antenna length

kj6yyb · Jul 29, 2012

I bought a Tram whip magnet mount antenna model #1100 and was wondering what length to cut it to. I plan on using 144mhz to 160mhz range but mostly in the around 151mhz. When I look at the cutting chart that came with the antenna it doesn't show a range of frequencies until you get to the 400mhz range. Do I cut it for the frequency in the middle which if I did my math right would be 152mhz and if so would that cover the whole range? I am in the process of getting a swr meter but don't have one yet.

Thank you for your help

Dan KJ6YYB

Tweekerbob · Aug 6, 2012

What frequencies will you be transmitting on? Just the 2M ham band or that plus 150-160?

About 19.3" for the ham band and about 18.6" for 151.

Use 2808 divided by Freq. in MHz to give you # of inches. Keep in mind your bandwidth will not be all that much, so if you generall use Ham, stick with that, and vice versa. If you only transmit on Ham and want to listen to 150-160, then cut it for ham.

jhooten · Aug 6, 2012

If you plan on doing much with antennas do yourself, your radios, and everyone on the bands a favor and buy the antenna analyzer instead. It will give you much more information, give it to you quicker, any will help keep you from keying your radio into a badly mismatched load.

KG4NEL · Aug 6, 2012

I'm confused...

If it's a ham rig, that isn't going to be type accepted for 151MHz, and a business-band rig isn't going to be the easiest to program for 2m (because you don't need type acceptance for a modified radio in the ham bands). So more work than necessary in the best case, and illegal in the other

W2NJS · Aug 6, 2012

The OP did not say that he intended to transmit on 151 mHz, so let's cut him some slack, okay?

kj6yyb · Aug 6, 2012

jhooten said:
If you plan on doing much with antennas do yourself, your radios, and everyone on the bands a favor and buy the antenna analyzer instead. It will give you much more information, give it to you quicker, any will help keep you from keying your radio into a badly mismatched load.

Thank you, I didn't know there was much difference between the two since everything I read said to use an swr meter.

kj6yyb · Aug 6, 2012

W2NJS said:
The OP did not say that he intended to transmit on 151 mHz, so let's cut him some slack, okay?

I belong to 2 fire departments and have authorization to transmit on 151 mHz and I plan to if needed. I have an Ht from the fire departments that I can use instead of the mobile. I believe that is legal and I am not trying to do something that is not legal. I hope that makes sense.

KG4NEL said:
I'm confused...

If it's a ham rig, that isn't going to be type accepted for 151MHz, and a business-band rig isn't going to be the easiest to program for 2m (because you don't need type acceptance for a modified radio in the ham bands). So more work than necessary in the best case, and illegal in the other

The radio I have is a Kenwood TK-760hg that my volunteer fire department gave me to use. I haven't tried to program it yet as I was concerned about the antenna first. I didn't want to mess with anyone around me if I messed up the antenna.

If I have to I could get 2 radios and leave the business band one alone but was hoping to be able to do both with one rig. At least that was my plan after reading the other posts about being illegal to mod the ham band radios. Just trying to stay legal since I just got my license last month.

Dan KJ6YYB

LtDoc · Aug 7, 2012

I would suggest making that antenna work well on the primary frequency of use. Then, just be satisfied with it's use on any secondary frequencies. That's how it's done most of the time. Almost any radio can be used on the ham bands, but ham radios can't be used on 'commercial' bands. It's a matter of it's specifications/abilities and it's certifications.
How well an antenna works depends on it's primary resonance point. Or, tune it for the primary frequency of use. If any secondary frequencies are harmonically related it may work there to, but don't count on how well it will work. That's about as simple a way of thinking about it as I can think of. There are antennas that can work well on multiple and not harmonically related frequencies, but forget about 'simple' and inexpensive. A 'do everything' antenna is like a 'one size fit's all' shoe, never fits right except in one size, sort of.
- 'Doc

kj6yyb · Aug 7, 2012

Thanks for the info that helps allot

Sent from my C771 using Tapatalk 2

W2NJS · Aug 7, 2012

The Kenwood radio you mentioned comes in two VHF versions; the type 2 unit covers 136 to 156 mHz and that's the one you should have if you want to do both 2M and FD on the same radio, and it would be definitely legal to do so. Problem, as noted above, would be lack of a VFO on 2M, but maybe you can live with that and just have the programmed channels for your ham use. The "other" version of the Kenwood starts at 148 mHz and might not be programmable in the 144-148 mHz ham band.

