RadioReference on Facebook   RadioReference on Twitter   RadioReference Blog
 

Go Back   The RadioReference.com Forums > Amateur Radio > Amateur Radio Antennas


Amateur Radio Antennas - For discussion of all amateur band designed antennas and related accoutrements. This includes base, handheld, mobile and repeater usage. For commercial antennas on the amateur bands please use Commercial Radio Antennas below.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1 (permalink)  
Old 12-24-2016, 8:40 AM
NC1 NC1 is offline
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: Feb 2014
Location: Surry County, North Carolina
Posts: 440
Default We know SWR, but what is Zx Rs and jX?

I am having a discussion about the Surecom SA-250 Antenna Analyzer with a friend, and he seems to have a difference of opinion as to what those last 3 abbreviations mean.

Being that my theory is a little rusty, I am beginning to question if I am correct or getting it confused with something else. A good hour in a google search has ended in futility because of all the results either want me to buy something, or gives me a multitude of other non-related results.

If somebody could clear this up, it would be greatly appreciated.
Reply With Quote
Sponsored links
  #2 (permalink)  
Old 12-24-2016, 11:02 AM
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: May 2015
Location: Hammond, IN
Posts: 1,620
Default

Quote:
Originally Posted by NC1 View Post
I am having a discussion about the Surecom SA-250 Antenna Analyzer with a friend, and he seems to have a difference of opinion as to what those last 3 abbreviations mean.
Zx is the characteristic impedance, i.e., the square root of L/C (inductance/capacitance).

jX is inductive reactance (if +) or capacitive reactance (if -)

Rs is the total resistance of the antenna system

In any case, I highly recommend reading this ARRL book:

Understanding Your Antenna Analyzer
https://www.scribd.com/doc/314785439...tenna-Analyzer
__________________
Bill
N4GIX - Ham / WQWU626 - GMRS
VV-898, TK-840(N), 2xTYT-7800, 2xUV5R v2+, HP1, BCD436HP, TMV7A, Ritron RRX-450 Repeater, MD-380, XPR7550, 2xCS800, Bridgecom BCR-40U Repeater, Elecraft KX3 + PX3
Reply With Quote
  #3 (permalink)  
Old 12-24-2016, 12:40 PM
NC1 NC1 is offline
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: Feb 2014
Location: Surry County, North Carolina
Posts: 440
Default

Quote:
Originally Posted by N4GIX View Post
Zx is the characteristic impedance, i.e., the square root of L/C (inductance/capacitance).

jX is inductive reactance (if +) or capacitive reactance (if -)

Rs is the total resistance of the antenna system

In any case, I highly recommend reading this ARRL book:

Understanding Your Antenna Analyzer
https://www.scribd.com/doc/314785439...tenna-Analyzer
Thank you for clearing that up. I was a little rusty on the Zx, but I was correct on the other two.

That link looks like a very worth while read so I can brush up a bit on what I have forgotten over the years. When you don't use it very often, it tends to get in the back of the line and all but forgotten

I appreciate your Christmas gift, hope you have a good one and get a shiny new rig under the tree tomorrow morning.
Reply With Quote
  #4 (permalink)  
Old 03-16-2018, 4:17 PM
Mikejo's Avatar
Member
   
Join Date: Jul 2007
Location: Waltham,MA
Posts: 108
Default

I Bought a Surecom SA-250 recently, and I'm trying to better understand the other parameters the Analyzer shows me.

I have a Dipole Antenna I recently made cut for VHF High 160Mhz range for listening to Railroad Frequencies on my scanner.

When I test it on my Analyzer I get VSWR 1.12, Zx 47.0, Rs 63.9, and jX -43

What are the other parameters telling me about this particular antenna?

For instance is a Zx of 47.0 a good thing or a bad thing? If bad, what would be good?

How about Rs of 63.9 ? Good/Bad? If bad, what would be good?

Finally, jX of -43 Good/Bad? If bad, what would be good?

(I'm not a HAM, and I don't have an ARRL Handbook, and if I did I would probably not understand it anyway).

