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Scanner / Receiver Antennas For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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  #1 (permalink)  
Old 12-04-2012, 5:49 AM
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Post Scanner Antenna signal issues

Hello everyone! First time posting here, but I'm sure not the last!!

I currently have RadioShacks Outdoor VHF-Hi/UHF Scanner Antenna (Model: 20-176) and have in fact have had it for many years now..

Recently I've gotten into SDR and decided to give this antenna a try since I usually had good luck with previous scanners (older Uniden Bearcat)

Current equipment:
Newsky TV301U DVB-T USB (Realtek RTL2832U)
Basic RF Amplifier upto 1Ghz +24db
Radioshack scanner antenna (Model: 20-176)
RG-6 Coax cable

The problem I've ran into is this:
When I had the scanner antenna on a ~10' Coax wire, 8' off the ground using my camera tripod, signals were coming in nicely (respectively) and the background noise seemed quiet low..

The other day I put the scanner antenna up 32' using 3-10' 3/4" galvanized steal pipes and a 24" 3/4" PVC pipe which holds the antenna which then the PVC pipe screws into the metal pipe.

After setting it up, and running the software, the signals seem to be weaker, and there looks to be a lot more background noise..
Even on an FM radio station.. The station itself vers the background noise doesn't have much of a level difference.. When I had it on the 10' cable and my camera tripod for testing purposes, the difference in the signal and background noise was much better..

So what am I doing wrong? Is there a reason for the loss in gain and higher background noise?

Appreciate any help!
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Old 12-04-2012, 8:19 PM
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Quote:
Originally Posted by SirOaf View Post
Hello everyone! First time posting here, but I'm sure not the last!!

I currently have RadioShacks Outdoor VHF-Hi/UHF Scanner Antenna (Model: 20-176) and have in fact have had it for many years now..

Recently I've gotten into SDR and decided to give this antenna a try since I usually had good luck with previous scanners (older Uniden Bearcat)

Current equipment:
Newsky TV301U DVB-T USB (Realtek RTL2832U)
Basic RF Amplifier upto 1Ghz +24db
Radioshack scanner antenna (Model: 20-176)
RG-6 Coax cable

The problem I've ran into is this:
When I had the scanner antenna on a ~10' Coax wire, 8' off the ground using my camera tripod, signals were coming in nicely (respectively) and the background noise seemed quiet low..

The other day I put the scanner antenna up 32' using 3-10' 3/4" galvanized steal pipes and a 24" 3/4" PVC pipe which holds the antenna which then the PVC pipe screws into the metal pipe.

After setting it up, and running the software, the signals seem to be weaker, and there looks to be a lot more background noise..
Even on an FM radio station.. The station itself vers the background noise doesn't have much of a level difference.. When I had it on the 10' cable and my camera tripod for testing purposes, the difference in the signal and background noise was much better..

So what am I doing wrong? Is there a reason for the loss in gain and higher background noise?

Appreciate any help!
The loss rate will be higher with the longer runs of cable. With RG-6 it should be relatively low-loss though. Try taking the amplifier out of the mix. With it, you'll raise the "noise floor" which means you hear a bunch of scratch. Try taking it off and measure your results.

Last edited by Redneck0410; 12-04-2012 at 8:21 PM..
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Old 12-05-2012, 5:04 AM
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I tried bypassing the amplifier, but not much of a change(if any).. The noise floor just seems much higher then it should be.. That's the big issue.. It seems like we have doubled the noise floor by putting it up 30'.. I totally understand the principal behind long wire runs, but at 40' of good coax that would be really hard pressed.. hopefully, lol Also the antenna is FAR from anything as far as interference goes.. I believe the power lines are ~100' away, and are only smaller residential lines.

Anything else to try, double check that I might have missed?

This weekend, weather permitting, my buddy and I are going to mess around more with the antenna(move it around.. etc), and double check the connections while he's looking at the computer to see if there is a change..

I also plan on getting a new scanner antenna very soon. Either the ST2 or the ST4.. haven't made up my mind yet. Still doing my homework on 'em.
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Old 12-05-2012, 11:23 AM
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There are a 1001 possibilities here: I'd be looking firstly very carefully at all coax/connector interfacing (i.e. where one is joined to the other) at both the antenna end as well as the ground side - all you need is a couple of loose strands of inner core conductor to stray across to the outer braiding and you are going experience exactly what you have described. The addition here is the longer coax run - start off by conducting a continuity test across the inner conductor and outer braiding: any reading other than a very high Mega Ohm or infinity reading on the multimeter will need to be investigated.

How are you connecting this long coax run to the dongle - directly or with connector adapters of some kind?

Secondly, I'd be looking carefully at the overall software settings & configurations - are you absolutely certain some or other config/setting is or has not changed?

I have a Real USB dongle with an Elonics E4000 chip in it, have played around for many hours with the thing, and have spent many hours playing around with firmware, software patches and changing all orts of settings. One accidental click of the mouse can have a big impact on performance.

By the way - are you using your dongle as a receiver only or as a demodulator only, or are you undertaking both reception and demod tasks through the dongle?

What firmware version are you running, what freq/bandwidth and IF are you using, in short Sir Oaf, exactly how have you set things up computer/firmware and dongle side?
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Old 12-05-2012, 11:52 AM
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Quote:
Originally Posted by SirOaf View Post
I tried bypassing the amplifier, but not much of a change(if any).. The noise floor just seems much higher then it should be.. That's the big issue.. It seems like we have doubled the noise floor by putting it up 30'.. I totally understand the principal behind long wire runs, but at 40' of good coax that would be really hard pressed.. hopefully, lol Also the antenna is FAR from anything as far as interference goes.. I believe the power lines are ~100' away, and are only smaller residential lines.

