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  #1 (permalink)  
Old 10-15-2017, 11:27 PM
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Default Am/Fm antenna used as a 2m/70 cm

I looked around the site all day and haven't found and threads about using a Am/Fm antenna as an antenna on my car. I have some aftermarket antennas that say they are for am/fm and can also be used for CB. They are 32" long of the actual rod and has a spring base. I am a licensed ham radio operator. The antenna was given to me for free. So I thought maybe i could use them as an antenna for my scanner or maybe my handheld radio external antenna. Please let me know if this would work. I do NOT have access to an SWR meter.
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Old 10-16-2017, 12:53 PM
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Sure, no problem. Seems to be cut for 100MHz. It wont be as effective as a proper 800MHz antenna if you try to receive those frequencies but will receive better than having an antenna on the inside, connected directly to the scanner.

/Ubbe
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Old 10-16-2017, 1:08 PM
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As a scanner antenna for receiving will work better than anything inside the vehicle (as noted). For transmitting with your HT (or mobile radio).... not so much. In fact, very poorly. Borrow or buy an SWR meter and check it out for yourself... I doubt you'll want to subject your ham rigs to that sort of mismatch. Use it for the scanner and be happy. Get a separate antenna for the ham equipment.
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Old 10-16-2017, 7:31 PM
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Quote:
Originally Posted by popnokick View Post
As a scanner antenna for receiving will work better than anything inside the vehicle (as noted). For transmitting with your HT (or mobile radio).... not so much. In fact, very poorly. Borrow or buy an SWR meter and check it out for yourself... I doubt you'll want to subject your ham rigs to that sort of mismatch. Use it for the scanner and be happy. Get a separate antenna for the ham equipment.
Ya i was affraid of that for the HT. I have yaesu equipment and I don't want to beat them up. If it was baofang that be a different story. I'll have to see if i can dig up a meter or cut the antenna down or something if possible. Like I said they were free so I'd like to use them if at all possible. I also know mag antennas are cheap as well. So I'll go that route if I have to.

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Old 10-25-2017, 1:27 PM
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Default Antenna

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Old 10-25-2017, 4:10 PM
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I'm not sure who left a post to my questions (possibly golay). But to answer your post... no I'm not using an existing car antenna. A friend of mine gave me 2 brand new antennas for fm radio use or they can be used for cb radio. The package also states that if they are being used for CB they can use two of the same antennas threw the use of a spliter and have 2 working antennas for CB. I would have to agree that they're cut for 100mhz range. I just wasnt sure what i would have to do to make them operate correctly for my handheld scanner on 1 antenna and the other antenna for my HT (Yaesu Ft-1D). Since the antennas where given to me for free I'd like to use them. I have to put ends on the wire so I can hook them up to the radios. Without the use of an SWR meter for those bands i wasnt exactly sure how long they needed to be. The 1 antenna should be ok for my scanner w/o any modifications correct? The other i can easly cut down to 19 in for the HT radio.
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Old 10-25-2017, 4:17 PM
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Also I was able to find SWR meter for CB band. I'm not sure how to use it with a dial it has on the front. It is a Motorola CB S-1352a Swr meter. ( https://m.ebay.com/itm/Motorola-CB-T...734?nav=SEARCH ) this is a link to the same meter. I don't know if i can use this with any type of accuracy on 2m/70cm. I don't have any instructions on how to use this meter so if anyone has any input or instructions it would be much appreciated. I have tried to look around the net but have not found anything other than sales for the unit.
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Old 10-25-2017, 4:31 PM
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Default AM/FM/CB

All of the AM/FM/CB antenna's I remember were basically a loaded whip resonant on 27 MHZ. The coax from the antenna went to a splitter box that isolated the AM (510-1600 KHZ) and FM (78-108MHZ) signals from the CB (27MHZ). One pigtail (Motorola style) to the AM/FM radio and one coax (w/ PL259) to the CB

I doubt that it will be even remotely resonant on either 2M or 440. I would just use it as receive antenna and get a proper 2M/440 antenna for HAM transmitting

