Does length matter? Scanner Antenna - Short vs. Long All-Band

[2Dangerous4u]

Does length matter? If the antenna is an All-Band 25-1300MHz antenna is the length just personal preference? Does performance vary by length? From 1 2/3" up to 17" all specify All-Band coverage from 25-1300MHz. Logically, I would think the longer length would get better coverage and clarity, but if I can get the same performance from an antenna that is 1 2/3" long why would I want one 17" long? BTW this is for a hand held scanner that is mostly used at home and stationary, however, on rare occasions I may use it while in my car and possibly even on my boat.

 

[sibbley]

Depends on the antenna IMHO. I have a Diamond RH77 wide band that is terrible at 470-512mhz, it's 16" long if I remember correctly. I have a 6" antenna tuned to 470mhz that is almost perfect at 470-512.

The Diamond does pretty well at 150-170mhz, but the 6" tuned to 160 pulls in more signals.

For a hand held scanner you just need to try different antennas and see what work best in your area. I've spent hundreds of dollars on antennas, to find that most are useless to me. It wasn't till I started buying specially tuned antennas for the band I was listening to that I found a happy place.

I have 2 1/2" tuned to 470 that receives almost as well as the 6" I mentioned above. The tuned antennas aren't that much more expensive either.

 

[PACNWDude]

Usually the closer you get to a full wavelength for a specific frequency, the better the receive capability.

That is in a perfect world with everything being textbook. Real world, if you can hear what you need to, your receiver is fine.

If you were transmitting, that is where it becomes a lot more important for things to be correct.

 

[DickH]

Does length matter? If the antenna is an All-Band 25-1300MHz antenna is the length just personal preference? Does performance vary by length? From 1 2/3" up to 17" all specify All-Band coverage from 25-1300MHz. Logically, I would think the longer length would get better coverage and clarity, but if I can get the same performance from an antenna that is 1 2/3" long why would I want one 17" long? BTW this is for a hand held scanner that is mostly used at home and stationary, however, on rare occasions I may use it while in my car and possibly even on my boat.

Antenna length depends on the frequency you want to receive. 1/4 wavelength is a commonly used standard. 1/4 wave for various freqs. are, roughly:
850MHz = 3-1/4"
460MHz = 6"
154MHz = 18"
46MHz = 60"
33MHz = 84"

 

[ab5r]

Some formulas (in inches) that may help:
1/4 wavelength 2808/freq. in Mhz.
1/2 wavelength 5616/freq.in Mhz.
Full wavelength 11232/freq. in Mhz.

Keep in mind these calculations are for specific frequencies and a BAND of frequencies. However, turning an antenna for the center of a band on frequencies will probably receive optimally.

A friend of mine once said jokingly, "Hell, you can receive on a wet noodle!"

Hope this helps.

 

[Voyager]

Dummy loads work from 25-1300 MHz, too, so don't put a lot of faith into resonance.

But, the replies you received already are good. I would only add that for receiving, generally the larger the antenna the better.

 

[ka3jjz]

Up to a point. If you're using a handheld, using a big antenna is quite likely to introduce issues with overloading. Most handhelds can't handle that large an amount of RF without choking in some manner.

Even in some urban areas, a good desktop might have overloading issues. So while size does matter, it's a little more complicated than that. Mike

 

[ko6jw_2]

All band antennas receive equally poorly on all bands.

 

[natedawg1604]

I recently installed 3 nmo antennas on my vehicle. I have a 49" Larsen vhf antenna tied to a dedicated scanner, which is awesome for VHF and airband. It gets noticeably better vhf reception on weak signals, compared to my Larsen tri-band.

 

[mmckenna]

"All Band" is a misnomer. I can call a rusty coat hanger an "all band"antenna. In reality, it will receive on "all bands", just not very well on most of them.

Also, "All Band" is very subjective. Does it really work on both 30KHz and 80GHz, because that covers most of the active spectrum. No? Didn't think so.

All Band means whatever your scanner covers. Yes, these "all band" antennas will work, but they'll often perform poorly in many areas.
Ideally you should focus on what you really intend on listening to. Dedicated antenna for those bands will work best. If you can't do multiple antennas, focus on where you need coverage.

 

[KE0GXN]

I guess the ideal way to do it, would be having a dedicated scanner and antenna for each band you wished to listen to.

