Makeshift antenna

[Hawk77]

Can I hurt my handheld scanner by using a wire tied to the antenna it came with? Will it help my reception any? I have an old 20 foot tv antenna that I am thinking about hooking up a wire to and run to my scanner antenna ( the basic 6 inch one). Will it hurt it or do any good? Thanks.....


Hawk man

 

[kb5udf]

Can't Hurt

Neither experiment you propose will hurt your scanner. Generally, you can use just about anything you like as an experimental antenna for a receiver/scanner as long as it isn't hooked up to a transmitter, or the antenna isn't too close to something transmitting a significant amount of power.

So, got for it.

 

[SAR923]

It won't hurt it, assuming that lightning doesn't strike the TV antenna - I assume you are talking about a roof mounted antenna. You didn't mention the kind of scanner you have but most have an antenna connector. On a portable, it is the BNC connector the rubber antenna uses. On desktops, there is usually a BNC or Motorola plug in the back. You can certainly just get some alligator clips and clip it on the telescoping antenna. A better solution would be to connect the coax to the antenna connector on the radio. If the TV antenna only has twin lead, which is thin, flat wire with two wires on each side, it's probably a waste fo time since so much signal will be lost.

If you do a search here on TV antenna, you'll find several threads where people have dismounted the antenna and used a couple of U-bolts to reattach the antenna so it's vertical. Since most signals you want to listen to are vertically polarized, that gets the antenna in the right orientation. If you want to listen to mostly VHF and UHF frequencies, TV antennas mounted correctly and using decent coaxial cable like RG-6 can do a suprisingly good job. Whatever you do, make sure you have a good ground for the antenna before using it just in case you do get a lightning strike.

 

[Hawk77]

thx

Hey thanks for the great info on the antenna. Appreciated greatly.. : )

 

[prcguy]

If the TV antenna has twinlead, just use a standard 300/75ohm matching transformer and then adapt to BNC or whatever. 300ohm twinlead has much less loss than RG-6, especially under high VSWR conditions.
prcguy

It won't hurt it, assuming that lightning doesn't strike the TV antenna - I assume you are talking about a roof mounted antenna. You didn't mention the kind of scanner you have but most have an antenna connector. On a portable, it is the BNC connector the rubber antenna uses. On desktops, there is usually a BNC or Motorola plug in the back. You can certainly just get some alligator clips and clip it on the telescoping antenna. A better solution would be to connect the coax to the antenna connector on the radio. If the TV antenna only has twin lead, which is thin, flat wire with two wires on each side, it's probably a waste fo time since so much signal will be lost.

If you do a search here on TV antenna, you'll find several threads where people have dismounted the antenna and used a couple of U-bolts to reattach the antenna so it's vertical. Since most signals you want to listen to are vertically polarized, that gets the antenna in the right orientation. If you want to listen to mostly VHF and UHF frequencies, TV antennas mounted correctly and using decent coaxial cable like RG-6 can do a suprisingly good job. Whatever you do, make sure you have a good ground for the antenna before using it just in case you do get a lightning strike.

 

[SAR923]

Twinlead has less dB loss in signal reception than good coax? Do you have a source for that statement? Remember, we're talking about receiving here, not transmitting.

 

[prcguy]

Try this: http://www.ocarc.ca/coax.htm
300 ohm generic twin lead @ 1GHz is still showing less loss than even LMR-400. If you look at 450 ohm ladder line, which is typical for ham use it shows about 1.1dB loss at 1GHz for 100ft compared to about 4.1dB loss for the same length of Times LMR-400. This assumes radio, feedline and antenna are matched. If you type in say, a 10:1 mis-match then you can see how the open wire feedline contributes much less to the overall system loss than coax. The results are the same for transmitting or receiving. These on-line calculators are not exact when you introduce VSWR, but do give you a look at potential performance.
prcguy

Twinlead has less dB loss in signal reception than good coax? Do you have a source for that statement? Remember, we're talking about receiving here, not transmitting.

 

[bwhite]

I'll buy into the loss info but don't know where SWR comes into receiving.

 

[prcguy]

I’ll make a general statement, as many things can affect a radio/feedline/antenna setup. If you have some extreme VSWR between the feedline and antenna, lets say from trying to use a 300MHz mil aircraft radio with a 150MHz VHF hi band antenna, you will have additional loss over the published feedline loss and the loss from the antenna/feedline mis-match will be the same transmitting and receiving. Adding a mis-match between the radio (receiver or transmitter) and feedline adds a layer of complexity to figuring out the entire antenna system loss. The online calculator in my last post will show you some of the additional loss incurred from high VSWR on the feedline and remember, this holds true for TX and RX.
prcguy

I'll buy into the loss info but don't know where SWR comes into receiving.

 

[SAR923]

OK, then why do we all pay so much for good coax if cheap 300 ohm twinlead with a matching transformer will give better results than LMR-400 at 800 mHz, according to that calculator? Either there's something wrong with the way those calculations are done or we've all been fed a line of bull since the start of scanners.

 

[prcguy]

They also fed us a line of bull when they said CDs sound better than vinyl. TV twinlead or ladder line is not for everyone but it has its place and I use it all the time for various HF antennas. Coax is very easy to install compared to TV twinlead and coax will also last much longer. I have not personally found a need to use twinlead or ladder line in a VHF/UHF scanner or ham install yet but it could happen.
prcguy

OK, then why do we all pay so much for good coax if cheap 300 ohm twinlead with a matching transformer will give better results than LMR-400 at 800 mHz, according to that calculator? Either there's something wrong with the way those calculations are done or we've all been fed a line of bull since the start of scanners.