CHP trouble

[avtarsingh]

if all else fails it seems you have 2 live audio feeds for humboldt county

they both list chp as part of their feeds

 

[humboldtMUD]

yea thats not quite the same as getting it on MY scanner. talked me into it, gunna get the diamond 130, let you know how it works. didnt even know c crane co. existed in fortuna, thanks--

 

[tomasG]

Sorry to be contradictory, but, umm, no.

- Elevation

Antenna, antenna, antenna. A good antenna mounted 20 feet above your roof will usually out-perform a crappy antenna at 1,000 feet. Humboldt County is mostly VHF and simple RG6 Quad shielded CATV cable is more than fine up through UHF.

- I set my squelch as tight as I can get it. As you loosen the squelch, you effectively reduce your sensitivity. Unless you are confident the signals you want are strong; pay attention to the squelch.

The squelch circuit on a scanner does not decrease the sensitivity. It increases the point at which it will open.

Don't expect to hear the cars (or the base) if your antenna can not "see" the transmitting antenna.

Partly true but not so much on VHF low. Most scanner listeners are nowhere close to being able to see the transmitting antenna. They hear the transmitter.

If your goal is listening to CHP, which I love, the better antenna is not the DJ130N. Their low band performance is terrible. Antenna gain is achieved by length (heigth.) A ST-2 that stands 9 feet tall will out-perform a DJ130N on low band without question. It's elements form a 1/2 wave antenna on low band.

 

[gmclam]

Antenna, antenna, antenna. A good antenna mounted 20 feet above your roof will usually out-perform a crappy antenna at 1,000 feet.

Let's compare apples to apples.... when you install an antenna, the HIGHER then antenna, the better the reception. The most common reason the antenna at 1000 feet does worse is because of LINE LOSS. But if one person is at 100 feet and another person is at 1000 feet, and they are using the SAME antenna and have the same line loss; the person at the higher elevation will generally have better reception.

Humboldt County is mostly VHF and simple RG6 Quad shielded CATV cable is more than fine up through UHF.

I am using RG6 quad shield CATV cable (swept to 2250 MHz) here and monitoring 800 MHz just fine. My install is 50 feet of "LMR-400" down from the antenna to a multicoupler. The longest run is 70 feet of RG6 (as stated). I have no issues with signals from Modesto (450 MHz), Sacramento (800+ MHz) or Shasta county (~150 MHz) at the other end of that run.

The squelch circuit on a scanner does not decrease the sensitivity. It increases the point at which it will open.

The squelch EFFECTIVELY reduces your sensitivity. Turn your squelch all the way on and tell me how much you are receiving. Now adjust it as tight as possible and tell me how much you are receiving.

Partly true but not so much on VHF low. Most scanner listeners are nowhere close to being able to see the transmitting antenna. They hear the transmitter.

I believe I put that "see" in quotes. It is not a literal statement. Certainly signals that "skip" in or are "ducted" are different; and that kind of stuff is common on low band. What I described here is what is needed for good reception under normal conditions.

If your goal is listening to CHP, which I love, the better antenna is not the DJ130N. Their low band performance is terrible.

I do agree that the discone is NOT the best antenna for CHP. It is a good "broadband" antenna with unity gain across its range of reception. But not too many people listen to only CHP and/or use a separate antenna just for CHP (low band).

 

[jeremyphoto23]

Humboldt CHP

I worked with both Ukiah and Humboldt CHP dispatch centers when I was working as a dispatcher in Mendo County. I have a dispatch buddy that has a scanner located in Willits, it is the law enforcement live feed for Mendocino County. CHP Green is programmed into the scanner because Mendo SO works closely with Humboldt CHP in the north county and they use it to monitor Humboldt.

CHP has a "voting" system with their radios, which means on the radio console, the radio system "votes" what repeater it thinks is the best repeater to use to transmit back to a field unit, but dispatchers can override the "voting" feature and choose what repeater to broadcast off of, most likely because they know from experience which repeater works better in which area. Pratt probably is the least used repeater for the Green Channel in Humboldt.

