50 vs 75 ohm rec only on 162.X

[FCVPI99]

i know scanners and radios are 50 ohm but will it really hurt if i use a 75 ohm? im trying to pick up far away NOAA radio stations so i dont need to transmit i just need something that can suck in signals from 50 to 100 miles away i was looking at a VHF UHF yagi on amazon for 100 but i dont need UHF all i want is VHF .. thinking maybe an old time VHF TV antenna might work im in Rockford and my goals are Dixon Freeport and Dubuque im thinking i could split freeport and Dubuque off of same Antenna as the are the same direction
Green is i get Yellow is i get but need better Antenna and red is i dont have enough radios yet .. lol
how hard is it to make a VHF NOAA use Yagi???? as i dont have the 300 bucks i keep seeing them for

 

[G7RUX]

For the most part, scanners may have a 50 ohm antenna connector but their actual input impedance can vary quite a bit across their operating range, so using a 75 ohm feeder and antenna won’t cause any problems.

In fact 75 ohm feeder is inherently lower loss than 50 ohm so there are some advantages to going this way, including being able to use reasonably priced cable/sattelite TV coax.

 

[mmckenna]

i know scanners and radios are 50 ohm but will it really hurt if i use a 75 ohm?

No, it will not hurt your radio to use 75Ω cable.

im trying to pick up far away NOAA radio stations so i dont need to transmit i just need something that can suck in signals from 50 to 100 miles away i was looking at a VHF UHF yagi on amazon for 100 but i dont need UHF all i want is VHF .. thinking maybe an old time VHF TV antenna might work im in Rockford and my goals are Dixon Freeport and Dubuque im thinking i could split freeport and Dubuque off of same Antenna as the are the same direction
Green is i get Yellow is i get but need better Antenna and red is i dont have enough radios yet .. lol
how hard is it to make a VHF NOAA use Yagi???? as i dont have the 300 bucks i keep seeing them for

Not sure what kind of antenna you are currently using to receive those, but a high gain Yagi with appropriate coaxial cable for the length of the run should help.
If you cannot hear the other ones currently, there is no guarantee that a new antenna is going to work. The higher gain antenna will help with weak signals, but it will not pull a signal out of the air that isn't there.

A TV antenna can work, but they are not tuned for 162MHz. A Yagi antenna tuned for 162MHz will work better.

There are web pages that will give you directions and tuning info to make your own Yagi antenna. For an easy option, look at the "tape measure" Yagi's. Get yourself one of the (periodically) free Harbor Freight tape measures and make your own.

But a good used VHF Yagi should be well less than $300.

 

[FCVPI99]

No, it will not hurt your radio to use 75Ω cable.



Not sure what kind of antenna you are currently using to receive those, but a high gain Yagi with appropriate coaxial cable for the length of the run should help.
If you cannot hear the other ones currently, there is no guarantee that a new antenna is going to work. The higher gain antenna will help with weak signals, but it will not pull a signal out of the air that isn't there.

A TV antenna can work, but they are not tuned for 162MHz. A Yagi antenna tuned for 162MHz will work better.

There are web pages that will give you directions and tuning info to make your own Yagi antenna. For an easy option, look at the "tape measure" Yagi's. Get yourself one of the (periodically) free Harbor Freight tape measures and make your own.

But a good used VHF Yagi should be well less than $300.

i get them all one way or another ... like i get Dubuque perfect but then i dont get some freqs i scan for so il getting deticated Ants for the WX radios for that certain channel ..

 

[217]

I use 75ohm. Made a 160 MHz yagi from a old tv antenna. The boom is long enough to support six elements. It works. Your post made me check KHB31 just now and it is doing 165 miles. If I had to do it all over again I'd use the short corner reflector booms to extend the main boom to support 8 elements.

 

[G7RUX]

So to put some figures to the issue, if you use 75 Ohm coax with an *actual* 50 Ohm input impedance receiver then you will see a mismatch loss of around 0.4-0.5 dB. This is not a lot and not really worth worrying about.

However, feeder loss increases as the msimatch increases so reducing the mismatch on the feeder by using a small attenuator *can* be helpful...just a 1 dB attenuator won't do much noticeable to your signal and can improve the cable loss somewhat, although whether this is worthwhile is questionable.

A 75/50 Ohm "minimum loss" matching pad has a typical loss of around 5.5 dB; you quite likely would notice that. Even if you use a 50 Ohm antenna, 75 Ohm coax and a 50 Ohm receiver with no pads you'll likely see mismatch loss from the transitions of around 1 dB, plus perhaps another 0.5-1.0 dB from the cable excess dielectric loss due to mismatch. Since you are considering receive only applications the excess losses in the fedder due to mismatch (resistive and dielectric) should be pretty small.

In summary, 75 Ohm coax will do just fine and is probably better than the similar-sized 50 Ohm choice. RG58 shows around 7 dB/100ft vs RG59 at around 5 dB/100ft at the frequencies you are considering.

Another advantage, not often discussed is that there are often already runs of cable/sat TV coax installed in buildings, etc, which can make the whole installation process less painful.

 

[FCVPI99]

So to put some figures to the issue, if you use 75 Ohm coax with an *actual* 50 Ohm input impedance receiver then you will see a mismatch loss of around 0.4-0.5 dB. This is not a lot and not really worth worrying about.

However, feeder loss increases as the msimatch increases so reducing the mismatch on the feeder by using a small attenuator *can* be helpful...just a 1 dB attenuator won't do much noticeable to your signal and can improve the cable loss somewhat, although whether this is worthwhile is questionable.

A 75/50 Ohm "minimum loss" matching pad has a typical loss of around 5.5 dB; you quite likely would notice that. Even if you use a 50 Ohm antenna, 75 Ohm coax and a 50 Ohm receiver with no pads you'll likely see mismatch loss from the transitions of around 1 dB, plus perhaps another 0.5-1.0 dB from the cable excess dielectric loss due to mismatch. Since you are considering receive only applications the excess losses in the fedder due to mismatch (resistive and dielectric) should be pretty small.

In summary, 75 Ohm coax will do just fine and is probably better than the similar-sized 50 Ohm choice. RG58 shows around 7 dB/100ft vs RG59 at around 5 dB/100ft at the frequencies you are considering.

Another advantage, not often discussed is that there are often already runs of cable/sat TV coax installed in buildings, etc, which can make the whole installation process less painful.

it will be 50 ohm RG 58 cable and can be as short as about 15 feet .. just have to go up the hole in the ceiling and then im golden .. im just trying to get in KZZ56 Freeport in better on my WX radio from Rockford (surprisingly hard) and trying to do it for as il money as possible - i can get an old pre digital TV ant from my parents attic ... if i have to il bite teh big one and het a chepo china yagi from amazon for 100 bucks but even that will hurt bad

 

[mmckenna]

if i have to il bite teh big one and het a chepo china yagi from amazon for 100 bucks but even that will hurt bad

Try the TV antenna, then. It won't hurt. Just remember to rotate it 90º so the elements are vertically polarized. It might do what you need.

 

[Ubbe]

The design of TV antennas often makes them have increased gain the higher up in frequency you go and then it drops sharply at its highest frequency. But going lower in frequency than what it is designed for usually only follows the gain slope. A VHF-HI TV antenna should cover 175-250MHz and at 160MHz it should still be a healthy gain and a direction pattern that can be used.

/Ubbe