Lowering SWR

[mmckenna]

Removing that boot immediately dropped my SWR down into the 1.5 - 1.6 range on 1, 19, & 40. I will still be playing with the sacrificial whip to see if I can get even more out of my set up.

The rf grounding to the ground plane that the vehicle provides is done via capacitive coupling. That capacitive coupling depends on spacing between the magnet and the vehicle roof. The boot increases that distance.

That was a good troubleshooting step.

Since the ground plane is capacitively coupled, it's not perfect, and some RF can still travel on the outside of the coax. Make sure your coax isn't all bundled up somewhere. Stretch it out and see if it impact SWR.

 

[slowmover]

Can buy this or DIY.

.

 

[707ways2Sunday]

Just for grins, try putting a layer of aluminum foil between the rubber boot and magnet!!!

 

[jhooten]

If I got a mag mount down to 1.5 I'd stop messing with it and call it good. As soon as the truck starts moving and the whip bends it will change for the worse anyway.

 

[707ways2Sunday]

If I got a mag mount down to 1.5 I'd stop messing with it and call it good. As soon as the truck starts moving and the whip bends it will change for the worse anyway.

1.1:1 on channel 1 and 1.2:1 up high where I spend most of my radio time, I will move resonance up the band. Minuscule loss I know. But that’s just me. I know I’m not alone. Squeeze every last little bit out of the antenna we can.

Same reason people run good quality low loss coax. Cheap stuff works just fine but where there is just a little bit more to be gained. Why not?


Same reason we buy or build better antennas and put them as high as possible. Sure a 1/2 wave dipole strung caddy corner across my room works fine. String it up outdoors at .5 wavelength off the ground Moe better.


My Mobil right now is a mag mount and it is the exact scenario I described above. I know the bandwidth capabilities of my antenna and I know it’s capable of 1.1:1 tune across the band is doable. Will I lose sleep over it? Of course not. Will I dial it in? Likely one day when I’m bored or sooner!!!

 

[KI4ZNG]

1.1:1 on channel 1 and 1.2:1 up high where I spend most of my radio time, I will move resonance up the band. Minuscule loss I know. But that’s just me. I know I’m not alone. Squeeze every last little bit out of the antenna we can.

Same reason people run good quality low loss coax. Cheap stuff works just fine but where there is just a little bit more to be gained. Why not?


Same reason we buy or build better antennas and put them as high as possible. Sure a 1/2 wave dipole strung caddy corner across my room works fine. String it up outdoors at .5 wavelength off the ground Moe better.


My Mobil right now is a mag mount and it is the exact scenario I described above. I know the bandwidth capabilities of my antenna and I know it’s capable of 1.1:1 tune across the band is doable. Will I lose sleep over it? Of course not. Will I dial it in? Likely one day when I’m bored or sooner!!!

Wouldn't lose any sleep over your current SWR readings.

 

[jhooten]

1.1:1 on channel 1 and 1.2:1 up high where I spend most of my radio time, I will move resonance up the band. Minuscule loss I know. But that’s just me. I know I’m not alone. Squeeze every last little bit out of the antenna we can.

Same reason people run good quality low loss coax. Cheap stuff works just fine but where there is just a little bit more to be gained. Why not?


Same reason we buy or build better antennas and put them as high as possible. Sure a 1/2 wave dipole strung caddy corner across my room works fine. String it up outdoors at .5 wavelength off the ground Moe better.


My Mobil right now is a mag mount and it is the exact scenario I described above. I know the bandwidth capabilities of my antenna and I know it’s capable of 1.1:1 tune across the band is doable. Will I lose sleep over it? Of course not. Will I dial it in? Likely one day when I’m bored or sooner!!!

Okay, I will admit to owning a mag mount. It is a leftover from the days when I spent too much time in rental or company cars. But it was for a v/u dual band not CB. And the coax on it has been replaced with LMR-240.

Now having said that, unless you are running one of the monster mag mounts with three 6" magnets, there just ain't enough capacitive coupling to the body for a mag mount to work well on any HF frequency.

 

[707ways2Sunday]

Okay, I will admit to owning a mag mount. It is a leftover from the days when I spent too much time in rental or company cars. But it was for a v/u dual band not CB. And the coax on it has been replaced with LMR-240.

