BNC Cable Extension to Antenna

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david_lexicon

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I have a Bingfu VHF UHF Scanner Antenna and I am going to place it on the roof. From the roof to my scanner there are10m (32ft). The first 3m (10ft) will be the cable of the antenna and I am adding a BNC cable extension to the Scanner.

Questions:

1) If the extension is a 50 Ohms BNC cable, the signal remains powerful?
2) If the extension is a 70 Ohms BNC cable, the signal that remains is better than a 50Ohms BNC cable?

Thanks.
 

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cmjonesinc

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I'll second that.

An impedance mismatch on a transmitting radio would be a bigger issue. But for what you're doing just get some good low loss cable and you'll be fine. I'm sure someone can break down the numbers and tell you for sure but I doubt it would be a huge difference especially at that length. One thing I would be concerned about is a ground plane for that antenna. If you're on a metal roof you'll be fine, but if not you may want to look in to something more purpose built as a base antenna and not a mobile antenna.
 

david_lexicon

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I'll second that.

An impedance mismatch on a transmitting radio would be a bigger issue. But for what you're doing just get some good low loss cable and you'll be fine. I'm sure someone can break down the numbers and tell you for sure but I doubt it would be a huge difference especially at that length. One thing I would be concerned about is a ground plane for that antenna. If you're on a metal roof you'll be fine, but if not you may want to look in to something more purpose built as a base antenna and not a mobile antenna.

What do you suggest for purpose-build antenna just for reception?
 

n5ims

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The antenna in your picture and as you describe appears to be a cellular booster antenna even though it's clearly marketed as a scanner antenna. The designed frequencies are not typically those used when scanning (although 800 MHz is close). Also, the coax used is basically crap. It's RG-174 that is designed for very short jumpers inside equipment (think inches, not feet) and is very lossy. At 800 MHz you'll have 3dB of loss in that initial 10 foot section. Not good.

Any of those antennas linked above would be a much better solution. Don't get hung up on the "transmit" vs "receive" thing. Anything can be a receive antenna (it may not work well, but it will receive, even a straightened out paper clip!). Where it can transmit is important since that is the frequency range(s) where it's designed to work WELL (not just work). That is because a receiver takes whatever signal is present and tries to pull a signal out of it.

A transmitter has to work with an antenna that is designed for the frequency (more like frequency range) being transmitted and if you don't have a good match your transmitter will shut down (at best) or let the magic smoke out of the final transistors. On receive where there isn't a good match you get signal, but not much so you'll get noise or nothing but when the match is good, there will be maximum transfer of signal from through the antenna and you'll have a better chance of picking up enough signal for your scanner to actually allow you to hear the transmission.

With those antennas you'll be able to use whatever coax you want (horrible, bad, OK, good, or even great) from the antenna all the way down to the scanner. As expected, the better the coax, the more it will cost, but it's generally worth the cost. Don't worry about the connectors not matching your scanner since that's an easy fix. Just order your coax with the connectors needed on each end. They don't have to match! For example, say you got the Tram1411 from the first link. That has an SO-239 connector so your coax will need a PL-259 to connect to it. Assuming that you got the Bingfu since your scanner has a BNC antenna connector just ask them to put a male BNC on the other end of your coax. For most installs, a "good" coax would be some quality LMR-400 (get the name brand stuff like Times, not some LMR-400 "like" coax from eBay or some low-end Amazon sellers). Most places can custom make cables at the length you desire and install quality connectors of your choice. To show you the difference, using Times LMR-400 you'll have about the same loss for 100' as the RG-174 has in 10'. With a 40' piece (you'll want a little extra length - but not much - so you can work around duct work or other obstructions) you'll have less loss on your entire run that the Bingfu has in that 10' section.
 

drdeputy

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Thank you for your reply. These Base Antennas are for transmission whilst I need them only for reception.
The fact that some antennas marketed for scanners are also resonant on certain frequencies for transmitting doesn't preclude them from being recommendable for scanners. I happen to like and own this:


It is capable of transmitting on the 2cm Ham bands, for example, which I have used, but it's just an extra benefit. I might go so far as to suggest that a scanner antenna which is also suitable for some transmitting might even be better made....do bear in mind that these antennas are unity gain across a broad spectrum. If you have specific needs, another design might work better for you.
 

chief21

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I have a Bingfu VHF UHF Scanner Antenna and I am going to place it on the roof. From the roof to my scanner there are10m (32ft). The first 3m (10ft) will be the cable of the antenna and I am adding a BNC cable extension to the Scanner.
If any of the connectors are exposed to the weather, don't forget to seal them from moisture/water penetration. Even a small amount of moisture in the connector or coax can degrade your reception significantly.
 

david_lexicon

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The antenna in your picture and as you describe appears to be a cellular booster antenna even though it's clearly marketed as a scanner antenna. The designed frequencies are not typically those used when scanning (although 800 MHz is close). Also, the coax used is basically crap. It's RG-174 that is designed for very short jumpers inside equipment (think inches, not feet) and is very lossy. At 800 MHz you'll have 3dB of loss in that initial 10 foot section. Not good.

Any of those antennas linked above would be a much better solution. Don't get hung up on the "transmit" vs "receive" thing. Anything can be a receive antenna (it may not work well, but it will receive, even a straightened out paper clip!). Where it can transmit is important since that is the frequency range(s) where it's designed to work WELL (not just work). That is because a receiver takes whatever signal is present and tries to pull a signal out of it.