I am able to receive CHP Green in Ukiah in my truck with mounted antenna and it is hitting off of the Cahto repeater. My suggestion is you don't program the PL tone into your scanner, you may be able to pick up traffic from another repeater.

 

[avtarsingh]

if you sweep the diamond on an ifr 7550 antenna analyzer you will see it does quite well on 42-45 mhz

it isnt meant for cb where it doesnt perform as well - but it still works fine even for cb

anything with a coil or trap designed just for chp freq range wont perform as well all over on the rest of the bands

i am sure he would like to listen to everything else thats going on and the diamond is the best sacrifice for all around performance

you can go cheaper and get a tram or workman discone antenna but they perform very poorly on uhf freqs


the purpose of him getting a diamond is that its only 95 bucks and it will perform on all bands for him
the purpose of him using good 50 ohm coax is to perform at its best in case he ever wants to transmit on it down the road

why purchase just a specified lot of rg6 or to buy a spool that costs 50 bucks at home depot -
when for about the same price you can have good long lasting 50 ohm coax thats already suited for ham transmit should he decide its something he wants to pursue ?

 

[humboldtMUD]

that makes alot of sense with the PL, thanks jeremy. so yesterday i had time to kill and made a crappy hillbilly antenna out of coax and put it up to the roof. i got chp a few times just since yesterday (makes me want a good antenna that much more). i have gotten mobile a few time (probably when they are driving by). another thing that happened is w/ the antenna on the roof the california preprogrammed channels hp,police,dot actually work. alot of frequencies ive never seen before w/ chp and sheriff. before i think i was getting far to much interference w/ the antenna in to house(plus the stock antenna is close to pointless here).

im running squelch at 1, the lowest setting. no garbage either.

thing about range w/ antenna purchase, chp is low, 40's, sheriff is 150's. also cal fire and ems is 150's which is quite important to me the only thing i listen to high is city ambulance which is 462.975.

my thinking is, maybe because my reception it so much improved just by making a coax antenna the st2 would be more than effective..price is nice too. but, i dont want to cheap out, want the best situation in the end. thanks!

 

[tomasG]

Let's compare apples to apples.... when you install an antenna, the HIGHER then antenna, the better the reception. The most common reason the antenna at 1000 feet does worse is because of LINE LOSS. But if one person is at 100 feet and another person is at 1000 feet, and they are using the SAME antenna and have the same line loss; the person at the higher elevation will generally have better reception.

We can agree to disagree without being disagreeable

As I said a good antenna 20 feet above your roof will out-perform a crappy antenna at 1,000 feet. The montra has always been antenna, antenna, antenna. I have worked Japan on 1 watt into a good antenna when 1,000 watts on a crappy antenna failed. Yes, if both users are using identical systems of a radio, cable and antenna in theory the antenna at 1,000 feet will receive further. That's because of the distance to the horizon. But that doesn't mean better. If your scanner reads RSSI try the experiment and note that there won't be a significant change in signal strength between altitudes. Either you hear it well or you don't. In fact with scanners it may be worse because of scanner front-end overload. Just putting up an exterior antenna freaks a lot of scanners out and intermod is created. Self-generated intermod when the mixer goes non-linear. Elevation gives you distance. If there are obstructions then yes elevation will render better performance but again, at a cost.

A discone is a compromise antenna and I have compared the DJ130 side by side with a ST-2 and a Ferret. The ferret was good (and expensive) but the ST-2 was the best for low band. This is because it has a 9 foot length. A CHP 1/4 wavelength antenna is roughly 4.3 feet per side. Hence, the ST-2 has better performance.

A ST-2 is $59 and a better choice for CHP than a discone. If he doesn't want that tall of an antenna then the discone would be a choice to consider. Antenna gain is achived by length and design. Ask yourself what a mobile antenna may be quoted as having 6db gain but a 20 foot tall Station Master also having 6db gain will kick its butt. Length. The ST-2 is a longer antenna with 1/4 wavelength lowband elements that form a 1/2 wave. A 1/2 wave antenna has 0db gain. Put the discone and ST-2 on an A/B switch and listen to the mobiles of CHP. The ST-2 will be the clear winner.

