Got the MFJ259 Analyzer, now what?
KG4FGN
it up to a small Yagi I built (for 2 meter). When I tune it, in the 144-148
range I get very high SWRs. The SWRs get real low when I tune up to the
158's. Now that I know this, what do I do? Obviously I need to change the
antenna somehow, do I need to lengthen or shorten the elements, or what?
I know it will probably be hard to give advice not knowing the exact design,
but advice on what direction to take next would be helpful. I guess what I'm
really asking is how to interpret what the analyzer is telling me?
Thanks for your help,
Robert, KG4FGN
Dick Hughes
elements are too short. Are you measuring the antenna where you will
use it, or on the ground? You need to get it reasonably clear of
metallic objects, trees, etc. before you take a measurement.
The ARRL Antenna Book, 15th Ed. shows the following for a 3-element
beam on a 1", 5' 5-9/16" boom. 0.2 wavelength spacing. 3/16"
non-insulated elements.
Reflector - 3' 4-5/8"
Driven El - 3' 2-3/16"
Director - 3' 1-1/2"
See how that compares to your yagi
Dick Hughes - W6CCD
On Sat, 4 Nov 2000 21:20:27 -0600, "KG4FGN" <kg4...@mindspring.com>
wrote:
N8wwm
comes down. Also, it is obviously too short. try adding the % difference to
each element with wrap around wire, etc. For example, if the antenna is 1 inch
too short, add 1/2 in. to each side of each element.
Just a suggestion...but play with the gamma rod first. Also, make sure you are
not near siding, wires, fences etc. These have an effect on SWR.
Dick Carroll
>
> OK, I picked up an MFJ-259 antenna analyzer at the swapmeet today. I hooked
> it up to a small Yagi I built (for 2 meter). When I tune it, in the 144-148
> range I get very high SWRs. The SWRs get real low when I tune up to the
> 158's. Now that I know this, what do I do? Obviously I need to change the
> antenna somehow, do I need to lengthen or shorten the elements, or what?
>
> I know it will probably be hard to give advice not knowing the exact design,
> but advice on what direction to take next would be helpful. I guess what I'm
> really asking is how to interpret what the analyzer is telling me?
>
> Thanks for your help,
>
Robert, a little logic is in order here. The higher the frequency the
shorter the wavelength. So if your antenna resonates above its intended
frequency, then the elements are too short. Lengthening them will bring
the resonant frequency down.
73, Dick W0EX
George, W5YR
may be why you found it ina swap meet.
How does your SWR meter reading compare with the 259?
Don't start sawing aluminum just yet . . .
72/73, George W5YR - the Yellow Rose of Texas NETXQRP 6
Fairview, TX 30 mi NE Dallas in Collin county QRP-L 1373
Amateur Radio W5YR, in the 55th year and it just keeps getting better!
Icom IC-756 PRO #02121 (9/00) Kachina #91900556 (12/99) IC-765 (6/90)
James Rosenthal
: I would start by verifying the frequency calibration of the 259. That
: may be why you found it ina swap meet.
Good thought.
The output on mine is ~+10 dBm so yours should be able to drive a counter
easily. Or listen for it on your 2m receiver and see if it's on freq.
: How does your SWR meter reading compare with the 259?
: Don't start sawing aluminum just yet . . .
Glup! Hope it isn't too late. ;(
: 72/73, George W5YR - the Yellow Rose of Texas NETXQRP 6
: KG4FGN wrote:
: >
: > OK, I picked up an MFJ-259 antenna analyzer at the swapmeet today. I hooked
: > it up to a small Yagi I built (for 2 meter). When I tune it, in the 144-148
: > range I get very high SWRs. The SWRs get real low when I tune up to the
: > 158's. Now that I know this, what do I do? Obviously I need to change the
: > antenna somehow, do I need to lengthen or shorten the elements, or what?
--
Jim Rosenthal, WA4STJ
KG4FGN
several radios, it always seemed to read dead on, so I suspect the unit is
OK.
Thanks for the explanations, especially to W0EX. After reading that I felt
like Dr. Watson after Sherlock Holmes just explained how he deduced who the
criminal was.
If I may indulge you on one other question, when you are building your
antennas, do you take some readings in the workshop to get a general feel
for the antenna, or is it always best to place it at the proper place and
take your readings at the end of the feed line?
Thanks,
Robert, KG4FGN
"KG4FGN" <kg4...@mindspring.com> wrote in message
news:8u2k20$kk4$1...@slb3.atl.mindspring.net...
> OK, I picked up an MFJ-259 antenna analyzer at the swapmeet today. I
hooked
> it up to a small Yagi I built (for 2 meter). When I tune it, in the
144-148
> range I get very high SWRs. The SWRs get real low when I tune up to the
> 158's. Now that I know this, what do I do? Obviously I need to change the
> antenna somehow, do I need to lengthen or shorten the elements, or what?
>
> I know it will probably be hard to give advice not knowing the exact
design,
> but advice on what direction to take next would be helpful. I guess what
I'm
> really asking is how to interpret what the analyzer is telling me?
>
> Thanks for your help,
>
> Robert, KG4FGN
>
>
Goldreged
like Dr. Watson after Sherlock Holmes just explained how he deduced who the
criminal was.>>
Also, you can play w/ the driven element/director spacing, it has an effect on
freq/impedance...
Ed G.
KB1DQX
(Please Remove "JUNKBLOK" to E-mail.
Unless it's a Flame.)
Brian Kelly
KG4FGN wrote:
>
>
> If I may indulge you on one other question, when you are building your
> antennas, do you take some readings in the workshop to get a general feel
> for the antenna, or is it always best to place it at the proper place and
> take your readings at the end of the feed line?
>
Design the antenna by the numbers but make the elements around 5% too long. Get
it outside and up in the air and away from mettalic objects, using the 259 at
the end of a short feedline tune the matching device (Gamma, Beta, whatever)
for minimum swr whatever that might be. Then plot the swr curve using several
freqs above and below the design freq to find the actual resonant freq of the
antenna. That freq should be a tad below the design freq. From there you
commence incrementally shortening the elements until the minimum swr freq is on
design freq. If parasitic elements are involved they also have to be shortened
in proportion to the shortening of the driven element which involves "working"
some arithmetic ratios in order to retain gain & F/B performance. Proper
element scaling can be a bit tricky so don't cut off any metal unless you're
quite certain you won't have "uncut" it later.
>
>
> Thanks,
>
> Robert, KG4FGN
> >
w3rv