1/4 wave vs 1/2 or 5/8th wave

[GBFD10]

Hey everyone... Happy New Year,

I currently have a 1/4 wave VHF antenna on my truck that gets decent reception. I know now that it isn’t in an optimal place, however because of the design of the hood on my 05 Silverado, I couldn’t install it up front (I was going to have the only local radio shop do a roof mount, however I guess he was too busy and forgot about me).

Anyway, my question is this... A) How much better would my reception be with a 1/2 or 5/8th wave antenna? B) How tall are these antennas (VHF 150-155). C) Would I need to change out the current mount I am using?

Thanks in advance,
-Sam

I'll also throw in a pic of my current mount so you have an Idea of what I'm working with.

 

[KC4ZEX]

The location of your current mount is not good at all. You get a lot of signal blockage from the back of the cab. If it were on a transceiver it would be unusable, but fair for a scanner. It needs to be at least 9 or 10 inches from the back of the cab. I have seen a few mounted behind the front stake hole on a corner or in a tool box in the middle. The 5/8 wave ant would be about 38 to 52 inches tall depending on the brand and the loading coil. For transmitting a 5/8 wave gives much better performance but doubt you will notice a great difference in receive.

 

[DaveH]

I agree that the current positioning is not good. If possible consider a permanent
mount on the roof, which requires drilling a hole. If you don't feel confident doing
it yourself, a 2-way radio shop could help. There are other less intrusive mount
options but some are temporary (mag. mount) or wouldn't allow positioning on
the cab roof (window clip etc.).

A 5/8 wave antenna gives moderate gain (3dB) over 1/4 wave and at 138MHz
stands about four feet (Larsen is 49" plus 1" or so for the coil). Higher is better for
recention, but you'd have to deal with garage doors, car washes etc.

Dave

 

[GBFD10]

Would I be better off w/ the antenna mounted on the hood lip? I had it set up that way on my old truck (01 GMC Jimmy) however this truck has an oddly shaped hood.. If this was a better option does anyone know of a company that makes mounts that will fit under the lip ?

I am still not sure that putting it in the roof is an option... there is no way i can do this myself (if you saw the cob-job of wiring that already exsist you would understand.) and the only radio shop in the area cant be bothered with "small" jobs.

Also, while I've got the experts... anyone konw of a good, safe place to route wires through the firewall in the 05 silverado? (slightly OT, but i may want to run my antenna wire thru there)... If so, can anyone provide pictures?

Thanks
Sam

 

[Tom_G]

Gain is not always better

Sam,
I have done a lot of research on antenna's and the bottom line is that higher gain is not always better reception.
Here is hilly Connecticut, many folks use quarter wave antenna's with better results.
Quarter wave antenna's have higher radiation angles then half or 5/8 wave antenna's.
The more gain you have the more signal you concentrate lower to the horizon. If you are at a fairly high elevation, this is good.
If you are down in a valley, like me, quarter wave antenna's do better.
As far as location goes, your antenna is pretty well blocked.
The roof is the best location. If you go with a front fender/hood install, make sure you have a good ground or the antenna won't tune and your SWR will be high.
If you have trouble getting a good RF ground you can always move up to a half wave ground independant antenna.
Best of luck.....

 

[GBFD10]

How do I ensure a good ground? Is it a matter of placement or do I physically have to ground the antenna??

 

[K5MAR]

As is generally the rule, the higher the better. The best would be the roof mount, you've got lots of room up there for a good ground plane under the antenna.

Another idea is to get a headache rack for your truck and mount the antenna(s) on it. Wouldn't be as good as on the roof, but it will get the antenna up in the clear. I've currently got 4 antennas mounted on my headache rack (5 if you count the GPS antenna) and they perform well for me. This was necessary to free up roof space for the other 5 antennas. (BTW, I have a '98 Silverado, the hood is a more normal type, "L" brackets can be mounted on it.)

Mark S.

 

[K5MAR]

How do I ensure a good ground? Is it a matter of placement or do I physically have to ground the antenna??

A physical mount needs a good electrical ground, which will give you an RF ground. Placement will help improve the RF groundplane, the more metal under the antenna the better. If the mount is screwed to the body, you should have the electrical ground. (This is simplified, I know, but close enough for govt. work.)

Mark S.

 

[BoxAlarm187]

The location of your current mount is not good at all. You get a lot of signal blockage from the back of the cab. If it were on a transceiver it would be unusable, but fair for a scanner.

Just a comment on this - I have the exact same thing on my truck. I use a Kenwood TK-780 45W model on VHF, with a VHF 1/4 wave mounted in the same position. I knew when I mounted it there that it was definately not in the "right" spot, but it was what I had to work with at the time. Regardless, I have many times talked back to the dispatcher with the signal "blocked by the cab" for a distance of over 20 miles (line of sight) without any problems.