$.02
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Old 10-25-2017, 4:54 PM
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Also I was able to find SWR meter for CB band. I'm not sure how to use it with a dial it has on the front. It is a Motorola CB S-1352a Swr meter. ( https://m.ebay.com/itm/Motorola-CB-T...734?nav=SEARCH ) this is a link to the same meter. I don't know if i can use this with any type of accuracy on 2m/70cm. I don't have any instructions on how to use this meter so if anyone has any input or instructions it would be much appreciated. I have tried to look around the net but have not found anything other than sales for the unit.
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Old 10-25-2017, 5:04 PM
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Quote:
Originally Posted by byndhlptom View Post
All of the AM/FM/CB antenna's I remember were basically a loaded whip resonant on 27 MHZ. The coax from the antenna went to a splitter box that isolated the AM (510-1600 KHZ) and FM (78-108MHZ) signals from the CB (27MHZ). One pigtail (Motorola style) to the AM/FM radio and one coax (w/ PL259) to the CB

I doubt that it will be even remotely resonant on either 2M or 440. I would just use it as receive antenna and get a proper 2M/440 antenna for HAM transmitting

$.02
Ill have to post a link for these antenna if i can find it again. They look like a standard fm antenna that would come factory on a car. They aren't the CB antennas that are black and have that plastic type coating. The have a normal motorola type end on it that would go in the back of a car radio. The only reason I want to use these antennas is 1 learning experiance and 2 the were free. I know the mag mount dual band antennas are about $30 super cheap. But i want to see what these type antennas will do when tuned (cut to proper length) for 2/70cm bands. But if any other situation you would definitely have a valid point.
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Old 10-25-2017, 5:20 PM
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I am a licensed ham radio operator.
Did you not cover this in the study for the licence? CB is CB, broadcast is broadcast, and the other bands again are different in terms of length. I just n' understand why you are asking such basic questions - really sorry, but something here doesn't add up at all?

Presumably you know about the relationship between the resonant frequency of an antenna and it's length? 30 odd inches and a spring base - which could be a coil and being used for matching, or could just be a spring? We don't know, but you should. 30 odd inches suggests 70MHz or so - which makes little sense, so it could be a CB band antenna with base loading. You need to decide what you want it to do - work as a proper antenna on VHF or UHF on your handheld? It will be too long to match. If it resonates at 27MHz, it will be just a bit of wire in the sky for the scanner - so it will work, to a degree. If you want to use it for transmitting then you NEED a VSWR meter. They are not expensive, and frankly, as a ham, you're always chasing output power, so you clearly need one.

I just can't work out how you don't know this stuff - I assume you are in the US, because here in the UK, our most lowly licence class requires this kind of level of knowledge, and I assumed the US system would be the same.

So will it work? Yes. Well? No! Will it damage the portable radio if you transmit? Probably not, most are well protected agains mismatched antennas with too much return power, but there are no guarantees.

If you have a transmitter, then a basic VSWR meter, and the ability to use it is pretty vital stuff in the ham world, I'd have thought!
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Old 10-26-2017, 4:27 PM
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Originally Posted by paulears View Post
Did you not cover this in the study for the licence? CB is CB, broadcast is broadcast, and the other bands again are different in terms of length. I just n' understand why you are asking such basic questions - really sorry, but something here doesn't add up at all?

Presumably you know about the relationship between the resonant frequency of an antenna and it's length? 30 odd inches and a spring base - which could be a coil and being used for matching, or could just be a spring? We don't know, but you should. 30 odd inches suggests 70MHz or so - which makes little sense, so it could be a CB band antenna with base loading. You need to decide what you want it to do - work as a proper antenna on VHF or UHF on your handheld? It will be too long to match. If it resonates at 27MHz, it will be just a bit of wire in the sky for the scanner - so it will work, to a degree. If you want to use it for transmitting then you NEED a VSWR meter. They are not expensive, and frankly, as a ham, you're always chasing output power, so you clearly need one.

I just can't work out how you don't know this stuff - I assume you are in the US, because here in the UK, our most lowly licence class requires this kind of level of knowledge, and I assumed the US system would be the same.

So will it work? Yes. Well? No! Will it damage the portable radio if you transmit? Probably not, most are well protected agains mismatched antennas with too much return power, but there are no guarantees.

