Whip Antenna Question

[njt462]

Ok I have a ball mount antenna that is 102" long that I am going to be using for monitoring the lowband state patrol. I however have a few questions about this antenna set up. My state patrol frequencies start at 42.000 and go up from there. I found an online calucator that said to start at 42 I should cut the antenna to 70 inches, was this correct? Another question is my local police is in the 155 and 156 range will I be able to still monitor those with the whip antenna since the calucator showed those at being a lower number then 70 and me cutting it at 70 to start at 42 range will it still cover the 155 and 156 or will I need to get a splitter and run two antennas off my scanner to get the antenna service that I am wanting? And with that question if needing two antennas am i asking for my scanner to go into shock mode? LOL Last question I drive a retired CVPI car and I have noticed that most states put their ballwhip antennas on the driver side of the car. Since my car is retired i was going to put it on the passenger side of the car so I do not get accused of anything I am not doing, but is there any difference behind why all marked patrol cars have it on the driver side is it better perference or just what they all choose to do back in the day?

Thank you all members in advance for your help with these questions.

Respectfully,
NJT

[k9rzz]

I would cut it for 42 mhz and just use it on 155. It will work fine, but lets crunch some numbers just to see.

234/42 = 5.57 ft for a quarter wave.

x 12 = 66.86 inches

One wavelength at 155 is 936/155 = 6.04 ft

So, your quarter wave at 42 mhz is almost one wavelength at 155. According to the ARRL Antenna book, it will have it's best performance about 40 degrees above the horizon.

I'd go for it, and see what you can hear on 155. If performance is less that what you want, then you know why.

John K9RZZ

[AG4WI]

I have a Stainless Steel whip that i used for the last 30 years to listen to 42 Mhz. You can use a C.B whip and cut it down for low band but always cut it down from the bottom end. If you cut a whip for 42.500 which is the center of the band it should be (66 in. long) 234 Divided by 42.500 ---66in
There are Five eights thread fittings that go on and tighten down with Allen screws.

I found this whip worked well all the way up to thru 460 Mhz.

The reason to mount it on the drivers side is so it don,t hit all the low hanging trees along the side of the road.
155mhz-156mhz will work O.K also with the whip!

[ReceiverBeaver]

You will be able to receive your target frequencies just fine without cutting the antenna at all. Leave it alone. That way you can use it again should you ever want to use a CB mobile. If you cut it shorter, you'll ruin it as a CB antenna.

[ipfd320]

why dont you try it at full length first and see how it performs...if is crappy then go ahead with the cuts
like i say bigger is better...lol...good luck

[DDan]

Originally Posted by ipfd320

why dont you try it at full length first and see how it performs...if is crappy then go ahead with the cuts
like i say bigger is better...lol...good luck

HaHa. Did you see how old the post was that you were responding to?

[ipfd320]

as a matter of fact i realized it after i left the reply...oh well it was worth a shot...thanks

[zz0468]

That's ok. Bringing this thread back can only serve to remind us how glad we all are that the receiver beaver is gone.

[blueangel-eric]

Originally Posted by zz0468

That's ok. Bringing this thread back can only serve to remind us how glad we all are that the receiver beaver is gone.

so what do you have to do to be "banned for the greater good"?

[capfiremedic]

I'm reading this as 6.04 feet is a full wavelength for 155 mhz. So that length is optimum for that freq? Would that also cover transmission? I want a whip for a cdm1250 motorola and the truck already has a ball & spring on it. the main freg used is 155.415 mhz. The radio puts out 25 watts. I'm thinking about using one of our older 100 watt radios in the rig.

[Wyandotte]

Originally Posted by capfiremedic

I'm reading this as 6.04 feet is a full wavelength for 155 mhz. So that length is optimum for that freq? Would that also cover transmission? I want a whip for a cdm1250 motorola and the truck already has a ball & spring on it. the main freg used is 155.415 mhz. The radio puts out 25 watts. I'm thinking about using one of our older 100 watt radios in the rig.

If you're gonna TX on the antenna, you would have to cut the whip down so that the total length of the antenna, ball and spring is about 19", make it a quarter wavelength. Having a "longer than resonance" antenna for RX is no big deal, it works good enough. But even though a full lengthwave will tune up to a good match, you gotta realize it's radiating more off the ends than the side.

