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VHF portable helical antenna loss

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radioman2001

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I went looking for this same information some years back and I looked through all my posts but see they start at April 2019. Someone here provided a white paper with this information that basically showed there is roughly a -9db difference between a portable helical VHF and a 1/4 wave or isotropic antenna. Does anyone have this document? I believe Mother M was the publisher.
 

RFI-EMI-GUY

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I went looking for this same information some years back and I looked through all my posts but see they start at April 2019. Someone here provided a white paper with this information that basically showed there is roughly a -9db difference between a portable helical VHF and a 1/4 wave or isotropic antenna. Does anyone have this document? I believe Mother M was the publisher.
You should find a link here:

 

William2910

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If used inside the well placed repeater coverage you'd not have issues I recall. Outside or areas of question, shadows from the repeater it was a all or nothing I remember on them.

I can say on a well placed voting multi site system they work fine but anything else seemed questionable.
 

radioman2001

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Wow this is even better than the last paper.
I will give you little background in what I am doing, I work for a state agency and with the last testing I did back in 2011 we were looking for loss factors due to belt mounted VHF HT-1250 radios inside railroad tunnels. We had numerous incidents where signal men were unable to talk to the rail controller in the middle of the tunnel even though it is only 1/4 mile long and the base was only 1/2 mile away, but offset by 50 yards from the mouth. VHF realy doesn't like tunnels, and the testing wasn't totally scientific, but we took DAQ reading (I know not very scientific) every 10 ft on the hip and at mouth level and even closer in the problem area. Then facing in 0,90,180,270 degrees from the end of the tunnel, but this gave us enough information for us to issue 5/8 wave antenna's like the EXH160 made by Laird. Which corrected the problems at this location.
Now this new testing is a little more intense and is scientific, we use EDX software to plot our systems coverage, and we are trying to determine the loss factors from inside a moving revenue car to a base station up to many miles away. I knew I had the original document that I believe was from Motorola, but cannot find it, and I basically remember a loss factor of -9db over isotropic.
This time for testing we are going to use 3 stationary Anritsu 410's outside the car located facing in the middle and at each end while we walk back and forth with a hip mounted portable transmitting 1k tone for a relative Sinad measurement and RSSI. This test will be run staticly in a yard clear of other cars on both sides, and many times to come up with an average that we will use as an offset against measurements taken outside the car.
As far as I can see this is the first time someone has tried to get such an offset on VHF for rail cars at least.
 

Ubbe

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Stockholm subway used to be on VHF 166MHz and when they started using radio in the 50's they did extensive tests in the tunnels. They had directional antennas at the tunnel wall and that worked fine for the drive when approaching the antenna but when he passed the antenna it was some 5-6 rail cars that filled up the tunnel between him and the antenna and all that metal killed the RF signal. You could forget about using a portable radio.

They had two guys with portable radios standing on the tracks in a tunnel and where not so far apart, they could still see each other, but the radio where unusable. Perhaps there where too much metal in the bedrock and where magnetic or something as the signal died very quickly.

They then installed leaky coax antennas along the tunnel walls and never had any problems since then and could also use portable radios, that the security personel use inside the rail cars. They still use that type of antenna today with their more modern 400MHz tetra system.

/Ubbe
 

radioman2001

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I am very familiar with tunnels and VHF I did similar studies at another tunnel of ours that's 1 mile long, and after only 100yds you could see and speak to the other person, but no VHF radio would work. I also brought along some UHF (470 mhz) radios and they worked perferctly along the whole length and even out the farside. That tunnel now has 2 passive repeater antenna radiax systems in it a 220 mhz for PTC and the 160 mhz for voice.
I have a white paper that actually describes that based on the radius of the tunnel it causes certain frequencies to negate or cancel out themselves.
Before there were radiax cable systems New York City Transit in the early 60's had custom made 300ohm ladder line. It was 2 #10 ga wires suspended in a 2 in Teflon type plastic sheath (To prevent adding to a fire load) manufactured in a nearby state. The 300 to 50 ohm baluns were iron cores wrapped with the #10 wires to make the impedance correct and all placed inside a Teflon type plastic 6 in by 2 ft tube. Most of that system was replaced in the 80's when I was there working for a contractor.

Quote"
Maybe use a repeater and radiax coax?

We could,but a little expensive just to cover a 1/4 mile tunnel. We could have just duplicated the PD by putting another station in the tunnel. Now we get into operator error for not choosing the right site since it is at the merger of a couple of lines, and we don't do voting systems. For rail and aircraft KISS is the best solution.
We ended up splitting the power output from the 1/2 mile away site and adding a 5 element beam that reflected the signal off one of the walls. Compensated the power loss due to the split, and that with the better portable antenna solved 99% of the issues.
 
