Quick antenna question

[GreggInFL]

How close to 462/467 must an antenna be to function? I have access to the antenna shown nearby. A friend ran into it and says, "Worthless label. 154/430Mhz. Made in China. About 6 feet tall. 58 cable with a BNC connector. Free to a good home."

I'd use it (if it can work with GMRS) on a 15-20' mast with a DB25-G (25W) in a flat, wooded area. I'm not talking 5 x 9 perfection, just adequate to be heard and understood over a short distance, say < three miles. I know, I know, "Try it and find out."

I hesitate to try it because 1) it might not work for GMRS and 2) as an apparent dual-band it might lure me into becoming a ham. 

What say the crowd?

[mb523]

You want your antenna to match the frequencies you're transmitting on as closely as possible. 154/430Mhz is the common VHF/UHF split for a dual band HAM antenna. It won't have good SWR on GMRS since it isn't tuned for the 462/467 range needed for GMRS. It may work, but it won't work well. 

You want to look for a GMRS specific antenna like this one:

 

 

[OffRoaderX]

43 minutes ago, GreggInFL said:

How close to 462/467 must an antenna be to function? I have access to the antenna shown nearby. A friend ran into it and says, "Worthless label. 154/430Mhz.

The only way to know for sure is to put a meter or portable antenna analyzer on it and test it.. 
But, like the @mb523 said, its not going to work very well.

[Lscott]

1 hour ago, GreggInFL said:

How close to 462/467 must an antenna be to function? I have access to the antenna shown nearby. A friend ran into it and says, "Worthless label. 154/430Mhz. Made in China. About 6 feet tall. 58 cable with a BNC connector. Free to a good home."

I'd use it (if it can work with GMRS) on a 15-20' mast with a DB25-G (25W) in a flat, wooded area. I'm not talking 5 x 9 perfection, just adequate to be heard and understood over a short distance, say < three miles. I know, I know, "Try it and find out."

I hesitate to try it because 1) it might not work for GMRS and 2) as an apparent dual-band it might lure me into becoming a ham. 

What say the crowd?

Only quick way to find out is test it with an SWR meter. Some of these multi band antennas show oscillation in the SWR across a range of frequencies. You might get lucky where the GMRS frequencies falls into one of the low SWR valley.

The link below is a test I did of a favorite wide band mobile antenna. Usable.

https://forums.mygmrs.com/gallery/image/268-ca-2x4sr/?context=new

And this link is for a test on a Ham dual band mobile antenna to see if it was usable. Doesn't look good.

https://forums.mygmrs.com/gallery/image/283-sg7500a-swr-scans-2jpg/

 

[WRTC928]

If the SWR is acceptable, it may work well enough for what you want. It won't be ideal, but hams use all kinds of weird crap for antennas and get a signal out. I saw a guy on YouTube use a bridge railing -- still on the bridge. If you put it on a 20' mast, you'd probably get 3 miles. It will never work as well as an antenna tuned for the GMRS band, but it may do what you want. "Good enough" is a valid concept.

[Bogieboy01]

2 hours ago, WRTC928 said:

If the SWR is acceptable, it may work well enough for what you want. It won't be ideal, but hams use all kinds of weird crap for antennas and get a signal out. I saw a guy on YouTube use a bridge railing -- still on the bridge. If you put it on a 20' mast, you'd probably get 3 miles. It will never work as well as an antenna tuned for the GMRS band, but it may do what you want. "Good enough" is a valid concept.

If swr is halfway decent it will work just fine... i have been operating a 25w anytone 778uv base setup(just upgraded to 50w anytone 5888uv, which seems to output about 42w on gmrs) off a "bingfu" 30" mobile dual band antenna literally electrical taped to a piece of conduit  with a radial ground plane, and can operate a repeater 22 miles away on a daily basis, on a $30 antenna showing approximately a 1.9-2.2swr on gmrs frequencies.... and i can hit the repeater better than someone right up the road from me also running 50w, thru a commercial 6' comet for gmrs, with a 1.4 swr across the repeater band.... 

 

All that said, TLDR..... get the free antenna and see what it can do.... worst that can happen is the FREE amtenna doesnt work well, and you end up padsing it along to someone else who can use it.... 

[GreggInFL]

^That's where I'm probably going to go with it. Thanks.

[SteveShannon]

17 hours ago, GreggInFL said:

How close to 462/467 must an antenna be to function? I have access to the antenna shown nearby. A friend ran into it and says, "Worthless label. 154/430Mhz. Made in China. About 6 feet tall. 58 cable with a BNC connector. Free to a good home."

