Another thing to learn ....

[redbeast]

Ok, so just picked up a new rigexpert aa55, and just want to throw out some shots. So, had tuned my sirio performer 5000 with old micronta meter, truck bonded fairly well, and on 27.205, it reads 1:1.1. So then installed the 55, and took a couple of initial readings on 27.205, just to see what it said. Now I havent really spent any time getting used to the functions and all, just picked the center point, set limits, and lit it up. M guessing that the numbers I'm seeing look pretty good, x could be lower, but on the whole would you agree? Where I'm trying to go with this is time the sirio to 10/11 meters, and see what the 55 tells me. Hoping I can get it to work on both bands. As this is my first journey into this area, would appreciate any comments or opinions. Yeah, I know, but haven't really spent any time using it yet; but will definitely do that. Overall so far??

 

[The DB]

As I recall, that antenna mount has a permanently mounted coax cable. In that case, X and R will be off to some degree, but SWR will still be accurate. It is an effect of coax between the meter and the antenna.

I wouldn't fret with those results at all. There are people who obsess over perfection, but perfection won't get you anything...


The DB

 

[redbeast]

As I recall, that antenna mount has a permanently mounted coax cable. In that case, X and R will be off to some degree, but SWR will still be accurate. It is an effect of coax between the meter and the antenna.

I wouldn't fret with those results at all. There are people who obsess over perfection, but perfection won't get you anything...


The DB

Thanks for the input, DB. No, the magnet mount did. This one has the coax running from the radio to a breedlove pocket mount with an so239 adapter. This was only my first use of the aa55, so it will take a little while for me to get used and understand, but unless I'm entirely wrong, I figure I'm pretty close to where I should be, especially given I've only had the micronta for all these years. Recently installed a radioddity qt80, and figured I'd need a better way of checking the setup if I was going to go down to 10 m, or up to 12,15.
So, like I say, being a ham newbie now, I appreciate any comments or critiques. Crawl before you run, right? Checked the 10 m band, and swr on the qt80 was triggering the warning, 3-4 range..... The 55 is only one day new to me, so I'll play with it and the sirio before I think about a different setup; the 55 should give me good input and help finding a spot that should work for 10/11 meters for a start. Thanks again, any and all comments are appreciated.

 

[redbeast]

Thanks for the input, DB. No, the magnet mount did. This one has the coax running from the radio to a breedlove pocket mount with an so239 adapter. This was only my first use of the aa55, so it will take a little while for me to get used and understand, but unless I'm entirely wrong, I figure I'm pretty close to where I should be, especially given I've only had the micronta for all these years. Recently installed a radioddity qt80, and figured I'd need a better way of checking the setup if I was going to go down to 10 m, or up to 12,15.
So, like I say, being a ham newbie now, I appreciate any comments or critiques. Crawl before you run, right? Checked the 10 m band, and swr on the qt80 was triggering the warning, 3-4 range..... The 55 is only one day new to me, so I'll play with it and the sirio before I think about a different setup; the 55 should give me good input and help finding a spot that should work for 10/11 meters for a start. Thanks again, any and all comments are appreciated.

Oh, yeah, btw- is that 4.91 on the x reading far off, or not really?

 

[338_MtRushmore]

All that matters is where the vswr dip is. Resonance is pretty easy to read at an antenna feed point, but adding a feedline adds a lot of complications.

 

[M0GVZ]

Antennas with matching sections aside X will not be at 0 where the SWR is at 1:1. Where X=0 is where your antenna is actually resonant. Where the SWR is 1:1 is where the impedance is 50 Ohms. Unless you're using an antenna designed so the feedpoint impedance at resonance is 50 Ohms they'll never align.

Lets take a 1/4 wave antenna as an example. The feedpoint impedance of a 1/4 wave antenna over a perfect ground is 36.8 Ohms. So if you've a perfect ground where X=0 the impedance should show 36.8 Ohms. Now of course this isn't going to show a 1:1 SWR for a CB or ham radio as thats only at 50 Ohms. You will see a 1:1 SWR at some point but X will not be equal to zero where it does.

When I'm doing mobile installs I'll always use a 1/4 wave antenna for testing the RF ground efficiency. I'll not even give a toss what the SWR is. I do not adjust the antenna at all for this, the reason will be explained later. I'm looking for the frequency where X=0 and what the feedpoint impedance is, not for a 1:1 SWR. The further away from 36.8 Ohms it is the poorer the RF ground. As I add more bonding etc I check again. What I expect to find with any improvement is two things:

1) The feedpoint impedance at resonance gets closer to 36.8 Ohms
2) The frequency where X=0 will get lower.

The reason I'm looking for point 2 is that as you improve a RF ground the length of the radiating element shortens for any given frequency (explained in ARRL Antenna Book). By not altering the length of the antenna as you improve the RF ground it means the antenna appears electrically longer so the resononant frequency drops. I continue to add more bonding and doing those two tests until I either hit 36.8 Ohms or the amount the resonant frequency is dropping with every change either stops or becomes very little. At that point you've got it as good as it'll go.