The trick is sneaking all those purchases past the wife

 

[n5ims]

One other thing to remember is that there are two different departments that a commercial antenna must pass through prior to it being released for sale. Both groups have their own agendas that generally diverge.

The most important is the engineering group. They design the antenna based on well defined antenna theory and fine tune this design to maximize performance in the frequency range(s) that it is designed to operate. They're constrained somewhat by cost and a few other factors (like this antenna shouldn't work better than one of their more expensive models), but generally this doesn't really matter much.

The final group is the marketing group. It's their job to make the antenna sound like it will do everything for everybody (even if not totally accurate) so more people will purchase it. You know, the old "It slices, it dices, it chops, it grates, it will make a refreshing, delicious, and healthy salad with only 3 quick presses of the handle". Since they have final say over the packaging and sales description, it may not be close to what the engineers designed or have proven with their testing.

For example, a popular dual band antenna is designed for and works very well on 144 - 148 MHz and 430 - 450 MHz ranges. Their claims indicate (correctly) that it has specified gain in these areas and reasonable SWR when transmitting there. Tests, reviews, and users generally indicate that the antenna does indeed work very well on those two bands on both transmit and receive and works quite well on receive on frequencies fairly near the listed range. Now to what marketing adds in large print on the package. "Also works on 120/150/300/450/800/900 MHz". Well, it may work there (so will a paper clip), but not necessarily work WELL. Just like that paper clip, if the signal is strong enough, the antenna will pass that signal down to the scanner. If the signal is weak (or often even moderate), you'll get mostly noise.

 

[sibbley]

For example, a popular dual band antenna is designed for and works very well on 144 - 148 MHz and 430 - 450 MHz ranges. Their claims indicate (correctly) that it has specified gain in these areas and reasonable SWR when transmitting there. Tests, reviews, and users generally indicate that the antenna does indeed work very well on those two bands on both transmit and receive and works quite well on receive on frequencies fairly near the listed range. Now to what marketing adds in large print on the package. "Also works on 120/150/300/450/800/900 MHz". Well, it may work there (so will a paper clip), but not necessarily work WELL. Just like that paper clip, if the signal is strong enough, the antenna will pass that signal down to the scanner. If the signal is weak (or often even moderate), you'll get mostly noise.

Yea, found this out the hard way. By spending hundreds on all types and brands of antennas, that ended up in a drawer.

 

[sibbley]

I guess the ideal way to do it, would be having a dedicated scanner and antenna for each band you wished to listen to.

The trick is sneaking all those purchases past the wife

This is what I do, with the exception of sneaking the purchases past my wife. I just buy her stuff too! Works every time.

 

[mmckenna]

Does length matter?

Yes. Element length = the resonate frequency. Antennas work best when they are cut to the proper length of the frequency you want to listen to.

If the antenna is an All-Band 25-1300MHz antenna is the length just personal preference?

See above, resonate frequency is what matters. Longer antenna elements are resonate at lower frequencies. Shorter antennas are resonate at higher frequencies. There are ways to combine elements to make them resonate a different frequencies.
Do keep in mind that if the antenna is not resonate at a specific frequency it does not create an "RF brick wall". The antenna will work, just not as well.

Does performance vary by length? From 1 2/3" up to 17" all specify All-Band coverage from 25-1300MHz.

Depends on where you are trying to listen. A 1 2/3's inch tall antenna is probably going to receive _something_ if the signal is strong enough. It'll likely work better at higher frequencies. I can tell you that a 1 2/3" antenna is going to absolutely suck eggs if you are trying to listen to 25MHz. Unless you are sitting on top the the transmitting antenna, you probably are going to have issues.
A 17" antenna is going to be resonate in the VHF High band. It may work well at higher frequencies too. It'll likely work better than the 1 2/3" antenna trying to receive near 25MHz, but still is going to be a compromise.

Logically, I would think the longer length would get better coverage and clarity,

Yes, no and maybe. There is a thing called "capture area" that sometimes can be dragged into this. This suggests that a longer antenna will pick up more signal. Resonance still rules, though. Other things come into play, the ground plane under the antenna, local noise floor, and maybe a million other random things.

but if I can get the same performance from an antenna that is 1 2/3" long why would I want one 17" long?

You will not get the same performance from the shorter antenna on the lower frequencies. It -might- work better up around 1300MHz. This is called "marketing hype". If you chose to believe the hype, let me know, I've got a great deal for you on a nice bridge sitting on some swamp land in Florida.