I'd use it (if it can work with GMRS) on a 15-20' mast with a DB25-G (25W) in a flat, wooded area. I'm not talking 5 x 9 perfection, just adequate to be heard and understood over a short distance, say < three miles. I know, I know, "Try it and find out."

I hesitate to try it because 1) it might not work for GMRS and 2) as an apparent dual-band it might lure me into becoming a ham. 

What say the crowd?

I would get it.  If nothing else the parts can be scavenged.  That looks a lot like the Comet dual band Antenna I have which works very well.   It also looks like they have a pretty long length of coax that might be worthless for GMRS but usable for lower frequencies.

[GreggInFL]

3 hours ago, SteveShannon said:

I would get it.  If nothing else the parts can be scavenged.  That looks a lot like the Comet dual band Antenna I have which works very well.   It also looks like they have a pretty long length of coax that might be worthless for GMRS but usable for lower frequencies.

Yeah, I noticed the cabling was not working in my favor for GMRS -- and, as you point out, there's a lot of it. I'll need to disassemble everything to be certain, but it appears the cable has a simple threaded connector, so it can probably be easily replaced.

[GreggInFL]

19 hours ago, Lscott said:

The link below is a test I did of a favorite wide band mobile antenna. Usable.

https://forums.mygmrs.com/gallery/image/268-ca-2x4sr/?context=new

Aha, learn something new every day. Interesting.

[SteveShannon]

8 minutes ago, GreggInFL said:

Yeah, I noticed the cabling was not working in my favor for GMRS -- and, as you point out, there's a lot of it. I'll need to disassemble everything to be certain, but it appears the cable has a simple threaded connector, so it can probably be easily replaced.

Yes, remove the bolts that hold the bottom tube on and you can easily get to the coax connector which is probably just a pl-259 on the cable and so-239 on bottom of the antenna. 

[GreggInFL]

This appears to be a fiberglass tube. So, I should be able to tune it to 462 by shortening it roughly 7", right?

A little less to split 462 and 467?

(<PE but not an EE)

[SteveShannon]

2 minutes ago, GreggInFL said:

This appears to be a fiberglass tube. So, I should be able to tune it to 462 by shortening it roughly 7", right?

A little less to split 462 and 467?

(<PE but not an EE)

Without knowing what is really in that tube I’m not certain. It could be a couple pieces of wire with a trap between them. If that’s so I would think (low confidence!!!) that the first (lower) wire is the UHF element and both elements together form the VHF element. The trap serves as a conductor at the lower frequencies so the two wires are connected together and becomes high impedance at UHF frequencies so only the bottom wire is the radiator. 
The difference between full wave GMRS and 70 cm is just a few centimeters and if the UHF antenna is intended to be a quarter wave it would be a quarter of that. 
But I don’t know if you can get the fiberglass radome off the base anyway. Mine appears to be epoxied. 

[tweiss3]

10 minutes ago, GreggInFL said:

This appears to be a fiberglass tube. So, I should be able to tune it to 462 by shortening it roughly 7", right?

A little less to split 462 and 467?

(<PE but not an EE)

No. It's probably a colinear array. Unless you want to redesign the whole array, it's not worth touching. If you are less than 3:1 at 462, leave it alone.

[LilRedDog]

22 hours ago, GreggInFL said:

, just adequate to be heard and understood over a short distance, say < three miles.

It will work.

 

That's what you want, no? You want to talk to hand-helds (HT) about 3 miles?

You will be fine.

If you stand on the TX, you may warm up the antenna, a little but not hurt it nor the equipment.

The HTs' OEM antenna's will do 3-5 miles on flat earth to each other. 

And if they were HAM spec'd (which most people buy, because of power, and know no better) they are 144/430 OEM antennas and people use them all the time.

You can buy a (advertised) 10watt HAM radio with a 144/430 OEM antenna and use it on GMRS channels and never know it; most of the time.

 

That said:

I have GMRS HT antennas from everyone and prefer the tiny, inefficient, stubby ones because I seldom need 5 miles in the leafy woods. If I stand on TX, they will warm up.

In the woods or a crowd antennas make a difference. Line of site is not, nearly, as affected.

[GreggInFL]

2 hours ago, tweiss3 said:

If you are less than 3:1 at 462, leave it alone.

Okay. So that's the magic number. I was thinking 2.0 might be the limit for protecting the equipment, but this is not my area of expertise. Thanks.

[GreggInFL]

1 hour ago, LilRedDog said:

It will work.

 

That's what you want, no? You want to talk to hand-helds (HT) about 3 miles?

You will be fine.

If you stand on the TX, you may warm up the antenna, a little but not hurt it nor the equipment.

Protecting the equipment is my primary concern, but it looks like "close enough" is not a problem. Thanks.