Thanks guys. Lots of good information here. I hope to have this thing up by Sunday. I have most of the parts I need. I may need some more pipe to clear to peak of my house, but it's a ranch style so I will be close with what I have now.
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Mounting A Mobile Antenna On A Mast
- Thread starter BubbaDX
- Start date
Eventually I probably will buy a base antenna. But for now, this is the one I have. Plus I enjoy trying to figure out how all this works. I currently have it hung up in my house and I am picking up conversations from repeaters about 30 miles away. Not sure if that's good or bad reception, but that's what i'm getting. I think it will get better when I mount it outside. Marconi, I was looking though your picture gallery, you have some nice equipment. You're like a mad scientist with antennas. I am going to mount the 4 radials in an X shape to be safe.
Doing as you suggest sure can make mounting easier, but you may have more of a problem getting the match you want and for sure if you're like most and just have to have below a 1.1:1 match to work that hooten-nater.
I have noticed with my Marconi models that the more radials I add the more Field Strength I am able to measure. This is probably true up to a point, but I don't think I've reached that point as yet with just 6 radials. Cooper's has a new GPK available that fits the base of most A99 type antennas and it allows for up to 8 radials symmertically set. Always try to add your radials as symmetrical as possible, I think it matters with the pattern even though I can't prove it in the venue.
I guess I am like a mad scientists when I get interested in something. I have followed that rule in all steps in my life, trying to understand and get the best bang for my buck. I just don't like to be matter-of-fact with things that I do. I go to more trouble to tune, but most don't see what I see when skipping all the steps and banking on being lucky as well as being pretty.
I also don't just punch up smilley faces and make coy little petty comments like many do on these forums I visit either and some don't like that I know.
BTW, ask Multimode200 why he's recommending you stop your trial and error testing and just go buy something cheap and then tell him there is no fun in doing it that way?
Good luck in your antennas design Bubba,
Marconi
I read that too. Tune the two radials like a dipole, then make them your ground radials. Just that it was hard to make people believe that 2 would work. So more were added for marketing. I use a SO239 1/4 wave on 2, all you need for local repeater work. Hardly ever use 2 anyway.
Rich
No one has said that two radials or one radial won't work. Just take a minute and consider symmetery as important, and it is. Think about if you have one element opposite the radiator, or like in a dipole you have to be careful with how you run the coax away from the feed point if you want to operate vertically. These issues are very important and the fact that adding radials to a ground plane increases the efficiency and effectiveness of a vertical antenna is pretty much undisputed in the science. Only folks who parrot these CB BS stories think that adding radials is all about marketing. The story is pervasive regarding the A99 and that is likely the source of all the BS, and even if Solarcon did decide not to add the radial kit to the antenna as a marketing ploy, the facts of adding radials is true, period. I can't say that you will see a big increase in signals when adding radials to the A99, but it definitely does make a difference and it is just because folks that say this---have never done a thing to really find out what affect radials have on the A99. n8fgb, if you took the time to compare the A99 with and without radials you would see a nice difference that is a benefit to any antenna, just by running a simple Bandwidth Curve and seeing how adding the radials give the A99 which typically has a relatively wide and flat BW curve of <> 2-3 mHz <2:1 SWR. Add 4 slanted down 72" radials and you will see this curve turn into a nice bowl shape of about 1-2 mHz <2:1 SWR and that is a pluse in Field Strength even if you can't measure the effect.
There is also a fairly new idea about this same A99 or any other end fed 1/2 wave showing increased effectivness when insulating the mast from the antenna too, and then for sure you need to add radials in order to provide a return path for the currents to flow back to the feed point. You boys are just behind the times with these old wives tales you love to parrot and don't know nothing about what you are talking about in this case.
In my testing of adding radials to my Marconi model, I noticed a nice Field Strenght increase every time I added an extra element, and it was even more obvious when the radials gained symmetery around the hub. This idea should be pretty easy to duplicate, cause I can build this antenna in about 30 minutes and have it on-the-air, if I have all the parts around and the parts are easy to find. If you live in an area of the country that has pretty good farm land that is relatively flat, and is not just mostly sand or rock, and you get the antenna up 30 feet or more, then you will see this antenna work just about as good and all these antennas we talk about.
