Batboard

Hey guys,

Im wondering if it is possible and safe to split a single antenna wire so I can connect 2 mobiles on the same band to 1 antenna using a splitter. I was told this is not safe as the transmitting mobile's power will be sent directly to the other mobile rather then the antenna.

What I want to do is have two mobiles on the same antenna without having to install a seccond antenna on the side of the building.

Is this possible?

If not, what do I need to do?

I know you only want two, but do some searching at various ham radio stores, http://www.hamradio.com, http://www.universal-radio.com, etc.

Here is one that does eight.

http://www.universal-radio.com/catalog/switch/0212.html (I just did some quick searching.

I am pretty sure he's wanting to use both radios at once, so a switch won't do.

If you want to TX from two mobiles on one antenna, you need a duplexer. One port provides isolation from the other. (provided they are different frequency band)

I'm using this: http://www.universal-radio.com/catalog/switch/1864.html BUT you want the same band..?? you need a duplexer as the above post says... we don't know the wattage or frequency...less of a headache for another antenna....and this switch is for 1 mobile at a time...

Even with two mobile radios and a duplexer the wideband frontends on the mobile radios are going to cause desense problems in the same band. Like someone said already, better to use two antennas and space them as far apart(horizontally) as possible.

Al wrote:Even with two mobile radios and a duplexer the wideband frontends on the mobile radios are going to cause desense problems in the same band. Like someone said already, better to use two antennas and space them as far apart(horizontally) as possible.

thanks Al I was thinking the same...
________________________________
great minds think alike

Well to make myself more clear I wanted to stack 2 mobiles on top of each other. Only 1 will be for trasmitting, the other will be for scanning. They are both VHF and will have identical channels. I would like to avoid installing a 2nd antenna so I would like to use 1 antenna with a spliter to connect the two.

So your saying I will need a duplexer for this operation.

Al has a good point. I have a police repeater 2 miles away on 156Mhz. It wipes out the 2 meter band. If your going to use radio A, to transmit & radio B, to scan, What are you going to scan on? If the Antenna is sending out RF? antenna? Of course if your not transmitting, then you could scan. Once you key-up, you won't scan. anything over 5 watts will find the second radio sooner or later.

A duplexer is not what you want.

You've told us that both radios will have the same channels, but you didn't say if they are repeated or simplex channels. If any of them are simplex, any filter based solution is right out, you can't very well filter the TX freq out if it's the same as the RX freq.

If all of the TX freqs are separated from all of the RX freqs by a wide enough margin, you may be able to do it with a preselector filter on the receive only radio, but all the planets would need to be aligned and you may need to kill a chicken or two

Some sort of electronic switching to disconnect the receive radio during transmit should protect the receiver, but would probably be technically prohibitive for your situation.

The radios will be in a building, so getting good antenna separation should be a lot easier than in a vehicle, your best bet is to just bite the bullet and go with two antennas. On the other hand, do you really need a second radio scanning? If they've both got the same channels why not just use one radio?

What you need is a Washington State Patrol Syntor X9000 with the antenna splitter on the receive side. This mobile was built to have an in-band receiver and would be perfect for this application.

Understand you will not be able to receive when you are transmitting, but this will allow the two receivers to run at the same time from the one antenna.

George

Any modern ham radio dualbander with dual display can do this. Both sides can do VHF or UHF at the same time. When txing on one side the other shuts down for safety if in the same band. One antenna, no duplexer. Since you didn't state what you will be using the radio for, I am suggesting a ham radio. Of course if this is for business or Public Safety then a ham radio wouldn't be applicable. GARY N4KVE

If you are using the second radio to RX only. Buy a splitter and use your AM FM antenna. I had a scanner in my truck for years and used that configuration. Worked dandy.

Fowler
KC5AEE

Wouldn't a simple PIN diode suffice to prevent RF from flowing into the receiving radio while the other transmits? Isn't that what manufacturers are still using in low-power (up to 50 watts or so, maybe?) radios to do TX/RX switching?

contrak10 wrote:Hey guys,

Im wondering if it is possible and safe to split a single antenna wire so I can connect 2 mobiles on the same band to 1 antenna using a splitter. I was told this is not safe as the transmitting mobile's power will be sent directly to the other mobile rather then the antenna.

What I want to do is have two mobiles on the same antenna without having to install a seccond antenna on the side of the building.

Is this possible?

If not, what do I need to do?

