repeater antennas

[lancerice]

I am building a vhf repeater I have a 60ft tower rg213 cable 2x gm300's but not sure about the antennas, if I was to use two mobile antennas how would these work as to having two base antannas. I'm not realy up on the db gain bit

thanks lance

[bayfire300]

3db gain antenna will double your power....but you will lose alot w/ rg213.........get a nice base antenna min of 3db gain ...and some andrew heliax.or even som lmr-400
IMO


here is a link for coax loss calculator to play with ....alot of good info here

http://www.arrg.us/pages/Loss-Calc.htm
Otto

[com501]

You'll have a lot better luck if you use a duplexer and ONE antenna.

For VHF, the DB loop antennas work well, unless you are in heavy snow country, then a fiberglass stick is a better deal.

Putting two antennas on the tower will mean that at HAM frequencies you will need to separate the two antennas quite a bit, 60 feet apart wouldn't be too much.

That is why a duplexer is almost a must unless you have a combining system and receiver multicoupler you are tying into.

[lancerice]

I was going to put two antennas about 6ft apart one tx and one rx, I am using 2 gm300's, would this be too close

[Jim202]

3db gain antenna will double your power....but you will lose alot w/ rg213.........get a nice base antenna min of 3db gain ...and some andrew heliax.or even som lmr-400
IMO


here is a link for coax loss calculator to play with ....alot of good info here

http://www.arrg.us/pages/Loss-Calc.htm
Otto

Do NOT USE LMR type cable in any repeater operation. You are only asking for issues with noise and intermod problems. It has been well documented that this type of cable will cause you untold grief with time. The shield of the LMR coax uses braided copper over a foil for the shield. The 2 different materials cause noise when used in a duplex type operation if ANY moisture migrates into the cable. The oxidation generates the noise and causes the problems to the repeater receiver.

Spend the money on better coax and use a heliax type coax. You will regret using the LMR coax in time and will end up replacing it with a heliax type cable anyway. Spend your money one time and save the aggravation.


Jim

[Bill_G]

Good morning Lance. Part of the fun of a hobby is you have a starting point, and you progress from there. No amateur racer built a winning dragster in his garage the first time out, and women keep making quilts because they get better and better at it. So, if you have a 60ft tower, can safely ascend it, and your starting point is a couple GM300 radios with RG213 and some mobile antennas, go for it.

You will probably have to fab some mounts. And you'll want to think about some lightning protection. And you'll want to consider weatherproofing the connectors. RG213 was the best cable around for a while, and people used it. You just have to figure out how to transition to a mobile mount.

And then, as you accumulate stuff, run into deals on used heliax and connectors, find decent base station antennas that are not too heavy for your tower, find good duplexers, you can incrementally improve your system.

[desperado]

Bill is exactly right.
You have a good starting point to build from.
One possible idea would be visit your local tower company. Some of them will have a junk pile of antenna's that they strip for scrap.
I have bought several very nice and expensive antenna's that were high gain 4 bay VHF and UHF units for $20 each and the guy was glad to sell them to me.

While there you might ask about end roll pieces of heliax feed line and connectors. Again some companies drag this stuff back to the office to scrap some don't.
A 100 foot section of 7/8 Andrew to a ham is like gold, but to a tower crew that works at 4 times that height, it's scrap. One thing to be aware of is 7/8 and above has a hollow center conductor
and will fill with water and corrode, so don't dig in a pile too deep as the stuff may have been there a while. Also, don't make the mistake of getting 7 ten foot sections and putting it all together with connectors. Each connector, properly installed is .5 db loss. so each junction will be 1 db loss. 7 sections would be 6 junctions, or 6 db. 3 db is half original power, so 6 db is half of half. 100 watts at the transmitter will put 25 watts at the antenna connector, plus line loss.

You may even find a set of cans (duplexer) for your project, but don't expect it.
Of course, be willing to pay his price unless it's silly high. 7/8 cable new is several dollars a foot. Connectors new range from $40 to $75 depending on what they are. Be willing to pay 25% of new.
Duplexers are very expensive, as in $1000 for a good set. Again, you might get some at scrap price, you may not.

As a side note. These guys are typically busy this time of year, so be quick, explain what you are after and don't bore them with ham stories and 100 questions about tower stuff. They really don't care.
And the scrap they are selling you is just that to them. You are asking them to sell you their junk. So be professional and friendly but they are not other hams and don't want to hear about your latest contact with Japan on 40 meters.

[litsnsirn]

Hi Lance,
You might want to throw out where you are. The only cable that I save(that I don't already have a purpose for) in less than 200' lengths is half inch. Besides a tower crew, you might run into a field guy that doesn't really want to hold onto short cable runs.

