Science is all about truth, and truth doesn't care how you feel about it. (ha). I'm only ever interested in truth, and if I'm wrong about something, I have no choice other than to alter my opinion to align with truth. It's the Vulcan way. ;-)
Well I'm glad that's settled LOL I got my first CB radio back in '76 when the 23 channel were on sale trying to make room for the new 40 channels coming in. My mom picked up a Panasonic RJ 3200 about 60% off right at Christmas. This set her back quite a sum. My Dad ran down to a local electronics store he bought parts from and picked up a Kraco Center load magnet mount about 24 in I think LOL after trying to talk around the neighborhood to no avail he ran over to RadioShack and got a barrel connector and a 10-foot length of coax. I know it don't sound right but that's how Radio Shack sold it. Added to my 17 ft of the magnet mount that gave me enough slack for the coax to go up onto the top of my swamp cooler. People always told me I had to run a ground wire. To appease one guy I got tired of his bitching) i went up and cut the rubber off the shield and soldered a four inch wire to it. Swamp coolers have that little screw for the manifold mount in the center so I moved the antenna offside a little bit and put a lug under that screw so I had a grounded antenna. Like you said nothing changed. Today I am retired and partially disabled pinched nerves and all and I don't feel like running to the den every time I hear somebody so I'm going to put a CB in the kitchen under the cabinet so I can just stay there and keep cooking or washing dishes and when a friend hollers I can holler back and not have to go anywhere. I'm going to blame it on my disability but probably I'm just lazy! Anyway I'm just going to throw up a 5-foot fire stick with one of those triple magnet mounts and now I know I don't have to ground it 🤓
You do have an electrical connection. The magnetic mount. That's exactly how a mag mount antenna works on a car/truck. I have a 2 meter mag mount antenna on a metal file cabinet in my bedroom. SWR is good, and I can easily work several local repeaters with it. I also have a Wilson 1000 mag mount antenna that I cut down for 10 meters, and have it on a metal plate just big enough for the base of the antenna, which is bolted to an old engine crane in the back yard. The engine crane is over 300 pounds of steel, but not flat. That has also worked very well, with under 1.5.1 SWR. I have also used a cut down 102" whip mounted on that same engine crane, which did have a solid connection, and it didn't really work any better.
I've heard that mag mount antennas form a capacitive electrical connection to the metal through their base. This made sense to me since the only thing you want traveling through an antenna is waveforms which should be able to bridge this capacitive gap. Much in the same way that voltage detectors won't work without you holding them because your body forms a capacitive path to ground. Awesome tip on tuning the antenna. I'll have to use that on a couple projects I have here that I need to get tuned in better.
I have been using a dual band mag-mount on top of my fridge for 20 years! I can work nearly every repeater I can hear on only 5 or ten watts! There is one very distant machine that needs 25 watts, but 2 dozen others work great on the lowest power levels. Oh yeah! The fridge is working just fine too!
Just what I needed to find out thanks (I'm new to this taking my test Aug 22 2019) going to set up a small mobile as a base and use a mobile antenna to get started. Seems to be a reasonable way to get started.
Ok, so I am hoping you have figured out that the magnet provides the RF coupling to the ground plane. It it very easy at higher frequency but as you go lower into the hf bands, you require more magnet influence to attain the RF coupling. Once you get up to 40M and lower frequency, you need to look at a physical boo d to get the RF coupling to ground.
Finally somebody that actually knows what a VSWR and antenna SWR are and ALSO knows how to use/read an SWR METER. hallelujah you can teach an old HAM new tricks. 👏 Thank you sir from an old "chicken bander" when you don't have too much equipment you can learn to use the equipment you HAVE 😉
This video and replies have answered a lot of questions I had about this exact scenario.... I have a dual band hershey kiss style antenna on my trunk and above 80mph the magnet just wasn't doing it so I added one ply of double sided tape to the antenna base and my reception instantly went to hell in a hand basket. .... I tried an electrical ground and nodda... removed the tape and bizam! Instant reception restored. .... I now have all my answers as to why. ... thanks folks!
I did the same in college in the 90's. 5/8 mag mount 2 meter ant. stuck to the metal case of the 3 amp power supply running my ht. Hit at least 4 repeaters full scale. Enjoyed my setup very much. N4TCM
Wow thanks for the post!!..just got a new wouxun 980p quad band.6/4/2/70 i have a diamond v2000 6/2/27 waiting for coax to put it up. I have a mag mount for 4mtrs i thought ide try and it had very bad swr on the table i was looking on youtube for answers,your tip came up big thanks🖖
I've got an MFJ mag mount that I bought to put on my pickup and now I use it on the patio. We have a propane fire pit that has a steel cover over the pit area and I stick the mag mount on the cover. Works real good and I get more contacts on 2 meter then on my after market rubber duck on my HT. KN4CQU
Someone said on thetruckersreport .com CB forum that you can add some radials to a small metal plate that the magnet antenna sets on. Usually radials are 2% longer than the vertical antenna and aimed down at a certain angle for optimum performance but can hang strait down or horizontol. They can be made from copper wire or aluminum tubing like a ground plane antenna .
