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View Full Version : How long is 5/8 wave for 2-Meters (nominally)



KB8CPR
04-30-2007, 06:41 PM
I know this would be easily found in the ARRL Antenna Book, or other good antenna book, & "should" be easy to find in the Internet, but a quick search turned up nada & I don't have the Antenna Book handy http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

I'm just trying to identify an old 2-Meter antenna recently given me by a local club member. I'm not sure if it's a 1/4 wave, or 5/8 wave. It's marked Spectral IsoPole 144 & the radiator is about 51" long from tip to connector, about an inch less if you exclude the black plastic base that houses the connector.

~Dave
KB8CPR

KE5FRY
04-30-2007, 06:48 PM
5/8 of 2 meters is 1.25 meters and 1/4 of 2 meters is .5 meters.

WA9SVD
04-30-2007, 07:02 PM
THAT was sure helpful...

Calculator time:

5/8 wave, at 146 MHz, (in a vacuum) would be about 50.3 inches. (at 144 MHz, it's a bit over 52 inches.) A real world conductor (whip) would be shorter. The whip may be designed to be trimmed to an exact length when a preferred frequency is determined; many antennas will purposely be cut slightly long to allow the end user a chance to cut it to an exact length.

KB8CPR
04-30-2007, 07:07 PM
Doh... That was kinda a dumb question http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

I didn't actually think of 2-Meters as "TWO METERS" wavelength. So, 5/8 wave is roughly 49.2 inches. That means the antenna I was given is a 5/8 wave. Excellent!

I bought a 5ft mast & Iíll just mount it on that & hang it in the attic for now. It should be enough to hit the local repeaters, even from the hole I live in.AA

KB8CPR
04-30-2007, 07:16 PM
Quote[/b] (wa9svd @ April 30 2007,12:02)]# #Calculator time:

# #5/8 wave, at 146 MHz, (in a vacuum) would be about 50.3 inches. #(at 144 MHz, it's a bit over 52 inches.) #A real world conductor (whip) would be shorter. #The whip may be designed to be trimmed to an exact length when a preferred frequency is determined; many antennas will purposely be cut slightly long to allow the end user a chance to cut it to an exact length.
This particular antenna has a two-section radial held together with a hose clamp. This may have been added after manufacture http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif It should permit the antenna to be shortened or lengthened slightly to adjust resonance. Iím pretty sure it will be fine as is though. A local club member loaned me a SWR meter for VHF/UHF, so I can check to see if itís close.

~Dave

K8JD
05-01-2007, 12:34 AM
How to ID :
A quarterwave mobile antenna is about 20 inches nothing in the base but a connection to co-ax and the 5/8 (actually .65 wave for maximum horizontal gain ) is about 47 inches with a matching coil at the base.

K8JD
05-01-2007, 12:39 AM
Your antenna may actrally be an enclosed quarterwave radiator with a coaxial decoupling sleeve taking up the bottom half of the enclosure's length, actually a dipole with one half folded back over the feedline. is it in a fiberglass tube with a connector on the bottom?http://www.qrz.com/iB_html/non-cgi/emoticons/rock.gif

A radial sticks out at near right angle to the main axis of the antenna. Is this at the bottom of the antenna near the connector, it may be a decoupling device, there are usually 3 or 4 sticning out at a downward angle near the lower end....

K9ZMD
05-01-2007, 05:41 AM
Spectral Isopole (http://www.isopole.com/) web site.

VE7NOT
05-01-2007, 06:18 AM
I should point out that often a 5/8 wave 2m antenna tunes as a 1/4 wave on 6m. http://www.qrz.com/iB_html/non-cgi/emoticons/wink.gif

K7JEM
05-01-2007, 07:17 AM
A 5/8 antenna is a non-resonant radiator. It can be almost any length from about .6 to .7 wavelength and work pretty well, with .64 to .66 being about optimum, but .62 will work fine, as will .68.

