Menu

Determining if reactance is capacitive or inductive.

Search this Thread

Prev

Previous Post

Next Post

Next

#8

Report Post

Old

December 20th 06, 01:16 PM posted to rec.radio.amateur.antenna

[email protected] jgboyles@aol.com is offline

jgboyles@aol.com is offline

external usenet poster

First recorded activity by RadioBanter: Jul 2006

Posts: 58

Default

Determining if reactance is capacitive or inductive.

wrote:

What concept am I screwing up here?

-Scott, WU2X

Here are the values I measured:

Freq R X SWR
--------------------------------------
144 44 2 1.1
144.25 46 4 1.1
144.5 55 7 1.1
144.75 60 7 1.2
145 68 0 1.3
145.25 78 0 1.4
145.5 79 0 1.4
145.75 73 11 1.5
146 63 21 1.5
146.25 53 23 1.5
146.5 46 21 1.5
146.75 40 18 1.5
147 37 10 1.5
147.25 35 8 1.4
147.5 37 6 1.3
147.75 41 10 1.3
148 48 15 1.3
148.25 59 19 1.4
148.5 75 16 1.6
148.75 90 0 1.7
149 96 6 1.9

Hi Scott, It probably means you are measuring the impedance through a
length of lossy coax. If you do the sweep using an electrical 1/2
wavelength of coax at say 146 MHZ you will probably see more of what
you would expect. I think the MFJ manual gives instructions for cutting
a 1/2 wave xmission line. If you have EZNEC you could do an SWR sweep
of your particular antenna and see what the impedances should be. Then
take the MFJ readings right at the antenna or through a multiple of 1/2
wave coax. The results should pretty closely agree.

If you still have problems, then there may be some strong RF present
that is disturbing the measurments, or YOUR presense in the near field
of the antenna could be upsetting things. If you are trying to measure
a voltage fed antenna like a J pole, if you are physically close to the
antenna it will foul things up. Good Luck.

Gary N4AST

Reply With Quote

Reply With Quote

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search
Display Modes
Switch to Linear Mode Switch to Hybrid Mode Threaded Mode

Posting Rules
Smilies are On [IMG] code is On HTML code is Off Trackbacks are On Pingbacks are On Refbacks are On

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Determining SWR and Transmission Line Losses	Frank	Antenna	7	June 11th 05 02:37 PM
Off-Center-Fed horizontal wire with capacitive loading	Chuck Olson	Antenna	0	May 24th 05 07:01 PM
Folded monopole dilemma	The other John Smith	Antenna	33	April 27th 04 02:00 AM
Antenna Reactance Question	alhearn	Antenna	83	April 4th 04 03:53 AM
Mobile Ant L match ?	Henry Kolesnik	Antenna	14	January 20th 04 04:08 AM

All times are GMT +1. The time now is 04:43 PM.

About Us

"It's about Radio"

Contact Us RadioBanter forum home Privacy Statement

Copyright © 2017