Booty Monster is the only one I know of that has built one. He made his out of very thin wire. He doesn't talk about it, so maybe he lives in an area with poor or extremely poor soil, or the antenna is built wrong, or old Marconi is dead wrong. What do you think?
Here it is again.
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Like everyone, I've read a lot of differnt concepts and theories about verticals with elevated groundplane radials. All I can do is try to study it all, mix that in with my own experience and try go find some truth that is balanced by practicality. I know that you can get a 1/4 wave veritcal to work with only 2 groundplanes...maybe if 1 under the right circumstances. I have also read that ther is a point of diminishing returns after you pass four radials. I've never measured or modeled that, so I don't know for certain. I have also read that symmetry of the radials is important, yet I also know that that is nearly impossible to accomplish with ground mounted verticals on the lower bands. I also understand that at some point on HF an inch or two variation of the radials in relation to each other is meaningless.
Anyway, we're getting a bit away from the topic of the original question which was how to make his mobile antenna a base. There are a lot of great ideas in this thread...now get out there and DO IT!
.
BTW Marconi, I looked at your signal report log charts and I'm not sure I agree with the point you're trying to prove. The feedpoint height is significantly different on those two antennas. You need to do that as an "apples to apples" comparision. It would also help to understand the elevation & distance of the other stations, but that might not be practical.
Anyway, we're getting a bit away from the topic of the original question which was how to make his mobile antenna a base. There are a lot of great ideas in this thread...now get out there and DO IT!
. BTW Marconi, I looked at your signal report log charts and I'm not sure I agree with the point you're trying to prove. The feedpoint height is significantly different on those two antennas. You need to do that as an "apples to apples" comparision. It would also help to understand the elevation & distance of the other stations, but that might not be practical.
multimode200,
That size/performance restriction thingy. How about because that's all you have and can't/don't want to buy anything? Or, as I think it was said, just something temporary, a 'make-do' thing.
I do agree, I would much rather use a 'full sized' antenna (rather than a shortened one) where possible. But the original question was only if using a mobile antenna was possible, nothing to do with performance.
Now, if you really wanted to be 'cheap-n-dirty' about the whole thing, all you'd need is a tree, about 30 feet of wire, some twine, coax, and if you wanted to get just a bit fancy, an SO-239 connector. Oh, and a 'chunker' to tie on the end of that twine so you can throw it over a tree limb. (A sock [new one so no holes in it] filled with sand/dirt works well as a 'chunker', by the way... Or maybe not?)
- 'Doc
(A pair of pantyhose makes two of them 'chunkers'. Be VERY careful with that! Going around asking for old pantyhose is very detrimental to your reputation! .. Or maybe not?)
That size/performance restriction thingy. How about because that's all you have and can't/don't want to buy anything? Or, as I think it was said, just something temporary, a 'make-do' thing.
I do agree, I would much rather use a 'full sized' antenna (rather than a shortened one) where possible. But the original question was only if using a mobile antenna was possible, nothing to do with performance.
Now, if you really wanted to be 'cheap-n-dirty' about the whole thing, all you'd need is a tree, about 30 feet of wire, some twine, coax, and if you wanted to get just a bit fancy, an SO-239 connector. Oh, and a 'chunker' to tie on the end of that twine so you can throw it over a tree limb. (A sock [new one so no holes in it] filled with sand/dirt works well as a 'chunker', by the way... Or maybe not?)
- 'Doc
(A pair of pantyhose makes two of them 'chunkers'. Be VERY careful with that! Going around asking for old pantyhose is very detrimental to your reputation! .. Or maybe not?)
Well, the base of my mast is buried in the ground with concrete. I started on the top of the mast where I am going to mount the antenna. Everyhting is coming together and I should have it fully erected this week.