If you are in the same band, transmitting will not work. One transmitter will blow the other receiver away. You can only use a diplexer if the radios are different bands (eg 150/470) and with a dualband antenna for those bands.
About all you can do is two low-profile antennas (as far apart as possible) or a good coaxial switch.

contrak 10,

I've actually performed this request as a Motorola Infrastructure SP Quantar Configuration in Schaumburg's Engineering for a Public Safety Department in the Ottawa, IL area. Mine was a T4-R4 configuration and provided Selective Wire Line Muting for the three extra Astro-TAC receivers all mounted below the Quantar Base Station in a 60" cabinet. The SP required the Enhance Wildcard Option, a Telco Punch Block, a 4-Port Passive Receiver Multi-coupler, some minor Wildcard scripting, some changes in the Quantar's standard RSS software configuration and you must have two individual antennas to accomplish the system requirements. Preferably you should mount the receive antenna at the top of the tower and the transmit antenna 60 feet below on a side arm to achieve better Tx to Rx Signal isolation.

BTW 925adam, a Diplexer can be used on the same frequency band for the transmit function. Motorola has been doing it since the 1960s, first in the IMTS Base Stations built for Western Electric (these were used for Mobile Telephone Service prior to the Cellular Base Station System) and secondly for antenna combiner systems.

Dan

Dan562 wrote:a Diplexer can be used on the same frequency band for the transmit function

Indeed it can, but not on the same frequency, as contrak10 is wanting to do.

As I asked earlier, wouldn't a simple PIN diode network at the antenna port of the receive-only radio do what he wants to do? Granted, there would be a slight impedance matching problem, but the correct lengths of the proper impedance coax as a matching section should handle that nicely.

I don't believe the simple PIN diode will work in this configuration simply because contrak 10 wants to simul-monitor all of the receiver frequencies that are programmed into the second mobile unit. Another thing I forgot to mention in my previous post, this is the channel / frequency spacing, as it will have a large impact on the second receiver's ability to over come the Desense level. I hope the channels aren't 12.5 or 25 kHz away from each other as the transmitter sideband noise will block any receive signals. If the channel spacing is 250 kHz or greater, contrak 10 has a chance of accomplishing what he wants to do but he will need separate antennas and at least a 60 Foot vertical separation.

The newer Motorola Subscriber Mobile Products do not support any form of a receiver bandpass pre-selector filter unlike the Infrastructure Base Station Products. All of the mobile receiver filtering is accomplished in the I.F. section. Since contrak 10 wants his second receiver to Scan all of the RF Channels, he's got to determine how to lock out the one thats being used for the transmit function otherwise the scanning receiver will always stop on that frequency / channel.

Dan

Strewth! I'm stopping this sketch, it's getting much too silly.

I don't blame you, Jack. It would help if everyone would pay attention and address the problems contrac10 gave, instead of trying to change his problem to what they want it to be.

Contrac10 wants the receiver to receive the same frequency the transmitter is transmitting on, plus a few different ones. The absolutely only way this can be accomplished with the setup he desires is by some type of switching setup that will disconnect the RX only radio while transmitting. I absolutely don't see why he wants to do this, but that's beside the point.

Contrac10, my last advise on the subject is to either use a tone/DC remote with multiple desk sets on a single radio, or a dual head setup on a single radio, like a Spectra or Syntor X9000. Otherwise, you are in for more trouble than its worth.

WOW that a some set of posts

abbylind wrote:If you are using the second radio to RX only. Buy a splitter and use your AM FM antenna. I had a scanner in my truck for years and used that configuration. Worked dandy.

Fowler
KC5AEE

This is the simple and best way for him to do it .

Now to stop the feedback, just turn down the knob
OR
If the TX radio has an extra P.T.T. on back or get inside the head to find it and add a relay to mute the scanning radio's
speaker. I would use a DPDT and a 8 ohm resistor to protect the audio amp.
Done this for years in police cars with scanners.
The people you talk to will also like the "loud squeal in the background" not there.

Save you money, and have some good holiday cheer.

The problem with using the AM/FM antenna... the radios won't be in a vehicle.

I'd mainly looked at the problem from the point of view of keeping the TX power from burning up the receiving radio. After further thought, taking into account the problem of feedback, I'm going to say I would opt for using one radio with scan, setup to tx on the selected channel, maybe with priority. I'm not sure why the OP wants to have a separate radio to scan the same channels, but I can't imagine any reason worth going through the trouble involved.

In contrak 10's original post, he stated the following information:

What I want to do is have two mobiles on the same antenna without having to install a seccond antenna on the side of the building.

Most of you people got side tracked with his use of two Subscriber Mobile units rather than understanding he is using these units as a Poor Mans consolette Base Station configuration. I think I may have a solution for this request, not that it's perfect by any means but it probably will work using only one Base Station Antenna.

contrak 10 will be required to purchase a Refurbished or Used Narda Model 3020A Bi-Directional RF Coupler from a test equipment supply company. These couplers can handle 500 Watts being fed through them to a RF dummy load or an antenna. They have two RF Input / Output Ports mounted on the top depending on which application is required. Each of these RF Ports have a -20 dB Insertion Loss which in most cases allow the ability to connect a signal generator RF output to either of the ports without doing any damage to the signal generator or any other piece of RF test equipment. The two ends each have "N" type connectors for the transceiver and the antenna to be connected in-line.

http://www.bellelect.com/products/9698/

Stating the information listed above contrak 10 you will not be able to Transmit any RF into the coupler's I / O test Ports with the Second Subscriber Mobile being used as a Scanning Receiver. It is also recommeded to insert a Band Pass Filter and a +10 to 20 dB adjustable Receiver Pre-Amplifier to compensate the -20 dB Insertion Loss using the Bi-Directional RF Coupler. These Narda 3020A couplers are not inexpensive even sold on the used market. The frequency coverage on this coupler is between 50 MHz through 1 GHz which will easily accommadate your requirements.

