Weird readings, need help

[msged2007]

Hey guys, thought I'd come to the experts for some help. I have a 2018 silverado single cab, long wheel base work truck. It has a jobox in the back behind the cab and side boxes along the rails on each side. I just installed a new President Andy cb radio with an everhardt tiger SOTT 1.5 wave 3' long with a wilson gumdrop mount in the front corner of the bed, driver side. The antenna sticks up above the cab about a foot to foot and a half. The antenna is top loaded. I have it connected with 18' RG58AU. My SWR/field strength meter is an Astatic PDC2. I have a 1' jumper to connect the meter to the radio.

Now, here's what I got. Best SWR I can get is 2.8 ch 1, 2.5 ch 20, 2.8 ch 40, but at that antenna height, the radio signal strength meter on TX is full (all 4 s-units) ch 1, 3 s-units ch 20, 2 s-units channel 40, field strength measurements taken 1.5-2' from base of antenna verify channel 1 is stronger than channels 20 and 40. At this point I removed the SWR meter and jumper to verify the radio is collaborating via s-unit output on TX - it is. So, instead of tuning with SWR, I switched to tuning with field strength. I adjusted until I got a balanced output with field strength meter 1.5-2' away from base of antenna. Radio is now outputting full s-units on TX on all 40 channels, and I did a radio check and got a response from about 5 miles away (line of sight) which said radio is sounding good.

So here is my question: Why didn't best SWR match best measured field strength? And has anyone ever tuned an antenna based off of field strength measurements instead of SWR? Thank you guys in advance. Have a good evening.

[jessejamesdallas]

I've never adjusted a antenna using a field strength meter, but lowest SWR is not always the best either...I use a antenna analyzer and try to get the lowest SWR, but more important I try to get X=0 on as many channels as possible...

as for your antenna...I'm surprised you can get 5 miles with it mounted where you have it, and being just a 3' antenna...those two combinations together is usually a deal buster for distance.

[msged2007]

jessejamesdallas - Yes, I didn't know how it would work out in the beginning. It is a top loaded antenna and the top loading coil is above the roof, but it's a compromise at best. I've tested this antenna against a 4' Firestik FS2 and a Wilson Silverload 5' on top of the cab with a 5" mag mount. At a distance of 4 miles, the Everhardt was clearer and louder than the other 2 (go figure...) so I just stuck with it. I've since sold the other 2 antennas. I do however have a tram 36" mag mount on the way for the top of the cab; we'll see which one is best....

As far as my original question, I wondered if the additional length of coax and the meter changed at which point along the coax the radio was "seeing" the reflected wave, and therefore a portion of the output is cancelled by the reflected wave, and this is showing up on the radio as less s-units on TX. I started to think I was crazy until the field strength meter verified what I was thinking. This seems to me to be the reason behind why people say use an 18' run of coax on a mobile install; 18' in coax is 1 wave length, so its as if the antenna is plugged directly into the back of the radio.... (I used to be a radar tech in the Navy) to me it makes sense....

Anyway, that made me think about the question more deeply, in that why are we making coax measurements (SWR) which has the implied "this is how the antenna is performing" when we can actually measure how the antenna is performing via field strength measurements. It seems to me that SWR is an indirect way to measure antenna output and field strength is a direct way.... Food for thought. Thanks for the reply

[MDYoungblood]

With the antenna only being 3ft, it is seeing more of the cab in that position, I think a 4ft Everhardt would have done better. Check those tool boxes for good bonding, most have plastic fastening hardware and insulating foam on the bed rails. Bonding the cab will help too, especially the flat (horizontal) surfaces. You can find all kinds of info on bonding in the forum topics.
The way you checked the SWR was "old school", it works, SWR meters are okay to a point, dip grid or signal strength meters are a tad better, but nothing beats the new antenna analyzers.
You might want to check the meter and jumper, something just doesn't seem not quite right there.

3's

Greg

[jessejamesdallas]

jessejamesdallas - Yes, I didn't know how it would work out in the beginning. It is a top loaded antenna and the top loading coil is above the roof, but it's a compromise at best. I've tested this antenna against a 4' Firestik FS2 and a Wilson Silverload 5' on top of the cab with a 5" mag mount. At a distance of 4 miles, the Everhardt was clearer and louder than the other 2 (go figure...) so I just stuck with it. I've since sold the other 2 antennas. I do however have a tram 36" mag mount on the way for the top of the cab; we'll see which one is best....