Anything else to try, double check that I might have missed?

This weekend, weather permitting, my buddy and I are going to mess around more with the antenna(move it around.. etc), and double check the connections while he's looking at the computer to see if there is a change..

I also plan on getting a new scanner antenna very soon. Either the ST2 or the ST4.. haven't made up my mind yet. Still doing my homework on 'em.
If I were you from my expierence, Im in a wood area with woods from 15 ft front and left side of my house, to 50ft on right and about 200 or so to the back. I had the ST4 discone, witch I call the sputnik, and the ST2 when I got it was by far better, I also have the 20-176 for a storm antenna in line with the peak, its actually off a stink pipe out of the roof and on it with a little pipe about 5 ft tall or so, so if storms come I can unplug from the higher antennas and plug into that one. But all in all Ive had all 3, and in my expierence the ST2 is way better, I could pick up all stations I had previously with at least 1 or 2 signal bars better then the ST4. Hope we can help you LOVE AND BLESSINGS
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Old 12-06-2012, 5:14 AM
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Thanks for all the info Benbenrf!

As far as how everything is connected:
Coax directly connected to the PL-259 connector; Soild connection all the way to an F male connector
Into the amp, then the amp into the USB device. Amp to the USB is a 3' coax cable.

Nothing else, and I'm using the dongle as the tuner.(if i understand you correctly) No other modulator.. yet!

I will triple check all the connections, and mess around with the software too.
Software is SDRSharp v1.0 As far as firmware, and all the other details, I'll have to get back to you.

-- wingmaker--

Thanks for the antenna info! I've often seen people more in favor for the ST2, and I think I've had my thoughts flipped to the ST2.
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Old 12-07-2012, 2:27 PM
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As a tuner only - meaning: just to tune into the rf signal frequency but not to undertake any demodulation. Yes, that is what I meant.

I think the concensus on the forum is that the ST2 is a pretty good wide-band antenna - better than a discone. I have never been a fan of any wide band antennas personally. I do use cone type antennas (e.g. discone, bicone, inverted cone etc etc .....) but when building one, will restrict dimensions to around 200Mhz - 250Mhz bandwidth. The result is if I want to cover 1Ghz I land up with around 4 or 5 antennas!

If you are confident that your coax/connector integrity is solid all the way from the antenna to the dongle, then I'm pretty sure you're going to find the solution in one or other of the software settings.

Let us know how things go.
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Old 12-08-2012, 12:07 PM
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Quote:
Originally Posted by SirOaf View Post
Thanks for all the info Benbenrf!

As far as how everything is connected:
Coax directly connected to the PL-259 connector; Soild connection all the way to an F male connector
Into the amp, then the amp into the USB device. Amp to the USB is a 3' coax cable.

Nothing else, and I'm using the dongle as the tuner.(if i understand you correctly) No other modulator.. yet!

I will triple check all the connections, and mess around with the software too.
Software is SDRSharp v1.0 As far as firmware, and all the other details, I'll have to get back to you.

-- wingmaker--

Thanks for the antenna info! I've often seen people more in favor for the ST2, and I think I've had my thoughts flipped to the ST2.
Cool, whatever works best for you Brother, Good Luck

LOVE AND BLESSINGS
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Old 12-23-2012, 8:28 AM
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Alright.. The issue was a bad ground(not sure how I messed that one up, yes.. I've disciplined myself already! ). But after getting the antenna properly grounded, we have decreased the noise floor by about 25db's!! MUCH better!!

We also got the FUNCube Dongle, and that has made a HUGE difference!!

We also built a 30'x30' (15'x4 'x') antenna for shortwave, and have been listening to shortwave radio stations from china, Netherlands, and Spain. SO much fun!!

ST2 has been ordered, and it on the way!!

One question.. We'd like to have both the ST2 and the home made shortwave antenna hooked up to the FUNCube.. Can we "y" them together, or can we perhaps just make an "a/b" switch(which would be hard)
Is it possible to "Y" both antennas together?
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Old 12-24-2012, 9:47 PM
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Quote:
Originally Posted by SirOaf View Post
just make an "a/b" switch(which would be hard)
I meant to say "wouldn't be hard"

Couldn't figure out how to 'edit' my post.. didn't see an option.. :P
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Old 12-25-2012, 3:27 PM
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Quote:
Originally Posted by SirOaf View Post
Thanks for all the info Benbenrf!

As far as how everything is connected:
Coax directly connected to the PL-259 connector; Soild connection all the way to an F male connector
Into the amp, then the amp into the USB device. Amp to the USB is a 3' coax cable.

Nothing else, and I'm using the dongle as the tuner.(if i understand you correctly) No other modulator.. yet!

I will triple check all the connections, and mess around with the software too.
Software is SDRSharp v1.0 As far as firmware, and all the other details, I'll have to get back to you.

-- wingmaker--

Thanks for the antenna info! I've often seen people more in favor for the ST2, and I think I've had my thoughts flipped to the ST2.
According to that,you have the amp on the wrong end of the coax. The amp should be at the antenna if you are going to use one. with it at the dongle end you are amping the noise the coax is picking up.
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