Mobile VHF antenna: Wide vs. Narrow

[fremont]

I'm brand new to ham and was looking at mobile VHF antennas.  I have a fender mount plate (NMO) and have really liked my Laird phantom "ghost" low (3.5") antenna in GMRS applications.  They make one in VHF at various frequency ranges.  My guess is that their 142-160 model would work fine for me, as I'm mainly interested in 146.520 for things like traveling, wilderness protocol, etc. and for the mid-150's to scan public safety, etc.

 

I've debated getting that vs. an antenna that goes 136-174, but, with SWR tuning, do you end up losing much of that range anyhow?

[mbrun]

Good evening Fremont.

 

With the ghost style wide-band antennas I do not believe there is any adjustment involved. They are plug and play.

 

In looking at the Laird site, it looks like the antennas have a gain of 3dBi or less. Only through use of the antenna will you be able to determine for certain if it satisfies your needs.

 

An antenna that sits higher above the vehicle and one with higher gain value will most certainly increase your range, that may or may not be important to you in your area of use.

 

An antenna that features an SWR of 2.5:1 (as some of the low profile Lairds have) will also certainly result in more signal loss in your cable which in turn will affect range.

 

I am not using any low-profile antennas on my vehicle. Everything I am using is a whip antenna in the 40” tall 6dBi +/- range. I have been able to hit some GMRS and VHF amateur repeaters in the Cincinnati area out to max of about 35 miles using just 5 watts. My SWR on both my dual band Amateur and GMRS mobile antennas is 1.2:1 and loss across the bands I use.

 

I am sure you will receive some additional opinions from others as well.

 

Good luck.

 

Michael

WRHS965

KE8PLM

 

 

Sent from my iPad using Tapatalk

[1URFE57]

I'm brand new to ham and was looking at mobile VHF antennas.  I have a fender mount plate (NMO) and have really liked my Laird phantom "ghost" low (3.5") antenna in GMRS applications.  They make one in VHF at various frequency ranges.  My guess is that their 142-160 model would work fine for me, as I'm mainly interested in 146.520 for things like traveling, wilderness protocol, etc. and for the mid-150's to scan public safety, etc.

 

I've debated getting that vs. an antenna that goes 136-174, but, with SWR tuning, do you end up losing much of that range anyhow?

I have no problem with mobile antenna that has 136-174 range I encountered a few with 136-174 range that have been center tuned at 145.000 manufacturers do this for SWR purposes.

[Radioguy7268]

If we are talking about the "low profile" VHF antennas that screw on to a standard NMO mount - they're about the size of an Oil Filter. They might not be tall, but they're still presenting quite a wide profile.

 

The Pulse/Larsen ones I'm familiar with also required on the vehicle tuning to achieve anything close to a 1:1 match, and you usually got frustrated around 1.5 and said it was close enough. The bandwidth when tuned wasn't more than 1 or 2 MHz above/below the tuned center freq. Hardly "wideband". 

 

I would probably recommend just using something like a standard 1/4 wave whip tuned to the frequency you're most interested in transmitting on - and then just live with the performance on the receive side. It will likely be good enough for 90% of what you're interested in listening to. If you need to work specific frequency bands outside the tune of the antenna, just carry a few different lengths to screw on in under 30 seconds.

 

If you're worried about what the antenna might hit, consider something like the Stico super flexible mast. If you really want low profile in VHF - then use a Transit style antenna like the Sinclair Excalibur - but get your wallet out. Those run @ $250 & still require tuning - with a narrow bandwidth.

[WRNA236]

On 12/1/2020 at 6:16 PM, 1URFE57 said:

I have no problem with mobile antenna that has 136-174 range I encountered a few with 136-174 range that have been center tuned at 145.000 manufacturers do this for SWR purposes.

Make sure to read the specs and measure the antenna.  A VHF antenna with 25% or 38 MHz of usable bandwidth is pretty unusual.  Bandwidth is defined as the range of frequencies where the antenna will show 2:1 or less SWR and a more typical bandwidth is on the order of 10% (that's the rule of thumb for a plain 1/4λ whip over a good ground). 

So this probably means the antenna can be tuned in the range of 136 to 174 and they've centered it at 145 MHz from the factory to be sold to ham customers.  The same antenna might come tuned to a different center (or just not tuned) from a commercial supplier. 

It's possible this particular antenna does actually have such a wide bandwidth but the radiation efficiency will be very low, meaning it's not going to perform all that well on the air with a lot of loss in the matching network.  The devil's in the details.  You generally can't have everything, so wide bandwidth comes at a cost in performance. 

But since you're presumably after a ham antenna for 2 meters we really only need about 3% bandwidth to cover our whole allocation of 144 to 148 MHz.