Like everyone, I've read a lot of differnt concepts and theories about verticals with elevated groundplane radials. All I can do is try to study it all, mix that in with my own experience and try go find some truth that is balanced by practicality. I know that you can get a 1/4 wave veritcal to work with only 2 groundplanes...maybe if 1 under the right circumstances. I have also read that ther is a point of diminishing returns after you pass four radials. I've never measured or modeled that, so I don't know for certain. I have also read that symmetry of the radials is important, yet I also know that that is nearly impossible to accomplish with ground mounted verticals on the lower bands. I also understand that at some point on HF an inch or two variation of the radials in relation to each other is meaningless.
Anyway, we're getting a bit away from the topic of the original question which was how to make his mobile antenna a base. There are a lot of great ideas in this thread...now get out there and DO IT!
BTW Marconi, I looked at your signal report log charts and I'm not sure I agree with the point you're trying to prove. The feedpoint height is significantly different on those two antennas. You need to do that as an "apples to apples" comparision. It would also help to understand the elevation & distance of the other stations, but that might not be practical.
Just for Moleculo wanting the feed points the same height. I didn't get them exactally alike but they are less than 4' feet different, with the I-10K being 49'4" and the Marconi 6x being 39'8". The report shows the FP heights.
Attachments
Well, my antenna is finally vertical. I still have to drill 2 holes to route the cable properly. But my reception is a lot better. I am picking up stuff that I was not picking up before. I ended up with 4 radials in an X pattern measuring 6'9" each. The radials are a couple feet above my gutter and the top of my antenna is not visible from the street. All in all, I am pleased with it so far. Tomorrow I want to finish routing my cable and I am planning to secure the mast to my deck. Maybe I will try and post a picture or two tomorrow.
I forgot to post my question. Is it OK to coil the extra cable or is it best to cut it to length and solder on a new fitting? Does it matter if the coil is by the radio or in the middle of the cable run?
Also, I notice a lot of antennas have a small coil of cable at the feed point of the antenna. Do I need to do this?
Also, I notice a lot of antennas have a small coil of cable at the feed point of the antenna. Do I need to do this?
Extra coax, cut/coil/whatever? Sort of depends on how much extra cable you have. Something up to, or around 10 feet? I'd just leave it, wouldn't cut it off. May want to move things to a different part of the room and it'd come in handy. Much more than about 10 feet, I think I'd either cut it off or just coil it up somewhere out of the way, or just throw it back up into the attic. A whole lot more than is sort of hide-able? Cut it off, save it for next time.
Those little coils near an antenna are probably 'chokes'. They help keep 'bad' RF off of the outside of the coax (Common Mode Currents). They come in all difference sizes, just depends on the type coax used and how much trouble you want to go to. The coils need to be large enough that bending the coax that sharply doesn't distort the coax. That coil radius is different for each 'size' of coax. RG-174 can be coiled around a pencil without hurting it. Try that with RG-8 and you will always break the pencil and ruin the coax too. If you have to force it to bend that much, then 'that much' is too much. A two-liter soda bottle makes a pretty good coil form for most coax, just something like that. There is such a thing as too large. If you have to fold up that coil to fit the space you want/need to put it, it's too large. Large is sort of subjective. It's only too large when you can't figure out where to put it, or it's just too ugly to have around. 'Best' size is whatever happens to work for you. Wrap it around the mast, that works too.
The best place for a choke is as close to the feed point of the antenna as you can manage. Any feed line between the choke and feed point might radiate, which isn't always good. More than one choke typically doesn't hurt anything. Might help, who knows. The worst part is the amount of feed line loss because of the 'extra' feed line length. A choke only affects what's on the outside of the feed line (bad stuff), not what's on the inside (good stuff).
You decide what you want to do with that extra coax. Oh, if it's more than about 75 feet, just send it to me, I'll store it for you.
- 'Doc
if you ask real nice, I might even put a 'cleansing' signal through it occasionally to get all them stray electrons off of it...