BTW this is for a hand held scanner that is mostly used at home and stationary, however, on rare occasions I may use it while in my car and possibly even on my boat.

Hand held radios are limited by the ground plane they present to the antenna system. I'll tell you this, it doesn't look good.
You can buy hand held radios that will transmit and receive down past 30MHz, but they don't work well due to the limited ground plane and the realities of fitting a resonate antenna onto a hand held radio.

You'd do much better by using an outdoor base station antenna for all your home use. You will pick up a whole lot more stuff to listen to. It'll cost some money to do it right, but if you are serious about hearing radio traffic from more than a few miles off, it's what you really need.

Inside your car is a big issue. A car is a metal cage often with metal filmed tinted windows. All this works really well at blocking radio signals. Sure, it'll work, but no where near as good as if you install a mobile antenna.

The boat really depends on the design. If it's a fiberglass boat or an open aluminum boat you will still see much better performance from an external antenna. A 17" antenna on the hand held will probably work. In fact, 17 Inches is pretty dang close to being resonate on the VHF marine band.

Don't shortchange your system. You can buy a $15,000 receiver and put a $10 antenna on it and it's going to perform like crap. Take a $100 receiver and put a $15,000 antenna on it and it's probably going to work really well.
I've got a number of radio systems at work and it's very realistic to spend as much on the antenna(s) and feedline as I spend on the radio repeater itself.
If you take a hand held scanner and stick a cheap antenna on top you will be disappointed. Invest some money in a good antenna for your home and car and you'll have a much better experience.
This is -exactly- why police cars, fire trucks and ambulances will almost always have a mobile radio with a properly installed mobile antenna even though the officers/firemen/EMT's will often have a hand held radio.

You can design a two way radio system to work well with handheld radios inside buildings and cars, but it takes a lot of money. Chances are that the systems you will want to listen to are not designed for that.

 

[MississippiPI]

I have an 18" antenna Larson trunk mount on my car for my vertex highband radio. Please keep in mind that it's a radio and not a scanner but it does in fact scan and I can and do transmit on it if the need arises. I have great reception, real pleased with it. For example, I can copy and transmit Scott County (MS) EOC from the Gulf Coast when I am down there.

Be Safe

 

[2Dangerous4u]

A big thanks to everyone!!!

Thanks to everyone for the information and lessons. Looks like instead of shopping for an antenna, I'll be shopping for scanners and antenna's. Unfortunately it seems I will need at least 3 more scanners,,
all with different antenna's. So if anyone has any surplus scanners or antenna's, I'll gladly take them off your hands.lol P.S. I won't even have to hide anything, I got rid of the husband years ago.lol

 

[darkness975]

Not to trudge up old threads, but I found it would be unnecessary to make a new one for my inquiry. One of my scanners, a BNC325P2, has a BNC-W100RX antenna. Unless I am travelling in a car or something, I leave it sitting on a tabletop or counter in my place and I leave the antenna fully extended. Personally, though I am by no means an expert, I wonder with all this talk of lengths VS frequencies why it is not more prudent to just leave it fully extended and call it a day. The only "choking" I get on it is due to my crummy location (in a valley in a heavily wooded area).

I am awaiting an adapter so I can try the antenna on my HP2 to see if it will improve the reception on that (same channels come in much worse than on the BCD325P2). If it does (I hope it does) I will get another antenna for that.

My location is so bad that my buddy who is an airplane pilot said he's amazed I can get anything at all, save for the local PD and FD.

 

[slicerwizard]

You should've started a new thread, IMO.


For maximum performance - and it sounds like you need it - a telescoping whip should be extended to an odd quarter wave multiple (1/4, 3/4, 5/4, 7/4, ...) of the signal you're trying to receive. Typically, the longer, the better, as you get more capture area and you're raising the antenna height. A tuned length vs a random length buys you an extra 5 to 10 dB; it's easily demonstrated with an SDR dongle's spectrum display.

 

[scanmanmi]

Some formulas (in inches) that may help:
1/4 wavelength 2808/freq. in Mhz.

as long as the old thread is up it's easier to remember quarter wave is 234/MHZ = feet

This is what I do, with the exception of sneaking the purchases past my wife.

I'm just afraid that when I die my wife will sell stuff for what I told her I paid.