A squelch circuit as used in a scanner (or commecial radio) is a noise gate. It allows the user to set a threshold over which a signal must be before opening the gate. The user is setting the noise level he is willing too listen to. But it doesn't reduce the sensistivity of the radio. Another type of squelch is a RF squelch which does effectively appear to decrease sensitivity because a signal must be a certain RF level to open the squelch. Ham radios usually use a RF squelch rather than a hysterisis type squelch circuit.

On cable, yes RG6Q is good up past 800 but with much higher loss. I didn't mention it because I looked at his county and didn't see any 800 operation. Mostly VHF and UHF. That isn't to say that RG6Q is bad cable and it is usuable up into the gigahertz range.

By the way and just as a reference, I am finishing my degree in electronics and communications system design. Last weekend I passed the extra class ham radio test. I'm not bragging - just trying to add credibility to my statements.

 

[cousinkix1953]

CAL-TRANS has some 800 mhz conventional repeaters in Humboldt county. You will hear more activity in the winter time; when there are problems with the roads. State parks will show up on 800 mhz sooner or later too. Prelican Bay state prison uses it's own Motorola trunked radio system...

 

[Tweekerbob]

QRP into Japan is not that hard a feat. But you're not talking apples to apples. VHF is line of sight, not ionospheric bouncing around like HF under the MUF. The mantra should be: put up a paper clip at 1000 feet and feed it with 1.5" or greater heliax and that will outperform your gain antenna at 20'. Reducing feedline loss and using quality connectors that also attribute to the reduction of this loss should be your new mantra for VHF and above.

It is true that overload (not so much what your call "internal intermod") will affect a receiver's performance. The receiver can become densensitized by transmissions in other bands. You can only build a receiver so tight. Notch and trap filters were created to help reduce the desense on receivers, particularly at repeater sites. I'm sorry, but is there a reason why high level repeaters are located on mountaintops and not on top of a two story building? Is it because several thousand different and highly funded agencies and companies couldn't afford good antennas?

A 1/4 wave antenna at 42 MHz is closer to 5.5 feet. A dipole or coaxial dipole will be close to 11 feet.

Congrats on passing your Extra exam Tomas! I did it 20 years ago when I was 13 years old.

 

[humboldtMUD]

tweekerbob, what is the 5.5 ft and 11ft referring to? sorry im novice, trying to grasp.

 

[gmclam]

tweekerbob, what is the 5.5 ft and 11ft referring to? sorry im novice, trying to grasp.

42MHz = 7.14 meters = 23.43 feet. That is the "wave length". One quarter of 23.43 = 5.86 feet....

To calculate the wavelength of an antenna, the formula is 234 / frequency in MHz for a 1/4 wave antenna .. so 234 / 42 = 5.5 feet. That is the size of the antenna for best CHP reception at 42MHz.

 

[avtarsingh]

there is a whole division of people with engineering degrees maybe thats why most of the chp cant talk to each other any more since those engineers did their "magic"

if you want a good cheap mobile antenna i recommend a simple motorola 1/4 wave vhf nmo antenna
will do just fine

its designed for 150 mhz but it works fine for chp in your area -that and an nmo install kit with cable (try to avoid the stranded cabling - makes the connector easier)

if you know any radio people at all they usually have a million lying around

all you need is a 7/8 hole saw to cut the hole in the roof not that hard

hopefully you know somebody up there who has a decent hole saw ? several companies make nice ones that only allow you to drill so far into the roof without nailing your headliner it always helps to pull the headliner down but you can never be too sure

i got my extra 23 years ago what do i win ?