Those little coils near an antenna are probably 'chokes'. They help keep 'bad' RF off of the outside of the coax (Common Mode Currents). They come in all difference sizes, just depends on the type coax used and how much trouble you want to go to. The coils need to be large enough that bending the coax that sharply doesn't distort the coax. That coil radius is different for each 'size' of coax. RG-174 can be coiled around a pencil without hurting it. Try that with RG-8 and you will always break the pencil and ruin the coax too. If you have to force it to bend that much, then 'that much' is too much. A two-liter soda bottle makes a pretty good coil form for most coax, just something like that. There is such a thing as too large. If you have to fold up that coil to fit the space you want/need to put it, it's too large. Large is sort of subjective. It's only too large when you can't figure out where to put it, or it's just too ugly to have around. 'Best' size is whatever happens to work for you. Wrap it around the mast, that works too.
The best place for a choke is as close to the feed point of the antenna as you can manage. Any feed line between the choke and feed point might radiate, which isn't always good. More than one choke typically doesn't hurt anything. Might help, who knows. The worst part is the amount of feed line loss because of the 'extra' feed line length. A choke only affects what's on the outside of the feed line (bad stuff), not what's on the inside (good stuff).
You decide what you want to do with that extra coax. Oh, if it's more than about 75 feet, just send it to me, I'll store it for you.
- 'Doc
if you ask real nice, I might even put a 'cleansing' signal through it occasionally to get all them stray electrons off of it...
Bubba, I suggest you leave the extra coax unless you have twice as much as you will ever need. If you ever decide to go higher it will come in handy and you could just lay the extra of the ground if the antenna is situated such as to allow that. Doing this may also help reduce and RF that you may get back at the radio end of the line. Seems I recall something about the mast being attached to a deck. If so you could just lay the extra line underneath and it would be out of the way would be good if not coiled up to tightly. If you wanted to add a choke then that is another discussion.
Regarding the x shape for your radials. That maybe OK, but if the elements are straight out at 90 degrees from the vertical and they are close to the roof you may be getting a bit of reflection off of the tips and your SWR may actually be higher than you are seeing. Also with your ground radials in the horizontal you will not get as good of match as with them slanted down 40 degrees or less and with them pointed down they probably will have more current flowing in them and will really need to be even further away from any object nearby, reflective or not.
During my recent work with my Marconi styled antenna shown above the antenna made better field strength readings with the radials slanted down and with more elements the FS also increased as well. My antenna had both horizontal and slanted down radials and seemed to work better with more radials. I also found that when I put any antenna parts below the peak of my roof I always noticed shadowing of the signal responses with TX/RX with the antenna being so close to my house even though it is all wood with AC and whatever else goes up in the attic of homes in the Southwest near the Gulf of Mexico.
If like me you may notice a very nice improvement in local responses if you get all of the physical antenna well above the peak of your roof. This affect of shadowing or lack of it can be even more significant than just raising the AT an equal distance well into the clear about the antenna. This possible affect will just have to be tested at your location to really know for sure, but if it is happening the response can be very destructive to any good communications and you may be surprised at how much that can be.
I find that these 11 meter 1/4 wave antennas are of a size that makes them particularally affected by things that are too close and these nearby objects may not even have to be something that is considered non-reflective like your roof on an all wood house. Just get your antennas as much in the clear as possible, going higher helps get into the clear and also gives you better range locally.
How about some nice pictures? Can't you borrow a camera from a buddy?
Did you say that your radials were only 6'9" long? Are these shortened and resonant antennas like the radiator? If these ground plan elements are shortened and still resonant then you may still see some noticable attentuation in responses when compared to full 1/4 wavelength elements and field strength testing will help show you that. If these short elements are not resonant then you will see even more attentuation and some attentuating affects are likely in your match. You may be showing a very good match (SWR) with your antenna on an inline meter, but you could also be showing heavy reactance at the feed point---and if so---that part of your complex impedance at the feed point is not radiating for you just like our friend 'Doc is always reminding us about. You might not be seeing this happen if you are just using an inline meter to help you determine match and resonance and it is probably really evident if your match (SWR) is unusually low, because that is not what you should be seeing---maybe 1.5 and even higher would be what should be expected for such a 1/4 wavelength setup with horizontal GP radials only.