Most commercial 5/8 mobile antennas are matched using a coil of wire at the base, that coil being about 9" long. This brings the "apparent" wavelength up to 3/4, which is a good match for 50 ohms. It also makes the antenna perform well at 1/3 of the tuned frequency, as a base loaded QW antenna. As NOT has said, it will work well at 6M, with minimal retuning.

Joe

KB8CPR
05-01-2007, 11:39 AM
Based on what I'm being told & information from the Spectral site (http://www.isopole.com/english/products-en/isopolevhf-en.htm), I believe I have the top portion of a Spectral IsoPole as the label on the base describes. #The ground radial kit is probably from a different antenna. #The Ham that gave me the antenna said that this combination should work just fine though we didnít get into details, as we were busy trying to repair an inexpensive ďJ-Pole in a PVC pipeĒ antenna. #http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

This means that itís a 5/8 wave with what appear to be ľ wave ground radials.

I need to get about 40ft of low-loss feed line, so Iíll probably get some RG8 from The Wireman (http://thewireman.com/coax.html). #Their model CQ 4XL is fairly low-loss at 1.5 db per 100ft at 150 MHz, very flexible & at 90Ę a ft itís fairly affordable. #I think itís similar to LMR-400, at least in loss specifications.

This is the antenna & ground radial kit.

http://members.arstechnica.com/x/tangleweb/IsoPole_non_standard_ground_radials_disassemble.JP G

Close-up of radial kit

http://members.arstechnica.com/x/tangleweb/IsoPole_close-up_non-standard_radial_kit.jpg

Close-up of base

http://members.arstechnica.com/x/tangleweb/IsoPole_close-up_base.JPG

Close-up of connector

http://members.arstechnica.com/x/tangleweb/IsoPole_close-up_base_connector.JPG

I'll post back here when I get a chance to mount the antenna on a mast & take some SWR measurements.

~Dave
KB8CPR

K7JEM
05-01-2007, 03:55 PM
The Isopole is a center fed double 5/8 type antenna, commonly referred to as an EDZ. The bottom section serves as a radiator also, and the original model had two aluminum cones mounted below the feedpoint, one to serve as the bottom section of the antenna, and the other to decouple the entire feedline from the antenna.

Link to Isopole instructions. (http://www.radioamateur.eu/schemi/ACC_antenna/AEA_isopole_user.pdf)

The antenna may or may not perform well without the bottom sections. Perhaps if the radials were positioned in the right place, it might work OK.

These were good working antennas, not real heavy duty, but worked quite well. They were used on lots of repeaters back in the late 70's and early 80's with pretty good results, a decent antenna if the repeater owner didn't want to spend $500 on a real antenna.

Joe

KB8CPR
05-01-2007, 04:12 PM
The good news is that I actually have an Original AEA IsoPole from the late 80's in a box in my garage. #I forgot that I had it http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif #It's never been mounted & is in like new condition, so I'll probably mount it on a mast on the outside of the house eventually, but for now I'll try the Frankenstein IsoPole in the attic & see what kind of SWR & performance I get.

By the way, does anyone know why my inline pictures reverted to links? #They showed inline in the preview before posting. #I sized them to 800x600, is there a size limit for inline pics?

K7JEM
05-01-2007, 04:14 PM
Quote[/b] (KB8CPR @ May 01 2007,09:12)]By the way, does anyone know why my inline pictures reverted to links? They showed inline in the preview before posting. I sized them to 800x600, is there a size limit for inline pics?
I am seeing the pictures just fine.

KL7AJ
05-01-2007, 04:16 PM
Quote[/b] (KB8CPR @ April 30 2007,12:07)]Doh... #That was kinda a dumb question http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

I didn't actually think of 2-Meters as "TWO METERS" wavelength. #So, 5/8 wave is roughly 49.2 inches. #That means the antenna I was given is a 5/8 wave. #Excellent!

