Our FD built a portable comm center - It consists of 3 VHF M1225 20 channel radios configured as three ac & standby powered bases.
The only hitch is having 3 antennas. One antenna would be nice.
So we thought since cavities would be too big, perhaps we could program the acc connector on the M1225's to output a voltage at transmit key down which would pull an antenna relay to that radio only during the xmit duration.
In the "no unit transmitting" or receiving mode the one antenna, and antenna relay system would be split with perhaps a ferite combiner back to all three M1225 units.
Is there another way. We do not want to mofify the antenna switch (pin diode) in the M1225's.
Cheers!
Ra
Combining TX Antennas - Ferite ?
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Combining TX Antennas - Ferite ?
Last edited by Ra on Tue Jul 16, 2002 8:57 am, edited 1 time in total.
do it the RIGHT way 3, as in (three, III, one two THREE) antennas.
Number one use the KISS philosophy
number 2 why would you want to introduce unnecessary losses.
number 3 why would you want to complicate things.
number 4 When one is xmiting the others are DEAF with your setup
(potential missed call, life lost, etc, you take it from there)
The only real way to come close to what you propose is to split the rec and tx ports on the radios and run each radio tx thru a circulator then a
cavity of a combiner. THEN, run a separate rec antenna with a multicoupler to the rec ports of all the recievers. Hmmm back to 2 antennas again. See you just cant get something for nothing can you.
Also if any of your frequencies are split (duplex) then your cavity per radio is out the window because the cavity has to be on either the rec or xmit freq. It cant do both and do its job also. By time you buy all of that stuff you can get an EXTRA THREE radios and antennas for the price
and pain of trying to make a rigup work. Phrawg
Number one use the KISS philosophy
number 2 why would you want to introduce unnecessary losses.
number 3 why would you want to complicate things.
number 4 When one is xmiting the others are DEAF with your setup
(potential missed call, life lost, etc, you take it from there)
The only real way to come close to what you propose is to split the rec and tx ports on the radios and run each radio tx thru a circulator then a
cavity of a combiner. THEN, run a separate rec antenna with a multicoupler to the rec ports of all the recievers. Hmmm back to 2 antennas again. See you just cant get something for nothing can you.
Also if any of your frequencies are split (duplex) then your cavity per radio is out the window because the cavity has to be on either the rec or xmit freq. It cant do both and do its job also. By time you buy all of that stuff you can get an EXTRA THREE radios and antennas for the price
and pain of trying to make a rigup work. Phrawg
Phrawg..............
You are right - 3 antenna it will be then - Extra switching crap is a problem - you are right about that too.
It was just a theoritical question anyway.
Thnaks
Ra
It was just a theoritical question anyway.
Thnaks
Ra
Re: Phrawg..............
Don't be in too big of a rush thinking your done.
Question: Are the radios single channel? Reason being is that your going to have desense if they are all in the same band. When you key up one, the others will not be able to hear a weak signal. Solution would be to put in suck out cavities on each of the radios for the other 2 frequencies. Bear in mind that this only works if the different frequencies have a decent separtion to them and your operating on fixed frequencies.
Question: What are you going to use for prime power for the radios? You need to have enough 12 volts available ( if that is what they operate on ) to be able to hold all 3 radios in TX. You can't control each operator to not TX while you want to talk. So plan on enough current to carry all 3. The chances of all wanting to key together are rather remote. But you still need to allow for it.
Question: How are you going to isolate the sound from each radio speaker. Makes it hard to listen to someone talking on a radio while another is blaring in the background. Maybe some sound proof walls between each of the radios.
It gets rather hecktic in time of crisis. You can't control when a radio will emit its noise from the speaker in a command center type operation. More noise leads to more confusion and repeat radio transmissions.
Just a few points to ponder.
Jim
Question: Are the radios single channel? Reason being is that your going to have desense if they are all in the same band. When you key up one, the others will not be able to hear a weak signal. Solution would be to put in suck out cavities on each of the radios for the other 2 frequencies. Bear in mind that this only works if the different frequencies have a decent separtion to them and your operating on fixed frequencies.
Question: What are you going to use for prime power for the radios? You need to have enough 12 volts available ( if that is what they operate on ) to be able to hold all 3 radios in TX. You can't control each operator to not TX while you want to talk. So plan on enough current to carry all 3. The chances of all wanting to key together are rather remote. But you still need to allow for it.
Question: How are you going to isolate the sound from each radio speaker. Makes it hard to listen to someone talking on a radio while another is blaring in the background. Maybe some sound proof walls between each of the radios.
It gets rather hecktic in time of crisis. You can't control when a radio will emit its noise from the speaker in a command center type operation. More noise leads to more confusion and repeat radio transmissions.
Just a few points to ponder.
Jim