Batboard

I've been told that this is the spot to ask questions and get answers.

I'm going overseas with a group of guys to the fun fun third world, and I'm responsible for putting the comms package together. What I have so far looks like this:

Handhelds: HT1000s w/earpieces and mikes
Mobiles: CDM1250s in each of two vehicles
Command post: CDM1250 in a base station cradle with an AC power supply.

My concern is that we're going to have our CP in a hotel in a small city, and the mobile guys will be venturing 30-40 miles out. I'd like some advice on base station antennas that I can erect on the hotel roof fairly easily that will get us the gain/range that we need to have reliable comms with the mobiles. The proprietors will be getting their palms greased, but I can't put up anything that does damage to the structure, and it has to be fairly stable and easy to transport via the usual crappy third world regional airline. The hotel/CP is going to be on the edge of the town closest to our (fairly flat and not built up) area of operations, and the CDM1250s put out 25-45 watts on high power and on 136-174 MHz.

Also, I'll need some good mobile antennas that will stay where they're put. Would I be better off with magnetic mounted antennas or with some kind of big whips that have to be a bit more permanently mounted?

Any recommendations from the gathered faithful would be greatly appreciated. If I must make offerings of the sacred frequency grease before the knowledge of the elders flows forth, please let me know.

Before knowledge starts flowing - care to share where you are going and what your doing there?

Where: Africa
What doing: A protection gig for some oil company employees

If you have a good LOS 'Line of Sight' of the entire area that you are going to work, then you won't have many problems with most antenna's. I would go with something like a higher gain Comtelco antenna or such, the length shouldn't be too bad to transport via air cargo, etc.

Same thing on the mobiles....go with a higher dbi antenna, maybe a factory Motorola Spectrum or as such. Only problem, these are NMO mount. You will lose sensitivity and range with a Magnetic mount and if you can't mount properly on the roof of the vehicles, then you're not going to get the range, etc.

Also, if you are in open country, then the VHF will work great, but if you are bouncing off buildings, etc., then maybe UHFers will be the way to go, but sounds like you already have your radio's.

Of course you'll have to snap up some cable, etc. and bring it with you, enough to run to your room that the base is going to be in, with the right connectors of course. Ever think of maybe picking up a Repeater....maybe a GR300 or such? Give you a little more range to hit the other handhelds if you are apart, unless of course the base can relay your messages.

It's not exactly like going into Toronto, Sao Paulo, London, or Mexico City - but they may have laws that will impact you flying in with your American radios and setting up shop without their approval.

"Third world" also covers their jails and judicial systems. I would hope that you would check into that with the State dept., and maybe the oil company has prior approval for some comm channels that you could use, with the appropriate equipment.

Having traveled a bit, I know a lot of countries are not too happy to have Americans show up and believe that the host country's laws don't apply to us because, "I'm an American, and you can't do that to me!".

Just be careful, and cover your bases (and your a**). It's a long way home.

Jack

elkbow wrote:Only problem, these are NMO mount.

NMO is antenna-speak for "drill holes in the rental vehicles," isn't it? That ain't gonna work.

Give you a little more range to hit the other handhelds if you are apart, unless of course the base can relay your messages.

The mobiles are going to be the relays back to the base for the guys with the handhelds.

jcobb wrote:It's not exactly like going into Toronto, Sao Paulo, London, or Mexico City - but they may have laws that will impact you flying in with your American radios and setting up shop without their approval.

The contracting company is handling the licenses and permits, and the radio stuff is in the contract, but thanks for the heads up.

Just be careful, and cover your bases (and your a**). It's a long way home.

Jack

Roger that. I don't want to star in a remake of "Midnight Express."

Sounds like you are probably covered.

If I were in that situation, I would feel more comfortable if there were "mobile extenders" in the vehicles. For instance, the guy in the vehicle is getting a cup of coffee, or is otherwise indisposed - and something happens that the guy with the handheld needs to talk to base - he may be out of range and there's no relay. Or if something happens that gets "danger close" and the guy in the vehicle gets out to cover his partner(s) - lost comms with base again, maybe.

Just a thought, thinking like I might be one of the guys in the vehicle or in the field.

Hopefully, it will all be a walk in the park - but 1 minute of "pucker time" could make it worthwhile.

