Many VHF/UHF mobile and base rigs provide the ability to crossband repeat - that is, to fully duplex, automatically repeat what is heard on 2 meters onto a 440mhz frequency and vice-versa. If you've never used this type of functionality or are just new to the whole concept, you might be thinking, "what does this do for me?" If you own an HT and also have a VHF/UHF rig with crossband repeat (or are considering purchasing a VHF/UHF rig for the house) wouldn't you like to have the freedom to move around the house & yard while talking to your buddies on the radio, but use the power and antenna capabilities of a base station? That's what crossband repeat can do for you.
You'll notice that I used the word "legally" in the thread title. The usage of this functionality has caused quite a bit of controversy for several reasons. The FCC requirements that are relevant to this discussion are that the Control Operator must ID every 10 minutes on all frequencies being transmitted on, remote stations must have ID timers, and remote stations must have a way to remotely control or shut them off. The latter two of the three requirements mentioned are the easiest to satisfy. Simply put, if you are capable of walking over to the rig doing the crossband repeating, it is under your direct control. You don't need a ID timer and you can just simply turn it off whenever you need to. The requirement to ID on every frequency is the tricky one to satisfy.
For the uninitiated, let's first go over the fundamental setup and concepts in play. The typical use-case scenario for this setup is like this:
Base Antenna <--> 2m <--> VHF/UHF Rig <--> 440mhz <--> HT
Anything that is heard on the Base Antenna on 2m, is picked up by the VHF/UHF Rig and broadcast simultaneously on 440mhz where the HT is listening. Conversly, anthing that is transmitted by the HT on 440mhz is picked up by the VHF/UHF Rig where it is simultaneously transmitted using the Base Antenna on 2m. You can probably now see the advantage of going through this excercise. You have the flexibility of moving aroud with the HT, but the power output and reception of the vhf/uhf rig and base antenna.
When you give your callsign using your voice on the HT, it will be transmitted out on both the 440mhz and 2m frequencies. When another station talking back to you IDs, it will also be sent on the 2m and 440 frequencies. Here's where it is easy to violate the intent of the FCC regulations: Let's say you have the UHF side of the rig set on full power. If your base antenna is a 2m/440 antenna, when the other station that you're talkign to ID's, it is being rebroadcast on 440Mhz at 35watts (probably) over a base antenna. No problem. However, when you ID on your HT, it is only being broadcast at 5 watts over a little rubber ducky on UHF. The VHF side gets the full 50 watts of the VHF/UHF rig and the power of the base antenna, but the 440mhz side only used your HT. Distant stations monitoring the 440mhz side will probably never hear your callsign. This is the problem that must be corrected to keep you legal.
Some of the newer crossband repeat rigs can auto-id on the 440 side while crossband repeating using CW. This makes the whole problem moot. However, for the vast majority of rigs that don't do this, there is a very simple way to solve this problem to keep you from getting written up by an "Official Observer". Simply put, the solution involves doing two things: 1. Reducing the power output of the VHF/UHF rig on the 440Mhz side and, 2. changing the antenna system used on the UHF side of the crossband repeater.
Step 1 is easy: Just turn the UHF power output on the crossband repeater to it's lowest setting. Most, if not all crossband repeat rigs have seperate power output settings for each band. The lowest power output setting for UHF is usually around 5 watts. However, if you're transmitting 5 watts into a base 440mhz antenna, your range will still be far greater than the 5 watts coming out of your HT duckie antenna. That's why you need step 2.
Step 2: Between the base antenna and the crossband repeater, install a VHF/UHF duplexer right at the rig. On the 2m side, attach the feedline for your 2m base antenna. On the 440 side install a very small antenna that will limit the range of your crossband repeater. I use a small 1/4 wave 440mhz rare earth gumdrop magmount antenna stuck on a piece of metal that is sitting on my window sill. The 1/4 wave 440 mhz antenna is only about 6 inches long. That, coupled with the feedline loss in the cheap coax on the magmount and the signal loss from passing through my house and adjacent houses gives my crossband repeat station an effective range of about 6 blocks. Your distance may vary based on your surroundings. Now I know that when I ID on my HT, the signal output from the HT on the 440mhz frequency is being carried farther than when the crossband repeater transmitts on 440. When I really want to reduce the effective range of the 440mhz side, I use a dummy load set on the floor for the 440mhz antenna on the crossband repeater. The dummy load still radiates a little and also receives my 440mhz HT transmissions, but the effective range is now reduced to about 1 house on either side of my own, if that.
Measuring the effective range of the crossband repeater is pretty simple also. Just set it up and find someone to talk to on 2m. Now start walking away from your station with your HT while having your conversation. When the other station starts to crackle and get hard to understand, you're reaching the end of your range. Now just ask yourself (or get a friend to help you) if your HT can be heard by itself on 440mhz back to your base from where you're at. If it can be, then you've met the requirement that you have ID'd on every frequency and any station that can hear the transmission from your crossband repeater can also hear your HT.
When setting up your crossband repeat base station there are a few other considerations worth mentioning. First, make sure you're using a 440mhz frequency that isn't allocated to something else nearby. If you've greatly reduced the effective range of the 440mhz side as suggested, this is not nearly that big of an issue but you should still do a little homework. Secondly, make sure you use a CTCSS tone or DCS code between your HT and crossband repeater. This will make it so someone won't accidentally get into your crossband repeater and unkowningly transmit on 440mhz. Also remember to turn the system off when not in use so that crossband repeater doesn't pick up traffic on 2m and start repeating it on 440mhz while you're not around to ID every 10 minutes.
