CDM re peater hangtime

[Terriers618]

I have two CDMs linked but I am not using a RICK.

I want to accomplish 2 to 3 seconds of hangtime at the end of each transmission so that we know we have reached the repeater.

Any thoughts on how to do this in the CPS?

Jason

[Al]

I don't believe you can accomplish what you want to do in the CDM codeplug. You'll probably end up using an external time delay implemented in hardware such as you would find in the RICK or most other repeater controllers.

[Terriers618]

the problem is the rick and other units are easily 200 dollars....

[chpalmer]

Truthfully- Thats pretty cheap...

Is this on a radio site with other equipment?

[Terriers618]

it is right next to a cell tower with the local emergency services equipment. I still need to get a duplexer as well.

[chpalmer]

Jason-

CDM mobile radios are not the radio of choice to be installed on a commercial radio site. And next to a cell tower, the ports of those radios will be seeing 24 hours a day of rf energy from the cellular stuff, due mainly to the fact that duplexers sold by all the big suppliers aren't designed to stop out of band signals... They are not true band pass units. CDM's do not have preselectors and circulators built into them. Because of this- your performance will suffer. The front end of your radio will be so busy with all the other higher power signals clobbering it that weak signals from your stuff will be impossible.

There is a reason we pay six grand or more for simple system to go into a site. So you do not have my pity on that $200 Rick. Sorry!

I dont write this to be a jerk or to give anyone a bad time but please take it as a warning and know that your headed for headaches... If not your own, maybe someone else's...

Im gonna give ya some homework... Read here first and see where Im coming from...

Good Luck!

[Terriers618]

This definitely must explain why I am having issues. The equipment is using two antennas on a roof of a building about 40 yards away from the cell tower which is probably whats causing me so many issues. It is working pretty impressively for how you describe but I am going to relocate the equipment up the hill to another building 500 yards away from the tower.

Thanks for the info!!

[whls3]

Don't be so quick to move, especially if it will cost you. Not to sound picky, but your use of the word "tower" may have confused the issue. Is it a tower, or a single cell site? A single site 40 yards away shouldn't cause too many problems. It's at 3 watts at 800mhz or higher.

Tell me about your antennae. What is the separation of the two? Transmit and receive antennae should have vertical separation to truly keep the two from interfering with each other. And what band are we talking about? I'm a fan of not using a duplexer, as there is measurable loss involved. As to your original question, the hang time is defined by the controller. One of those single cable interfaces does not have the capacity to provide features like hang time, courtesy tones, and ID.

[Terriers618]

The IDs come through.

I have two UHF whip antennas. The TX is above the roof on a small pole next to an unused directional yagi. the receive is a magnetic mount uhf whip mounted on a metal cabinet about 10-15ft below the tx inside an attic.

We are talking about 460-465mhz.

The tower, next to the building, houses 4-5 cell carriers including verizon, nextel, sprint, tmobile, cingular, maybe one other. The tower also houses antennas for 6 repeated channels. all between 453-460mhz. The only channel that has much activity is 460mhz. The others are only used during calls a few times a day.

The only other TX from the tower would be from a dispatch console on lowband or vhf which transmissions are very rare.

I think my major issue is the lack of decent antennas. I could use some recommendations on solving this issue. I should be able to get decent range out of this!!!

[whls3]

Now we have a much better picture of what is going on. Certainly the UHF on the tower has some effect on you rig. But my guess is that your antennae are giving you the most trouble. Or more so the cable. And let me guess, you had to extend at least one of them.

The vertical separation you have is just about right, although I would put the receive on top. However, mobile antennae are not appropriate in this situation. And there is no substitute for good cable. And there will be noticeable loss with each splice in the cable run.

Now I don't want to be hard core about this, but what do you mean "the IDs come through"? A repeater of any kind is required to ID itself, with an FCC callsign, every hour. Even Cross band repeaters, although if they use the same callsign, it can be just one that IDs, while the other re-broadcasts.

[Terriers618]

ok gotcha. I figured if the TX was further away from the cabinet it would help for less desensitization.

This repeater does not ID, its more of an experimental project anyways and is going to be used for GMRS once working properly. Aside from those details.