If you have a transmitter, then a basic VSWR meter, and the ability to use it is pretty vital stuff in the ham world, I'd have thought!
I don't understand what your point is. yes it was all covered on test yes I passed and didn't miss a single question. Yes I have a very extevsive electrical background. I understand the difference of all the bands. My questions has nothing to do with it. All I was saying is what the antennas were originally used for. the spring base is just that, a spring base. I don't know about you and your daily life and ham background. Bt I work over 60-70 hrs a week I have 5 kids, a bunch of animals and a crew of people that I have to run. I don't sit around all day having Ham radios my life. How do you come to the conclusion that I don't know what I'm talking about, or what I'm asking in my question. My question is very clear to the info I want to know. we can sit here all day talk about frequecies, resonants or anything else all day long but as i said earlier i dont have time. You can sit there and say for a certain frequency an antenna needs to be x inches long or what have you, but its a starting point and in theroy. that's where a meter to test comes into to play. they may be cheap, but I'm not building enough antennas to need a meter to test them out I will just buy what I need and be done with it. But as I stated these perticular antennas were given to me. I have 0 use for them for the FM or CB Band. so the reason for my post is to ask for any quick info that someone may have to say cut this long my experiance works well, decent, crap what ever. that's all I was really looking for an someone has answered that and other have given there input and was appreciated. But you are in a leauge of your own. you assume I need meters and what not in the ham world. I didn't get my license cuz its a hobby I got it for one reason I will not state and the other is to show my kids how to talk to the ISS. I'm not going to spend a bunch of money on meters to test antennas that I won't be custom building. I would buy the meter to test this 1 antenna. Then what...... Put it in a box in my attic? I can think of better things to do with my money and spend my time better like with my kids and family since I work so much. An jst an FYI I dont know what it would be for you in your part of the world but my license level is General. I paid $15 to go take the technican level test and passed that with a perfect score. Then the people that were giving the test asked if I wanted to try the general level for free, I said sure, and smashed that. So next time in the future maybe you should not assume anything about anyone because all you did was make a assume out of yourself.
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Old 10-27-2017, 11:07 AM
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I didn't assume. I took the question and found it unusual for a qualified person to ask? A very basic question typical of somebody who has NOT passed any kind of knowledge based test.

I understand you being upset, as you are indeed qualified and experienced. Having me question your ability was an error on my behalf. I just smiled when you said "I don't have time". Not enough time to engage the knowledge you already have and answer your own question, and enough time to expect us to second guess your asserted low competence as being laziness rather than lack of ability.

You know that ham radio is a hobby that is all about the self-development of skills. You got into a hobby you have no interest in, joined a forum that is for the keen hobbyist, and won't even share your purpose.

Kind of strange. You state you KNOW the maths, you KNOW the physics, and know what you want to do. I just read your post and wondered how you didn't know the answer, and to be honest, I still have no clue as to why you don't? We're happy to answer honest basic questions from newcomers who are stranded and struggling - I've got a pretty good record for doing this - but in this case I smelled a rat. Were you trolling? You knew the answer and were hoping for bad advice, or maybe you were pretending to be qualified and didn't know. I'm still no wiser. You won't give proper details about the antennas - is the coil a coil, or is it a flexible connection? No idea. How can we guess? Clearly you have some antennas. Will they work? Yes? How well? No idea because you are being vague! I'm truly sorry if I've upset you, but all the clues were you were not quite firing on all cylinders. Obviously I was wrong and you just want confirmation that your opinion is the correct one, based on your knowledge and experience. However - I'm not sure what your opinion actually is?

Don't worry - your time's more precious than mine of course, and I'll leave this with you as you are probably a secret agent, unable to explain further for National Security reasons. Still a stupid question from a qualified radio ham. (I mean me, of course, not you!)
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Old 10-27-2017, 12:45 PM
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I think everyone involved in this thread should stop making assumptions. If you have an answer to the OP's question, feel free to post. If you are going to question the OP's abilities or motivations, I'm not sure what purpose your post serves.

To the OP, if you intend to just use these antennas with your scanner, they will probably work as most scanners will still receive signals even without a resonant antenna. If you intend to use them as transmitting antennas for VHF/UHF, you can spend a lot of time, which you say you don't have, experimenting until you stumble onto a solution. Or, you can buy a SWR meter or antenna analyzer and come to a solution fairly quickly. That said, unless you can tell us exactly what antenna you have and exactly how you plan to use it, I doubt anyone here can simply guess at a correct answer for you.
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Old 10-27-2017, 6:05 PM
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Understanding mobile communications antennas is not something you learn on a ham test, let-alone in the real world.