That was a surprise. I guess the capacitance between the base of the antenna and the metal plate forms the connection to ground. That would make sense because. Never thought of it before. Good job. Hats off to you for admitting you were wrong! You make a good Vulcan 8-)
I'm still a little puzzled over it. I'm tempted to do a tear down of the antenna base to see if we actually have an electrical connection between the magnet and coax shield. I might do that tomorrow.
I came onto youtube looking for to aswers, one do mag mounts work better on a metal plate and two do you need an electric connection and you have answered them both and proved it, thank you for that. My only other question was would it work ever better if the metal plate was earthed to the house wirring? However thank you for this video
Alot of mag mounts have rubber shoes on the bottom of them so that you dont scratch your car when you take it on/off your car so I doubt there needs to be an electrical connection with the groundplane
Thanks for that. I was pondering whether it was worth my time to work out a grounding scheme for the HF mobile antenna I ordered to use with a mag-mount. Now I know it won't be any less lousy if I make a ground - hah!
Awesome to hear you tested it, no hate but doesn’t that kinda stand to reason since these antennas are designed to be on cars and your not wiring it to the car like you did with you little leg nor is your car truly grounded as it sits on rubber tires right?
The metal roof of the car should be electrically tied to the frame and negative (ground) of the battery and radio. It's about providing an electrical ground plane for the antenna, right at the feed point. Not the actual earth ground.
While you have proved that adding the metal plate lowers swr you have not proved that antenna performance has been improved. You have made a common mistake that many hams do now days of equating low or lower swr to increased antenna performance, ie. can you hear or be heard better. While I don’t doubt that it has improved that performance, an antenna analyzer will not measure that.
A lower stand wave ratio on a resonant antenna means that less power is being reflected by the radiating wire, therefore more of the applied power is creating a magnetic field. i.e. more of the applied power is being radiated. So of course, in the case of a resonant antenna at the operating frequency, lower SWR = better performance.
Kevin Loughin In most cases yes, and of course almost everyone knows that a vertical antenna needs a good ground plane to be effective. My point is we cannot always assume that an antenna with a low swr is an efficient and effective antenna. A good example is a ground mounted 1/4 wave vertical. Let’s say I put up a 40 meter 1/4 ground mounted vertical with with no radials and just a ground rod. I will be able to adjust that antenna to a very low swr and the swr line will be very flat across the whole 40 meter band. But, the performance of that antenna without an effective ground plane will be very poor. The low and flat swr readings are a result of terrible ground losses. Now, if I install 30 radials I will find my swr is no longer flat and has probably increased a lot, and the resonant point has shifted. I now adjust the length again so the lowest swr is now in the middle of the band. But now I find that the lowest swr is no longer quite as low as it was before, and I no longer have a flat swr line. It’s now a curve, perhaps reading 1.3:1 in the middle of the band, but now rising to 1.8:1 or even 2:1 at the ends - exactly like it should be! The antenna, now with a higher swr that before, is a much more efficient and effective antenna than it was. Usually the only thing that has a low flat swr across an entire band is a dummy load!
Is not that you need to have an electrical connection. The magnet is already doing that for you because the shield of the coax is connected to the magnet and the dialectic of the coax is your whip connection. No counterpoise needed. The plate is the antenna reflector. The bigger the plate the better but you should get decent performance on just a cookie sheet or pizza pan.
It could be that yours does not have the capacitive plate in the base and would need an actual ground connection to the metal it's sitting on. It could also be an older one where water has gotten into the base and coax, or rusted the base inside.
That's funny. A mag mount antenna is designed to use on a vehicle roof. I don't see any benefit to tuning a very wide band antenna! I had a nice 5/8 2 meter mag mount antenna that some jackass cut off when I forgot to remove it one night. Probably a CBer who thought it was a 10 or 11 meter antenna!
no, this proves the mag base is what the theory of operation says, that is a conectiin is made thru the magnets to what is usually a automobile. On parts of my Saturan that are plastic. thd mag antenna swr was high.. A further "proff would be to place a thin plastic sheet between the base and metal plate . In my experiance the swr went high.
electrical ground is different than a rf ground plane. it works via induction. the magnet is electricly grounded withen the base. if the gap between the magnet and top of the car were to become greater. the capacitance changes and the swr's goes high. I had a three puck magmount and I could never correct the swr's because of that capacitance. I tried making an electrical ground for it. nothing.