I'm indicating the following information will be very crucial to the performance of the Second Scanning Receiver and this is the RF Channel Frequency Separation because the closer spaced RF Channels will be suspecible to higher Desnse levels when the transmitter is keyed-up and there's no way to avoid this problem for your configuration. If you have not already purchased the Subscriber Mobile units, then I suggest to include the Optional Enchaned Wildcard for each mobile unit. This will provide the option to script each Wildcard table to perform a Selective Audio Muting matrix function between the actual transmitter and the Second Receiver's RF Channel Scanning option. Therefore when the main transmitter's RF channel is changed from F1 to F3 or Fn (whichever channel is selected), the Scanning receiver is automatically inhibited from selecting the chosen RF channel and preventing a recovered audio feedback loop from being heard at the point of Dispatch. Of course, you will be required to interface a wiring harness between the two Subscriber Mobile unit I / Os for this feature to work corretly.

Oh Yeah, whatever you do when constructing your radio configuration, do not place both Subsciber Mobiles units physically close together. Allow at least 1 to 2 feet between the units otherwise the internal synthesizers will radiate into each other, therefore causing even more system problems.

Dan

Dan562 wrote:In contrak 10's original post, he stated the following information:

What I want to do is have two mobiles on the same antenna without having to install a seccond antenna on the side of the building.

Most of you people got side tracked with his use of two Subscriber Mobile units rather than understanding he is using these units as a Poor Mans consolette Base Station configuration. I think I may have a solution for this request, not that it's perfect by any means but it probably will work using only one Base Station Antenna.

contrak 10 will be required to purchase a Refurbished or Used Narda Model 3020A Bi-Directional RF Coupler from a test equipment supply company. These couplers can handle 500 Watts being fed through them to a RF dummy load or an antenna. They have two RF Input / Output Ports mounted on the top depending on which application is required. Each of these RF Ports have a -20 dB Insertion Loss which in most cases allow the ability to connect a signal generator RF output to either of the ports without doing any damage to the signal generator or any other piece of RF test equipment. The two ends each have "N" type connectors for the transceiver and the antenna to be connected in-line.

http://www.bellelect.com/products/9698/

Stating the information listed above contrak 10 you will not be able to Transmit any RF into the coupler's I / O test Ports with the Second Subscriber Mobile being used as a Scanning Receiver. It is also recommeded to insert a Band Pass Filter and a +10 to 20 dB adjustable Receiver Pre-Amplifier to compensate the -20 dB Insertion Loss using the Bi-Directional RF Coupler. These Narda 3020A couplers are not inexpensive even sold on the used market. The frequency coverage on this coupler is between 50 MHz through 1 GHz which will easily accommadate your requirements.

I'm indicating the following information will be very crucial to the performance of the Second Scanning Receiver and this is the RF Channel Frequency Separation because the closer spaced RF Channels will be suspecible to higher Desnse levels when the transmitter is keyed-up and there's no way to avoid this problem for your configuration. If you have not already purchased the Subscriber Mobile units, then I suggest to include the Optional Enchaned Wildcard for each mobile unit. This will provide the option to script each Wildcard table to perform a Selective Audio Muting matrix function between the actual transmitter and the Second Receiver's RF Channel Scanning option. Therefore when the main transmitter's RF channel is changed from F1 to F3 or Fn (whichever channel is selected), the Scanning receiver is automatically inhibited from selecting the chosen RF channel and preventing a recovered audio feedback loop from being heard at the point of Dispatch. Of course, you will be required to interface a wiring harness between the two Subscriber Mobile unit I / Os for this feature to work corretly.

Oh Yeah, whatever you do when constructing your radio configuration, do not place both Subsciber Mobiles units physically close together. Allow at least 1 to 2 feet between the units otherwise the internal synthesizers will radiate into each other, therefore causing even more system problems.

Dan

http://www.bellelect.com/products/9698/
This is $450.00 Dan...... I see your point, but another antenna would be a whole lot cheaper!
Jim

Alright... we've gone out in left field, over the fence, through the weeds, off to the nearby pasture, and have summarily flogged the deceased equine.

I think we've covered about every possible option, and the OP hasn't bothered to chime in in over a week.

Contrak, if you need more info, I'd suggest a follow-up post with quite a bit more info about what you want to do.