Sr. Citizen (very) Antenna Questions For New Scanner, & Getting Back Into Hobby, Please

[BOBRR]

Hello,

Getting back into hobby after many, many years, and would like to ask a few very general questions on antennas
for a new scanner (Uniden SDS 200) that I should have in a few days.
I am really weak when it comes to antenna's, and antenna theory in general. Would appreciate any thoughts on.

So, I see it comes with a telescopic "whip" antenna that is extendable probably to different lengths.

I also have a Diamond RH77CA from many years ago.
It's spec's on the case are:
2m/70 cm
120/ 150/ 300/ 450/ 800/ 900 MHz Bands.

a. I do not want to fiddle with optimizing the length of the Uniden included telescopic antenna any.

I will of course experiment with both, but how do you think, assuming I find some compromise length for it, how it would it compare to the Diamond ?

I seem to remember from many, many years ago that I was very happy with the Diamond on a Home patrol 1

b. For now, I will probably be very happy picking up anything and everything I can with the new Scanner. (live outside of Boston)
e.g., Aeo, PD, BAPERN, Utility, Maritime, etc. I would be happy with most anything for a while, until I learn how to use the SDS 200.

**What would the Diamond be good for, and more important, what broadcast "types"would it not cover ?

I don't remember what type of broadcasts are on what frequency bands. (but will hopefully learn)

c. Also have a very old Disconne in attic. Any thoughts on using it instead ?

Much thanks, really appreciate the help,
Bob

 

[mmckenna]

Hello,

Getting back into hobby after many, many years, and would like to ask a few very general questions on antennas
for a new scanner (Uniden SDS 200) that I should have in a few days.
I am really weak when it comes to antenna's, and antenna theory in general. Would appreciate any thoughts on.

So, I see it comes with a telescopic "whip" antenna that is extendable probably to different lengths.

I also have a Diamond RH77CA from many years ago.
It's spec's on the case are:
2m/70 cm
120/ 150/ 300/ 450/ 800/ 900 MHz Bands.

a. I do not want to fiddle with optimizing the length of the Uniden included telescopic antenna any.

I will of course experiment with both, but how do you think, assuming I find some compromise length for it, how it would it compare to the Diamond ?

I seem to remember from many, many years ago that I was very happy with the Diamond on a Home patrol 1

b. For now, I will probably be very happy picking up anything and everything I can with the new Scanner. (live outside of Boston)
e.g., Aeo, PD, BAPERN, Utility, Maritime, etc. I would be happy with most anything for a while, until I learn how to use the SDS 200.

**What would the Diamond be good for, and more important, what broadcast "types"would it not cover ?

I don't remember what type of broadcasts are on what frequency bands. (but will hopefully learn)

Probably won't see much difference. A tuned/resonate antenna is going to work better than one that isn't, but that totally depends on what frequencies you are listening to. If you are scanning more than one band, you'll have mixed results.
The Diamond is essentially a 1/4 wave VHF antenna, and will work best towards the bottom end of the VHF High band. It'll also be 3/4 wave on UHF, probably centered around the 440MHz area.
Same would go for the telescopic whip if you made it the same length. Benefit is that you can make it a bit shorter (17-18") and it should work a bit better on the public safety part of VHF and UHF.

For having a "set and forget" antenna, you can use either one if you are happy with the VHF/UHF performance. You'll find it probably won't work as well on 700/800MHz at that length.

c. Also have a very old Disconne in attic. Any thoughts on using it instead ?

Much thanks, really appreciate the help,
Bob

Antenna height is key. If the discone is higher than the whip on the back of the scanner, it's very likely going to work better. If your roof isn't metal, no foil backed insulation between the discone and what you are trying to listen to, and your coaxial cable is in good shape, you are probably much better of with that.

And the discone will cover the 700/800MHz bands better than a random length telescopic whip and the Diamond will.

Nice thing is that you have 3 antennas to try, and you'll know what works best by trying them out.

 

[BOBRR]

Hi,

Thanks for reply and info.
Really a clear explanation.

Just curious, and trying to learn:

Re "height": if the discone is in the attic, perhaps 10 feet higher than the Diamond, would you still
expect the discone (with its zero gain) to do better than the Diamond with its "tuned" bands ?

Height that big a factor in comparing the two ?

Regards,
Bob

 

[ka3jjz]

Indeed it is. Keep in mind that as you go higher in frequency, wavelengths become shorter, and are more prone to being blocked by objects such as trees and buildings. Under normal conditions, frequencies in the 'scanner' range are line of sight (there are exceptions). So yes, height is an important factor. The higher in frequency you go, the more line of sight they become.

You're not going very high, so this is not a factor for you, but if you do decide to go higher - cheap coax is very lossy the higher in frequency you go, and the longer the run. If you do decide to go higher, time to change the coax.

