAYVERTICAL
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Posts: 875




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« Reply #2 on: October 04, 2010, 11:01:52 PM »

Hi Gary,

It may be a bit too short before your trip, but if you are on a limited budget and are ok at kit building
it may be worthwhile looking at the VK5JST antenna analyser kit.
The price is reasonably low and works from 2 to 30 Mhz with reasonably accuracy.
It is however a kit and needs some work making the holes for the display in the case and so on.
So if homebrew is not your forte, ignore this suggestion.
I have built one and find it as accurate as a MFJ269, but only covers HF.
Probably takes a week to build if you are as slow as I am.
There are some videos on Youtube by U.K. user "Byronlocal" if you would like to investigate.

As the previous poster suggested however, if you put the power down to 1 watt or even 0.5W
and use a cheap SWR meter, it should not be too dangerous to the rig and allow tune up.
It may not be enough power to give full scale deflection on the meter on 40m but may be ok on 20m
since these type of swr meters become more sensitive as the frequency increases.
In any case you don't need full scale deflection unless you want an accurate SWR reading,
just get the reflected voltage reading to the minimum and you should be in the ballpark.

73s es good trip.
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KA1DBE
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Posts: 122




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« Reply #3 on: October 06, 2010, 12:00:58 PM »

Hi Gary,

I use a MFJ-207 with my Buddipole.  Works just fine.

Good luck and 73's

Jeff
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WB8YYY
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Posts: 159


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« Reply #4 on: October 13, 2010, 10:07:37 AM »

Gary

I would try out that buddipole set at home, and see if you really must have an antenna analyzer.  While I would not mind owning one, I have done ok without one.  I am not familiar with how easy it is to use the FT817s VSWR indicator vs having a separate VSWR meter, but it may be good enough.  Keep in mind you don't really need a 1.0:1 VSWR all the time!  But something say better than 2.0:1 to keep coax losses low and get full output.  The main advantage of the antenna analyzer is you can set up much faster, but if you operation is more than a few minutes that may not be a factor!  Once you get acquainted with adjusting the buddipole for these bands, at a similar mounting height to your portable location, likely you can tune it quick enough with a VSWR indicator.  You can enjoy the 'stash' of gear you already have. 

73 Curt
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AA4PB
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Posts: 14388




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« Reply #5 on: October 13, 2010, 11:23:00 AM »

I've set up a Buddipole plenty of time just using a simple SWR bridge. The settings don't change much with installation, so if you set it up at home and mark the settings you can set it up pretty quickly in the field. You can probably cover the phone portions of the 40M and 20M bands with one setting per band and stay under a 2:1 SWR.
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Bob  AA4PB
Garrisonville, VA
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