This is also why some people find that with mobile CB antennas they can't seem to tune them. Manufacturers create the lengths assuming a piss poor install because most are so they make the whips quite long. Because the user has got a very good RF ground it means the resonant frequency is below the CB channels but there's not enough adjustment in the antenna to bring it back up without cutting. They think there's something wrong because they don't have an antenna analyser so can only check the SWR on the frequencies their CB can transmit on which often won't be enough. As an example I have very good RF grounding on my mobile install. Sticking my Sirio 5000 on the first time it was resonant at 26MHz. I had to cut almost 3 inches off the whip to bring it back into the CB band. Every CB antenna I install I have to cut.

NanoVNAs are dirt cheap, £40 or so and will save a lot of people a lot of time chasing red herrings and trying to find faults in an installation that don't actually exist but which they think do because of the limitations of the testing they can do with just a transceiver and SWR meter.

 

[338_MtRushmore]

Antennas with matching sections aside X will not be at 0 where the SWR is at 1:1. Where X=0 is where your antenna is actually resonant. Where the SWR is 1:1 is where the impedance is 50 Ohms. Unless you're using an antenna designed so the feedpoint impedance at resonance is 50 Ohms they'll never align.

Lets take a 1/4 wave antenna as an example. The feedpoint impedance of a 1/4 wave antenna over a perfect ground is 36.8 Ohms. So if you've a perfect ground where X=0 the impedance should show 36.8 Ohms. Now of course this isn't going to show a 1:1 SWR for a CB or ham radio as thats only at 50 Ohms. You will see a 1:1 SWR at some point but X will not be equal to zero where it does.

When I'm doing mobile installs I'll always use a 1/4 wave antenna for testing the RF ground efficiency. I'll not even give a toss what the SWR is. I do not adjust the antenna at all for this, the reason will be explained later. I'm looking for the frequency where X=0 and what the feedpoint impedance is, not for a 1:1 SWR. The further away from 36.8 Ohms it is the poorer the RF ground. As I add more bonding etc I check again. What I expect to find with any improvement is two things:

1) The feedpoint impedance at resonance gets closer to 36.8 Ohms
2) The frequency where X=0 will get lower.

The reason I'm looking for point 2 is that as you improve a RF ground the length of the radiating element shortens for any given frequency (explained in ARRL Antenna Book). By not altering the length of the antenna as you improve the RF ground it means the antenna appears electrically longer so the resononant frequency drops. I continue to add more bonding and doing those two tests until I either hit 36.8 Ohms or the amount the resonant frequency is dropping with every change either stops or becomes very little. At that point you've got it as good as it'll go.

This is also why some people find that with mobile CB antennas they can't seem to tune them. Manufacturers create the lengths assuming a piss poor install because most are so they make the whips quite long. Because the user has got a very good RF ground it means the resonant frequency is below the CB channels but there's not enough adjustment in the antenna to bring it back up without cutting. They think there's something wrong because they don't have an antenna analyser so can only check the SWR on the frequencies their CB can transmit on which often won't be enough. As an example I have very good RF grounding on my mobile install. Sticking my Sirio 5000 on the first time it was resonant at 26MHz. I had to cut almost 3 inches off the whip to bring it back into the CB band. Every CB antenna I install I have to cut.

NanoVNAs are dirt cheap, £40 or so and will save a lot of people a lot of time chasing red herrings and trying to find faults in an installation that don't actually exist but which they think do because of the limitations of the testing they can do with just a transceiver and SWR meter.

When all that is said and done, the frequency with the lowest vswr is the most efficient.

It is kind of funny watching guys detune their antennas by increasing ground loss when they move it closer to the edge of the roof.

 

[Alexis Mercado]

As long as the X be 4 or less ( SWR can be around 1.4 ) antenna is resonant. That means the ohms is not around 50. Sometimes achieving a 50 ohms and X less than 4 is not possible for a number of reasons.

 

[redbeast]

As long as the X be 4 or less ( SWR can be around 1.4 ) antenna is resonant. That means the ohms is not around 50. Sometimes achieving a 50 ohms and X less than 4 is not possible for a number of reasons.

Well, my original plot had set at 1:1.21 with x at 4.91. Thought that was pretty good, but in changing antenna length to try and tune to 28.800, finding I can drop swr but x goes out bad. I'm going to try adjusting the whip shorter.....think I have a spare around. Had already cut the whip down about 3" from stock length to get it to tune at 27.205, so I'll see what happens. Still in the process, but if it ain't broke, don't fix it. Would probably have less issues if I could mount it on roof but that would mean no garage. Maybe another antenna at rear bed pocket instead of front bed pocket. Don't doubt the antenna being affected by proximity to cab....5" at bottom of antenna, 11.5" top of cab to whip.

 

[Alexis Mercado]

readbeast

Those are good numbers

 

[redbeast]

readbeast

Those are good numbers

Thanks. So my plan is to shorten the whip some more, intention to see if I can get to a point where I can be good for 10/11 meters. Did some playing yesterday up and down.....so as you can see on 28.040 got good reading for x, but swr up. So I'm going to try a shorter whip and run an swr graph to check dip for resonance, and recheck......will let you know. Thinking maybe antenna position not the best, but guess we will see. Trying to see if I can get close to the center of 10/11 and run a chart and some figured. Worst case, it goes back the way it was and I do something else for 10 m. General word, and what I've been seeing is that tuning to best swr dip should pretty much give me what I need, thinking that the sirio should come in to this area, especially looking at this last screen. Just a matter of keeping set and xwithin decent limits. So, back to work.