A Signal Problem...

[RANGERDALEXP]

I think these are the main questions as of now

1) Is there a advantage or a disadvantage between 50 ohm or 75 ohm on a receive only scanner set up?

2) Will using 75 ohm wire harm the radio gear?

3) Is RG 6 Quad better then RG 58u or Mini 8?

4) Will RG 6 quad cut down on the multi path problem due to it's superior shielding.

 

[W6KRU]

If you have a multipath problem, the coax isn't going to help. A yagi antenna might help.

 

[RANGERDALEXP]

If you have a multipath problem, the coax isn't going to help. A yagi antenna might help.

Multipath was a problem that was suggested. I do not think it could be that for these reasons listed prior.

1) The problem has never been there for the last year or so on the old antenna.
2) It only became a problem after several days of use on the new antenna in the same old location.
3) My radio guy says multi path it is unlikely because of my location. But who knows....

There is a 10 foot section that was replaced when the antenna was upgraded and I am thinking it is in the splice or the connector at the antenna itself. It was metered at the time of install but that does not mean it did not fail afterwards. If going up and dealing with this is what needs to happen, then it would be best to change the cable. Is there a problem using RG 6 or not, It seems to me there is some conflicting feelings now on this now.....

I do not mean to sound testy on this, I am just trying to get to the bottom of this and some of it don't make sense or not enough information on why....

 

[ridgescan]

I am following your thread and bottom line is you have a compromised coax situation-not only is it the 58u with the mediocre shielding-but I believe you said you spliced it along the run? That is causing a discontinuity in your run, as I have learned from this forum. That coax has to be solid from the radio to the antenna shielding wise AND no crimps either. I say bag that coax and run a nice clean line of the RG6 (a ton of guys here use it and love it) and do a good job on it and I bet your issue goes away.

 

[RANGERDALEXP]

I am following your thread and bottom line is you have a compromised coax situation-not only is it the 58u with the mediocre shielding-but I believe you said you spliced it along the run? That is causing a discontinuity in your run, as I have learned from this forum. That coax has to be solid from the radio to the antenna shielding wise AND no crimps either. I say bag that coax and run a nice clean line of the RG6 (a ton of guys here use it and love it) and do a good job on it and I bet your issue goes away.

I am 95% sure it is the cable run and that will be the plan next week to take care of. There was a lot of good suggestions on the problem at hand. Thanks and I will let you guys and girls know what the outcome is when it is completed.

Just for the question, What is the best all band Discone Antenna out there now days just in case I would like to change it down the road. I hate to buy a hunk of junk and waste money....

 

[ridgescan]

Diamond D-130J discone Product Reviews

 

[prcguy]

For some of the better made commercial Discones check out Kreco, Astron, Telewave and Hascall-Denke. These came to mind right away but there are many more.

If your looking at less expensive I think the Diamond D-130J is good choice over Radio Shack, Workman, Hustler (POS) and others.
prcguy

I am 95% sure it is the cable run and that will be the plan next week to take care of. There was a lot of good suggestions on the problem at hand. Thanks and I will let you guys and girls know what the outcome is when it is completed.

Just for the question, What is the best all band Discone Antenna out there now days just in case I would like to change it down the road. I hate to buy a hunk of junk and waste money....

 

[W4KRR]

I think these are the main questions as of now

1) Is there a advantage or a disadvantage between 50 ohm or 75 ohm on a receive only scanner set up?

2) Will using 75 ohm wire harm the radio gear?

3) Is RG 6 Quad better then RG 58u or Mini 8?

4) Will RG 6 quad cut down on the multi path problem due to it's superior shielding.

1. No disadvantage; no scanner will maintain a constant 50 ohm impedance over its entire frequency spread.

2. No.

3. Yes.

4. No.

If you have a lot of RG-6 lying around, then it won't cost you anything (or very much) to try it out. It will almost certainly be an improvement over any type of RG-58.

 

[nanZor]

I often visit a friend who is in between some multi-site LASD systems and have the same issue. If you stay up in the wee hours of the morning, you'll hear the system doing automated phase testing with tones. At least that is what I was told last time I was there.

It is very possible that the LASD system has changed their multi-site coverage a few days after your new install, and your new antenna has directional properties that make it worse than the old one. If LASD hasn't changed their site setups, it is possible that you are getting some new multipath from some other source out there - new buildings etc which your new antenna is sensitive to.

A directional antenna might help attenuate one of the sites more than the other to make things tolerable. In the past, I've successfully homebrewed UHF "half-squares" very easily to try and put one of the sites in the azimuth null. It doesn't always work depending on the location of the sites, but the half-square vertical is easy to make for permanent or portable work - although you will get some stares.

The half-square vertical is a broadside antenna, with nulls along the ends. Basically it is just phasing two 1/4 waves together, and fed at one corner. Quick example: Cut 6-inches of say #12 house wire. Attach this to the center conductor of the coax. Now cut 18 inches of wire and attach that to the shield. 12 inches away from the shield, bend 6 inches of this 18 inch wire upwards so that you have the two vertical elements in line with each other - ie a half-square shape. You can use it with the wires hanging down, or the wires facing upwards - your choice. Rotate in azimuth to try and put one of the systems into the null. I've used broomsticks for the boom. For best results, try to run the coax feedline straight away from the antenna for at least a few feet.

Forgot to mention that broadside, you'll get about 3 db gain over a single quarter wave vertical. But I think that for LASD, you'll be more interested in the sharp nulls.

Reference: ARRL handbook, 20th edition, Page 6-17. While they describe using it for low HF bands, it still works at UHF.

This might be a cheap and simple antenna for your LASD monitoring - although depending on the system, you may have to rotate it.

 

[jim202]

Let me jump in here and being a new comer to this discussion, I may have missed some of the very early comments. I could not find in the thread if the system your trying to monitor is a simulcast system or a system with a number of sites that you can hear. Either way, you would be wise to figure out which site is closest to you and use a directional antenna pointed toward that site.

If your also trying to listen to other agency systems with the same antenna, as long as you can hear them with the yagi, your OK. If not, then your SOL.

I have seen a number of dispatch centers that have their omni (not legal) antenna on the control radio they are using to get into the trunking system with mounted way up in the air. They are having the same issue with hitting too many of the sites. Yet a portable inside the dispatch center works just fine. As a suggestion, they were told to use a directional antenna mounted outside the window the coax was going through. To my knowledge, they still haven't done anything until snow sliding off the roof ripped the coax off the antenna on the peak of the roof. Since then they have been using an antenna mounted on the side of the building right by the window. Funny thing is their signal has improved greatly and they no longer have the digital warble you hear on your scanners at times.

 

[RANGERDALEXP]

Here is the update, I changed the cable and all of my problems have gone away. The system has never worked better, Now even though it is weak, I receive LAPD as well AS LASD mobile in units from lost hills which should be imposable from my distance and location. All my signals are way cleaner and stronger then ever and I can hear farther out...

I was a bit on the fence about the RG6 thing but I am now a believer. there is much less noise and I can use less SQ. I will never use RG58 for scanners ever again and thanks to all who helped, there was a lot of good information.....