A transmitter has to work with an antenna that is designed for the frequency (more like frequency range) being transmitted and if you don't have a good match your transmitter will shut down (at best) or let the magic smoke out of the final transistors. On receive where there isn't a good match you get signal, but not much so you'll get noise or nothing but when the match is good, there will be maximum transfer of signal from through the antenna and you'll have a better chance of picking up enough signal for your scanner to actually allow you to hear the transmission.

With those antennas you'll be able to use whatever coax you want (horrible, bad, OK, good, or even great) from the antenna all the way down to the scanner. As expected, the better the coax, the more it will cost, but it's generally worth the cost. Don't worry about the connectors not matching your scanner since that's an easy fix. Just order your coax with the connectors needed on each end. They don't have to match! For example, say you got the Tram1411 from the first link. That has an SO-239 connector so your coax will need a PL-259 to connect to it. Assuming that you got the Bingfu since your scanner has a BNC antenna connector just ask them to put a male BNC on the other end of your coax. For most installs, a "good" coax would be some quality LMR-400 (get the name brand stuff like Times, not some LMR-400 "like" coax from eBay or some low-end Amazon sellers). Most places can custom make cables at the length you desire and install quality connectors of your choice. To show you the difference, using Times LMR-400 you'll have about the same loss for 100' as the RG-174 has in 10'. With a 40' piece (you'll want a little extra length - but not much - so you can work around duct work or other obstructions) you'll have less loss on your entire run that the Bingfu has in that 10' section.
Thank you for your extensive reply. I appreciate it a lot. I am an Aviation Enthusiast and I generally use the Air Band (108.0–136.9875 - Aircraft Band). The Antenna that I bought makes a huge difference. I am new to this hobby so some terms can confuse me. When using the Bingfu VHF UHF Scanner Antenna, the reception improves a lot. If you look at the below map, my apartment is a few miles from the ATC transmitter/receiver. When the aircraft is more than 120 miles away I do not hear the pilot however I hear clearly the ATC quite well. I need an antenna to pick aircraft conversation of more than 120 miles away.
 

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mmckenna

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The issue isn't your antenna. The issue is that the earth isn't flat, although there is a scary amount of people that want you to think it is.
Curvature of the earth gets in the way. Since VHF ~usually~ works by line of sight, once the aircraft is over the horizon, your chances of being able to reliably hear it will be greatly reduced.

The ATC gets around this by having many transmitters/receivers at various locations that give them a bigger view of the airspace. Those radios are linked back to the air traffic controllers and allow them to cover a much larger area than you will with one receiver at one location.

Since VHF is mostly line of sight, there really isn't a whole lot you can do. No amount of antenna is going to help you get a signal that just isn't there. You can raise your antenna up higher, but it takes a lot of height to overcome that curvature of the earth. Other option is to use a remote controlled receiver at a higher location.
 

david_lexicon

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The issue isn't your antenna. The issue is that the earth isn't flat, although there is a scary amount of people that want you to think it is.
Curvature of the earth gets in the way. Since VHF ~usually~ works by line of sight, once the aircraft is over the horizon, your chances of being able to reliably hear it will be greatly reduced.

The ATC gets around this by having many transmitters/receivers at various locations that give them a bigger view of the airspace. Those radios are linked back to the air traffic controllers and allow them to cover a much larger area than you will with one receiver at one location.

Since VHF is mostly line of sight, there really isn't a whole lot you can do. No amount of antenna is going to help you get a signal that just isn't there. You can raise your antenna up higher, but it takes a lot of height to overcome that curvature of the earth. Other option is to use a remote controlled receiver at a higher location.
Thank you for your extensive reply.

Below see photos. I have an antenna installed by Flightradar.com to track aircraft. If I attach my small antenna as per photos, is it ok?

Thanks.
 

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mmckenna

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Thank you for your extensive reply.

Below see photos. I have an antenna installed by Flightradar.com to track aircraft. If I attach my small antenna as per photos, is it ok?

Thanks.

You can certainly do that, but it's going to impact performance greatly.

Aviation VHF is vertically polarized, so you want your antenna vertical also. By mounting it horizontally like that, you are reducing your received signal by at least 30dB.
 

david_lexicon

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You can certainly do that, but it's going to impact performance greatly.

Aviation VHF is vertically polarized, so you want your antenna vertical also. By mounting it horizontally like that, you are reducing your received signal by at least 30dB.
I see. I have to place it somewhere else, in an upright position. Thank you so much for your feedback. Cheers.
 

mmckenna

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I see. I have to place it somewhere else, in an upright position. Thank you so much for your feedback. Cheers.

No problem, glad I could help.

Nice looking photos. I've never been to Malta, but it looks similar to some costal areas of California I travel through. Similar latitudes, similar topography.
 

david_lexicon

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Thank you for your compliment. Malta has the same climate like Los Angeles however we have a sea around us but California has ocean currents more powerful. California is also on a tectonic plate so it is very dangerous to live on such a shifting landmass. Between May and October is does not rain so we turn seawater into water by reverse osmosis. The water is not good for consumption: it is too heavy: it is 1200ppm. We use the water for laundry and cleaning. The water is not good for vegetation either. We live on a rock and try to survive.
 
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