Since you have a ball and spring already, try to find a Hustler SF-2 antenna. This is a 5/8 sold for the two meter ham band with a 3/8" 24 tph mount on the bottom. You'll need to tune it for your freq. Ask any ham, he can do it for 'ya, or know another ham that can. I'll testify from personal experience, it's a great antenna, got a small coil and about a 4 foot whip. It's about $20.

[capfiremedic]

Appreciate it Wyandotte. Our area is using a repeater for the VHF's piggybacked into an 800 system with a mix of radios. Prior to Katrina, we had a dual repeater rig on the vhf's. The 800 system was stuffed down our throats by FEMA. The 800's are about as useless as jake brakes on a turtle so far, and the vhf's have a few dead spots that I'm trying to overcome. Whatever advice I can get is appreciated.

[prcguy]

A full wavelength will not tune up to a good match for 50ohm coax, it will be similar to an end fed half wavelength which is very high impedance and the radiation pattern would be really bad for mobile use. Using a ball mount with spring will also make the whip requirements very short, the entire thing with mount will be around 12" long. If you need good performance on VHF hi band you would be much better off installing a separate dedicated VHF hi antenna.
prcguy

Originally Posted by Wyandotte

If you're gonna TX on the antenna, you would have to cut the whip down so that the total length of the antenna, ball and spring is about 19", make it a quarter wavelength. Having a "longer than resonance" antenna for RX is no big deal, it works good enough. But even though a full lengthwave will tune up to a good match, you gotta realize it's radiating more off the ends than the side.

Since you have a ball and spring already, try to find a Hustler SF-2 antenna. This is a 5/8 sold for the two meter ham band with a 3/8" 24 tph mount on the bottom. You'll need to tune it for your freq. Ask any ham, he can do it for 'ya, or know another ham that can. I'll testify from personal experience, it's a great antenna, got a small coil and about a 4 foot whip. It's about $20.

[Wyandotte]

Originally Posted by capfiremedic

Appreciate it Wyandotte. Our area is using a repeater for the VHF's piggybacked into an 800 system with a mix of radios. Prior to Katrina, we had a dual repeater rig on the vhf's. The 800 system was stuffed down our throats by FEMA. The 800's are about as useless as jake brakes on a turtle so far, and the vhf's have a few dead spots that I'm trying to overcome. Whatever advice I can get is appreciated.

Just curious how long your repeater's been up?
Many times, the root cause of dead spots or poor performance in general, is old feed line and antenna. They both should be changed about every 10-15 years. The feed line will get lossy, which attenuates the signal. And the antenna, if it's metal, will corrode, or if it's fiberglass will crack and moisture will get into it. Changing the feed line and antenna can be much more cost effective than buying a new system.

And if you got anything to say about it, I suggest using a new antenna and coax every time a mobile gets moved from one vehicle to another. Someone's going to pop in here and say it's not necessary, but that's what I always do.

[capfiremedic]

The repeaters themselves are new since Katrina. The old ones took a salt water douche and were scraped by Motorola as unsalvageable. Currently we run one VHF repeater in the north end of Hancock County and the 800 system. Prior to the storm there was also a co-phased second vhf repeater in the south end of the County. We had the ability to chose which repeater to use as they each had their own foibles, but our coverage was very satisfactory. With this 800 system, the coverage is nowhere near as good and we can't afford to go completely with Motorola products anyway. We wanted to add some Kenwood gear, but our local Motorola distributor refuses to release the "keys" for the programming... So much for APCO 25...

[riccom]

Originally Posted by capfiremedic

The repeaters themselves are new since Katrina. The old ones took a salt water douche and were scraped by Motorola as unsalvageable. Currently we run one VHF repeater in the north end of Hancock County and the 800 system. Prior to the storm there was also a co-phased second vhf repeater in the south end of the County. We had the ability to chose which repeater to use as they each had their own foibles, but our coverage was very satisfactory. With this 800 system, the coverage is nowhere near as good and we can't afford to go completely with Motorola products anyway. We wanted to add some Kenwood gear, but our local Motorola distributor refuses to release the "keys" for the programming... So much for APCO 25...

capfiremedic

I live in slidell and i will say that the vhf sounds much better then the 800mhz you guys have, i can get it much better and have added it to my scanning feed,

but as far as vhf , this system sounds good on a whip antenna i use here, its not that big and monted on a (laughs) direct t.v. arm mast

and i do get bay st louis pd vhf and hancock vhf like if i was right next to the tower.