I just would like a laymans term explanation ( if possible), to know if any of these other parameters could help me make adjustments. or indicate a cable problem and the such.
Reply With Quote
  #5 (permalink)  
Old 03-16-2018, 7:06 PM
n0nhp's Avatar
Member
  Audio Feed Provider
Audio Feed Provider
Amateur Radio Operator
Amateur Radio
 
Join Date: Dec 2005
Location: Grand Junction
Posts: 689
Default

Much of that is going to depend on the receiver you are using.
If you are using a scanner or other wide band receiver, your input impedance to the radio is not going to be a "perfect" 50 ohms. Even with a dedicated VHF High/ high split radio the receive impedance is pretty problematic.
For a transmitter however you really want the transmitter output impedance to match the input impedance of the antenna so you are wasting as little power as heat as possible. Even that said most of today's wide-band transmitters are very tolerant of a very wide impedance mis-match.

Zx of 47.0 = 50 ohms within any tolerance. Your antenna is well matched as is your coax.
Rs of 63.9 is again showing close enough to 50 Ohms to be within tolerances
jX of -43 is showing that the the antenna is showing capacitance may be a bit high. Could be a sign you are using slightly under-sized coax and could possibly be losing some signal there or it may just mean that the over-all design is capacitive. You could take the analyzer to the roof and see if things change.


One of the joys of building your own antenna systems is seeing where the theory and practice converge and diverge.

On receive the things that will make the most difference is altitude and transmission line.
A paper clip stuck in the connector with a good line of sight will out perform the highest dollar antenna that is stuck down in the attic.

Good luck
Bruce
__________________
N0NHP
Reply With Quote
Sponsored links
  #6 (permalink)  
Old 03-16-2018, 7:36 PM
Mikejo's Avatar
Member
   
Join Date: Jul 2007
Location: Waltham,MA
Posts: 108
Default

Thanks Bruce, (I am well aware that I really don't need to have everything perfect with a receive Only antenna). I'm glad you gave me the information I was looking for, for both impedance and resistance I would just like to know where one should draw the line as to where it would be considered bad; let's say for the resistance to be "greater than "70"? Would that be where the line should be drawn?

Regarding "JX", let's say it's showing The antenna to be more capacitive than inductive, what could I do to change that? Is there a way to add either inductance or capacitance to straighten it out? Would this mean just using an antenna tuner to accomplish such a thing or could I add electrical components in the line to accomplish the same thing?

I know it's only a scanner antenna, but what I'm really interested in doing is making it as sensitive as possible, because the area I live in makes it difficult to hear anything but the dispatcher. I would like to try and see if I could pull in some of the actual trains and hear them as well.
Reply With Quote
  #7 (permalink)  
Old 03-16-2018, 8:07 PM
n0nhp's Avatar
Member
  Audio Feed Provider
Audio Feed Provider
Amateur Radio Operator
Amateur Radio
 
Join Date: Dec 2005
Location: Grand Junction
Posts: 689
Default

The capacitive reading could (one reason I suggested testing at the antenna) be due to coax that is showing a fairly high capacitance at that frequency. This is why the higher the frequency and the longer the coax runs, the larger (for the most part) the coax used is. Using the appropriate formula (and no I don't remember it (Electronic tech classes were 40+ years ago) you can calculate the attenuation of the signal at the frequency you are interested in. Easier is to look at the spec sheets and see what the manufacturer specs are.
Adding inductance will probably not help as you would be putting a coat of paint on to make the meter tell you what you want but not actually curing the problem (If any).

The dispatcher is using a remote base placed on a tall tower or mountain top where at least in Colorado the tracks are almost always within spitting distance of a stream or river. Not conducive to distant comms.

Bad would be where whatever skyhook you had in the air didn't pick up anything.

Will spending some money on better coax or a higher gain antenna help?
I can't answer.
I have spent a lot of money on aluminum and copper pieces that are now playing host to insects in the storage sheds when they didn't work as well as what I had up. But I always have hope that the next experiment will be the best thing since sliced bread! :-)

Good luck
Bruce
__________________
N0NHP
Reply With Quote
  #8 (permalink)  
Old 03-16-2018, 8:57 PM
Mikejo's Avatar
Member
   
Join Date: Jul 2007
Location: Waltham,MA
Posts: 108
Default

Well, the the analyzer I have can't test the coax( at least I don't think I can) , but I can test the antenna at the other end. I'll see if it's a tad too short for the freq I want, if so, I can quickly cut a few more elements and start over.

Thanks for the help!
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

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



All times are GMT -5. The time now is 2:22 PM.


Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
All information here is Copyright 2012 by RadioReference.com LLC and Lindsay C. Blanton III.Ad Management by RedTyger
Copyright 2015 by RadioReference.com LLC Privacy Policy  |  Terms and Conditions