Another (non-intelligent donkey) antenna question . . .

[KB2GOM]

I purchased a Comet BNC-W100RX antenna. It is telescopic (about 39 inches fully extended), double-jointed (it will fold down alongside my BC125AT) antenna that I have been using to listen to:

121.5 air emergency
156.8 marine emergency
NOAA weather radio (roughly 162 MHz)
GMRS 462-465

and the results have been acceptable so far, but . . .

Since the antenna can be adjusted in length . . . any suggestions for setting the length for optimal reception?

Yes, I realize these are different frequencies. Is there a particular length that could be a happy compromise?

Maybe there isn't any, but I thought it might be worth asking.

​

 

[prcguy]

A 1/4 wavelength is good and about 127” for VHF air and 16” for most other VHF. 6” is good for UHF but most will not go that short so 3/4 wavelength of 16 to 18” should be fine for UHF.

 

[KB2GOM]

A 1/4 wavelength is good and about 127” for VHF air and 16” for most other VHF. 6” is good for UHF but most will not go that short so 3/4 wavelength of 16 to 18” should be fine for UHF.

Soooo, 16 inches might be a good compromise? A little long for vhf air, but not bad for other VHF and UHF, if I am understanding correctly.

 

[prcguy]

Soooo, 16 inches might be a good compromise? A little long for vhf air, but not bad for other VHF and UHF, if I am understanding correctly.

On a handheld receiver you probably won’t notice much difference.

 

[GROL]

16 inches is probably not the best compromise for VHF Air and Marine depending upon whatever the other half of the antenna is. It may be, but not likely. It depends on the other half of the antenna. For a handheld radio that other half varies greatly depending on who and how the radio is held. 1/4 wavelength in feet = 234/frequency. A quarter wave element is ~23 inches at 121.5 mhz and ~18 inches at 156.8 mhz. 17.25 inches at 162.5 mhz so pretty insignificant difference from 18 inches. The median compromise frequency is ~139 mhz and ~20 inches for one quarter wave element. 16 inches is a quarter wave for 175.5 mhz. For UHF receive 20 inches is likely okay.
You are no going to hear much of anything ever on 121.5 mhz. Most of the time emergencies are declared on whatever frequency the aircraft is already in contact with ATC. To check your reception you can try to pick an airport frequency very near you close to 121.5. Aircraft in flight are not a good reference due to altitude and distance variations. Also if you are not near the coast or the Great Lakes you are not likely to hear much on 156.8.

 

[KB2GOM]

16 inches is probably not the best compromise for VHF Air and Marine depending upon whatever the other half of the antenna is. It may be, but not likely. It depends on the other half of the antenna. For a handheld radio that other half varies greatly depending on who and how the radio is held. 1/4 wavelength in feet = 234/frequency. A quarter wave element is ~23 inches at 121.5 mhz and ~18 inches at 156.8 mhz. 17.25 inches at 162.5 mhz so pretty insignificant difference from 18 inches. The median compromise frequency is ~139 mhz and ~20 inches for one quarter wave element. 16 inches is a quarter wave for 175.5 mhz. For UHF receive 20 inches is likely okay.
You are no going to hear much of anything ever on 121.5 mhz. Most of the time emergencies are declared on whatever frequency the aircraft is already in contact with ATC. To check your reception you can try to pick an airport frequency very near you close to 121.5. Aircraft in flight are not a good reference due to altitude and distance variations. Also if you are not near the coast or the Great Lakes you are not likely to hear much on 156.8.

Thanks! I must admit I have yet to hear anything on 121.5. I have heard several pan-pan-pan-pan messages on 156.8, plus the unusual announcement of "messages to mariners." I'm in Troy, NY, far from NYC and the coast. I don't know where the transmitter is.

 

[nd5y]

I have heard several pan-pan-pan-pan messages on 156.8, plus the unusual announcement of "messages to mariners." I'm in Troy, NY, far from NYC and the coast. I don't know where the transmitter is.

https://www.navcen.uscg.gov/sites/default/files/images/marcomms/cgcomms/Rescue21/SecNY.jpg

 

[GROL]

Thanks! I must admit I have yet to hear anything on 121.5. I have heard several pan-pan-pan-pan messages on 156.8, plus the unusual announcement of "messages to mariners." I'm in Troy, NY, far from NYC and the coast. I don't know where the transmitter is.

A bit unusual that far away, but the coast stations may be on very high towers to get far off the coast. So you happen to be in a lucky spot.

 

[chrismol1]

not exactly a lucky spot, the coast guard, while not exactly the coast, has coverage and operations up the hudson river and has radio stations along the hudson river one of which is in Troy, the OP is on top of. Probably the one of well known of their operations up there are the ice breaking to the port of albany. But yea, a lot of traffic will be on 156.650 too and considering the canal lock operations in that area

 

[GROL]

not exactly a lucky spot, the coast guard, while not exactly the coast, has coverage and operations up the hudson river and has radio stations along the hudson river one of which is in Troy, the OP is on top of. Probably the one of well known of their operations up there are the ice breaking to the port of albany. But yea, a lot of traffic will be on 156.650 too and considering the canal lock operations in that area

There ya go. Hudson river.

 

[bearcatrp]

I have a couple of those antennas. Look along the side of the antenna. It shows what length you should extend based on frequency you’re listening to. It’s a better antenna than stock antenna’s.

 

[merlin]

Sheesh, all this hoopala about how long a receiving antenna should be. Its nuts.
For VHF/UHF down to air band, About 19 to 20 inches will pick up everything getting to you.
Double that length and you will never notice the difference.
The secret is how high you are and how high the TX antenna is,
Higher is better at both ends.

 

[Ubbe]

When I use telscopic antennas I pull them out to full length and when listening to a steady signal from a basestation I quickly push in maybe 2 inch and let go of the antenna and listen to the background noise of an analog signal. Then quickly push another 2 inch and so on. At some points it receives the best, it can be at two or three different lenghts, I tape measure the lenghts and note them down with the signal and frequency. Then check other frequencies the same way. I select the lenght for the frequency that's the most important to me and that isn't full strength. Or pick the length to even be able to hear a weak and interesting transmission.

At one time I was living very close to a water tower, 1km, and had to adjust the telescope to minimize a strong VHF datatransmitters signal that would otherwise overload the scanner.

/Ubbe

 

[KB2GOM]

Sheesh, all this hoopala about how long a receiving antenna should be. Its nuts.
For VHF/UHF down to air band, About 19 to 20 inches will pick up everything getting to you.
Double that length and you will never notice the difference.
The secret is how high you are and how high the TX antenna is,
Higher is better at both ends.

Well, the "nut" is the dude operating the radio (me!) and in my mania, I sought to optimize reception.

 

[KB2GOM]

When I use telscopic antennas I pull them out to full length and when listening to a steady signal from a basestation I quickly push in maybe 2 inch and let go of the antenna and listen to the background noise of an analog signal. Then quickly push another 2 inch and so on. At some points it receives the best, it can be at two or three different lenghts, I tape measure the lenghts and note them down with the signal and frequency. Then check other frequencies the same way. I select the lenght for the frequency that's the most important to me and that isn't full strength. Or pick the length to even be able to hear a weak and interesting transmission.

At one time I was living very close to a water tower, 1km, and had to adjust the telescope to minimize a strong VHF datatransmitters signal that would otherwise overload the scanner.

/Ubbe

That is a very useful and practical technique . . . and no oscilloscopes or signal strength meters involved. Thanks!