 

[GBFD10]

That's the thing... as far as "getting out" goes... I really don't have any trouble at all (I live 2 blocks from the tower for our EMS/PD dispatch, and line of sight from the fire- dispatch tower). As a matter of fact, my portable has a blown internal connection between the antenna assembly and the main circuitry, but I can still transmit from my living room and talk to, and hear, our EMS dispatch with no issues at all.

My real interest is boosting the reception side of things as I have a number of channels programmed into the radio that are set to monitor only (I do the programming myself)...

 

[mgosdin]

I've got a 5/8 wave antenna mounted in the "behind the cab" position on my S10.

Never a detectable problem receiving anything.

I cant speak as to transmitting, I have added a dual band VHF Hi + UHF 1/4 Wave to the opposite side of the truck bed in anticipation of fulfilling on of my New Year's Resolutions and getting a HAM license this year. It works quite will for receiving on my scanners, time will tell how it works as a transmitting antenna.

Mark Gosdin

 

[Tom_G]

The issue I had on my SAAB 9-5 was that I could not get a good RF ground.
I could get a good DC ground with a ohmmeter, but my quarterwave antenna would not tune uo. The SWR was terrible.
I switched to a half wave, ground independant antenna, and it tunded fine.
I could of added some ground straps to my trunk lid and tried to get a better RF ground but I didn't want to get into all of that.
The SAAB is a great driving car, but not a great radio car. (not much room for radios)
So the bottom line is that DC ground and RF ground are different animals.

 

[PluckyPleco]

Ask a SKILLED ham...

I am still not sure that putting it in the roof is an option... there is no way i can do this myself (if you saw the cob-job of wiring that already exsist you would understand.) and the only radio shop in the area cant be bothered with "small" jobs.

If you're friends with any of the local ham radio folk, you might ask them if there is anybody around who is _skilled_ at drilling roof holes.

We've got two guys around here, one a retired "radio guy," who live for the opportunity to "hack metal."

Plec

 

[Randall]

Sam,
I have done a lot of research on antenna's and the bottom line is that higher gain is not always better reception.
Here is hilly Connecticut, many folks use quarter wave antenna's with better results.
Quarter wave antenna's have higher radiation angles then half or 5/8 wave antenna's.
The more gain you have the more signal you concentrate lower to the horizon. If you are at a fairly high elevation, this is good.
If you are down in a valley, like me, quarter wave antenna's do better.
As far as location goes, your antenna is pretty well blocked.
The roof is the best location. If you go with a front fender/hood install, make sure you have a good ground or the antenna won't tune and your SWR will be high.
If you have trouble getting a good RF ground you can always move up to a half wave ground independant antenna.
Best of luck.....

i would agree with that, also 1/4 wave antennas often work better in downtown areas surrounded by very tall buildings.

 

[SLWilson]

04 Tahoe

Hey everyone... Happy New Year,

I currently have a 1/4 wave VHF antenna on my truck that gets decent reception. I know now that it isn’t in an optimal place, however because of the design of the hood on my 05 Silverado, I couldn’t install it up front (I was going to have the only local radio shop do a roof mount, however I guess he was too busy and forgot about me).

Anyway, my question is this... A) How much better would my reception be with a 1/2 or 5/8th wave antenna? B) How tall are these antennas (VHF 150-155). C) Would I need to change out the current mount I am using?

Thanks in advance,
-Sam

I'll also throw in a pic of my current mount so you have an Idea of what I'm working with.

Hey Sam,

Your hood is similar to my 2004 Tahoe. I have a 1/4 wave on the front driver's side fender using an "L" bracket built for Chevy mounting. See below. Also, depending on where I'm going or what the action of the day is, I use the 1/4 wave MOST of the time. If I know I'm going WAY out in our county, I switch to the 5/8 antenna (which is in the back of the truck all of the time)...Same mount accepts both antennas.....Steve/Gallia

 

[kf4lne]

There is a mount made for a Dodge Ram that may work on your hood with some modification.

 

[GBFD10]

Hey Sam,

Your hood is similar to my 2004 Tahoe. I have a 1/4 wave on the front driver's side fender using an "L" bracket built for Chevy mounting. See below. Also, depending on where I'm going or what the action of the day is, I use the 1/4 wave MOST of the time. If I know I'm going WAY out in our county, I switch to the 5/8 antenna (which is in the back of the truck all of the time)...Same mount accepts both antennas.....Steve/Gallia

The hood on my truck is actually very different then the one on your tahoe. Where your hood is flush with the fender, mine actually comes down with about a 1 inch lip over the fender, eliminating the nice gap for the L- bracket. (its hard to see in the pics, I'll try and take a better one when the snow stops tomorrow)

 

[KC4ZEX]

The antenna in the back of the cab usually causes a bad mismatch transmitting and Rf feeding back into the cab and usually results in a motorboating over the radio everytime you key the mike. Seen it many times in over 30 yrs on several models. The corner mount shown in mgosdin's photo works fair on some models. The hood mount is ok if you don't get ignition or alternator interference from being so close. Usually a roof mount can be put in fairly easy by putting it in the middle at back of cab just above the dome light. Run the coax down thru the double wallaround rear window an out down behind seat.