Yeah I'm trying to figure out this ground plain thing right now I have a extra Wilson 5000 mobile antenna and I wanted to put it on my house and run it as a base antenna but from what I'm reading I need a special mount with a rod to act as a ground plane if there's no metal underneath it ughh so much conflicting info out there I did test the theory with a magnet mount had a very high standing wave until I stuck it to my metal door so the magnet Mount needs metel under it but I'm not sure about the 2,000 with a regular 3/8 mount if I mounted it to a wooden post would it have a high swr unable to tune?
You could just add radials under it if mounted to a pole. At least four, equally spaced, more is better. They should be connected to the shield side of the coax connection. The base housing the magnet should be electrically connected to the shield already.
@@loughkb okay so you're saying they should be grounded to the Mount sort of not insulated by that plastic washer? I really appreciate the info just trying to set up another base station at my house but I can't really put a big ground plane up or anyting like I used to run
@@trackpackgt877 The radiator, connected to the center of the coax, should be insulated from ground or any mounting hardware. The ground side of the antenna, connected to the shield of the coax, should have the ground plane connected to it. You can verify the wiring with your multi-meter.
Hi Kevin...I would like to use my 5/8 vhf mag mount antenna on my roof which is aluminum. Obviously not magnetic, so can I buy a 3 x 4 foot sheet of galvanized metal and place that on the roof so that the mag mount adheres? Does the antenna then use the ground plane provided by the sheet metal, or the sheet metal AND the aluminum roof around it as well? And if the latter, do I have to have conductivity between the roof and the sheet metal since the aluminum is painted? Thanks.
So the metal plate doesn't have to be inductive? Just metal, even if the magnet doesn't stick to it? I know this is an old vid but I'm hoping you reply. Always looking to learn something new. Thank you
I got one of those old mobile car radios with a mag mount antenna and I live in the city so I can’t put it up on my roof but I was wondering if I could slap it on a big peace of sheet metal in my attic and try that but then I was wondering if it would be ok bc it’s not grounded pls help if u can
Yes you can do that. You want at least 1/4 wave length of metal going out in all directions from the antenna. So at least 19.5 inches for 2m and 6.5 inches for 440cm.
Explain this, i have almost the exact setup right now but in my backyard. Wilson 1000 on a 2ftx2ft steel plate. With the plate laying flat on the ground (Earth, grass and all) my SWR is hitting 2.2 But if i set the whole thing up on my truck box also sitting in the yard my SWR drops to about 1.2 So i placed the plate up on top of my shed and the SWR jumps to 3 or higher? I'm assuming the antenna is using the Earth itself as the plain? Any ideas how i could get this setup to run better on the roof?
Down at 27 mHz, a half wave is 16ft. You'd need a bigger ground plane than at VHF frequencies. About 8 feet for CB. The truck gave the best result since the vehicle is long enough to get closer to 1/4 wave. Run four 8 ft. wires out from the plat in four directions and trim them an inch at a time until you get the best SWR.
Kevin Loughin Thanks for the advice and explanation. I figured that was the case, so it must be performing a little better being closer to the ground rather than in air on the roof. I'll give that a try maybe,, as my intention was only temporary anyways for testing purposes. But after i got it going i got the bug and wanted more, lol. So thought i would get by for awhile until i can get a proper antenna from down the street. I have a local radio guy that has everything i need. Just gotta save up a bit. Not sure if i have wire that would stand out like I'd need for this as i want it on the roof. So the wires would not have any support. Thanks again!
Kevin Loughin It's funny, i figured that out before seeing your reply just yesterday. My man down the street has the old school M400 starduster I'll be buying soon and i took notice of the ground plane extensions on it were angled rather sharp downwards. Thanks.
I seen a video where the person had a magnetic mount antenna sitting on 3 to 4 inch by 14 inches long metal That's for ham and 3 to 4 inch by 9 foot long metal for cb radio He said it works good
Many mag mounts do have a metal plate in the base that's connected to the braid. However, this doesn't make an electrical connection to ground. In the case where someone has the antenna sitting on a file cabinet or metal plate, you'd have to have bare metal on the base and scrape any paint away from the surface it's sitting on.
Kevin Loughin i think if you test it you'll find it does. Capacitive coupling may not be AS effective through paint but if you remove that braid from the magnet your swr will sky rocket and you'll measure incredible amounts of impedance on the ground side through the magnets which will drop to normal as soon as that connection is remade.
Yes. Because, the metal of the plat or the magnet is providing one half of a capacitor, the metal of the car roof is the other half. There is no direct electrical connection through the paint or plastic seal on the bottom of the antenna. It is all capacitive coupling.
I just tried this on the 11 m with my toolbox that's completely made of steel and what you're saying is not completely accurate if you don't believe me try it on the 11-meter yourself with the proper antenna
Unfortunately a tool box is way too small of a surface area for ground plane at 11 meters (27mhz). It would need to be like a 9 foot wide tool box. 2 meters (146mhz) only needs to be 18 inches.