Some of us did work with those Disguise antennas in the professional world, and most were a compromise. So one has to make changes to the 'splitter box' and coax cable so the CB 27 mHz antenna AND splitter box / cable work together on VHF high band and UHF ham bands, again something not covered in the ham tests.
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Old 10-27-2017, 6:51 PM
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Originally Posted by W9BU View Post
I think everyone involved in this thread should stop making assumptions. If you have an answer to the OP's question, feel free to post. If you are going to question the OP's abilities or motivations, I'm not sure what purpose your post serves.

To the OP, if you intend to just use these antennas with your scanner, they will probably work as most scanners will still receive signals even without a resonant antenna. If you intend to use them as transmitting antennas for VHF/UHF, you can spend a lot of time, which you say you don't have, experimenting until you stumble onto a solution. Or, you can buy a SWR meter or antenna analyzer and come to a solution fairly quickly. That said, unless you can tell us exactly what antenna you have and exactly how you plan to use it, I doubt anyone here can simply guess at a correct answer for you.
I agree with the beginning of your post 100% WHY?!

I have to find the packaging for the antennas. An they aren't anything special and they may be at best an Auto Zone special Am/Fm/CB antenna with a motorola end on it that would plug in to an automotive radio. One of them I will use for my scanner no biggie there. The other I will use for my HT. They are 32" long. By the numbers I can cut it down to 19.5" and be a 1/4 wave for 2m and about 3/4 on 70 cm. An that's probably the best place to start with or with out a meter and still using for dual band. I'm just wondering if anyone out there has done this type of quick antenna cut or quick home brew type of thing. The spring base on the antenna is just a base to make it flexible thats it nothing special. I'm not looking to squeeze every little 1/10 of a watt out it, I just don't want it to beat up the front end of my radio up to bad. An the reason I'm asking these questions is because someone out there may have already done this type of a adjustment or experiance with this situation or close enough to say hey" you want to have it x long for this an that and will have x db/dbi etc etc etc...." I don't have unfortunetly a lot of time to do anything really with running my business, family etc.... I wish I did. Then maybe I could spend more time to mess around with this antenna and have more fun with it and incorporate my kids in the project as well.

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Old 10-27-2017, 6:53 PM
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Originally Posted by cmdrwill View Post
Understanding mobile communications antennas is not something you learn on a ham test, let-alone in the real world.

Some of us did work with those Disguise antennas in the professional world, and most were a compromise. So one has to make changes to the 'splitter box' and coax cable so the CB 27 mHz antenna AND splitter box / cable work together on VHF high band and UHF ham bands, again something not covered in the ham tests.
Thank you

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Old 10-27-2017, 6:59 PM
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Quote:
Originally Posted by camofarmer13 View Post
They are 32" long. By the numbers I can cut it down to 19.5" and be a 1/4 wave for 2m and about 3/4 on 70 cm. An that's probably the best place to start with or with out a meter and still using for dual band.
My guess is that your plan won't work.

In order for a 32" long antenna to have a hope of working at CB frequencies, there has to be a matching coil. A quarter wave for CB is about 108" long. To bring that down to 32" requires some matching so that the transmitter thinks its seeing a 50 ohm load. Granted, the matching may be happening in the splitter. If so, cutting off the splitter and just running a coax from your radio to the antenna and then cutting the antenna to 19.5" (including the length of the spring) may work. But, if the matching is a coil that is built into the base of the antenna, then you are not likely to make this work on 2m or 70cm.
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Old 10-28-2017, 1:07 AM
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I agree with the beginning of your post 100% WHY?!

I have to find the packaging for the antennas. An they aren't anything special and they may be at best an Auto Zone special Am/Fm/CB antenna with a motorola end on it that would plug in to an automotive radio.
If you still have the packaging please post a model number or some other info. I'm interested for the opposite reason, I have a car that I would like to do a CB install on but I don't want to add any additional antennas other than the stock AM/FM whip.
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