Newbie Question

[ES13Raven]

I have a simple newbie question for ya. I tried searching the FAQ but couldn't find the answer.

In My Area, it shows the Sheriff's frequencies as 154.x but most of them have no Input. On the CHP frequencies, they have 42.x frequencies and different Inputs.

My question is what are Inputs and do I need to scan them? Is the Frequency one side of the conversation and the Input the other side?

Thanks for your help!

[W4KRR]

If there's no input listed, or the listed input is the same frequency as the output, then it's a simplex channel, that is, the conversation takes place on one frequency for all mobile and base units. An input usually means the input to a repeater. In that case, you only need to monitor the output, and you should hear both sides of the conversation, because the input is rebroadcast on the repeater output frequency. So in this case you don't need to monitor the input frequency.

In some cases, you have a semi-duplex channel, that is, the base station transmits to the mobile units on one frequency, and the mobile units reply on a different frequency, with no repeater involved. In this case, you would need to monitor both frequencies in order to hear both sides of the conversation. In the case of the CHP, I believe you have to monitor both frequencies in order to hear both the base and mobile units.

[ES13Raven]

Originally Posted by W4KRR

In some cases, you have a semi-duplex channel, that is, the base station transmits to the mobile units on one frequency, and the mobile units reply on a different frequency, with no repeater involved. In this case, you would need to monitor both frequencies in order to hear both sides of the conversation. In the case of the CHP, I believe you have to monitor both frequencies in order to hear both the base and mobile units.

Thanks... How can you tell if it is a semi-duplex channel?

[W4KRR]

Originally Posted by ES13Raven

Thanks... How can you tell if it is a semi-duplex channel?

Listen to the base frequency. If you can't ever hear any of the mobiles, then it could be semi-duplex. Look for a second frequency that the mobiles use to talk back to the base (like CHP). Sometimes, on a single frequency simplex system, you may hear mobiles only some of the time; this is due to some mobiles being closer to you that others, and you're only hearing mobiles that are closest to you.

[kb2vxa]

Hi all,

Let's clear something up right now, repeaters are semi duplex. That means when a party is talking he can't hear anything, one way at a time. I get a laugh when a dispatcher tries to tell a unit he has an open mike, he can't hear the dispatcher when the mic is open. Full duplex means both parties can talk at once such as on a land line or radio telephone.

Split channel operation is also semi duplex as described above, no repeater involved. In the case of land line or microwave linked repeaters the repeat function may be turned off. This comes in handy when the mobiles get into a hen party annoying the dispatcher trying to catch up with the paperwork.

Raven, think a minute. If you hear only one side of the conversation it COULD be non repeated split frequency operation but highly unlikely. That's only used by the old VHF taxis and a few industrial and commercial users where field units only need to talk to the dispatcher, not each other and it's usually a remote base connected to the dispatcher by land line. If you can only hear one side of the conversation most likely you're listening to a repeater input so you only hear the field units, or simplex and only hear the dispatcher, the field units being too weak.

[loumaag]

Just to set the record straight, the CHP entries (linked above by the OP) are not displayed correctly in accordance with the current policy of the site. Those entries are supposed to be two lines each. One for the Base and one for the mobile.

The easy way to see if you need to have both is to look at the Type column, if it says BM or MB and there is a different frequency in the Frequency and Input columns then there is no repeater involved and you must monitor both to hear the conversation. Naturally if they were entered in the DB properly they would be on two lines and both frequencies would be in the Frequency column.

[ES13Raven]

Originally Posted by loumaag

The easy way to see if you need to have both is to look at the Type column, if it says BM or MB and there is a different frequency in the Frequency and Input columns then there is no repeater involved and you must monitor both to hear the conversation. Naturally if they were entered in the DB properly they would be on two lines and both frequencies would be in the Frequency column.

Thank you, that was very helpful.

[hotdjdave]

Originally Posted by loumaag

Just to set the record straight, the CHP entries (linked above by the OP) are not displayed correctly in accordance with the current policy of the site. Those entries are supposed to be two lines each. One for the Base and one for the mobile.

The easy way to see if you need to have both is to look at the Type column, if it says BM or MB and there is a different frequency in the Frequency and Input columns then there is no repeater involved and you must monitor both to hear the conversation. Naturally if they were entered in the DB properly they would be on two lines and both frequencies would be in the Frequency column.

So, Lou, should this be fixed?

[wayne_h]

Originally Posted by hotdjdave

So, Lou, should this be fixed?

It's not broken, so no fixing is needed. If it doesn't meet the policy then the policy should be changed considering how CHP operates their network. To separate them would cause confusion and just add more unnecessary data.

[hotdjdave]

Originally Posted by wayne_h

It's not broken, so no fixing is needed. If it doesn't meet the policy then the policy should be changed considering how CHP operates their network. To separate them would cause confusion and just add more unnecessary data.

That is what I thought, I was just trying to figure out how Lou thought it should be.