As far as my original question, I wondered if the additional length of coax and the meter changed at which point along the coax the radio was "seeing" the reflected wave, and therefore a portion of the output is cancelled by the reflected wave, and this is showing up on the radio as less s-units on TX. I started to think I was crazy until the field strength meter verified what I was thinking. This seems to me to be the reason behind why people say use an 18' run of coax on a mobile install; 18' in coax is 1 wave length, so its as if the antenna is plugged directly into the back of the radio.... (I used to be a radar tech in the Navy) to me it makes sense....

Anyway, that made me think about the question more deeply, in that why are we making coax measurements (SWR) which has the implied "this is how the antenna is performing" when we can actually measure how the antenna is performing via field strength measurements. It seems to me that SWR is an indirect way to measure antenna output and field strength is a direct way.... Food for thought. Thanks for the reply

actually 18' is almost half-wave...full wave is little over 36' for 11 Meter.

[msged2007]

Jessejamesdallas - In coax? I didn't know that. Thanks.

[msged2007]

MD Youngblood - something seems off about that to me too. I'm going to have to redo it after I check everything.....

[MDYoungblood]

Yes, 18ft is a half wave at 27mhz. As far as coax goes, as long as it goes from the antenna connection to the radio connection it is long enough, no real magical numbers for length, (unless it is recommended by the antenna manufacturer). Most coax that come with antennas are 18ft, this is an average distance from the mount to the radio in most vehicles.

3’s

Greg

[jessejamesdallas]

Yes, 18ft is a half wave at 27mhz. As far as coax goes, as long as it goes from the antenna connection to the radio connection it is long enough, no real magical numbers for length, (unless it is recommended by the antenna manufacturer). Most coax that come with antennas are 18ft, this is an average distance from the mount to the radio in most vehicles.

3’s

Greg

Bingo! you win a cookie...

Too many variables with coax for that to be true...Different velocity ratings, different diameters of wire used, ratings vary from manufacturer...When it comes to coax, just use whatever it takes to get from A to B...Only times you need to pay attention to lengths in coax is when your doing something like a End-Fire array set-up, or bounce-back, two-hots, or beam set-ups like guys use in competition shoot-outs, or co-phase set-ups...In those cases you want the signal to hit one antenna, then a spit second later the other to get the right pattern your looking for...But in just a single antenna set-up, length doesn't factor...actually, the longer the coax, the worst because your dealing with more resistance from the wire...May look good on a meter tho.

[msged2007]

Thanks for the info guys. You've been good help. I'm going to tinker with it to see what I can do. I may just go to a mag mount on the roof. I know that works.

[msged2007]

So I figured out that this meter combo doesn't like the 1' jumper between the radio and the meter. I tried a 12' run that I had laying around and it seems that the meter and the radio agree on SWR and Power output on the S-meter of the radio. I know this because of experiments with an inverted V about 30' off the ground that performed very nice one night while talking local. A station roughly 5 miles away said I had him in the red and I could communicate with another roughly 30 miles away, and this with an out of box, barefoot radio. A 1/2 wave over 1/4 wave J-pole is in the planning....

And so I'd though I try that mag mount. I bought a TRAM 3' mobile mag mount and placed it on the roof of my work truck. SWR said that the antenna was too short, beyond what I could adjust for, the whip was now only under one of the two allen screws on the base to whip lock-down section. So I opened it up and added a half a turn on the base loaded coil with 14 awg wire and solder. Now, with the whip fully seated under both lock-down allen screws, I get a good match on SWR and the radio is indicating full power output across all 40 channels; multiple contacts have been made while on I-10 in FL over the last few days and they've all said that I'm sounding good.

I am somewhat of a newbee as compared to a HAM radio operator, but I am also an ex radar technician for the US Navy, so I understand a little more than the basics when it comes to RF propagation and antennas, although in the GHZ range, and I also really like experimenting with DIY antennas and gain. I've built a few dipoles, elevated verticals, ground mounted verticals, and now and inverted V, all using standard output power (a few radios were tuned, but 25 watt swings, no linears) and I guess I am more interested in what I can get an antenna to do using a standard 4 watt output (tuned radios included, maybe swing to 25-30 watts) than high power linear amplifiers. I don't know, maybe it's just me, but I am interested in learning more about antennas. I know that the antenna is what determines a stations performance. I heard a long time ago that if I had $100 to spend on a CB radio system, spend 30% on the radio and 70% on the antenna. Just my interests.....