[com501]

If you don't get a duplexer, you need to separate your TX and RX antennas a good 20 feet, minimum.

I've been throwing out older duplexers until it occurred to me to give them to the local ham club....

[n8obu]

most of us throw out short runs of hardline less than 100 foot you do not list were you are so we cant say swing by and we will hook you up. i am more than willing to help out anyone that has the right thoughts and just needs a hand getting going we all started on the bottom my first repeater was a johnson fleetcom 60 watts and motorola duplexers and 75 ohm catv feedline with home made matching transformers and an gp9 comet ant on an gas station pole .. now i have 2 900 mhz 1 vhf and 4 uhf and an atv repeater most linked with linkcomm dsp 404s using viop all motorola powered but the atv its an 500 watt glenayre ampon 900 mhz things change in this hobbie just by blinking . i am willing to tune cans for most if they just ask i just wish there were great folk back when i started out ...like there is here on this board!!!.. like most i spent the long dollar to get anything done.. mike b n8obu
http://cmen.us/

[lancerice]

thank you for all your replies they are all very helpful, One thing i'm still not sure, you say that if I use 2 antennas thery would need to be 20ft apart, is that so when one is in tx it don't bleedover the rx one, if I was to have tx frequency 163 and the rx frequency at 174 would i be able to have the antennas closer, like 6ft apart
thanks lance

[lancerice]

thank you very much for all your advise and answers, I am getting to where I want to be now, as for the antennas having to be 20ft apart, if I was to have the frequencies 165 tx and 173 rx would I then be able to have the antennas closer, like 6tf apart.
thank you all again lance, I am in essex, UK

[com501]

At VHF its even worse, you want to have them as far apart as possible, 20 feet would be a good start.

[techtonics]

I have never had a problem with LMR400.....

[Jim202]

I have never had a problem with LMR400.....

If your using it on a repeater, given enough time you will start to get the scratchies. It happens to all that have used the LMR400 and larger LMR cables. No matter how hard you try to keep it out, the moisture will migrate into that style cable and the different shield material will start to act as a diode junction in a high RF environment. When that happens, you will start to hear the noise. It will be more pronounced with the wind moving the cable around.

Jim

[HLA]

if you can't space the two antennaes 20 feet apart, put them on top of each other, put the recieve up top and the transmit 5 or 6 feet under it and make shure you use a ground plane

[lancerice]

so if i mount the antennas on top of each other this will work, thank you very much, i would use a duplexer but im not up on tunning them.
Thanks for all your help lance

[lancerice]

what dose rg mini 8 compare to rg8 and rg213 cable, I know it is a lot thinner and cheaper, but dose any one know how much better or not that it is.
Thanks Lance

[desperado]

If you are talking about using mini 8 for a repeater, forget it. That stuff is good for HF and CB..not much else.

I realize that this stuff costs money,,,, and alot of it. But here's the hard truth. You are wanting to play with the big boys and the big toys.
Big toys are big money... there is no way around that.
There are two ways of doing things.
Cheap and inexpensive

Cheap is running a repeater system with mini 8 cable and hammy antenna's
Inexpensive is asking around, finding deals on stuff and buying it as you have the funds to do it.

Repeater projects sometimes take time to get the materials together. It's all expensive stuff and you have to until you have the money to do it.
If it was as simple as plugging a couple radios into a controller and connecting an antenna to it, everyone would have one at home.

Be patient, buy materials as you can,,, don't sweat it not being on the air a month after you decide to commit to building a repeater.
I have several repeaters, duplexers and controllers sitting here at the house. I finally found a good site for them and I am working on the specifics of being on the site right now.
This project have been 5 plus years in the making and I am still not on the air with it and it will be 6 before I am most likely.
Things will happen when they happen, don't go into hock over getting a repeater up unless it's a commercial deal and you are getting money for it.
If that is the case, then have the customer pay for it, don't cobble it together.

[Jim202]

Now that this thread has gone on for about 5 months, have you learned anything from it?

My best support for your project is to take a look at the repeater builders web site and start spending a bunch of time learning about repeaters before you go much further. Without a solid knowledge of what your trying to do and how to get there, your not going to have much success.

It would be in your best interest to try and find someone in your area to work with you as a mentor. What that person can show you and teach you in a short time will take years to learn on your own.

You haven't said where your from, so not much anyone can do to help locally until you do. I would try and locate a ham club near you and see if anyone in the club can lend a hand. Most of the clubs have a meeting at least once a month. Go to a meeting and ask questions of those that are there at the meeting. Most hams are friendly and don't bit. They may even point the way to a person that could help you.

