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-   -   137-174 MHz wide band antenna (http://forums.radioreference.com/scanner-receiver-antennas/130421-137-174-mhz-wide-band-antenna.html)

lightingnut 01-06-2009 10:25 AM

137-174 MHz wide band antenna
 
Hello everyone, I am a new member and hope someone can help me. I have a Maxrad 132-174 MHz 24 MHz Bandwidth antenna.

I want it to work from 144 to about 161 MHz. So if i was told right, the center frequancy should be about 157.780. So my question is what length do I need to cut the antenna at.

Thanks for your help, I look forwad to being apart of the group.

lightingnut 01-08-2009 11:46 AM

Antenna length
 
I did not know this question was so tough. Anyone have any ideas on how long the antenna needs to be so I can use it from 144 to 161. The info that came with the antenna says it has a 24 MHz range. So the center frequency should be about 157.780. So my question is what length would the antenna need to be to get the right SWR readings.

kb0nly 01-08-2009 2:41 PM

Whats the model number? Is it about 48" long? That would make it a MWV1322, i have deal with them before, but i recall them as being a 20 or 26 Mhz bandwidth in the spec sheet.

You could use the 142-170Mhz cut length as that is the closest to the range you want.

http://wildcard.pctel.com/images_pro...BANDHDRevA.pdf

Have a look at this installation sheet and see if thats what yours is. The cutting chart will get you close, but you still need a good wattmeter showing forward and reflected power or one with an SWR scale to get it really close if you want a good low SWR. However, your trying to cover a wide spread there, do you only need transmit on the ham band, 144-148? I assume you wanted 144-161 so you can monitor out of band also. I would tune it for the best SWR where your going to be transmitting.

If you know someone with an antenna analyzer it makes it a total snap.

lightingnut 01-09-2009 12:53 AM

Hello kbOnly,
You are right, that is the model I have and without the spring. The 142-170 MHz would work pretty well I'm guessing.

My paper work that came with the antenna did not have that cut listed. Even the PDF that Maxrad sent me did not help. They had listed 132-148, 134-151, 140-158, 150-170 and 152-174 MHz and that is a SWR rating of 2:1.

I will have to check with my local ham club and see if someone has an antenna analyzer or a good SWR or wattmeter I can barrow. The only SWR meter I have is a very old Radio Shack model that was used for CB radios. Would it work for this? I think I would be better off finding one that is much newer.
Thanks for your help.

kb0nly 01-09-2009 2:41 PM

Your going to have to find a SWR meter for VHF, that CB one won't do you any good at those frequencies.

I would try the 142-170 cut length and then check the SWR, if you need to adjust from there remember only take off a small bit at a time! With the stainless whips they are a bit harder to work with, but if you have a sawzall and a metal cutting blade i have done that, even better is a dremel tool with the fiber reinforced cutoff wheels, thats what i normally use. Then i can take off small increments, 1/4" at a time and get it really close.

Just remember the number one rule for tuning antennas, you can take more off but you can't put it back on!

And also, remember Lower=Longer.. The lower in frequency you want to go the longer the antenna needs to be. So cut it a bit long and then work your way to the frequency you need. The more you take off the higher the resonant frequency will be.

MPSCS 01-09-2009 3:18 PM

Quote:

Originally Posted by lightingnut (Post 969270)
Hello everyone, I am a new member and hope someone can help me. I have a Maxrad 132-174 MHz 24 MHz Bandwidth antenna.

I want it to work from 144 to about 161 MHz. So if i was told right, the center frequancy should be about 157.780. So my question is what length do I need to cut the antenna at.

Thanks for your help, I look forwad to being apart of the group.


I would think it would be fine as-is. Your working range of 144-161 falls right in the middle of the antenna's specs of 132-174.

If you shorten it to tweak performance at your low end of 144, you'll throw it off on your working high end of 161.

If you were to lengthen it to tweak performance at your working high end of 161, you'll throw it off on your working low end. Are you transmitting above 148MHz?

lightingnut 01-09-2009 4:21 PM

I had thought about leaving the antenna the way it is. With out a proper SWR metor I have no way to check it.

There is a chance that I might be transmitting above 148, once in a great while. That is why I got this antenna.

kb0nly 01-09-2009 6:23 PM

Quote:

Originally Posted by SIG-INT (Post 972430)
I would think it would be fine as-is. Your working range of 144-161 falls right in the middle of the antenna's specs of 132-174.

If you shorten it to tweak performance at your low end of 144, you'll throw it off on your working high end of 161.

If you were to lengthen it to tweak performance at your working high end of 161, you'll throw it off on your working low end. Are you transmitting above 148MHz?

Its not intended to be used for that entire range without cutting. They say it covers 132-174 because you can cut it for anywhere in that range. Trust me, i've done a lot of these from Maxrad and a few other companies that sell similar products.

I would cut it for the 142-170 length and just don't worry about it until you can get a SWR meter and check it on transmit.


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