Thank you guys for your help.

[443 Arizona]

i have used Field Strength meter to tune an antenna, but first i used an swr meter.
your FS meter can show you the exact antenna propagation.
as you state, your ex-navy, with more than basic knowledge as applied to RF.
I knew 2 guys with the same ex-navy qualification.
the one guy could have wrote the book on radio, the other was a coax greaser.
both jobs were vital.
For my 2 cents, I'd put the antenna on the top. plus you wont radiate yourself.

[arcone]

A few things worth mentioning here.
Coaxial length will affect the SWR if there is a difference in impedance between the radio and the antenna. The length chosen will act as an impedance transformer. It's likely that when you changed out that patch lead, the transformation was closer to 50 ohms... or the 1ft patch could have been faulty.
Coaxial length will change an SWR reading because of it's attenuation too.
I believe common mode current will alter an SWR reading also. A lot of end fed antennas will exhibit common mode.
A slightly high SWR does not effect your efficiency by as much as you think, actual losses are minimal.
The half wave cable (without taking in the velocity factor of the cable) has some applications, but I don't think they apply here. However if you cut your cable to an electrical half wavelength, it can have some advantages, RG58 would be around 3.6m long for example. The impedance of the antenna will be shown at the radio end of the cable with no transformation. That is why antenna analyser manufactures recommend a half wave line, or multiples thereof, for true impedance measurements of the antenna. In fact you could use a coax of any impedance and it will have no ill effect as long as you don't go outside of the design frequency. If it is cut to length accurately taking in the velocity factor, the system ignores the impedance of the cable. That's when it is important to use military spec cables for things like phasing harnesses because you can be more confident that the cable is made to a standard and the data given is correct.
I hope this clears a few things up and helps you utilize certain lengths of coax to your advantage.

[Gunner357]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

[arcone]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Okay. I bought one of those nano VNAs recently. I did an installation for a mate with Heliax the other month and made sure I knew the exact coaxial length. Then I made up a test lead for the analyser so that when hooked up to the main run, it would add up to multiples of a half wavelength (taking in the two different velocity factors). That way it gives a more accurate indication of the complex impedance at the antenna. I phased a pair of six element yagis for him.
So if you know the length of your cable and its VF, you could do the same.

[Gunner357]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Okay. I bought one of those nano VNAs recently. I did an installation for a mate with Heliax the other month and made sure I knew the exact coaxial length. Then I made up a test lead for the analyser so that when hooked up to the main run, it would add up to multiples of a half wavelength (taking in the two different velocity factors). That way it gives a more accurate indication of the complex impedance at the antenna. I phased a pair of six element yagis for him.
So if you know the length of your cable and its VF, you could do the same.

Yeah I need to do some work I raised the antenna 20 more ft and put 60 feet of rg213 on it and SWR went from 1"2 to 1"8-2.0 over 2.0 with power so I need to mess with it after my RigExpert Analyzer shows up

[arcone]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Don't you hate it when that happens.
A lot of analysers can test cable in various ways too, it's just learning how to use the bloody things.
It would be good if you could test the antenna on its own to see what's going on there and possibly eliminate it as the culprit.

[Gunner357]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Don't you hate it when that happens.
A lot of analysers can test cable in various ways too, it's just learning how to use the bloody things.
It would be good if you could test the antenna on its own to see what's going on there and possibly eliminate it as the culprit.

OH YEAH!!!

[arcone]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Don't you hate it when that happens.
A lot of analysers can test cable in various ways too, it's just learning how to use the bloody things.
It would be good if you could test the antenna on its own to see what's going on there and possibly eliminate it as the culprit.

OH YEAH!!!

What type of antenna is it? How high off the ground was it and are there any surrounding objects?
Certain antennas can be more sensitive to this.

[Gunner357]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Don't you hate it when that happens.
A lot of analysers can test cable in various ways too, it's just learning how to use the bloody things.
It would be good if you could test the antenna on its own to see what's going on there and possibly eliminate it as the culprit.

OH YEAH!!!

What type of antenna is it? How high off the ground was it and are there any surrounding objects?
Certain antennas can be more sensitive to this.

