R11 vs R6 coax

[mikec10]

I had 100 feet of r6 coax for my SDS200 antenna connection. I took 20 feet off and reconnected. It appears that my analog reception is better but my disital is reduced. I was going to replace the coax but wondering if r11 would be better than r6. I was going back to the 100 foot length. I reduced the r6 thinking I would improve the digital reception. Most of my listening is digital. I am receiving close signals but distant is all but gone. I redid the connection twice on the f connection.

 

[kb5udf]

Fundamentally, the coax does not care if a signal is digital or analog, so that is not your problem. Assuming a perfect piece of r6 connected to an antenna perfectly terminated, shortening said piece of coax should ultimately deliver more signal to the receiver from the antenna, but in this case the difference should be minor going from 100 feet to 80 feet.

If reception of something is worse, with presumably more signal, that suggests some type of undesired signal is getting in.

Are you digital and analog signals in different bands?

 

[prcguy]

CATV/satellite type RG-11 has close to half the loss of RG-6, for example at 450MHz RG-6 has about 4.7dB loss/100ft where RG-11 is 2.9dB loss.

 

[mikec10]

Yes. Analog is VHF and digital is P25 850-860mhz. Was not expecting this result.

 

[mikec10]

CATV/satellite type RG-11 has close to half the loss of RG-6, for example at 450MHz RG-6 has about 4.7dB loss/100ft where RG-11 is 2.9dB loss.

I have heard that but was wondering with actual application if this would work better....I thought shortening the coax would work better

 

[prcguy]

I have heard that but was wondering with actual application if this would work better....I thought shortening the coax would work better

Loss is loss, you can eliminate some by shortening your coax or going with a lower loss coax or use a shorter run of lower loss coax for the most benefit.

 

[mikec10]

Loss is loss, you can eliminate some by shortening your coax or going with a lower loss coax or use a shorter run of lower loss coax for the most benefit.

yeah I know or I think I do. I will monitor my scanner for the next couple of days and see what happens. I believe I will be using r11 quad sheild as a replacement. Subject to change.......

 

[paulears]

Shortening the cable reduces cable losses. That's it. As said above, any other changes are perhaps to do more with things more weird.

There is a chance that the digital receiver is being impacted by the increase in strength of an interfering signal in the UHF band. with digital the receiver is only interested in the ability the receiver has to determine a 0 from a 1, hence why signal strength changes in digital systems are often masked - you can use an attenuator to demonstrate that a particular path from source to you is solid, or in the no mans land where it's only 'just' good. Add 3dB and it may disappear. You have no way of telling the 'goodness' of a digital link without other equipment. It's feasible that a signal that is going to create interference products could be destructive if your receiver gets impacted. So a lower wanted signal could be messed up by the presence of the other. That's possible but a bit rare. How are you judging the digital loss? A number of different sources and one or two no longer there? 100 ft of cable at 800MHz is lossy - that's just how it is. cutting loss with a shorter cable should not make digital worse unless something else is happening? Do you have an SDR where you could see what is coming down the cable? This may help?

 

[prcguy]

yeah I know or I think I do. I will monitor my scanner for the next couple of days and see what happens. I believe I will be using r11 quad sheild as a replacement. Subject to change.......

Quad shield has the same loss as single shield, no reason for it unless your bundling a lot of coax tightly together with high level signals.

 

[KevinC]

Cutting off 20’ of RG-6 gives about 1 dB less loss at 700, so I doubt reducing the length made an appreciable difference.

 

[mikec10]

I believe my main source of loss is at the new fitting at the end of the coax. I tried twice with a compression fitting as instructed but I felt the signal was less based on the strength meter and rssi reading on the scanner. Also the one county that is over 30 miles away I lost everything. They are simulcast for Fire EMS and PD. Prior to me cutting the coax I could get a signal of 2 bars and transmission was clear. Now nothing. Other closer simulcast counties that are closer I can receive but not as strong signal. At this point I think it would be easier to replace the coax and leave it at 100 feet and going to r11 which is less loss.

 

[wtp]

the thing about simulcast is that if you can receive more than one tower, the signal can be cut out.
i should know as that is what happens to me.

 

[Low-Band]

I will agree that RG11 has less attenuation than RG6, but I would be more concerned about the loss due to impedance mismatch.

RG6 and RG11 are 75 ohm impedance.
I'm not sure about your antenna, but the SDS200 is 50 ohm impedance.

Each time there is an impedance mismatch, more attenuation will be experienced. 75ohm <> 50ohm. If your antenna is 50ohm impedance, then you have 2 points of impedance mismatch.

Before you invest in new RG11, I would recommend you look at 50 ohm impedance coax such as LMR400. LMR400 is 50ohm impedance, and has similar attenuation as RG11.

Just my 2 cents.

 

[TexScan780D]

Yes. Analog is VHF and digital is P25 850-860mhz. Was not expecting this result.

VHF can be Analog or P-25 Digital.

 

[mmckenna]

I will agree that RG11 has less attenuation than RG6, but I would be more concerned about the loss due to impedance mismatch.

RG6 and RG11 are 75 ohm impedance.
I'm not sure about your antenna, but the SDS200 is 50 ohm impedance.

Each time there is an impedance mismatch, more attenuation will be experienced. 75ohm <> 50ohm. If your antenna is 50ohm impedance, then you have 2 points of impedance mismatch.

Before you invest in new RG11, I would recommend you look at 50 ohm impedance coax such as LMR400. LMR400 is 50ohm impedance, and has similar attenuation as RG11.

Just my 2 cents.

The slight impedance mismatch is going to amount to tenths of dB.

However, since we don't know what kind of antenna the OP is using, and unless it is tuned correctly, it's probably not a perfect 50Ω.
And I doubt the scanner is 50Ω across its full range of coverage.

80 feet of RG-6 will have about 7dB of loss at 850MHz
80 feet of RG-11 will have about 3dB of loss at 850MHz
So, even if they did change, there's going to be a substantial improvement in performance, even with a slight impedance mismatch.

 

[prcguy]

The slight impedance mismatch is going to amount to tenths of dB.

However, since we don't know what kind of antenna the OP is using, and unless it is tuned correctly, it's probably not a perfect 50Ω.
And I doubt the scanner is 50Ω across its full range of coverage.

80 feet of RG-6 will have about 7dB of loss at 850MHz
80 feet of RG-11 will have about 3dB of loss at 850MHz
So, even if they did change, there's going to be a substantial improvement in performance, even with a slight impedance mismatch.

When feeding resistive loads a 50 to 75 ohm mismatch can be just a few tenths of a dB. When resonant antennas or L/C components are involved the loss can be all over the place with the length of the 75 ohm cable becoming an impedance transformer and the resulting impedance extremes being much greater.

 

[Kiniutech]

Check this
Coax Attenuation Chart
and this
Coax Calculator

 

[trap5858]

Is it possible you have a bad connector or possibly a short?

 

[mikec10]

Well I feel silly or stupid or both. After I attached the fitting on the cut end of the coax that I did not shield the end where the f fitting and the bnc adapter is. I wrapped a couple of layers of electrical tape and there was a big difference. Not sure if there is anything else to shield the end better. But it appears my signal is stronger and clearer. If I can do more to shield the end I am open to suggestions. I never did like to cut coax.

 

[dlwtrunked]

If I am reading correctly, you really need to read how to properly install the connector. There is no leeway for doing it wrong, and if adding electrical tape helped, you did it wrong. Taking the time to do it right can make a huge difference.