Scanners & Discone Question

[slowbob]

Hello, I have a perplexing question pertaining to my scanners and antenna & cable. At present I have both a Pro-433 and just recieved a GRE PSR-600 because the area is switching some agencies to digital. My antenna is a discone WBD-40 and 100 ft of RG58/U which has been working great with the PRO-433 with no problems what so ever, I am picking up stations 60 miles away, I can even pick up airband out of Minneapolis MN from Duluth MN. Now here's the wierd part, When I hook my PSR-600 to the antenna using the same connectors and cable I get VERY POOR reception, and it will NOT pick up ANY OF the digital signals at all, but if I remove the cable, attach the indoor antenna that came with it, it will pick up those signals, not the best but it does pick them up, the discone does not. I am seriously thinking of buying a new antenna maybe an ST2 from Antennacraft, along with 100ft of LMR400 cable. At present I have my PSR-600 sitting in the window to recieve transmissions, but this is not where I need the scanner to be located,it needs to be in the computer room, ANY IDEAS?

 

[jackj]

I think your problem is your feed line. You don't mention the frequencies you can and those you can't pickup but 100 ft of RG58 is going to have a LOT of loss at anything above about 30-50 Mhz. As the frequency goes up, the loss will also go up.

Coax Cable Signal Loss (Attenuation) in dB per 100ft*
Loss* RG-174 RG-58 RG-8X RG-213 RG-6 RG-11 RF-9914 RF-9913
1MHz 1.9dB 0.4dB 0.5dB 0.2dB 0.2dB 0.2dB 0.3dB 0.2dB
10MHz 3.3dB 1.4dB 1.0dB 0.6dB 0.6dB 0.4dB 0.5dB 0.4dB
50MHz 6.6dB 3.3dB 2.5dB 1.6dB 1.4dB 1.0dB 1.1dB 0.9dB
100MHz 8.9dB 4.9dB 3.6dB 2.2dB 2.0dB 1.6dB 1.5dB 1.4dB
200MHz 11.9dB 7.3dB 5.4dB 3.3dB 2.8dB 2.3dB 2.0dB 1.8dB
400MHz 17.3 B 11.2dB 7.9dB 4.8dB 4.3dB 3.5dB 2.9dB 2.6dB
700MHz 26.0dB 16.9dB 11.0dB 6.6dB 5.6dB 4.7dB 3.8dB 3.6dB
900MHz 27.9 B 20.1dB 12.6dB 7.7dB 6.0dB 5.4dB 4.9dB 4.2dB
1GHz 32.0dB 21.5dB 13.5dB 8.3dB 6.1dB 5.6dB 5.3dB 4.5dB
Imped 50ohm 50ohm 50ohm 50ohm 75ohm 75ohm 50ohm 50ohm

I hope the tabs reproduce okay.

This table will give you some idea of how cable length and frequency affect loss.

Discone antennas do not have gain at any frequency but the have some saving graces. They maintain a feed-point impedance reasonably close to 50 ohms across their entire frequency range. They also are resonate across a very wide frequency range. There are other antennas that will work just as well but you always have trade offs when you try to get a wide frequency range out of an antenna.

 

[chrislxq]

Scanner & Discone Question

My first thought to impove your conditions, is to change the cable to LMR 400. The well grounded discone antenna may not be the problem, but it is also better to use an antenna dedicated for the band you want to receive. A discone has some compromise. I have also used a simple in-line amp to improve my discone.

 

[nd5y]

When I hook my PSR-600 to the antenna using the same connectors and cable I get VERY POOR reception

It is probably being overloaded and desensed by strong signals on the outdoor antenna. Using the attenuator might help. GRE is infamous for oversensitive receivers that are easily wiped out by strong signals. If you can determine what is causing it (FM broadcast or cellular for example) you can filter it out. Otherwise there is not much else you can do.

 

[slowbob]

Thanks to all who replied, the frequencies this is affecting is the145 -174 Range, what's weird is the pro 433 can recieve the digital signal,(not decoded of course) but the psr-600 never sees it on that same antenna. I don't believe I am recieving any Stronger than normal signals as I live in the country, the tower which broadcasts both analog and digiatal on the same frequency is located about 8 miles from me. To better describe my problem let me say that on the pro-433 with the same coax and same antenna everything is fine, but when I switch radios, the signal becomes weak from many stations and does not even hear the digital signal being broadcast just 8 miles away. The digital signal is being broadcast on the same old frequency that the analog used to be on, if fact they still switch back and forth on occation.

 

[tcomm_specialist]

Is it possible that you somehow activated the attenuator setting on the PSR-600???

 

[slowbob]

PSR600 & Discone

My first thought to impove your conditions, is to change the cable to LMR 400. The well grounded discone antenna may not be the problem, but it is also better to use an antenna dedicated for the band you want to receive. A discone has some compromise. I have also used a simple in-line amp to improve my discone.

Thanks for your reply, I know that what I have going on for coax is sub standard, so I am going to go that route first, replace it with LMR-400 If that's not it, I am going to try a relocate of the antenna itself, although I don't believe that's the problem, it might do the trick. Last but not least, I guess I will have to try a different antenna.

 

[slowbob]

Discone and PSR-600

It is probably being overloaded and desensed by strong signals on the outdoor antenna. Using the attenuator might help. GRE is infamous for oversensitive receivers that are easily wiped out by strong signals. If you can determine what is causing it (FM broadcast or cellular for example) you can filter it out. Otherwise there is not much else you can do.

I kind of replied to your suggestion I believe in another post by saying I don't believe that I am being overloaded by any other transmissions, however a thought just occured to me, I have a Davis Vantage Vue wireless weather system on that same mast, is it possible this is my problem?

 

[nd5y]

I kind of replied to your suggestion I believe in another post by saying I don't believe that I am being overloaded by any other transmissions, however a thought just occured to me, I have a Davis Vantage Vue wireless weather system on that same mast, is it possible this is my problem?

It might be. Does it transmit continuously? Turn it off and see if the problem goes away.
A low power transmitter just a few feet away can be much stronger than a high power transmitter several miles away.

 

[eaf1956]

Desense

It might be. Does it transmit continuously? Turn it off and see if the problem goes away.
A low power transmitter just a few feet away can be much stronger than a high power transmitter several miles away.

I had desense on my 996XT when I transmitted on 2 meters and the antenna are like 20 feet apart. I had to change the scanner to a 800 Mhz Yagi and get rid of the VHF-UHF Omni. No biggie as most traffic here is 800 Mhz trunked systems.

 

[slowbob]

PSR600 & Discone

Is it possible that you somehow activated the attenuator setting on the PSR-600???

After your reply it got me thinking about the attenuator setting, and this is what I discovered, although my coax and antenna do play a part, so does this attenuator setting, what I found was that some stations, need it turned on to receive them and some stations do not, so I have been listening to one scanner in the backround and seeing if the new one needs the attenuator setting turned on or off, this has been working, but is a long process. Thank you for your input, I would not have thought about this setting otherwise. So after playing with this setting, I am NOW ABLE to receive the stations I was previously having trouble with, however I already ordered new LMR-400 coax and a new Antenna.....oh well I will but both to good use!