[TAC Solutions]

You can use two antennas but you would be better using a single antenna with a duplexer. If you use two antennas, one for transmit and one for recieve you will need to have both horizontal and vertical seperation of each antenna.

Phil

TAC Solutions
www.tacsolutions.ca

[lancerice]

right I have the antenns up and the repeater running, BUT!!! if I use one antenna an a time talking at a distance of 20miles the radio works alot better than if the repeater is on and using the two antennas, I have a vertical seperation of about 4ft and a horizontal seperation of about 20ft, Would this be that the antennas are still too close???

I am now thinking of tring a duplexer like a lot of people have said already, any body know of one out there for vhf 165 TX and 170 RX???

Thanks Again to you all

[Jim202]

right I have the antenns up and the repeater running, BUT!!! if I use one antenna an a time talking at a distance of 20miles the radio works alot better than if the repeater is on and using the two antennas, I have a vertical seperation of about 4ft and a horizontal seperation of about 20ft, Would this be that the antennas are still too close???

I am now thinking of tring a duplexer like a lot of people have said already, any body know of one out there for vhf 165 TX and 170 RX???

Thanks Again to you all

Way back in the beginning of this thread, I believe you mentioned using a mobile antenna. This is not a good idea as most of the mobile antennas are looking for a metal ground plane under them to function correctly.

Trying to use the radios without a duplexer will not work. You need something in the order of 80 db or better of isolation between the TX and RX frequencies. You can get this with vertical or horizontal separation, but the numbers are really large to obtain the isolation you need.

The use of two antennas using RG213 might also not give you enough isolation due to the coax cables not having enough shielding. This type of coax will have some leakage and would cause the TX to leak into the RX coax cable. You also don't want to run the coax cables right next to each other on the run down the tower. I would say to run them on different legs of the tower to keep them isolated.

Jim

[AEC]

You'll have a lot better luck if you use a duplexer and ONE antenna.

For VHF, the DB loop antennas work well, unless you are in heavy snow country, then a fiberglass stick is a better deal.

Putting two antennas on the tower will mean that at HAM frequencies you will need to separate the two antennas quite a bit, 60 feet apart wouldn't be too much.

That is why a duplexer is almost a must unless you have a combining system and receiver multicoupler you are tying into.

Exposed dioles hold up far better in snow and ice buildup.
I have several pics of sites I used to work at on mountaintops that routinely go above 9,000 ft. And I can say with experience, the fiberglas sticks take a beating and break apart.
I have taken them down from being bent over, and poking through tower leg on he opposite side, others were snapped in half, lost their radomes, and the internal elements all twisted and broken. I have had a few dipoles break, mainly from excessive twisting and bending, but those were very few. Pinal peak, Mt. Graham, Greens peak....All have a large snowfall with associated high winds.
Every fiberglas stick has to top guyed to prevent damage, but the snow and ice get them and they routinely rarely survive.

[Ben]

Just read this topic for the first time and it has good info for somebody trying to get a repeater up and running. I'm in the same boat. Wanting to get my first repeater on the air and not very sure of anything. Several people pointed to the best person around to help, even had some used stuff for sale I could really use. Now my trouble is I got together with him and started talking about getting some help. He was very open about this until I said I wanted to put up a MotoTRBO repeater, since it was not D-star he didn't want to help any more or even have anything for sale. So sad this is where ham radio has gone. What happened to hams helping hams? I got so worked up thinking of having my first repeater up and running and this just about ended my dream. Was thinking I would start slow and cheap and upgrade as I had the money and knowlege to do it better. It was so nice to read this topic and think maybe there is guys out there that will help.

[AEC]

Just read this topic for the first time and it has good info for somebody trying to get a repeater up and running. I'm in the same boat. Wanting to get my first repeater on the air and not very sure of anything. Several people pointed to the best person around to help, even had some used stuff for sale I could really use. Now my trouble is I got together with him and started talking about getting some help. He was very open about this until I said I wanted to put up a MotoTRBO repeater, since it was not D-star he didn't want to help any more or even have anything for sale. So sad this is where ham radio has gone. What happened to hams helping hams? I got so worked up thinking of having my first repeater up and running and this just about ended my dream. Was thinking I would start slow and cheap and upgrade as I had the money and knowlege to do it better. It was so nice to read this topic and think maybe there is guys out there that will help.

Ben:
Give me a call/text, or even Email, and I will be happy to help you if I can!

Please use the information in my signature below.