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SWR trouble

Ok, to help you see the Smith Chart versus the Nano - you are using the best tool out here in this thread - the Nano-VNA "smith chart overlay" is to help demonstrate what many need to know when it comes to making the right choices in not just antenna, but the mount and the Location they all get put in.

If one of the three is not the best, right or ideal - all the other pieces of the puzzle just don't fit...


Ok, the numbers...

Your "1" shot
upload_2021-11-12_7-47-11.png

Number 2 shot
upload_2021-11-12_7-47-52.png

Ok, number 1 is "best" (1.2093 If I read this right)

Number 2 reading is "worse" 1.12108...

To help with this - look to the right "Green lettered"

Number 1 41.92Ω while number 2 is 41.88Ω

On the smith chart - that "+j Component" is inductive - usually means the "reason" it is off is due to what it senses as an INDUCTIVE reactance to the signal - it's reflection shows inductance.

You lengthened the antenna - you ADDED wire, or INDUCTANCE - So Number 2 is telling you - you went the wrong way. Your "+j Component" ...

Another thing - see the "ohmic" result?

Number 1 - 41.92Ω
Number 2 - 41.88Ω

So what this tells you is the readings the "resistive" element is lower on Number 2 - but was it due to length or was is due to inductance - length being "resistance" while Inductance is the uH change upwards.

In the first One - compared to the 2nd one - change the radiation or what it appears as in resistance - being lower in Number 2 - it uses the inductance changes as being the requirements the VNA needs to has recomputed the expected - FROM: (Where you want to go)

So when you added - the uH went up - and so did the SWR but the working Resistance went down.

Ok, SWR "best" is 50Ω - so return antenna to Number 1 setting...

  • Sidebar: This is a good example of Radiation; the losses or the gains - one being how much the reactive component changes the antennas "resistance" appearance. OR What it thinks it needs to make itself 50Ω - so the VNA calculates the components -/+ j and then tells you with the SWR change - your antenna has this "Value of resistance" which when your SWR is worse, non-1:1 or when it is lower - or HIGHER then the "Where you want to be" or your 50Ω results of idealized transfer to the "ether" Your end results is a number - the closer the number is to 50 the better off you'll be.
  • So why is the low SWR show Inductance? When I add wire the SWR becomes worse - ok let's stop and figure out what was discussed earlier - Mount and Location are your two most likely culprits - against the antenna - because you didn't re-create the SIRIO original test conditions that show their antennas' MEETING the 50Ω mark or lowest SWR - or did they? I mean, What does it take to make this thing have a 1:1 SWR? Come on guys! HOW?
  • No, they probably didn't take a photo of the antenna as it was mounted and tested - no verification except it was shipped in a container and shrink-wrapped to seal - SIGH...What you have to go on in trust is far less than what you actually got - which when you look at how this fly-by-wire mess of commercial manufacturing is these days, you're doing great - it could have gone far worse. You have a working antenna built in some fashion that works well - so why split hairs - let alone the Atom?

(In the previous post - I mentioned you're beating yourself up fiddling and trying to beat the antenna to the Blue Point - this is those headaches when you're so close, you just want to scream...:))
 
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Ahh...so location, mount, adaptor from nmo to PL, connectors, chokes and antenna....all affect each other!! Ya I am pretty close to the “blue” spot. I remember reading that 50ohm is center...so I am not too far. As most of us in radio we usually can’t leave things alone. Chasing that elusive dragon!!!

That was a great explanation!!! Easy to follow for this beat up brain. I feel good about my work now! I get compliments on how my mobile sounds and now I know why it sounds technically the way it does.

I am going to subscribe to this thread or cut and paste to my build thread.

To the OP...I didn’t mean to hijack your thread! Hopefully some of this extra stuff can help you out. But get a VNA...I will really give you a clear view on what your antenna system is doing!!!
 
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forestrunner,

if you have access to the first 16 or so inches of the coax coming down from the feedpoint, try putting about a foot or more of type 31 ferrite snap on chokes right at the feedpoint and see what that does to your VNA readings.

it's pretty much impossible to make a truly balanced antenna system on a vehicle, so there are always some common mode currents trying to come back down the shield.

putting the ferrite on the coax forces more of the signal out of the antenna and just might have an effect on the inductive component of your readings.
(i actually don't know if it will affect it or not, im just guessing)

however, putting a bunch of ferrite at the feedpoint of a mobile install is always a good idea.
LC
 
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I have 5-6 snap beads at the feed point under the headliner and also a mix 61 FT240 toroid with 12 wraps crossed in the middle. That actually helped a lot! The snap on’s were meh but left them on.

I believe now that all those factors affect the antenna in one way or another. Without the VNA one is just in the dark. To be honest I am really happy with the performance of this rig!! A tad more power would be nice!
 
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forestrunner,

in general you don't want to choke the common mode currents anywhere but at the feed point because they will still travel down the shield to wherever your choke is.

i can imagine that the 5 or 6 beads didn't do much because there just wasn't enough of them.
you really need to do like a foot and a half to two feet worth to get the desired effect.

yes, you can also just wind the coax into a choke at the feedpoint, but that can be logistically difficult because of headliners and other obstructions.

however you get there, the idea is to stop the common mode currents right at the feedpoint.
anywhere past that, and you have coax shield as part of your radiating system.

im just throwing out ideas, not knocking what you have in there now.

if you haven't done it already, the next biggest change you can make in your receiving and transmitting range is to bond the different parts of the vehicle together with copper strap.

i couldn't believe the difference this made in my S10 pickup.
receive was quieter, but i could hear further, as well as my signal reaching out a bit further.
LC
 
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I have more beads but I think I will leave it alone....for now. LOL I didn’t want to put the toriod under the headliner because I believe the coax and toroid will touch the metal on the roof. That gets really hot.

Ah bonding!!! Well it’s bonded pretty good. I have 4 1” straps on both sides (8 total) from body to frame. Same goes with hood(2), doors, hatch(2), alternator to frame, engine to body and steel bumper to frame. I think bonding made a HUGE improvement on RX/TX. Since I am not using big power, KL203, I need every little help.
 
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ForestRunner98 said:
Ahh...so location, mount, adaptor from nmo to PL, connectors, chokes and antenna....all affect each other!! Ya I am pretty close to the “blue” spot. I remember reading that 50ohm is center...so I am not too far. As most of us in radio we usually can’t leave things alone. Chasing that elusive dragon!!!

That was a great explanation!!! Easy to follow for this beat up brain. I feel good about my work now! I get compliments on how my mobile sounds and now I know why it sounds technically the way it does.

I am going to subscribe to this thread or cut and paste to my build thread.

To the OP...I didn’t mean to hijack your thread! Hopefully some of this extra stuff can help you out. But get a VNA...I will really give you a clear view on what your antenna system is doing!!!
Click to expand...
Hey ForestRunner98, since you mentioned the NMO to PL adapter, are using the SIRIO where you had a LARSEN? If so, did you see a gain in performance and range with the SIRIO?
 
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Rebel Outlaw said:
Hey ForestRunner98, since you mentioned the NMO to PL adapter, are using the SIRIO where you had a LARSEN? If so, did you see a gain in performance and range with the SIRIO?
Click to expand...

No...I went with the NMO in case I wanted to try a different antenna like the Larson. Also Breedlove didn’t make a PL to terminal end anymore.
 
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