If you do a search on this board there has been a lot written about the legalities of using amateur transceivers on other than ham bands. While they often will work and work well outside the ham bands, they're still illegal and the legal exposure of your FD if you do so can be mind boggling should someone be injured and it is discovered that you were using a non-certificated FCC radio.

kj6yyb · Aug 7, 2012

W2NJS said:
The Kenwood radio you mentioned comes in two VHF versions; the type 2 unit covers 136 to 156 mHz and that's the one you should have if you want to do both 2M and FD on the same radio, and it would be definitely legal to do so. Problem, as noted above, would be lack of a VFO on 2M, but maybe you can live with that and just have the programmed channels for your ham use. The "other" version of the Kenwood starts at 148 mHz and might not be programmable in the 144-148 mHz ham band.

If you do a search on this board there has been a lot written about the legalities of using amateur transceivers on other than ham bands. While they often will work and work well outside the ham bands, they're still illegal and the legal exposure of your FD if you do so can be mind boggling should someone be injured and it is discovered that you were using a non-certificated FCC radio.

I have version 1 and I haven't tried to program it yet. I am not sure I want to give up the VFO that ham radios have so in the long run I may end up getting a second radio when I figure out what I want.

I read a lot of posts about the legalities of using ham radios for fd and decided against it.

Sent from my C771 using Tapatalk 2

KG4NEL · Aug 7, 2012

LtDoc said:
There are antennas that can work well on multiple and not harmonically related frequencies, but forget about 'simple' and inexpensive. A 'do everything' antenna is like a 'one size fit's all' shoe, never fits right except in one size, sort of.
- 'Doc

Discones and LPDAs come to mind, but neither are very practical for mobile use :twisted:

busher12 · Sep 1, 2012

Tweekerbob said:
What frequencies will you be transmitting on? Just the 2M ham band or that plus 150-160?

About 19.3" for the ham band and about 18.6" for 151.

Use 2808 divided by Freq. in MHz to give you # of inches. Keep in mind your bandwidth will not be all that much, so if you generall use Ham, stick with that, and vice versa. If you only transmit on Ham and want to listen to 150-160, then cut it for ham.

where does the 2808 come from? i am looking to tune an antenna for 153

wa4yur · Apr 13, 2014

In reference to use of ham radio on commercial frequencies

It is legal to use commercial radios on ham bands but it is VERY ILLEGAL to use ham radios to transmitt on commercial channels. Doing this will get you a hearty fine and possibly a Hefty jail sentence. Ham radios are not type accepted for transmitting out of the ham bands. You can use commercial radios on ham frequencies but reprogramming could cause improper operation on the commercial channels and that will get the operator and also the licensee in trouble with the FCC. Unless you really know what you are doing its best to use separate radios for each service. Wa4yur / wqln265 Mike Ray Arrl/FCC official observer

LtDoc · Apr 13, 2014

That '2808' is '234' multiplied by 12 to convert the usual 'feet' answer to 'inches'.
- 'Doc

AK9R · Apr 14, 2014

wa4yur said:
It is legal to use commercial radios on ham bands but it is VERY ILLEGAL to use ham radios to transmitt on commercial channels.

We've been through all this before. The topic of this thread is how to cut a 1/4 VHF antenna.

antenna length

kj6yyb

Member

Tweekerbob

Member

jhooten

Member

KG4NEL

Member

W2NJS

Member

kj6yyb

Member

kj6yyb

Member

LtDoc

Member

kj6yyb

Member

W2NJS

Member

kj6yyb

Member

KG4NEL

Member

busher12

Member

wa4yur

Member

LtDoc

Member

AK9R

Lead Wiki Manager and almost an Awesome Moderator

Similar threads