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Antenna tuning question

Zambo

Well-Known Member
I have one of these but I need to cut it to length. I believe 40" is correct for our race frequency in the high 151.x mhz range. My question is when I cut it, do I leave 40" sticking out of the base, or do I just cut it to 40" and bury about 1.5" or so inside the mount where the set screws are? Thanks!
 

rugged1

Well-Known Member
If you're not going to be using an SWR meter, whatever cutting you're gonna be doing is sort of guesswork. We cut our antenna whips to 39" before shipping, but thats because we SWR meter our equipment to find the baseline antenna length when mounted properly. My suggestion would be to cut the antenna so 40" is sticking out of the base. The reason I'm suggesting that is because if eventually you are able to meter the antenna, you won't want to find out that you cut it too short. This will err on the side of caution until you are able to tune it with the SWR meter. You're more than welcome to stop by at any event we're at and get you're antenna tuned at no charge.
 

_

Well-Known Member
John,

My suggestion is, purchase a proper SWR meter, learn to use it properly, then put into to practice a regular maintenance schedule for all chase and race vehicle antennas/coaxes. Not only will this allow you to get the most out of every radio, it will allow you to easily identify coax breakdowns before they have a significant negative effect on your radio operation. Understanding SWR meter operation is very simple and well worth the effort to learn. At the same time, you will be surprised at how the smallest of obstructions will have on the proper tuning length of your antenna.

A non-commercial, good quality SWR meter can be had for under $100.

It is my opinion (for whatever that's worth), every race team who spends significant money should have an SWR meter in their tool box and practice a regular maintenance schedule for all chase and race radios with the race car being checked prior to every race.
 
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_

Well-Known Member
John,

I'm not to thrilled with the unit you provided a link to. It has very poor reviews. I think you need to be closer to the $100 range.
Here's are few recommendations. Also, don't be afraid of eBay to find a good used unit.

1st choice: Yaesu YS-500, These are old, out of production units, but very reliable and accurate. I own two of these meters (one which travels and one which stays at the shop. Both are over 20yrs old.) Here is a link to a used one for sale. For Sale - VHF SWR/Power Meter & Pre-Amps
(If I need a meter, I would jump on this now.)

2nd choice: Diamond SX-400, Used units show up on ebay regularly. Note: These units are outfitted with an "N" connector requiring you to purchase adapters to go from the "N" connectors on the meter to the PL259 (UHF) connectors found on almost all of the radios used in off-road.

3rd choice: Avair AV-601, These units are a copy of the Diamond SX-400 and use the same "N": style connector which will require the adapters. I'm not sure if the quality is as good, but they do look identical.
 

Zambo

Well-Known Member
Thanks man! So do you tune a specific frequency as close as you can get it or do you tune more for a range of frequencies? I watched a few videos but they were all about tuning CB radios to receive the whole channel 1-40 range.
 

wrightracing.net

Well-Known Member
It is good to know what the band width is on your antenna and what frequency your race channel is. Then center the range so it covers the frequencies you want to use. Most of the time I set the antenna at 152.500Mhz, with a 1/2 wave no ground plane antenna and a 5Mhz bandwidth. That gives you a good tune from 150MHz to 155Mhz. If you run in higher frequencies then you need to slide up the band, but make sure you cover the frequency your Race promoter uses for emergencies like Weatherman 151.625Mhz for Score.

On my F350 chase truck, I have a 5/8 wave ground plane antenna that has a 6 Mhz band width and the antenna is set at 154Mhz to cover 151 MHz to 157 Mhz.

There are wider band width antennas but most are 5 or 6 Mhz and different vehicles have different needs due to the mounting place of the antenna.

I hope that was not to confusing...

Sent from my SM-T900 using Tapatalk
 

Zambo

Well-Known Member
Not confusing at all! Basically what you said is I need to go to a radio guy and have it done, lol!
 

Mike321

Well-Known Member
Not confusing at all! Basically what you said is I need to go to a radio guy and have it done, lol!
I started with a SWR meter and spent a while cutting away at the antenna. I got a second antenna from PCI cut to the desired frequency -- there is maybe one mm difference.

Just order from PCI and specify your race frequency, it will be optimal and save you a lot of time and no need for a SWR meter.
 
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