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MATCHING IMPEDANCE

The ONLY thing I can find regarding the "Probe 5800" is in a post on eHam:

http://www.eham.net/articles/1964

Look for posts on May 28, 2001 by a Northern Ireland (GIØ) ham. He just mentions that he has one. If you had the name of a manufacturer it might help.

And what's wrong with a 1.6:1 SWR?? Any radio that won't withstand a piddly mismatch like that isn't worth having. If the power starts to scale back, you might try tuning the antenna itself for something a bit closer to 50 ohms. My IC-738 will run into 2:1 mismatches all day long without complaining.
 
HI BEETLE :D YEP I HAVE READ THAT REVIEW ON E HAM, IT SOUNDS TO ME LIKE THAT GUY HAS THE BASE TO AN A99 ASWELL AS THE ORIGINAL BASE TO THE PROBE 5800, AS I ALSO HAVE AN A99 HERE ASWELL & HIS DESCRIPTION SEEMS TO MATCH UPTO WHAT I HAVE HERE,I CANNOT TUNE THE PROBE 5800 AS IT DOES NOT HAVE TUNING RINGS AT THE BASE.& I KNOW AN SWR OF 1.6:1 IS O.K, BUT I WAS WANTING TO GET IT LOWER BEFORE I HAVE THE ANTENNA INSTALLED ON MY ROOF,ALSO IT WON T BE PUTTING OUT 100% POWER OUT OF THE END OF THE ANTENNA AS SOME OF IT WILL BE REFLECTING BACK DOWN THE FEEDLINE & I MIGHT WANT TO RUN A LINEAR INLINE AT A LATER DATE. THERE IS A METHOD TO MATCH IMPEDANCES & UNFOTUNATLY I CANT SEEM TO FIND HOW TO RECTIFY THIS,ALL I KNOW IS THAT I NEED A BALUN OR A TRANSMISSION LINE TRANSFORMER, HOPEFULLY SOMEBODY READING THIS WILL BE ABLE TO GIVE ME THE INFO TO RESOLVE MY IMPEDANCE MISMATCH BETWEEN THE END OF THE FEEDLINE & THE ANTENNA BASE. CHEERS,SHAUN. :D
 
WARBY said:
HI BEETLE :D YEP I HAVE READ THAT REVIEW ON E HAM, IT SOUNDS TO ME LIKE THAT GUY HAS THE BASE TO AN A99 ASWELL AS THE ORIGINAL BASE TO THE PROBE 5800, AS I ALSO HAVE AN A99 HERE ASWELL & HIS DESCRIPTION SEEMS TO MATCH UPTO WHAT I HAVE HERE AS THE A99 IS LONGER LIKE THAT GUY DESCRIBES,I CANNOT TUNE THE PROBE 5800 AS IT DOES NOT HAVE TUNING RINGS AT THE BASE.& I KNOW AN SWR OF 1.6:1 IS O.K, BUT I WAS WANTING TO GET IT LOWER BEFORE I HAVE THE ANTENNA INSTALLED ON MY ROOF,ALSO IT WON T BE PUTTING OUT 100% POWER OUT OF THE END OF THE ANTENNA AS SOE OF IT WILL BE REFLECTING BACK DOWN THE FEEDLINE& I MIGHT WANT TO RUN A LINEAR INLINE AT A LATER DATE. THERE IS A METHOD TO MATCH IMPEDANCES & UNFOTUNATLY I CANT SEEM TO FIND HOW TO RECTIFY THIS,ALL I KNOW IS THAT I NEED A BALUN OR A TRANSMISSION LINE TRANSFORMER, HOPEFULLY SOMEBODY READING THIS WILL BE ABLE TO GIVE ME THE INFO TO RESOLVE MY IMPEDANCE MISMATCH ETWEEN THE END OF THE FEEDLINE & THE ANTENNA BASE. CHEERS,SHAUN. :D
Click to expand...
 
warby all the power is radiated minus the loss in feedline and antenna matching network even the reflected power re reflects from the output matching network in the transmitter and is radiated eventually,

you need to get the antenna up in the air where you are going to use it as the feedpoint impedance will very likely change once you get it up there in the clear,

i would never tune an antenna near the ground and other conductive objects then errect it on a pole and expect the same feedpoint impedance,

if it is still not as you like then you can make the radio happy and deliver its full power to the feedline by trimming the feedline until you find the spot that gives a good match to the radio,
your feedline is a transformer whenever it is not terminated with its characteristic impedance at both ends or not cut to exact electrical halfwaves when its terminating impedance is not 50ohms,

that wont cure the vswr on the line but it will look like 50ohms to the radio and allow full power,

try adding an extra section of coax as an experiment and trim that so your not cutting your main run,

heres a couple of good threads to read on feedlines and reflected power

http://forum.worldwidedx.com/viewtopic.php?t=14618&postdays=0&postorder=asc&start=45

http://forum.worldwidedx.com/viewtopic.php?t=15499&postdays=0&postorder=asc&start=0

good luck.

i should read what i type :oops:
 
Warby, a BALUN is used to match a balanced transmission line to an unbalanced line. If your antenna system is balanced, a BALUN will work and there are numerous designs already calculated with instructions that will help.

However if the antenna is not balanced, then you would need to know the generators (CB, Amp, etc...) complex impedance output and antennas complex impedance feedpoint input. With these values an electrical wavelength length (angle/length) of coax can be calculated that will transform, or conjugate match these values.
 
Since you are not willing to accept a mismatch of 1.6:1, and are trying to achieve perfection, I suggest that you use a twelfth-wave-transformer. This will match your 50 ohm coax to 75 ohm coax, or load. It is much easier than using a quarter wave matching section. I have used this method for years when using free CATV hardline.