Homemade Dipole style[Please login or register to view this link] just about 40 to tip of stinger

[arcone]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Don't you hate it when that happens.
A lot of analysers can test cable in various ways too, it's just learning how to use the bloody things.
It would be good if you could test the antenna on its own to see what's going on there and possibly eliminate it as the culprit.

OH YEAH!!!

What type of antenna is it? How high off the ground was it and are there any surrounding objects?
Certain antennas can be more sensitive to this.

Homemade Dipole style[Please login or register to view this link] just about 40 to tip of stinger

That's most likely why the swr went up. A dipole is 70 odd ohms. A vertical dipole would vary depending on height above ground, the bottom half would be the most sensitive to ground and surrounding objects. In the vertical situ, the antenna is no longer symmetrical.
How are you feeding the antenna? Technically you should be using a 1:1 current balun, the antenna is balanced (sort of) and coax is an unbalanced feedline. There will be current flowing on the outside of the coax. The swr could have changed because of the change in length of the coax and how it is routed.
To save starting all over again, try a 1:1 balun or at least a coaxial choke at the feedpoint. I probably wouldn't bother with a 'messy' choke, I like to use ferrites. I use FAIRITE brand 61mm toroids in #43 material from Mouser. Glue 5 together and pass the coax through 4 times to create 3 evenly spaced loops (not to tight).
If things still don't work out I would strongly suggest a quarter wave droopy. Preferably make the top half of your antenna adjustable and have at least three quarter wave radials drooped away at somewhere around 45 degrees. You could use wire. This would be a superior antenna in my opinion with a great bandwidth, is unbalanced and a 50 ohm impedance is very achievable. I would still employ that choke for common mode current.
Sorry, there was no short way to explain. If you want any more advice, maybe start a new thread as I feel I have hijacked this one.
Jeremy.

[Gunner357]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Don't you hate it when that happens.
A lot of analysers can test cable in various ways too, it's just learning how to use the bloody things.
It would be good if you could test the antenna on its own to see what's going on there and possibly eliminate it as the culprit.

OH YEAH!!!

What type of antenna is it? How high off the ground was it and are there any surrounding objects?
Certain antennas can be more sensitive to this.

Homemade Dipole style[Please login or register to view this link] just about 40 to tip of stinger

That's most likely why the swr went up. A dipole is 70 odd ohms. A vertical dipole would vary depending on height above ground, the bottom half would be the most sensitive to ground and surrounding objects. In the vertical situ, the antenna is no longer symmetrical.
How are you feeding the antenna? Technically you should be using a 1:1 balun, the antenna is balanced (sort of) and coax is an unbalanced feedline. There will be current flowing on the outside of the coax. The swr could have changed because of the change in length of the coax and how it is routed.
To save starting all over again, try a 1:1 balun or at least a coaxial choke at the feedpoint. I probably wouldn't bother with a 'messy' choke, I like to use ferrites. I use FAIRITE brand 61mm toroids in #43 material from Mouser. Glue 5 together and pass the coax through 4 times to create 3 evenly spaced loops (not to tight).
If things still don't work out I would strongly suggest a quarter wave droopy. Preferably make the top half of your antenna adjustable and have at least three quarter wave radials drooped away at somewhere around 45 degrees. You could use wire. This would be a superior antenna in my opinion with a great bandwidth, is unbalanced and a 50 ohm impedance is very achievable. I would still employ that choke for common mode current.
Sorry, there was no short way to explain. If you want any more advice, maybe start a new thread as I feel I have hijacked this one.
Jeremy.

The problem is it was at 1:2 untill i raised it up I was think about going with a Ugly Balun however the guy I got the plans from said dont waste my time....I have rg213 right from the radio to the antenna aprox 60 feet

[Gunner357]

sorry we hi jacked the thread Ill start new one.....

[arcone]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Don't you hate it when that happens.
A lot of analysers can test cable in various ways too, it's just learning how to use the bloody things.
It would be good if you could test the antenna on its own to see what's going on there and possibly eliminate it as the culprit.

OH YEAH!!!

What type of antenna is it? How high off the ground was it and are there any surrounding objects?
Certain antennas can be more sensitive to this.