Good luck, if this little antenna is right, you will be surprised at how well it can work for you. Get us some pictures, OK?
Regarding the x shape for your radials. That maybe OK, but if the elements are straight out at 90 degrees from the vertical and they are close to the roof you may be getting a bit of reflection off of the tips and your SWR may actually be higher than you are seeing. Also with your ground radials in the horizontal you will not get as good of match as with them slanted down 40 degrees or less and with them pointed down they probably will have more current flowing in them and will really need to be even further away from any object nearby, reflective or not.
During my recent work with my Marconi styled antenna shown above the antenna made better field strength readings with the radials slanted down and with more elements the FS also increased as well. My antenna had both horizontal and slanted down radials and seemed to work better with more radials. I also found that when I put any antenna parts below the peak of my roof I always noticed shadowing of the signal responses with TX/RX with the antenna being so close to my house even though it is all wood with AC and whatever else goes up in the attic of homes in the Southwest near the Gulf of Mexico.
If like me you may notice a very nice improvement in local responses if you get all of the physical antenna well above the peak of your roof. This affect of shadowing or lack of it can be even more significant than just raising the AT an equal distance well into the clear about the antenna. This possible affect will just have to be tested at your location to really know for sure, but if it is happening the response can be very destructive to any good communications and you may be surprised at how much that can be.
I find that these 11 meter 1/4 wave antennas are of a size that makes them particularally affected by things that are too close and these nearby objects may not even have to be something that is considered non-reflective like your roof on an all wood house. Just get your antennas as much in the clear as possible, going higher helps get into the clear and also gives you better range locally.
How about some nice pictures? Can't you borrow a camera from a buddy?
Did you say that your radials were only 6'9" long? Are these shortened and resonant antennas like the radiator? If these ground plan elements are shortened and still resonant then you may still see some noticable attentuation in responses when compared to full 1/4 wavelength elements and field strength testing will help show you that. If these short elements are not resonant then you will see even more attentuation and some attentuating affects are likely in your match. You may be showing a very good match (SWR) with your antenna on an inline meter, but you could also be showing heavy reactance at the feed point---and if so---that part of your complex impedance at the feed point is not radiating for you just like our friend 'Doc is always reminding us about. You might not be seeing this happen if you are just using an inline meter to help you determine match and resonance and it is probably really evident if your match (SWR) is unusually low, because that is not what you should be seeing---maybe 1.5 and even higher would be what should be expected for such a 1/4 wavelength setup with horizontal GP radials only.
Good luck, if this little antenna is right, you will be surprised at how well it can work for you. Get us some pictures, OK?
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I will leave the coax. I like the idea of coiling it under the deck, and there is plenty to go another 10-15 feet. The length of the radials is because of the materials I used. I made them of aluminum L channel because I had it already. I do have more of it, so I could extend them. From what I found on the internet, I think I need them to be about 2' longer. Adding another 10' section to the mast to put it above the peak of my house would be fairly easy.
Here is a picture I took this morning. You can see the radials are a couple feet higher than my gutter, but they are not directly over it. I still need to get a meter. What is a good one to pick up that does multiple bands? My radio transmits on 10m, 6m, 2m and 70cm. Up until now I have not worried about my SWR because all I can do is listen. But I plan to take my test on Tuesday, so I will be on the airways SOON!
Here is a picture I took this morning. You can see the radials are a couple feet higher than my gutter, but they are not directly over it. I still need to get a meter. What is a good one to pick up that does multiple bands? My radio transmits on 10m, 6m, 2m and 70cm. Up until now I have not worried about my SWR because all I can do is listen. But I plan to take my test on Tuesday, so I will be on the airways SOON!