Repeater Setup: Several part question...

RESCUE161 · Post by **RESCUE161** » Wed Nov 12, 2003 1:03 pm

What is the MINIMUM distance between two UHF antennae. The most I'll be able to seperate will be about 10 - 12 feet vertically. If I go this route, I'd be using two Yagis with the higher gain on the bottom and hooked to the transmitter. It would be at about 22 feet above ground (about 50 feet above surrounding territory) and the receive antenna would be at about 35 feet.

What type of antenna is better for repeater operation, a Yagi or Folded Dipole? I have both, but if the dipole is used, a duplexer will have to be used, as I don't have enough space on the 'monoploe'...

If two antennas are used, feedline wouldn't be a problem due to short runs. I really don't want to use a duplexer at first because it's going to be a Securenet repeater (HOPEFULLY), and I don't want too many things to go wrong/be out of whack while I'm trying to 'get it right' and the duplexer would just throw another loop into my plans.

Okay, last part:
If the duplexer is used, is there any pros/cons to using a yagi on a repeater? What about a dipole? Thanks in advance.

w7com · Post by **w7com** » Wed Nov 12, 2003 1:56 pm

The choice between a yagi and a dipole depends on where you want coverage. If you us a directional antenna for TX and an omni for RX you are going to have one strange coverage map. Since you say this is for a securenet (and therefore a commercial) system you should with the cans and a single omni. I think you may have to change your license if you go directional with the yagi. You would only ever use a yagi on a repeater in very specific situations. UHF duplexers are not that expensive and, when tuned right (not that hard to do) will make your system much more reliable than trying to deal with dual antennas. Anyway, IIRC you would need something like 70-90' vertical seperation to get away with it anyhow.

Is this going to be setup outside the US?

Cam · Post by **Cam** » Wed Nov 12, 2003 2:23 pm

Whats the repeater going to be used for?
The use of yagis in a repeater app. has a very limited uses, ones that I very much doubt are what you are trying to do.
You most likely want to use the (folded?) dipole and a duplexer to set this up. I'd get everything set up, working and tested, then you can start to play with the nonessential toy like signaling or Securenet or whatever you think you want to use. Yes, I know everybody wants to feel cool and start off with all the cool toys, but you really need to get your system working first, you will be much happier with it.

Good Luck,

Cam

Nand · Post by **Nand** » Wed Nov 12, 2003 3:07 pm

The separation of the antennas depends on several items, the separation of the TX and RX frequency, the power level of the transmitter and the sensitivity (needed) for the receiver.

A 1 (one) watt transmitter with a typical receiver spaced 5 MHz on UHF would require a 15 foot antenna separation.

Using Yagis will make the repeater very directional. Diploes on the other hand give you more of an omni pattern. Assuming that the Yagis are vertically polarized, they do not take more space on the mast compared to the diploes.

Using a duplexer may be the best solution and will let you use higher power levels if antenna separation is a problem. Just be sure that the antenna is of good solid quality and the feed line is equally suitable for repeater use.

Nand.

RESCUE161 · Post by **RESCUE161** » Wed Nov 12, 2003 8:48 pm

It's outside of the US on a military base. It's going to be our 'med' channel for the hospital. The reason for the yagi is that the repeater is pretty much backed up against one side of the base and I was going to point the yagi to the other side. Getting a central location is out of the question cause the flight line is in the middle of the base.

Well, the duplexer thing is a 'go' now.

I've heard that the folded dipoles build up less static than other types. Should I be worried about that with a yagi as long as I use propper grounding?

I'm more than likely going to try both antennae to see which one works better (simplex first).

The Securenet isn't a must, it's just a patient privacyissue for the hospital here. I've been trying to get up with Will on getting a module for two Secure Spectras, but I haven't heard anything back. If it's going to be that much of a hassle for the Securenet 'repeater', we may just have to use simplex without handhelds.

The whole reason behind this idea is that I have a bunch of radios that will do the job for free and I'm just trying to make do with what I have without buying anything else. I do have a couple of duplexers that I'll have to send off for tuning. The splits are up in the air right now, they will be anywhere on the 406-420 side of things. I will assume that we'll be able to use any split, not just 5 MHz due to everyone else being on VHF.

I think I covered everything...lol More to come.

Cam · Post by **Cam** » Wed Nov 12, 2003 9:01 pm

RESCUE161 wrote:It's outside of the US on a military base. It's going to be our 'med' channel for the hospital. The reason for the yagi is that the repeater is pretty much backed up against one side of the base and I was going to point the yagi to the other side. Getting a central location is out of the question cause the flight line is in the middle of the base.

Well, the duplexer thing is a 'go' now.

I've heard that the folded dipoles build up less static than other types. Should I be worried about that with a yagi as long as I use propper grounding?

I'm more than likely going to try both antennae to see which one works better (simplex first).

The Securenet isn't a must, it's just a patient privacyissue for the hospital here. I've been trying to get up with Will on getting a module for two Secure Spectras, but I haven't heard anything back. If it's going to be that much of a hassle for the Securenet 'repeater', we may just have to use simplex without handhelds.

The whole reason behind this idea is that I have a bunch of radios that will do the job for free and I'm just trying to make do with what I have without buying anything else. I do have a couple of duplexers that I'll have to send off for tuning. The splits are up in the air right now, they will be anywhere on the 406-420 side of things. I will assume that we'll be able to use any split, not just 5 MHz due to everyone else being on VHF.

I think I covered everything...lol More to come.

It sounds like your letting the Securenet thing get in the way of setting up a good system. I didn't think I've ever heard of a hospital using a "secure" radio system, not that it can't be done. I know it cool to play with all the new stuff, but that can could come after you set up your system. Giving up a repeater and handheld radios seams like a lot just to get "secure" radio for a hospital.

My two cents,

Cam

Will · Post by **Will** » Thu Nov 13, 2003 1:04 am

The folded dipole antennas seem to receive much better due to the area to capture the signal is much larger, several wave lenths.

I did communicate with rescue 161 on the repeater issue and am working out the details with him. The Repeater Module I build for the Spectra will work in this application. Simple, just a couple of jumpers in the Spectra and the Repeater Module is "plug and play".

RESCUE161 · Post by **RESCUE161** » Thu Nov 13, 2003 3:01 am

Thanks Will, email sent!

60hzEE · Post by **60hzEE** » Fri Nov 14, 2003 5:37 am

Since you plan to use Spectras, you can expect significant de-sense/front-end overload of your Spectra repeater receiver unless you use a duplexer, even with some decent vertical separation. The reason: Spectras use a broad-band, untuned receiver front end (as opposed to earlier radio designs like the Maxtrac, Mostar, Micor, etc.). The earlier radio front end passbands were only a couple MHz at best and as a result, less subject to de-sense.

Lee

Jim202 · Post by **Jim202** » Sat Nov 15, 2003 6:00 am

While your talking about the secure operation, don't forget that the repeater throughput audio levels will be very important. You can't run the repeater audio into compression and expect your secure audio to function properly.

You may need to make sure there is some way to adjust the audio level leaving the receiver and feeding the transmitter. Not having played with Will's module before, I don't remember him saying anything about adjustable audio level. Check with him on this issue.

Make sure that all your cables at the duplexer are double shielded like RG-9 or RG-214. The smaller "Heliax" type cables also work just fine. Don't use any RG-8 type cable for anything to do with the repeater. This includes the cable going to the antenna.

Jim