Jack

Tell me more of these mobile extenders. Is this basically a radio relay?

Quick and dirty answer - yes. You would have two radios, on different bands in the vehicle. They are tied together so that whatever is rec'd. on the one radio is retransmitted on the other.

So if your mobile and base are on let's say, VHF - that is what the main radio in the vehicle is set to. The second radio would probably be UHF, and the handhelds would be UHF. They would talk to the second mobile radio, and it would feed into the primary VHF, causing it to retransmit to the base. And when the primary radio rec'd a signal from base on the VHF channel, it would feed the secondary radio and it would retransmit out to the handhelds on the UHF channel.

It would have the same effect as having a person in the vehicle to relay, but it is automated and the vehicle does not have to be occupied for it to work.

Will, on this forum, makes extenders to work with a variety of radios and would be much better at explaining how it works - and how to get the radios you have chosen to work in a system like I described.

You would have to change the band of the HTs, and add two more mobiles and the corresponding antennas - but it could be worth it, depending upon the threat level.

Jack

Sounds just like the MRC-110 radio retrans vehicles I used in the Marines. They're basically HMMWVs with two radios mounted one over the other up front with a retrans box hooking them together, and two big antennas. Receive on the freq dialed into one, and automatically retrans out on the other.

You got it. Not as big or as "bullet-proof" but same concept.

You didn't mention a time frame - you're going next week or next month, or do you have time to maybe investigate the extenders and put it together before you leave?

Not prying, but I hope you have some time to check into this a little further. I know Will would be happy to chat with you about it.

Jack

I sent Will a PM; I doubt that he will join us in real-time, but he will have a lot of good, valuable input for you on the mobile extenders.

Jack

It's looking like Jan/Feb 2003. Thanks.

Good - you've got time - but not a lot. Hopefully Will can peek in here tomorrow (today?) and give some good responses.

Take care.

Jack

The Extender module for CDM's has not been fully tested, but one is in testing phase now.
These plug into most Motorola mobiles providing retransmission on the second radio like the milatary setup, but much less money and about the size of a pack of cig's.
With a simple mobile duplexer, you can do in-band repeating from the portable to one radio in the vechicle thru the extender module and transmitted out on the second radio to the base operation station. The reverse caries the signal from the base back thru the mobile to the portable radio.
Some call this a bi-directional repeater, but it does "extend" the range of a portable to that of the vechile radio, hence "extender module". Lots of fire departments, and others, use my modules through out the US and eastern Canada with excelent results.

Will, that sounds great. Just like the military retrans gear in effect.

I'd be interested to hear about it when you get the one for the CDM tested and fielded. It may be a task to convince my principals that the number of mobile radios required for the job just doubled, though.

Does anyone else have any antenna suggestions, either for the mobiles or the base station?

Just use FRS. You can just turn on the privacy codes to make it secure

nmfire10 wrote:Just use FRS. You can just turn on the privacy codes to make it secure

Now why didn't I think of that?

Which brings to mind another question: Are the HT1000s and CDM1250s capable of encrypted or secure comm?

The subject you've raised is pretty complicated, and this board probably has a page limit on responses; so here are two thoughts only:

If your base is at the edge of your mobile ops area -- that is to say, the mobiles will always been in the same approximate compass direction from your base -- consider something like a 2- or 4-element folding dipole for the base. Cheap, easy to dismantle for transportation, and some usable gain in the forward direction (assuming all of the elements point the same way).

If you're going to put the antenna on the roof of the hotel and the radio in your room, how are you going to get the feedline from the room to the roof? What will be the length of the feedline run? As a practical matter, the run length is likely to give you huge feedline losses, resulting in a negative system gain even with a gain antenna.

Consider mounting the radio on the roof (assuming some out-of-the-weather and secure enough location) and controlling it remotely. You'll need a remote, remote termination, and someone to make you a mounting cable to connect the termination panel to the accessory connector on the back of the 1250. The connection between the remote (in the room) and the termination panel (on the roof with the radio) can be a simple 2-wire pair, and run length is effectively unlimited. However, in this configuration, you are limited to one channel, no scan.

