Which coax for an 800Mhz passive repeater?

nmfire10 · Post by **nmfire10** » Sat Jun 25, 2005 9:23 pm

I'm going to be putting a passive repeater on my house. I am reasonably confident it will work. No signal in the house. One or two bars standing on the roof. Should be even better on the mast 25' above the roof. I'm planning on a 10.2db 7-Element yagi pointing at the tower and some kind of indoor panel antenna. Coax length should only need to be about 40-50' at the most.

What kind of coax should I be using for this. Obviously the lower the loss, the better but I also need to be practical. Would something like LMR600 work?

Jim202 · Post by **Jim202** » Sun Jun 26, 2005 5:01 am

Use the best coax you can aford and still be able to install. Don't get your hopes up too high. You may not like the results you get when your all done with the hard work.

Jim

[quote="nmfire10"]I'm going to be putting a passive repeater on my house. I am reasonably confident it will work. No signal in the house. One or two bars standing on the roof. Should be even better on the mast 25' above the roof. I'm planning on a 10.2db 7-Element yagi pointing at the tower and some kind of indoor panel antenna. Coax length should only need to be about 40-50' at the most.

What kind of coax should I be using for this. Obviously the lower the loss, the better but I also need to be practical. Would something like LMR600 work?[/quote]

nmfire10 · Post by **nmfire10** » Sun Jun 26, 2005 6:08 am

Yea, I've read enough of the passive repeater threads on here to know that it might just not work. We'll see.

RKG · Post by **RKG** » Sun Jun 26, 2005 12:14 pm

We made one that required a 75' feedline (first floor comm room to roof of 3-story muni building); used 1/2" Heliax (since we had extra feeds to the roof) and it works: we can now use our Nextels from inside the comm room. Donor antenna was a 4' long base station fiberglass omni (don't recall the gain rating offhand) and the client antenna is a 2-1/2" end-fed quarter wave mag mount, mounted upside down above the hung ceiling.

nmfire10 · Post by **nmfire10** » Thu Jul 07, 2005 1:35 pm

I'm frustrated now. I'm getting absolutely nothing at all out of this thing. I could believe having a small effect, but I'm getting NOTHING.

10.2db comtelco Yagi on the mast about 15 ft above the roofline. 50' of LMR600 to a 3db cieling mount antenna. I get nothing at all with the cieling antenna. Even if I take the antenna off and jam the N connector on the LMR600 into the antenna of the cell phone, I get nothing.

Any ideas on what I can check here?

tvsjr · Post by **tvsjr** » Thu Jul 07, 2005 1:56 pm

I've got a friend doing this to get cell coverage in his home. Works good. LMR600 should be sufficient.

One of the big tricks is that you don't want the antennas to "see" each other (via RF). RKG's setup probably worked for him because of the vertical separation and I'd put money on good shielding in his comms room. You may not have that advantage.

What are the vertical beamwidths of your antennas? Are they shallow?

How is the client antenna positioned relative to the donor? Is the client close to being directly under the donor? Most antennas don't have lobes straight up, so if the two are stacked vertically, you have much less chance for the two seeing each other.

Have you tried putting something directional on the client antenna? This is an excellent application for a panel antenna.

A spectrum analyzer would be a handy tool to come up with.

kcbooboo · Post by **kcbooboo** » Thu Jul 07, 2005 2:10 pm

What would the spectrum analyzer be good for, in this situation?

Bob M.

PRR · Post by **PRR** » Thu Jul 07, 2005 2:43 pm

Even if I take the antenna off and jam the N connector on the LMR600 into the antenna of the cell phone, I get nothing.

Have you checked to see if the donor antenna, connection and coax are all good? Are you sure the donor antenna is aimed to the correct cell tower for the service you seek? (Hell, are you sure the cell tower is online?)

Henry

tvsjr · Post by **tvsjr** » Thu Jul 07, 2005 3:34 pm

kcbooboo wrote:What would the spectrum analyzer be good for, in this situation?

Bob M.

I don't know, looking at absolute signal strength? Sweeping the feedline with a return loss bridge (assuming you have a tracking generator in your analyzer)? All sorts of fun things.

nmfire10 · Post by **nmfire10** » Thu Jul 07, 2005 8:20 pm

I don't have a compass so I'm aiming the yagi by the seat of my pants. I doubt 1" in either direction will make all-or-nothing difference. There are 3 sites I can aim it at, none of which do anything.

The yagi is about 15' up a mast on the end of the house above the roof peak. The indoor antenna is about 25' below the level of the yagi and 30 ft across the house in the opposite direction the yagi is pointing. It's a cieling mount omni.

The only tool I have is a multi-meter. I'm going to check some things with it tommorow. Honestly, I've never had the need or desire to meter anthing like this. If the yagi is on one end, what kind of resistance should I get between center and shield from the opposite end? Obviosuly a dead short would be bad, I know this much.

apco25 · Post by **apco25** » Thu Jul 07, 2005 8:30 pm

not unless you have antenna that is design to be DC grounded!

440roadrunner · Post by **440roadrunner** » Thu Jul 07, 2005 9:15 pm

Is the Yagi horizontal or vertical?