 

[humboldtMUD]

ok i was just looking at that at Whip Antenna Length And Frequency Calculator (frequincy calculator). i understand now thanks for the info. i need to just get a book, not enough info on the internet.

i was looking for a base antenna, not mobile-
so i went and ordered a st-2. seemed like it should work for my situation and found it for $38. worst case scenario waisted $50(shiping/tax). ill post my results when its hooked up and runnen.

 

[tomasG]

Yes, I gave the wrong measurement. For some reason I was thinking of 6 meters. But Your analogy to a paper clip doesn't work.

There are two reasons that a repeater is at an elevated point. 1) To get above local obstructions, and 2) range. Back on topic, a discone on lowband does not compare to ST-2 and element length. Element length is what captures the signal. Yes, a discone will work on lowband. But not as effectively. Most agencies are not on mountaintops so as to limit their range. Either you have line of sight or you don't. For municipal coverage the FCC won't generally issue a license to a high altitude repeater. A county would be an exception. But not dispatch channels for CHP. Except for the Blue's they are designed for a 40 nile radius, give or take.

But as Ryan, AB6OI, knows about internally generated intermod, it is caused by the mixer becoming non-linear and generating what sounds like intermod. It is not true intermod but is created by frontend overload.

The more we go back and forth on this the more it resembles an argument. A small, short antenna will never compare to a Super Station Master II.

 

[Mike_G_D]

Yes, I gave the wrong measurement. For some reason I was thinking of 6 meters. But Your analogy to a paper clip doesn't work.

There are two reasons that a repeater is at an elevated point. 1) To get above local obstructions, and 2) range. Back on topic, a discone on lowband does not compare to ST-2 and element length. Element length is what captures the signal. Yes, a discone will work on lowband. But not as effectively. Most agencies are not on mountaintops so as to limit their range. Either you have line of sight or you don't. For municipal coverage the FCC won't generally issue a license to a high altitude repeater. A county would be an exception. But not dispatch channels for CHP. Except for the Blue's they are designed for a 40 nile radius, give or take.

But as Ryan, AB6OI, knows about internally generated intermod, it is caused by the mixer becoming non-linear and generating what sounds like intermod. It is not true intermod but is created by frontend overload.

The more we go back and forth on this the more it resembles an argument. A small, short antenna will never compare to a Super Station Master II.

I know I should be listening to my "little voice" telling me to stay out of this but...

1) Height's important - so is the antenna and its design - 'Nuff said.

2) A TRUE discone DESIGNED for a low frequency start equaling that of the CHP should work fine for listening to the CHP. Bear in mind that the Diamond and similarly designed hobbyist discones are only TRUE discones above about 100MHz or so. The Diamond and its brethren "cheat" for low frequency coverage by adding a base loaded whip tuned for the middle of the VHF-Low band and then using the sloping angled radials of the discone as a shortened (relative to the low band quarter wavelength) groundplane. Just about any true halfwave dipoles tuned correctly for that same frequency would outperform the Diamond-types. A true discone with a low frequency start of 30MHz or 40MHz would be quite large and its angle of radiation would be somewhat high for most LMR reception on the higher VHF and UHF frequencies and nearly useless on the 800MHz stuff. The Diamond and its close cousins like the Radio Shack discone function as a weakened ground plane antenna, weakened by having the ground plane radials too short relative to the desired frequency design, rather than as a discone at the VHF-Low frequencies.

3) All mixers are non-linear or else they wouldn't be mixers! Internal receiver intermod can be caused within the mixer(s) but is also often caused in other stages such as the front end amp, usually by overloading in the presence of two or more strong in-band signals in which case that amp becomes an unintended "mixer". And that's still "true intermod" as far as I know. Any case wherein you have two or more strong signals combining in a non-linear way (aka "mixing") and causing resulting products is intermodulation, aka "intermod" whether it is inside the receiver or external to it. There is also "desense due to overload" which is a different matter though both issues can occur simultaneously under the right conditions. Desense can be caused by the the front end amp being driven to non-linearity and thereby effectively "reducing" its gain (bad - it becomes non-linear so susceptible to non-linear issues such as intermod) or by the action of AGC-type circuits which are designed to reduce the gain of the front end amp in the presence of strong signals in order to keep the amp FROM going non-linear under such conditions (not as bad - at least it's not non-linear!).