Do a search on "twelfth wave transformer". Read and learn.

Rich
 
FWIW, it installed the PDC30 Para Dynamics CB Antenna Matcher I noted in my last post. I had some reservations because it cost $20, and looked cheaply made.

I began with an SWR of 1.7:1, and, after much delecate adjustment and fiddling around, I got the SWR down to 1.4:1, as measured with an MFJ 259B. While this is less than ideal, it is useful, and especially since it only cost me $20 and 1/2 hour of futzing around. However, the controls were very touchy, and nothing took away from my first impression that the PDC30 was was cheaply made. I experemented with other frequencies, and it seemed to bring the SWR down from very high levels, but had difficulty putting too fine as point on it. I'll test the PDC30 again in a week or so to see if it held its adjustment, but I wouldn't be surprized to find that it hasn't.
 
Hamin' X said:
Since you are not willing to accept a mismatch of 1.6:1, and are trying to achieve perfection, I suggest that you use a twelfth-wave-transformer. This will match your 50 ohm coax to 75 ohm coax, or load. It is much easier than using a quarter wave matching section. I have used this method for years when using free CATV hardline.

Do a search on "twelfth wave transformer". Read and learn.

Rich
Click to expand...

HI HAMIN X, IM NOT THAT HI TECH MINDED TO WORK OUT MEASUREMENTS TO MAKE ONE OF THESE, SO WHAT LENGTHS WOULD I HAVE TO MAKE FOR EACH ONE OF THESE TWO PIECES OF COAX TO MAKE A TWELTH WAVE TRANFORMER??? I KNOW I NEED A 1 50 OHMS PIECE & A 75 OHMS PIECE ASWELL. AS I HAVE BEEN READING THIS http://www.phys.unsw.edu.au/~map/weather/notes/buildyourown/lindenblad.html#vhf_uhf_manual THANKYOU FOR ALL YOUR HELP,SHAUN. :D
 
If you are not tech minded enough to figure it out, then you probably should not attempt to build them. There are too many variables for me to explain it easily. You have an SWR of 1.5:1 as it sits and it will not make any difference that anyone will see, if you get it any lower. Please just take my word for it.

Rich
 
i do have one other method
you might not like it
but then this large type and caps i dis-like %&*
(so we are even)

Get a different antenna :idea:
like the A99

they are cheep :twisted: :wow

:rknrl :rknrl
 
i do have one other method
you might not like it
but then this large type and caps i dis-like
(so we are even)

Get a different antenna :idea:
like the A99

they are cheep :twisted: :wow

:rknrl :rknrl
 
KingCobra_CDX882 said:
i do have one other method
you might not like it
but then this large type and caps i dis-like
(so we are even)

Get a different antenna :idea:
like the A99

they are cheep :twisted: :wow

:rknrl :rknrl
Click to expand...


I ALREADY HAVE AN ANTRON 99, YES THEY ARE CHEAP & NASTY! http://www.geocities.com/cobra269/files/a99-uncovered.pdf THE ANTENNA I AM TALKING ABOUT ON THIS THREAD IS A 5/8 WAVE WHICH HAS SEEN A 1 S POINT DIFFERENCE IN MY SIGNALS. WHICH I PREFER FOR GETTING OUT LOCAL, THE REASON FOR THIS IS BECAUSE THE 5/8 WAVE HAS A LOWER RADIATION PATTERN THAN THE ANTRON 99 & ALSO A HIGHER DBd GAIN. THE ANTRON WILL NEVER SEE ANOTHER DAY ON MY RADIO AS THE 5/8 WAVE OUTSHINES IT ALL THE WAY!!!!!
 
An SWR of 1.6 will result in a loss of 5.3% (or so they say). What you what you want to look for in addition is ERP (Effective Radiated Power). This power is calculated by antenna gain and height while also accounting for the insertion loss of the coax, connectors, meters, etc.

Technically speaking you will always have a modest (small) loss (attenuation) because the feedline and connectors exhibit loss however, the antenna gain will more than make up for these losses.

I see your main concern is keeping the SWR low due to amplifier usage...

Hope you found a fix for this problem!

Carry on
 
Geekster said:
An SWR of 1.6 will result in a loss of 5.3% (or so they say).
Click to expand...

Or so who says? This kind of blanket statement is what is wrong with the radio world (CB & Ham). Myths, rumors, hearsay and just plain wrong information. What length of feedline is used? What type of feedline is used? What brand of feedline is used? These are just some of the conditions that must be known before one can begin to calculate loss.

For example:

1.
50 feet of good quality RG-8X (Belden 9258), at 27mHz and a mismatch of 1.6:1 will result in 18% power lost. But, 16.5% of the power would be lost with a perfect, 1:1 match, just to line loss. So, only 1.5% of the loss is due to the 1.6:1 mismatch.

2.
50 feet of good quality RG-8 (Wireman CQ102), at 27mHz and a mismatch of 1.6:1 will result in 8% power lost. But, 7.2% of the power would be lost with a perfect, 1:1 match, just to line loss. So, only .8% of the loss is due to the 1.6:1 mismatch.

With 50 feet of good RG-8 coax and a mismatch of 1.6:1, your total power loss is only .36 dB. of this, only .03 dB is due to the mismatch. To put this into perspective, it takes 6 dB to equal 1 S-Unit. It would take 200 times as much loss as the mismatch is creating to equal 1 S-Unit! Do you really think that anyone could detect .03 dB on the receiving end? The wind blowing your antenna, or the temperature of the air, will have more effect than this.

Rich
 

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