I bought a 5ft mast & Iíll just mount it on that & hang it in the attic for now. #It should be enough to hit the local repeaters, even from the hole I live in.AA
Think in terms of cubits. 2 meters is 4 cubits. http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

KB8CPR
05-01-2007, 04:30 PM
Quote[/b] (K7JEM @ May 01 2007,09:14)]
Quote[/b] (KB8CPR @ May 01 2007,09:12)]By the way, does anyone know why my inline pictures reverted to links? #They showed inline in the preview before posting. #I sized them to 800x600, is there a size limit for inline pics?
I am seeing the pictures just fine.
That's odd... #perhaps it's because it's my own post that I see it that way. #I see it as links on 2 different computers on 2 different Internet connections. #I'll try logging out & viewing the thread.

EDIT 1 - I logged into a different computer where I'm in QRZ as a "guest" & I see the inline pictures, so I guess it's only if I'm logged in as myself, that I see it as;
(IMG: link_text). #
That's one mystery solved http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

EDIT 2 - Another oddity; I don't see other members Icons by their forum name when I'm logged in as me, but I see them if I browse as a "guest". #Must be a setting in my preferences somewhere.

EDIT 3 - I went into my control panel, under "Account Options" & saw that I had "view members avatars" as "Yes", but made a small change & saved it, now I'm seeing avatars AND my inline pictures. #Go figure http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

N2NH
05-01-2007, 07:47 PM
For the lazy there is always the Frequency Wavelength Calculator (http://www.csgnetwork.com/freqwavelengthcalc.html)
http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

K6UEY
05-01-2007, 07:53 PM
I don't have a tape measure handy, how long is a 12" ruler ??

KA0GKT
05-01-2007, 08:26 PM
Quote[/b] (K6UEY @ May 01 2007,12:53)]I don't have a tape measure handy, how long is a 12" ruler ??
30.48 cm

73 DE KAōGKT/7

--Steve

KB8CPR
05-01-2007, 09:15 PM
You guys are killin me http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

The Frequency Wavelength Calculator is pretty useful though. Especially if you want to cut your dual trucker antennas for channel 19 (/jk)

By the way, what is the number for 911? http://www.qrz.com/iB_html/non-cgi/emoticons/tounge.gif

KC9ECI
05-02-2007, 01:48 AM
Quote[/b] (KB8CPR @ May 01 2007,16:15)]By the way, what is the number for 911? # # http://www.qrz.com/iB_html/non-cgi/emoticons/tounge.gif
If you find out, let me know, because I can't find the eleven on my phone.

K6UEY
05-02-2007, 02:01 AM
That is similiar to the story he told the officer,he could not dial 911 because his cell phone only went to "9" !! http://www.qrz.com/iB_html/non-cgi/emoticons/laugh.gif

KI4LZK
05-02-2007, 02:47 AM
911 is the number for that big free taxi cab right? (People actually seem to think this is true.)

Josh KI4LZK

KB8CPR
05-02-2007, 10:37 AM
I was a police officer when first licensed in 1987, so the KB8CPR call was especially welcome http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif I was a volunteer in the Fire/EMS service before that, so I can definitely relate to the 911 "Taxi" calls.

I don't want to turn this into Rag Chew Central, so I'll post back here once I have some info on how the Frankenstein IsoPole performs. It may be a while since I have to move my son home from the College of Charleston for the summer. He'll be in a shared apartment or house next year.

Thanks to all who provided good info on this antenna, especially K7JEM for details on IsoPole construction that will help me understand why the non-standard ground kit may not work on the IsoPole radiator.

~Dave

KL7AJ
05-02-2007, 04:38 PM
Quote[/b] (ka0gkt @ May 01 2007,13:26)]
Quote[/b] (K6UEY @ May 01 2007,12:53)]I don't have a tape measure handy, how long is a 12" ruler ??
30.48 cm

73 DE KAōGKT/7

--Steve
2/3 of a cubit

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