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RFI-EMI-GUY

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Radioman;
I would very much like a copy or link to your paper dealing with tunnel radius. I am actually at this instant, working on a project where the tunnel is actually a complete radius (ring) and am curious to about unaided simplex propogation, even though this will likely be a "radiax" project. This project is public safety grade so we add a DAQ factor above receiver noise floor (EIA/TSB-88D) to assure a DAQ3.4.

Another thing I am finding is that whereas coupling loss used to be specified by cable manufacturers at 20 feet, it is now 6.5 ft (2 meters) due to some Eoropean spec. So for my 16.5 ft tunnels, I have to figure out how to extrapolate another 10 feet coupling loss (UHF) .

I am very familiar with tunnels and VHF I did similar studies at another tunnel of ours that's 1 mile long, and after only 100yds you could see and speak to the other person, but no VHF radio would work. I also brought along some UHF (470 mhz) radios and they worked perferctly along the whole length and even out the farside. That tunnel now has 2 passive repeater antenna radiax systems in it a 220 mhz for PTC and the 160 mhz for voice.
I have a white paper that actually describes that based on the radius of the tunnel it causes certain frequencies to negate or cancel out themselves.
Before there were radiax cable systems New York City Transit in the early 60's had custom made 300ohm ladder line. It was 2 #10 ga wires suspended in a 2 in Teflon type plastic sheath (To prevent adding to a fire load) manufactured in a nearby state. The 300 to 50 ohm baluns were iron cores wrapped with the #10 wires to make the impedance correct and all placed inside a Teflon type plastic 6 in by 2 ft tube. Most of that system was replaced in the 80's when I was there working for a contractor.

Quote"
Maybe use a repeater and radiax coax?

We could,but a little expensive just to cover a 1/4 mile tunnel. We could have just duplicated the PD by putting another station in the tunnel. Now we get into operator error for not choosing the right site since it is at the merger of a couple of lines, and we don't do voting systems. For rail and aircraft KISS is the best solution.
We ended up splitting the power output from the 1/2 mile away site and adding a 5 element beam that reflected the signal off one of the walls. Compensated the power loss due to the split, and that with the better portable antenna solved 99% of the issues.
 

radioman2001

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I can't find the one by a Russian team I sent to a contractor of ours doing GCT and subway tunnels years ago, but I did find some others.






There a lot more, and I have not read these.
Have fun.
 

prcguy

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A tunnel at VHF or UHF will act like waveguide but a tunnel for vehicles will be very large in wavelengths and multiple modes will propagate along the tunnel with signals arriving in phase and out of phase at any given point with huge peaks and nulls. I'm not surprised you can see someone in the tunnel and not talk to them on a radio.

I am very familiar with tunnels and VHF I did similar studies at another tunnel of ours that's 1 mile long, and after only 100yds you could see and speak to the other person, but no VHF radio would work. I also brought along some UHF (470 mhz) radios and they worked perferctly along the whole length and even out the farside. That tunnel now has 2 passive repeater antenna radiax systems in it a 220 mhz for PTC and the 160 mhz for voice.
I have a white paper that actually describes that based on the radius of the tunnel it causes certain frequencies to negate or cancel out themselves.
Before there were radiax cable systems New York City Transit in the early 60's had custom made 300ohm ladder line. It was 2 #10 ga wires suspended in a 2 in Teflon type plastic sheath (To prevent adding to a fire load) manufactured in a nearby state. The 300 to 50 ohm baluns were iron cores wrapped with the #10 wires to make the impedance correct and all placed inside a Teflon type plastic 6 in by 2 ft tube. Most of that system was replaced in the 80's when I was there working for a contractor.

Quote"
Maybe use a repeater and radiax coax?

We could,but a little expensive just to cover a 1/4 mile tunnel. We could have just duplicated the PD by putting another station in the tunnel. Now we get into operator error for not choosing the right site since it is at the merger of a couple of lines, and we don't do voting systems. For rail and aircraft KISS is the best solution.
We ended up splitting the power output from the 1/2 mile away site and adding a 5 element beam that reflected the signal off one of the walls. Compensated the power loss due to the split, and that with the better portable antenna solved 99% of the issues.
 

RFI-EMI-GUY

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I can't find the one by a Russian team I sent to a contractor of ours doing GCT and subway tunnels years ago, but I did find some others.






There a lot more, and I have not read these.
Have fun.
Thanks! In my reading of manufactures specs, I did find how to extrapolate the radiating cable coupling loss to a distant point, basically 20Log (n/2) where n is the desired distance in meters and 2 is the coupling loss in meters.
 

DeoVindice

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I can't find the one by a Russian team I sent to a contractor of ours doing GCT and subway tunnels years ago, but I did find some others.






There a lot more, and I have not read these.
Have fun.
I'm working on a project that will eventually require a leaky feeder radio system, so thank you for the links - I have some reading to do. It will be the primary method of surface-underground communication, with Femco mine phones as a backup.
 
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