----- Original Message ----- From: "Art McBride" kc6uqh@cox.net To: "'i8cvs'" domenico.i8cvs@tin.it; "'Pete Rowe'" ptrowe@yahoo.com; "'AMSAT BB'" amsat-bb@amsat.org; "'Howard Kowall'" hkowall@shaw.ca Sent: Monday, March 07, 2011 2:38 AM Subject: RE: [amsat-bb] Re: Antenna Analyzer
Domenico,
A. It is much smaller than MY H/P 8410 + 8414 + test set, & sweep generator.
Hi Art, KC6UQH
I agree that the MFJ-269 is smaller than your above banch set-up
B. It will tell me if the resistive arm is above or below 50 Ohms.
Only it tell you the resistive part R of the impedance up to 30 MHz but the instrument is sold to measure R up to 170 MHz
C. It will give me the reactance Vs frequency with in 10 ohms.
Only it tell you the inductive reactance +jX up to 30 MHz but the instrument is sold to measure +jX up to 170 MHz
D. It is battery operated, portable, and can be used on a tower.
When you are on the tower with your MFJ-269 you can adjust the antenna for the lovest VSWR only looking at the VSWR on display without exactly know Z = R+/-jX above 30 MHz and so a more simple VSWR meter does the same job.
E. It costs less than a 1 month rental of a quality Network Analyzer.
I agree
F. A VSWR measurement will not separate the resistive and reactive arms
I agree and this is why for a given VSWR we need an antenna analyser capable to measure the value of the resistive part R and the reactive part +jX or -jX of the impedance particularly when we are over the tower to adjust the matching system and cancel out the inductive or the capacitive part of the impedance. Using the MFJ-269 if you don't look at the VSWR but you look only at R and +jX or -jX being on the tower it is like to drive a car above 30 MHz without to know if rotating the wheel you will go to left or right on the road !
G. When tuning an antenna you never start at 1.5 :1!If it is that good there is no need to tune it.
To tune an antenna you don't need mandatorily an antenna analyser but only you need a VSWR meter to move the maching arness for the lovest VSWR An antenna analyser is indeed needed only to cut or prolong in advance stubs and matching lines or antenna elements to get a matching as close as possible to 50 ohm resistive and 0 ohm reactive i.e to get an impedance as close as possible to Z = 50 + j0 ohm but unfortunately the MFJ-269 does satisfactorily this job only up to 30 MHz !
73, Art, KC6UQH
73" de i8CVS Domenico
-----Original Message----- From: i8cvs [mailto:domenico.i8cvs@tin.it] Sent: Sunday, March 06, 2011 12:30 PM To: kc6uqh@cox.net; 'Pete Rowe'; 'AMSAT BB'; 'Howard Kowall' Subject: Re: [amsat-bb] Re: Antenna Analyzer
Hi Art, KC6UQH
If you are satisfied with an antenna VSWR in the order of 1.5 : 1 then you don't need an antenna analyser but only a VSWR meter.
An antenna analyser must be able to measure with accuracy the real part
and
the imaginary part of the impedance i.e. the resistive and the reactive
part
of the impedance Z = R +/- jX
For example the same antenna VSWR of 1.5 : 1 can be obtained with an antenna impedance having the following values and all of them are laying over the same VSWR circle of the Smith Chart
Z1 = 38+j13 ohm Z2 = 66+j16 ohm Z3 = 58- j20 ohm Z4 = 34- j0 ohm
Since the same VSWR can be found over a VSWR circle then the values of the impedance giving the same VSWR are infinite values.
The MFJ-269 analyser make acceptable R +/-jX measurements only up to 30 MHz but fail to measure accurate resistive and reactive part of the impedance above 30 MHz and in other words it is not a respectable antenna analyser.
Why to wast money to buy an antenna analyser to measure wrong values of Z= R+/- jX if been happy with only the value of the VSWR you need only a VSWR meter ?
73" de
i8CVS Domenico
----- Original Message ----- From: "Art McBride" kc6uqh@cox.net To: "'i8cvs'" domenico.i8cvs@tin.it; "'Pete Rowe'" ptrowe@yahoo.com; "'AMSAT BB'" amsat-bb@amsat.org; "'Howard Kowall'" hkowall@shaw.ca Sent: Sunday, March 06, 2011 7:38 PM Subject: RE: [amsat-bb] Re: Antenna Analyzer
Domenico,
For most Amateur Radio work a VSWR of 1.5:1 is adequate. I personally
have
never expected MFJ products to be in the League of Anristu, HP and Rohde
and
Swartz. MFJ is a yard stick, the others are a micrometers Art, KC6UQH -----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of i8cvs Sent: Sunday, March 06, 2011 9:41 AM To: Pete Rowe; AMSAT BB; Howard Kowall Subject: [amsat-bb] Re: Antenna Analyzer
Hi Pete, WA6WOA
I do not recommend the MFJ-269 antenna analyser because it is very inaccurate particularly on 435 MHz I have compared the MFJ-269 with several professional network analysers
and
I have found that at most the MFJ is usable up to 30 MHz maximum because above 30 MHz the inaccuracy on the real part and the imaginary part of
the
impedance reading becomes absolutely unacceptable.
My MFJ-269 was purchased as new but connecting to it a professional 50 ohm termination good up to 12 GHz the VSWR shown at 435 MHz was 1.1
I have sent back my MFJ to the factory for inspecting and calibration
but
I
belive that the above instrument was a very bad affair for me and will
be
a
bad affair for all that intend to use the analyser above 30 MHz.
Be happy with your MFJ-269 even if dreaming while sleeping I am sure
that
my message made you suspect a wrong real part and a wrong imaginary part on your impedance reading !
Best 73" de
i8CVS Domenico
----- Original Message ----- From: "Pete Rowe" ptrowe@yahoo.com To: "AMSAT BB" amsat-bb@amsat.org; "Howard Kowall" hkowall@shaw.ca Sent: Sunday, March 06, 2011 4:45 PM Subject: [amsat-bb] Re: Antenna Analyzer
Hi Howard I wouldn't be without my MFJ-269 analyzer. It is very accurate and a
handy
size. Highly recommended. (no, I don't own stock in MFJ) One word of caution: mine (and maybe there is something wrong with mine) draws some power from the batteries with the power switch OFF. So I take
one
of the batteries out when not in use.
73, Pete WA6WOA
--- On Sun, 3/6/11, Howard Kowall hkowall@shaw.ca wrote:
From: Howard Kowall hkowall@shaw.ca Subject: [amsat-bb] Antenna Analyzer To: "AMSAT BB" amsat-bb@amsat.org Date: Sunday, March 6, 2011, 6:16 AM
Hello to everyone I am seriously thinking about buying an antenna analyzer,I build enough antennas to justify buying one.I enjoy building HF,VHF,UHF antennas of
all
flavors.The standard swr bridge is just not cutting it anymore.So I
guess
what I am looking for is one that will do 3mhz to 500mhz,nice to have computer interface but not a priority.I have seen a few on the internet
but
its nice to get some user input,rather then the sales pitches. Thanks to all who read and reply in advance Howard VE4ISP _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite
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Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
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