Homemade Dipole style[Please login or register to view this link] just about 40 to tip of stinger

That's most likely why the swr went up. A dipole is 70 odd ohms. A vertical dipole would vary depending on height above ground, the bottom half would be the most sensitive to ground and surrounding objects. In the vertical situ, the antenna is no longer symmetrical.
How are you feeding the antenna? Technically you should be using a 1:1 balun, the antenna is balanced and coax is an unbalanced feedline. There will be current flowing on the outside of the coax. The swr could have changed because of the change in length of the coax and how it is routed.
To save starting all over again, try a 1:1 balun or at least a coaxial choke at the feedpoint. I probably wouldn't bother with a 'messy' choke, I like to use ferrites. I use FAIRITE brand 61mm toroids in #43 material from Mouser. Glue 5 together and pass the coax through 4 times to create 3 evenly spaced loops (not too tight).
If things still don't work out I would strongly suggest a quarter wave droopy. Preferably make the top half of your antenna adjustable and have at least three quarter wave radials drooped away at somewhere around 45 degrees. You could use wire. This would be a superior antenna in my opinion with a great bandwidth, is unbalanced and a 50 ohm impedance is very achievable. I would still employ that choke for common mode current.
Sorry, there was no short way to explain. If you want any more advice, maybe start a new thread as I feel I have hijacked this one.
Jeremy.

The problem is it was at 1:2 untill i raised it up I was think about going with a Ugly Balun however the guy I got the plans from said dont waste my time....I have rg213 right from the radio to the antenna aprox 60 feet

Like I said in my previous post, all of those things are going to affect your swr. The antenna was previously happy with the height above ground, its surroundings and the coaxial length and routing. All of those things have been changed so I am not surprised.
I do not recommend a messy balun either (it's not a balun by the way, it's a choke). A ferrite choke like I described is more effective and useful for other applications. If you're not addressing the balanced feedpoint with anything, it is a recipe for disaster.
These vertical dipoles seem to be popular in the states, and I can understand when it comes to limited space and appearance. I personally would not bother with one, but if I did, I would take particular attention to the feedpoint.

[Gunner357]

Funny you post that Im having issue with upgraded coax and a relocation of my base antenna....Im waiting on my new Analyzer before I start messing with it

Don't you hate it when that happens.
A lot of analysers can test cable in various ways too, it's just learning how to use the bloody things.
It would be good if you could test the antenna on its own to see what's going on there and possibly eliminate it as the culprit.

OH YEAH!!!

What type of antenna is it? How high off the ground was it and are there any surrounding objects?
Certain antennas can be more sensitive to this.

Homemade Dipole style[Please login or register to view this link] just about 40 to tip of stinger

That's most likely why the swr went up. A dipole is 70 odd ohms. A vertical dipole would vary depending on height above ground, the bottom half would be the most sensitive to ground and surrounding objects. In the vertical situ, the antenna is no longer symmetrical.
How are you feeding the antenna? Technically you should be using a 1:1 balun, the antenna is balanced and coax is an unbalanced feedline. There will be current flowing on the outside of the coax. The swr could have changed because of the change in length of the coax and how it is routed.
To save starting all over again, try a 1:1 balun or at least a coaxial choke at the feedpoint. I probably wouldn't bother with a 'messy' choke, I like to use ferrites. I use FAIRITE brand 61mm toroids in #43 material from Mouser. Glue 5 together and pass the coax through 4 times to create 3 evenly spaced loops (not too tight).
If things still don't work out I would strongly suggest a quarter wave droopy. Preferably make the top half of your antenna adjustable and have at least three quarter wave radials drooped away at somewhere around 45 degrees. You could use wire. This would be a superior antenna in my opinion with a great bandwidth, is unbalanced and a 50 ohm impedance is very achievable. I would still employ that choke for common mode current.
Sorry, there was no short way to explain. If you want any more advice, maybe start a new thread as I feel I have hijacked this one.
Jeremy.

The problem is it was at 1:2 untill i raised it up I was think about going with a Ugly Balun however the guy I got the plans from said dont waste my time....I have rg213 right from the radio to the antenna aprox 60 feet

Like I said in my previous post, all of those things are going to affect your swr. The antenna was previously happy with the height above ground, its surroundings and the coaxial length and routing. All of those things have been changed so I am not surprised.
I do not recommend a messy balun either (it's not a balun by the way, it's a choke). A ferrite choke like I described is more effective and useful for other applications. If you're not addressing the balanced feedpoint with anything, it is a recipe for disaster.
These vertical dipoles seem to be popular in the states, and I can understand when it comes to limited space and appearance. I personally would not bother with one, but if I did, I would take particular attention to the feedpoint.

I will address that thank you