Do you think it is worth it to do this?
- Thread starter scubasky
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k5ttt
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- Jan 25, 2004
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Probably not. I think the Scantenna is unity gain, meaning it has no gain. So running something like RG-213 would give you a loss of more than 7db at 30MHz. At 800MHz, your loss would be greater than 44db. I think I would rather put a rubber ducky inside a coffee can and bury it 4 feet deep off the back porch!
Really though the cost of the coax could be much better spent on a high gain log periodic that covers 100MHz - 1000 MHz and installed above the roof.
If you were going to do it, I think you would really need to use something like 1 7/8" heliax (hardline) or larger, which is usually more than $5/foot. If you could find it at $5/foot that would be $3200 just for the coax.
Remember, that for every 3db in loss, your signal power is cut in half.
Here's a good online coax loss calculator.
http://www.ocarc.ca/coax.htm
Here's my dream scanner antenna.
M2 (M Squared)
100-1000VLP22 100-1000 MHz 7.5 dBI gain, 12 dB FB, 8’ mast.
http://www.m2inc.com/logs2.pdf
I know this doesn't help much but it does sound like an interesting idea.
Really though the cost of the coax could be much better spent on a high gain log periodic that covers 100MHz - 1000 MHz and installed above the roof.
If you were going to do it, I think you would really need to use something like 1 7/8" heliax (hardline) or larger, which is usually more than $5/foot. If you could find it at $5/foot that would be $3200 just for the coax.
Remember, that for every 3db in loss, your signal power is cut in half.
Here's a good online coax loss calculator.
http://www.ocarc.ca/coax.htm
Here's my dream scanner antenna.
M2 (M Squared)
100-1000VLP22 100-1000 MHz 7.5 dBI gain, 12 dB FB, 8’ mast.
http://www.m2inc.com/logs2.pdf
I know this doesn't help much but it does sound like an interesting idea.
As Tony Soprano would say... "Forget about it!" 
k5ttt
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- Jan 25, 2004
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That might be OK if he limited his listening to a single band. You can get excellent pre-amps that will not increase intermod but they are only good for a few MHz wide. A wideband preamp for 30-800 would be like a hoover vacuum cleaner and increase the amount of intermod and spurious emissions and wouldn't be fun to listen to.
BUT...
While we're thinking on this level (money is not an object), it would be possible to put separate pre-amps up the tower for each band. Then you build a relay system to switch between pre-amps. That would take quite a bit of current going up the tower to power the pre-amps and the relays, but that might be something that could be done. Switching the relays between pre-amps would be done in the shack. Then write the software that interfaces with the scanner to do the switching for you according to which channel/band is being monitored.
BUT...
While we're thinking on this level (money is not an object), it would be possible to put separate pre-amps up the tower for each band. Then you build a relay system to switch between pre-amps. That would take quite a bit of current going up the tower to power the pre-amps and the relays, but that might be something that could be done. Switching the relays between pre-amps would be done in the shack. Then write the software that interfaces with the scanner to do the switching for you according to which channel/band is being monitored.
jcmios
Member
If you use 9913 or LMR400 it would be well worth it, but keep in mind the cost per foot is $0.69 to $0.89 undelivered. I personally use 9913 in all my runs over 15 feet and find it to be easier to work with when it comes to soldering PL259 connectors then LMR400, both have solid center conductor but 9913 uses an air incorporated dielectric and the braid is a bit easier to solder IMHO. This is all I use for my Ham equipment and 3 scanner antennas as they have a 135+ foot run.
Height is almost everything and if you use the right coax or even better hard line you will reap the benefits.
Height is almost everything and if you use the right coax or even better hard line you will reap the benefits.
jonny290
Member
Remember, it's not 400 feet, it's 640 feet (let's say 650 after trimming). That's $600 for coax _alone_ and you're still going to have over 40 dB of attenuation at 860. Vote "no go".
Got 2k to spend? try this.
Figure out a way to get 120v power to the top of the tower safely and in accordance with building codes.
Put an Icom PCR1500, a laptop computer and an 802.11 wireless access card in a weatherproof box (edit: and I mean WEATHERPROOF), mount it all at the top of the tower and put a discone on top of the tower, connected to the radio.
Use Microsoft Remote Desktop (included with Windows) to access the laptop. Remote Desktop will stream audio to your PC in the shack and will let you view/control the laptop. (and thus, the receiver).
You'll hear _everything_.
Got 2k to spend? try this.
Figure out a way to get 120v power to the top of the tower safely and in accordance with building codes.
Put an Icom PCR1500, a laptop computer and an 802.11 wireless access card in a weatherproof box (edit: and I mean WEATHERPROOF), mount it all at the top of the tower and put a discone on top of the tower, connected to the radio.
Use Microsoft Remote Desktop (included with Windows) to access the laptop. Remote Desktop will stream audio to your PC in the shack and will let you view/control the laptop. (and thus, the receiver).
You'll hear _everything_.
Last edited:
jonny290 said:Remember, it's not 400 feet, it's 640 feet (let's say 650 after trimming). That's $600 for coax _alone_ and you're still going to have over 40 dB of attenuation at 860. Vote "no go".
Got 2k to spend? try this.
Figure out a way to get 120v power to the top of the tower safely and in accordance with building codes.
Put an Icom PCR1500, a laptop computer and an 802.11 wireless access card in a weatherproof box (edit: and I mean WEATHERPROOF), mount it all at the top of the tower and put a discone on top of the tower, connected to the radio.
Use Microsoft Remote Desktop (included with Windows) to access the laptop. Remote Desktop will stream audio to your PC in the shack and will let you view/control the laptop. (and thus, the receiver).
You'll hear _everything_.
Why 120V, when it could all be done with 12V?
jonny290
Member
GreatLakes said:
Well, I was thinking that I2R losses would be really bad, but my calculator shows that 240 feet of awg 10 has .75 volts of drop if the computer and radio draw 3 amps. So, we could probably put a 13.8 supply at tower bottom and feed it fine, maybe tweaking the voltage up a bit. Good call.
N
N_Jay
Guest
jonny290 said:Well, I was thinking that I2R losses would be really bad, but my calculator shows that 240 feet of awg 10 has .75 volts of drop if the computer and radio draw 3 amps. So, we could probably put a 13.8 supply at tower bottom and feed it fine, maybe tweaking the voltage up a bit. Good call.
You put the 12V regulator at the top and feed it with unregulated 15V.
Get really fancy with some 12V Gel-Cels, and a solar array to charge them.
jonny290
Member
yeah, that was the alternative. If you programmed the laptop's power management right, you could put it in low power standby when you're not using it, wake it up via the wireless LAN.
k9rzz
Member
It might be do-able if you could run CATV hardline. If you went with the 7/8 inch stuff or bigger it might be worth your while. The whole installation would be a chore, but the cable could be had for free with some scrounging.
FWIW.
John K9RZZ
FWIW.
John K9RZZ
jcecklund
Member
GreatLakes said:As Tony Soprano would say... "Forget about it!"
LOL I think that is exactly what he would say!! That is funny!
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