Coax Jumper Cable

[mikec10]

About 8 months ago I purchased a SDS200 scanner after owning a SDS100 scanner. Very pleased with the unit. I installed my antenna in my attic and attached them with 100 feet of LMR400 coax cable. I was pleased the results, but the stiffness of the coax cable restricted me on placement of the scanner. I was able to receive transmissions from 30 plus miles away which was my goal, and I did not have to worry about the antenna outside in weather. If it were outside above the roof line it would be 3 stories up and I am too old to make that trip. Anyway, I just purchased a 3-foot jumper cable with BNC male and female to put in line with the LMR400 coax and attach to the scanner so I would have more flexibility with placement of the scanner. I was not sure if it would affect the reception or not. I was very surprised, and I checked the results more than once. The reception is better based on the RSSI meter. Not sure why. I purchased the LMR400 from ScannerMaster and per the description it is copper coated aluminum wire, and the jumper is solid copper wire. The jumper is RG8X. Any thoughts on why reception might be better. Again, I have rechecked this more than once. Thank you for any thoughts.;

 

[Ubbe]

You can't trust the RSSI level from a SDS scanner. It is impacted from adjacent frequencies and the automatic power control, that the receiver IC has, reduces sensitivity when it sees a too high level of signals even 7MHz away that could cause overload issues. The more interferences you have the more the signal strength will change from the true value of the frequency you monitor. A little attenuation will reduce the interference and other signals might then be below the level where the power control starts to engage and it will start to show a better signal strength.

RSSI in SDS scanners

/Ubbe

 

[mikec10]

Not disagreeing on what you are saying. When I installed the jumper, I instantly noticed a difference. I thought I was Imagining the difference. I rechecked certain frequencies (VHF) several times and the same results. Then I went to the NOAA weather stations and picked a distant frequency that barely registered on the RSSI and no signal strength on the signal meter. I put the jumper on and a very solid increase on both meters. I am quite happy with the unexpected results, and it is consistent.

 

[Ubbe]

I always recommend to use a variable 0-20dB attenuator on the coax when using external antennas. That way you can change the signal level and see if the signal improves when reducing the signal, that indicates an overload issue. SDS scanners are very suspect to be impacted from signals many MHz away due to the hardware being used.

/Ubbe