I've been using this setup for years in the busy Los Angeles metro area with no problems. If you haven't thought about setting this up, give it a try and free yourself from your desk
.
You'll notice that I used the word "legally" in the thread title. The usage of this functionality has caused quite a bit of controversy for several reasons. The FCC requirements that are relevant to this discussion are that the Control Operator must ID every 10 minutes on all frequencies being transmitted on, remote stations must have ID timers, and remote stations must have a way to remotely control or shut them off. The latter two of the three requirements mentioned are the easiest to satisfy. Simply put, if you are capable of walking over to the rig doing the crossband repeating, it is under your direct control. You don't need a ID timer and you can just simply turn it off whenever you need to. The requirement to ID on every frequency is the tricky one to satisfy.
For the uninitiated, let's first go over the fundamental setup and concepts in play. The typical use-case scenario for this setup is like this:
Base Antenna <--> 2m <--> VHF/UHF Rig <--> 440mhz <--> HT
Anything that is heard on the Base Antenna on 2m, is picked up by the VHF/UHF Rig and broadcast simultaneously on 440mhz where the HT is listening. Conversly, anthing that is transmitted by the HT on 440mhz is picked up by the VHF/UHF Rig where it is simultaneously transmitted using the Base Antenna on 2m. You can probably now see the advantage of going through this excercise. You have the flexibility of moving aroud with the HT, but the power output and reception of the vhf/uhf rig and base antenna.
When you give your callsign using your voice on the HT, it will be transmitted out on both the 440mhz and 2m frequencies. When another station talking back to you IDs, it will also be sent on the 2m and 440 frequencies. Here's where it is easy to violate the intent of the FCC regulations: Let's say you have the UHF side of the rig set on full power. If your base antenna is a 2m/440 antenna, when the other station that you're talkign to ID's, it is being rebroadcast on 440Mhz at 35watts (probably) over a base antenna. No problem. However, when you ID on your HT, it is only being broadcast at 5 watts over a little rubber ducky on UHF. The VHF side gets the full 50 watts of the VHF/UHF rig and the power of the base antenna, but the 440mhz side only used your HT. Distant stations monitoring the 440mhz side will probably never hear your callsign. This is the problem that must be corrected to keep you legal.
Some of the newer crossband repeat rigs can auto-id on the 440 side while crossband repeating using CW. This makes the whole problem moot. However, for the vast majority of rigs that don't do this, there is a very simple way to solve this problem to keep you from getting written up by an "Official Observer". Simply put, the solution involves doing two things: 1. Reducing the power output of the VHF/UHF rig on the 440Mhz side and, 2. changing the antenna system used on the UHF side of the crossband repeater.
Step 1 is easy: Just turn the UHF power output on the crossband repeater to it's lowest setting. Most, if not all crossband repeat rigs have seperate power output settings for each band. The lowest power output setting for UHF is usually around 5 watts. However, if you're transmitting 5 watts into a base 440mhz antenna, your range will still be far greater than the 5 watts coming out of your HT duckie antenna. That's why you need step 2.
Step 2: Between the base antenna and the crossband repeater, install a VHF/UHF duplexer right at the rig. On the 2m side, attach the feedline for your 2m base antenna. On the 440 side install a very small antenna that will limit the range of your crossband repeater. I use a small 1/4 wave 440mhz rare earth gumdrop magmount antenna stuck on a piece of metal that is sitting on my window sill. The 1/4 wave 440 mhz antenna is only about 6 inches long. That, coupled with the feedline loss in the cheap coax on the magmount and the signal loss from passing through my house and adjacent houses gives my crossband repeat station an effective range of about 6 blocks. Your distance may vary based on your surroundings. Now I know that when I ID on my HT, the signal output from the HT on the 440mhz frequency is being carried farther than when the crossband repeater transmitts on 440. When I really want to reduce the effective range of the 440mhz side, I use a dummy load set on the floor for the 440mhz antenna on the crossband repeater. The dummy load still radiates a little and also receives my 440mhz HT transmissions, but the effective range is now reduced to about 1 house on either side of my own, if that.
Measuring the effective range of the crossband repeater is pretty simple also. Just set it up and find someone to talk to on 2m. Now start walking away from your station with your HT while having your conversation. When the other station starts to crackle and get hard to understand, you're reaching the end of your range. Now just ask yourself (or get a friend to help you) if your HT can be heard by itself on 440mhz back to your base from where you're at. If it can be, then you've met the requirement that you have ID'd on every frequency and any station that can hear the transmission from your crossband repeater can also hear your HT.
When setting up your crossband repeat base station there are a few other considerations worth mentioning. First, make sure you're using a 440mhz frequency that isn't allocated to something else nearby. If you've greatly reduced the effective range of the 440mhz side as suggested, this is not nearly that big of an issue but you should still do a little homework. Secondly, make sure you use a CTCSS tone or DCS code between your HT and crossband repeater. This will make it so someone won't accidentally get into your crossband repeater and unkowningly transmit on 440mhz. Also remember to turn the system off when not in use so that crossband repeater doesn't pick up traffic on 2m and start repeating it on 440mhz while you're not around to ID every 10 minutes.
I've been using this setup for years in the busy Los Angeles metro area with no problems. If you haven't thought about setting this up, give it a try and free yourself from your desk
.