Right, mobile antennas are definitely no good, cable extension - correct! For the TX. The RX actually works better than the TX which is probably due to antennas etc.

Any/all recommendations are awesome. What is the best antenna? which should go on top? are the eBay duplexers crap? I have the power set to 40watts rather than 48 on the TX unit so I dont burn it up right away.

What are the regs on the repeater IDing? Currently our system on the tower (govt use) does not transmit an ID.

[whls3]

Regarding the govt repeater- The govt can pretty much do whatever it wants, just like the police. But if they were to follow their own rules, it would ID. It may ID, you just might not be able to hear it because of PL GMRS rigs should also ID. Not to repeat my self(no pun) this is done in the controller. And again, I like the two antenna design, which means you don't need a duplexor.

Let's start with the cable. I love hardline. The downside is that it is expensive. A single connector is $40-50.00. So let's think reasonably. I would use no less than 9913. you can get it at Radio Shack(most of them) and you can use common($3-5.00) connectors. Antennae are going to be a little harder to get, but the internet should make it easier. And again, you could spend a lot of money, but you can get away with less and still do okay. I've been out of this business for a few years, so my product knowledge may not be up to date. Maxrad made an okay product at a good price. A fiberglass base antenna in the 450-470mhz range would be good for both transmit and receive. Get both antennae outside. The receive should be on the top because you are probably using a lower wattage radio to get to the repeater. And with FM, altitude is everything. And then spend the money on a RICK or some other controller. And you mentioned a cabinet. Is it an all metal cabinet? If so, and you follow my suggestions, you should have minimal interference issues, either from the tower near by, or self inflicted.

[chpalmer]

Just wanted to provide another link.

http://wwcic.org/wwcic_es.html

We do split antenna systems all the time, and all of them get filters.

Your CDM's may be designed for a given frequency range but that does not mean that equipment transmitting out of band on that site wont get into the front end and cause everyone issues.

At the very least you need a circulator on the transmitter and pass-cans on those radios. Its just about being a good neighbor.

Have you looked at your receivers for desense? Looked at the antennas for reflected power? Remember, if you are using lossy coax as you are the reflected power from the antenna will also be victim of that loss. You would measure 3 watts reflected right at the antenna but say you have 6 db of loss total from the transmit port to the antenna... Out of 40 watts, only 10 make the antenna. Of that 10 you have 3 watts reflected (as an example as I dont know your antennas match) you would only see .75 watt reflected at the radio. 40 in 3/4 back doesnt look so bad right? But your antenna system is only about 25% efficient.

A company called CES Wireless makes a little box called a repeater maker plus. New it goes for about $300. but you might find one on E-bay or elsewhere cheaper... It does PL tones and also has a CW IDer. Nice thing is it is programmable with DTMF tones. And it has hangtime available... Just one of many options.

[wavetar]

As to the original question, you can give it hangtime following the directions in Nand's circuit here:

http://www.storm.ca/~nand/990/RICK/rptr.pdf

Second last paragraph from the bottom gives details on hangtime.

Todd

[Terriers618]

WHLS3,

The only way I was able to accomplish the 15ft elevation gap was to put one antenna inside. The pole on the roof is only roughy 7-8 feet in height.

I am using crappy coax and mobile antennas which I guess is the issue. I am going to check out that cable at radio shack and then find connectors online if I dont have some already.

I have access to an antenna distributor and will look into the antennas you suggest as well.

One I get there I will certainly need help with reflection and all that other testing. I have some SWR meters for UHF but never fully understood how it worked.

Thanks for all the support so far guys. I am looking into those other links as well! I will report back in a week or so when I make more headway on this.

Jason

[whls3]

Sorry for the delay in responding. I am currently at the beach(pool,hot tub,alcohol), and don't get online as much. That and because I'm a newer member, my responses are moderated.

What part of the country are you in? It would be easier to communicate if we were close. This may end up with a phone call anyway as the SWR instruction could be intensive and I'm not good at the keyboard.

Standard TV mast is cheap, so adding or just replacing would be best. Getting both antennae outside is key in making your system work. What kind of SWR meter do you have?

I'll be sure to check back soon, although the pool is heated.