If you can't run feeline up to the antenna, you could always put the antenna and a repeater on the roof self-supporting and just talk though the repeater from the hotel room. 2 Maxtracs and a R*I*C*K or W*I*L*L Module would do that.

Been there done that. In the past, I have spent quite a few years of my radio life building and maintaining various radio systems throughout the African continent. Including 3 years in Nigeria and other projects related to the oil business. So, after giving some of my qualifications. Let me lay out a few things for your consideration. For your VHF equipment make sure that your client has the frequencies cleared and licensed for your use. Don't depent on a single frequency, most 3rd world countries give the better frequencies to those that can pay the most under the table. Second, pursue a group of HF-SSB frequencies, in the tropics propagation requires a spread of frequencies for reliable operation. This would entail having a VHF and a HF-SSB radio in each vehicle but this is the normal mode of operation in the developing countries. If y9ou have any specific questions email me at w5rdf@direcpc.com
Radio Consult

If the hotel roof is quite high and there is a good line of sight to the bases, i would use larsen "nmo" types of antennas with the round magnet mount bases for the mobiles.

i have used this config on several ham radio fox hunts with very good results and a 30 mile range.

also, i have used larsen type "om" 3 inch flange mounts on vhf as base antennas the om mount is designed for mounting on a flat metal or fiberglass surface but i have mounted the coil (om) on a metal 3 in pipe flange that accepted a 1/2 in water pipe.

then the pipe coming from the flange is attached with large hose clamps to a vent pipe or other vertical pole.

larsen and others do make base mounts for mobile coils (they have a plate for the coil to mount on and have radials to provide a ground plane).

Yes Will's Extender would work just fine.

One base unit with extender would do great.
3 DB gain mag-mounts sounds like the easy way
to go.
If you have more than 10 mhzs between
TX and RX then you do not need a duplexer.
Just use two antennas. It is very important
to match the antenna to the operating freq.
for maximum range.Ant. location on vech. is important.
If most vech. are travelling together
then maybe one or two mobile extenders are needed.

The extra cost of the radio gear is nothing if you will be
saving a life.More than one freq. is a must.
Make sure ( You Get training)
that you can get the programming RSS and laptop
computer so if you can load working freq. in the radios
Most companys will let you load their freq. in your
radio when they find out that you can be of help to
them.
In Search and Rescue we learned that most
businesses will be glad to help out.

GOOD LUCK.

RKG wrote:If you're going to put the antenna on the roof of the hotel and the radio in your room, how are you going to get the feedline from the room to the roof?

The plan is to get a top-floor room in order to have as short a feedline as possible.

Consider mounting the radio on the roof (assuming some out-of-the-weather and secure enough location) and controlling it remotely.

I know nothing about remotely controlling radios, except for the AN/GR-39 radio remotes that the Marine Corps uses/used. Again, cost starts to raise its head as layers of complexity are added to the plan. I don't hold the purse strings on this job, and will have to justify every expense. It's a great idea though if we can't get close to the antenna site.

About $500 for a good DC remote and termination panel, and about $100 for a qualified tech to wire the termination panel to your CDM accessory plug.

Two cents time again..
I've been in that area of the world that you're going to, and they do tend to give the best channel authorizations to the locals and visitors get the lousy ones. Two items that could be used, (which I've used for temporary setups and system testing...) The first would be to use a repeater maker, RM20+. That device can allow you to perform cross band repeat operation,if mobile power limits are for HT use, use a TPL mobile power amplifier. Same could be used for the CDM radio equipment as well. The other (more costly too....) would be to obtain Harris RF3200 series AM/SSB equipment. Worked very well, HF from ~100Khz to 30Mhz and if you hook up a packet radio modem you can send text files as well...For the fixed end, various antenna manufacturers have good quality antennas and the like, but I'd strongly suggest that you use stainless steel for nearly every mount if you're going to setting up for semi-permanent mounting as the air quality (read SMOG and acid rain...take a good look at the skies in Botswanna...BCI mines there have a nice lovely cloud of caustic material floating around...) the mounts will last a bit longer than the "duct tape" mount...
Good luck....and BTW...get your shot record updated....if possible as well is to have all that nice equipment shipped in via dip pouch. otherwise, you might wind up with stuff missing....
Cat