4) A typical squelch circuit used for narrow band FM LMR is a noise gate just as ThomasG said. It does not affect the sensitivity of the receiver at all. Period. Turning it up causes the audio path of the receiver to mute at progressively less noisy FM signals so that at its highest setting only a very quiet FM signal would unmute the audio. Since FM quieting is a function of the strength and signal quality of the FM signal then it stands to reason that since weak signals equal noisy signals and strong signals equal quiet signals then increasing the squelch action would mean you only unmute for relatively strong FM signals. Squelch circuits used for other modes use different methods and do not rely on noise gating; RF gain type squelch is one alternative. A note here - I am baffled by gmclam's use of "tight" in reference to setting the squelch. In all of my experience in RF design and test as well as that of an even longer radio hobbyist and amateur radio operator, "tightening" the squelch means turning it up so as to mute progressively noisier signals while "loosening" the squelch means reducing the squelch action so as to unmute at very weak noisy signals and not the other way round.

-Mike

 

[humboldtMUD]

fair enough, im still trying to get chp. got the st-2 and installed on my roof. my homemade coax antenna worked better. this is making no sense. it came w/ 50' of rg-6, im probally using 30' of it (coiled up the rest). dont know what i did wrong, but seems somthings up here..
should i be pointing this thing towards somwhere or does that matter?

 

[Mike_G_D]

fair enough, im still trying to get chp. got the st-2 and installed on my roof. my homemade coax antenna worked better. this is making no sense. it came w/ 50' of rg-6, im probally using 30' of it (coiled up the rest). dont know what i did wrong, but seems somthings up here..
should i be pointing this thing towards somwhere or does that matter?

Well if you've done all of that and still no joy then I am beginning to think that you have an issue with your receiver. I am not familiar with your location topology so I cannot comment on that aspect but I find it hard to believe you are so geographically challenged so as to negate low band RF signal reception from less than 50 miles distant given a base/mountain top signal origin. I have a Uniden BCT15 that I use for low band CHP listening and it works quite well (given my antenna system is very poor - indoor only). My only suggestion at this point is to try and get ahold of a different make and model of receiver and hook it up to the same antenna and see if it works better. At least that would tell you whether or not the problem might be with your receiver or with the location, etc. See if you can hook up with someone else in your general vicinity who is a radio hobbyist also and who can loan you a radio to try. Alternatively, for testing purposes, you might consider buying a cheap scanner to try - Radio Shack has a 30 day return policy and you surely don't need anything fancy to just test low band signal reception! And I assume that others have also suggested this - make sure your attenuator is turned off on the BCT15X.

-Mike

 

[gmclam]

fair enough, im still trying to get chp. got the st-2 and installed on my roof. my homemade coax antenna worked better. this is making no sense.

Is there a lot of tall trees or buildings around you? Is your house "in a valley"? Can you see the mountain top from your roof? There must be some other issue at work here.

it came w/ 50' of rg-6, im probally using 30' of it (coiled up the rest).

If you were trying to receive anything other than low band, I'd make a comment that coiling up all that coax is a no-no. Can you say "attenuator"? That's what it is. Fortunately a lot less on low band than other frequencies.

Also, all RG-6 is not created equal. Some of it these days is very good, but there is some out there that is not worth its weight.

 

[humboldtMUD]

ok, my friend has a pro-51 with its rubaduck ant it deffinetly was worse than my set up. hooked up to my antenas there is no positive change over my bct15x. whats wired is that coax thing i stuck on my roof actually did really quite good, 30% better then the st-2. i thought with a real antena it would be that much better.

miranda is in a bit of a valley, up the eel river is garberville about 13 miles away. pratt mt is not far from garb.
there are lots of big redwood trees close by to where my house and antenna is. there are holes tho, not mega thick.