Mike

 

[W5lz]

There are no single antennas that work -well- on multiple bands unless that antenna is adjustable (manual/automatic) and is as high as practical. The biggy is that antennas work on 'size' according to frequency/band, and that also include the minimum "usable" height for each freq/band. (Got enough variables yet? There are more... just depends on how 'exacting'/picky you wanna get.

 

[Hit_Factor]

if the discone is in the attic, perhaps 10 feet higher than the Diamond, would you still
expect the discone (with its zero gain) to do better than the Diamond with its "tuned" bands ?

Gain relates to the shape of an antenna's main lobe. More gain means more nulls someplace else on the lobe. Generally, nulls are not what you want in a receive antenna for a scanner. Zero gain is essentially a round lobe.

Yagi antenna (elongated lobe) are used for receiving a specific tower, but that is not a general use scenario.

 

[jeatock]

To a degree, parroting mmckenna. Without getting too deep here is the theory behind why the wrong antenna higher still works better on receive than the right antenna lower.

Proviso- My Rule of Thirds: Radio is one third science, one third experience in the black arts, and one third dumb luck.

Any antenna resonant and with more gain on certain wavelengths is less resonant with less gain on others. 2-meter and 70CM armature frequencies were chosen because the wavelengths of the frequencies are happy multiples - that does not apply as you move from 145 to 155 VHF - a 7% change -and 440 to 460 in UHF - a 4% change (okay, not exactly accurate math, but you get the idea).

All dipole antennas are no-gain resonant at 1/2 of the wavelength (remember that a 1/4 wave whip uses the roof as the other half of the 1/2 wave dipole). The higher the gain, the narrower the wavelengths it will receive. 3db (double) gain antennas are cut and/or coiled to be 5/8 of the resonant wavelength and work by redirecting TX signal away from birds and earthworms towards the horizon (think of combined/nulled waves from two rocks dropped into a puddle). High gain 6db antennas (4x gain) do so by stacking phased elements. The same effect works for both in receive.

The resonance of the back-of-set antenna is adjusted by changing the length (think tuning fork) to a 1/4 or 1/2 wavelength. Discones are equally resonant with little gain change from VHF to Gigahertz.

Its all about the signal strength (in db's) of the signal you want to hear at the place the antenna catches it, and not losing db's in the coax.

The math is really simple:

DB's are logarithmic - every 3db change doubles (or halves) the signal. Every 6db is a change of 4x. Every 9db is a change of 8x, and so on.

Say an -100 db signal is available at the receiver. If the telescope is resonant at the wavelength you want to hear -100db will go to the receiver. Any non-resonance only makes things worse, and you cannot make signal stronger without an antenna that multiplies one wavelength's signal at the expense of others.

10 feet higher there is a -97db signal (twice as much because it is not attenuated by buildings, trees and rocks). A no-gain antenna catches -97db but the coax looses 3db. Back to -100db at the receiver. (-97 minus 3 = -100)

At +10 feet and -97db, a 3db gain antenna puts -94db into the coax. The coax looses 3db, but the net is a -97db to the receiver- twice as much as before. (-97 plus 3 minus 3 = -97... -97db is double -100db)

At +20 feet there is a -90db signal (more line of sight and less attenuation from there to here). A non-resonant antenna puts -93db (half) into the coax, and crap coax looses another 4db. Happily the receiver still gets -97db, twice as much as the -100db back of set antenna. At the same height a discone (or other resonant no-gain antenna) puts -90db into the coax, and better coax only looses 3db. The receiver sees -93db, an order of magnitude better.

I used -100db as a reference for easy math. Even so, in the real world a signal may be scratchy at -100db and clear at -97db. Your mileage may vary. Unless you are in the shadow of the transmitting tower the actual signal may be in the -85 to -95db range, but the math is unchanged. For local operations the system builder is trying to put at least -85db into a portable with the antenna buried in someone's armpit, so let them do the heavy lifting. Distant sources are more challenging.

The key is getting 'just enough' signal to be usable. Anything more is over-kill. If a -95db fully quiets the receiver, a -75db is still fully quiet and no more better.

Receiver sensitivity/selectivity, interference and amplifiers are all chapters of their own.

Hope this helps and makes sense.

 

[MisterLongwire]

STOCK ANTENNA WORKS FINE FOR MY PURPOSES

 

[Hit_Factor]

STOCK ANTENNA WORKS FINE FOR MY PURPOSES

Shh, no yelling

 

[jeatock]

STOCK ANTENNA WORKS FINE FOR MY PURPOSES

My Uniden 996 in the kitchen has a 90-degree BNC adapter with a 6" piece of 20GA wire poked into it. Not elegant, but more than enough to go full quieting on the 850MHz trunking tower four miles away.

 

[bearcatrp]

If you don’t want to mess around with an outdoor antenna, check out the diamond D220R mini discone antenna, Diamond® Antenna ~ D220R . It helped in my house during the winter. Mounted it on a gutted floor lamp to get it close to my ceiling. But suggest you first try the antenna that comes with it first to see if it’s picking up what you want to listen to. No need to spend money if not needed. Good luck.