Do you even know if the three sites support your service?

tvsjr · Post by **tvsjr** » Fri Jul 08, 2005 6:41 am

The Comtelco antenna claims a vertical beamwidth of 45deg with a 20dB front-to-back ratio. Even making the assumption that the omni has a vertical beamwidth approaching 0 (it's got plenty of vertical radiation, but to keep things simple), they're seeing each other.

Rig something up to move the omni directly underneath the yagi and see what happens.

Jim202 · Post by **Jim202** » Fri Jul 08, 2005 10:12 am

You might try changing the length of cable by a couple of inches. Try using some adapters. This will change the phasing and may indicate if you managed to get the length at a null point.

Jim

[quote="tvsjr"]The Comtelco antenna claims a vertical beamwidth of 45deg with a 20dB front-to-back ratio. Even making the assumption that the omni has a vertical beamwidth approaching 0 (it's got plenty of vertical radiation, but to keep things simple), they're seeing each other.

Rig something up to move the omni directly underneath the yagi and see what happens.[/quote]

nmfire10 · Post by **nmfire10** » Fri Jul 08, 2005 12:36 pm

I know the sites I'm pointing it at have everything. The three of them are 3, 4, and 5 miles away.

The indoor antenna shows 0 ohms center to shield. The coax with the yagi also shows 0 ohms center to shield. I can't go up on the roof now to disconnect the yagi because we are having a monsoon.

I moved the indoor antenna to a position about 25' directly below the yagi, no change.

I don't have anymore coax with N connectors so to change the length, I stuck a polyphaser on the end of the coax, no change.

kcbooboo · Post by **kcbooboo** » Fri Jul 08, 2005 4:03 pm

Depending on the design of the antenna, there could be a matching network of some kind that might use a shorted stub. If so, you should see zero ohms when you measure the coax with the antenna connected. I have a 440 MHz beam that uses a shorting stub to match the 50 ohm coax to the driven element. My 900 MHz beam also has a dead short across the connector.

The last yagi-style antenna I recall that did NOT have a short across it was an old TV antenna. It used 300 ohm twin lead and each conductor went to one lf the two driven elements.

Luckily the monsoon is over. Sure was wet around here Friday!

Bob M.

nmfire10 · Post by **nmfire10** » Fri Jul 08, 2005 5:05 pm

Tommorow, I will take the antenna down and check the coax with nothing attached. I suppose it is possible that this just won't work without a BDA, but I'm holding out hope there is just something wrong.

Dan562 · Post by **Dan562** » Sat Jul 09, 2005 9:37 pm

What I haven't seen in this forum is the Path losses caused by Trees .... only -15 dBm with mature 40~70 foot tree foliage, Hills only -12 dBm for a 50 foot change in elevation and Commercial Buildings 4 stories or less -10 dBm all at the 800 MHz frequency band.

I researched the Comtelco Yagi Antenna and it states +10.2 dB Forward Gain, +20 dB Front to Back but in the Acrobat Spec sheet the documentation reduces the Forward Gain to +8.6 dB. It seems to me something doesn't jive here with the antenna gain. Times Cable advertises -2.5 dB Line losses per 100 feet for LMR600 at 900 MHz so 50 feet would equal -1.25 dB.

Hopefully when you installed the LMR600, you provided gentle curves to the coaxial cable rather than sharp 90 degree bends which can cause major impedance bumps to the signal. If you took a map of your area and plotted out the 3 different cell site locations from your house, then with an ordinary protractor took the readings in degrees from North, went up on your roof with North as your reference, you could probably determine which way to point the Yagi antenna towards the closest cell site.

Just keep in mind if you have mature trees with full foliage, this could be attenuating the signal before it even reaches the antenna.

Dan

nmfire10 · Post by **nmfire10** » Sun Jul 10, 2005 4:32 am

Yea, the antenna is certainly not above the tree line. Would be nice, but I can only stack the antenna masts so high before it becomes unstable. It is just using two chiminey straps to hold it up.

I would need a compass to orient the protector, at that point I would just use the compass to aim the antenna. I'm going to try and hunt one of those down today too.

We have BDA at town hall that hasn't been installed yet. Perhaps I can convince the OEM director to let me borrow it to test this. That would save me the money of buying one and finding out it is useless.

RKG · Post by **RKG** » Mon Jul 11, 2005 6:50 am

Go back and read tvsjr's comment. Sounds like you are lacking the required isolation between the donor and client. We were four stories down in a steel-framed building into an interior room with no windows.

Post by **wavetar** » Mon Jul 11, 2005 7:18 am

Maybe a stupid question, but are you even sure the service is 800MHz?

tvsjr · Post by **tvsjr** » Mon Jul 11, 2005 9:20 am

RKG wrote:Go back and read tvsjr's comment. Sounds like you are lacking the required isolation between the donor and client. We were four stories down in a steel-framed building into an interior room with no windows.

Well, he did move the omni directly underneath the yagi. However, I prefer directional-to-directional for such use - an omni tends to radiate straight up rather well.

A BDA is definitely the right answer (although you still have the isolation issues), but I still think it could be made to play as a passive system.

Which coax for an 800Mhz passive repeater?

Which coax for an 800Mhz passive repeater?

Re: Which coax for an 800Mhz passive repeater?

800 MHz Path Loss