Now having said that, unless you are running one of the monster mag mounts with three 6" magnets, there just ain't enough capacitive coupling to the body for a mag mount to work well on any HF frequency.

Is that true? Just asking.. I would think, and correct me if I’m wrong, if you get resonance your capacitive reactance and inductive reactance zero out. Without sufficient capacitive coupling is that even possible??? I just do this for fun so not an expert by any stretch. Not to mention my mobile with one magnet seems to perform pretty well.

 

[jhooten]

Is that true? Just asking.. I would think, and correct me if I’m wrong, if you get resonance your capacitive reactance and inductive reactance zero out. Without sufficient capacitive coupling is that even possible??? I just do this for fun so not an expert by any stretch. Not to mention my mobile with one magnet seems to perform pretty well.

Yes, resonance means the inductive and capacitive reactivities are equal. Low SWR is not an indicator of resonance.

Yes, a mag mount can work. So can a 2 foot Firestick. An anecdote, back in the dark ages, I mean the 1970s at the height of a very active solar cycle a group of young GIs left their barracks and headed south on the Autobahn to go to the BIG Audio Club store in Stuttgart. The store had just got in a shipment of Sharp 40 channel CB radios. One was bought along with one of those cheap 16" center loaded mag mount antennas and a cigarette lighter plug. The new rig was hooked up in the car. On the trip back north another American car was seen headed south with a large CB whip on it. Being the perpetual smartasses young GIs can be one of the car occupants keyed up the mic and, in his best imitation of a southernrednecktruckdriver, said "BREAK FOR A SOUTH BOUND SMOKIE REPORT". (to make a long story short) "we" spent the next 45 minutes talking to truckers all over Florida, Georga, and Alabama. SO, you can talk great distances with a box stock cheapie radio and the worst possible antenna. That is not to say you can claim it is a high performance station.

We are at the higher edge of the solar cycle now. Give it a few years and see how well it still works.

Oh, and nothing beats a quater wave stainless steel whip in a properly installed mounts.


(edited to add) BTW, the capacitive coupling between the mag mount and the car body is not part of the capacitive reactence of the antenna. It is a susbtitute for the direct ground between the mount and the vehicle body it is mounted to.

 

[707ways2Sunday]

Yes, resonance means the inductive and capacitive reactivities are equal. Low SWR is not an indicator of resonance.

Yes, a mag mount can work. So can a 2 foot Firestick. An anecdote, back in the dark ages, I mean the 1970s at the height of a very active solar cycle a group of young GIs left their barracks and headed south on the Autobahn to go to the BIG Audio Club store in Stuttgart. The store had just got in a shipment of Sharp 40 channel CB radios. One was bought along with one of those cheap 16" center loaded mag mount antennas and a cigarette lighter plug. The new rig was hooked up in the car. On the trip back north another American car was seen headed south with a large CB whip on it. Being the perpetual smartasses young GIs can be one of the car occupants keyed up the mic and, in his best imitation of a southernrednecktruckdriver, said "BREAK FOR A SOUTH BOUND SMOKIE REPORT". (to make a long story short) "we" spent the next 45 minutes talking to truckers all over Florida, Georga, and Alabama. SO, you can talk great distances with a box stock cheapie radio and the worst possible antenna. That is not to say you can claim it is a high performance station.

We are at the higher edge of the solar cycle now. Give it a few years and see how well it still works.

Oh, and nothing beats a quater wave stainless steel whip in a properly installed mounts.


(edited to add) BTW, the capacitive coupling between the mag mount and the car body is not part of the capacitive reactence of the antenna. It is a susbtitute for the direct ground between the mount and the vehicle body it is mounted to.

I do realize I can talk 1K plus miles on 3 watts with a speaker wire antenna with the help of Mother Nature. My assessment of my mobile working well was strictly based on local performance. But I suppose works well is individually defined. Without sufficient capacitive coupling to the literal other half of the antenna, I don’t believe resonance nor SWRs would be easily achieved. Which also applies to a poor direct connection. I’m not arguing that a hard mounted antenna installation isn’t better. Was just questioning by how much and to what degree. Like I said in an earlier post many of us like to squeeze every little bit we can out of what we have. Especially an antenna system.