However, for CHP I program both frequencies in my scanner, one for the "B" and one for the "M." I don't consider each channel as one channel, but rather two channels. They are mislabeled in the database, one channel is not an input and output like other channels, rather a base channel and a mobile channel.

[loumaag]

Originally Posted by wayne_h

It's not broken, so no fixing is needed. If it doesn't meet the policy then the policy should be changed considering how CHP operates their network. To separate them would cause confusion and just add more unnecessary data.

Oh wait, I see, we should base the entire conventional database on how one state's highway patrol operates! Try again, first they don't operate any different then several other states, including mine. Second, the way it is is wrong for several reasons first because there is no input frequency in a duplex operation just discrete channels. And as I said, it it contrary to the policy; Wayne & Dave, see Pet Peeves II started by me.

[hotdjdave]

Originally Posted by loumaag

Wayne & Dave, see Pet Peeves II started by me.

"Your search - Pet Peeves II - did not match any documents."

[slicerwizard]

Originally Posted by loumaag

Just to set the record straight, the CHP entries (linked above by the OP) are not displayed correctly in accordance with the current policy of the site. Those entries are supposed to be two lines each. One for the Base and one for the mobile.

The easy way to see if you need to have both is to look at the Type column, if it says BM or MB and there is a different frequency in the Frequency and Input columns then there is no repeater involved and you must monitor both to hear the conversation. Naturally if they were entered in the DB properly they would be on two lines and both frequencies would be in the Frequency column.

OK, I think I got all that - so why, on that CHP page (and any others like it), isn't there a block of text explaining that BM/MB records with two different frequencies document a mobile-to-dispatcher link and a dispatcher-to-mobile link and that both frequencies must be monitored to hear both sides of a call?

If that little tidbit had been explained, this thread wouldn't exist.

[kb2vxa]

Hi Lou and all,

Thanks for clearing that up, in part at least. Just so we get our semantics straight, that split frequency operation isn't necessarily duplex full or semi, see my post above. In many cases it's what might be called "split frequency simplex" if I may coin the term.

I see some confusion here, it looks like the database tries to follow the old Hughes Police Call designation system. What can be confusing is the MB/BM designators, IMO the mobile frequency should simply be M and the base B rather than mobile to base and base to mobile as it appears to me. If I remember right Hughes used BM to designate a base and mobile simplex frequency with separate base and mobile frequencies as above.

In any case scanning can be a real bear, to hear both sides one would have to scan only one pair at a time with no delay to catch both sides without cutting one or the other off AND only one pair to avoid the scanner moving on to another conversation entirely. No wonder Eric Estrada got fat and now sells swamp land in Florida. (;->)

[wayne_h]

Originally Posted by loumaag

Oh wait, I see, we should base the entire conventional database on how one state's highway patrol operates!

RELAX, you misunderstood me. There should be exceptions to systems that operate out of the norm such as this. I'd rather not see an individual row for EVERY CHP frequency considering the Base and Mobile freqs are not physically paired together (like a traditional receiver voting system). Also, some CHP setups do not follow the normal setup (SoCal for example). I definitely don't want to figure out which areas do or do not; and not everyone can get inside a vault to see it either.

The more complicated you make it the more difficult it will be for people new to the CHP network. Not everyone is as smart as you Lou, sorry to inform you. There shouldn't be a preface to an agency because the listing is so complicated you can't figure it out with one take. These split systems are less than 3% of the database. I think we can make an exception. Regardless, the CA Admin aren't in agreement with changing so.....

[hotdjdave]

Originally Posted by wayne_h

Regardless, the CA Admin aren't in agreement with changing so.....

I understand the CHP system the way it is now in the RR, but I didn't think about how others (newbies) would view it. Another factor is if you look in most scanner books, the pairs are listed as "base" and "mobile," not "frequency" and "input" (or "output" and "input"); however, they are usually one entry. Also, I am not sure why some entries have "BMR" and some just "BM."

I think what is most important here is how people are going to put the frequencies in their scanner. Are they going to put in just one of the paired frequencies, or put in both of the frequencies as two separate channels (base and mobile). I do the latter.

[wayne_h]

Originally Posted by hotdjdave

I understand the CHP system the way it is now in the RR, but I didn't think about how others (newbies) would view it. Another factor is if you look in most scanner books, the pairs are listed as "base" and "mobile," not "frequency" and "input" (or "output" and "input"); however, they are usually one entry. Also, I am not sure why some entries have "BMR" and some just "BM."

You're right but another thing is the database isn't quite setup for this particular duplex operation. It's the same either way; it's just not fitting to CHP's arrangement.

Any further discussion should go in the DB Forum. We need to come to some agreement. Or perhaps poll the CA Forum users.

[hotdjdave]

Wayne, sent you a PM.

[loumaag]

Originally Posted by wayne_h

Any further discussion should go in the DB Forum. We need to come to some agreement. Or perhaps poll the CA Forum users.

Sorry for being out of the loop for a few days...In any case, I agree, this is a discussion that belongs in the DB Admin forum.