What antenna would be good for CHP scanning? Im wanting to put a base antenna on my roof. I don’t want to use a discone for CHP as I want to put a discone up for my other scanner that’s scanning different frequencies. I have a scanner just for CHP alone.
CHP Scanner Antenna?
- Thread starter Legal1313
- Start date
Obviously, a Low-Band VHF Ground Plane type antenna probably be your best bet. The mobiles transmit on 42 MHz to Dispatch and receive Dispatch and Car-to-Car traffic on either 39 MHz or 45 MHz depending on location. It's possible that there still may be a couple of 42 MHz Tx/Rx freq pair combos still in use if the separation is more than 300 KHz apart..
avdrummerboy
Member
What's wrong with the discone? Most go down to 25MHz or so, perhaps a splitter for the multiple scanners.
mmckenna
I ♥ Ø
Short loaded top whip over a less than ideal ground plane. They are poor low band antennas unless you are really close to the transmitter.
Yeah discone goes down to 25MHz and that's what I am using for CHP (and everything else) with no issues. I hear what my antenna can see (higher is typically better) including direct from mobiles. Certainly I can understand a desire for a dedicated antenna for low band. Not sure what the ROI would be. Another thing to consider here in 11/2023 is that at least some of CHP is expected to migrate to CRIS.
700 Mhz in the metro areas and 150 Mhz in the rural areas.
oldradioguy2010
Member
Right now, subject to change, a CB base antenna works great.
I live in Southern cal and worked from Ventura to San Diego.
DW
So. Cal
I live in Southern cal and worked from Ventura to San Diego.
DW
So. Cal
Most Discones like the Radio Shack, Diamond, etc, have a base loaded top whip sharply tuned to 50.0MHz. At it’s resonant point of 50.0MHz it’s a pretty lousy antenna being a ground plane with resonant top whip over a wholly inadequate ground plane and the top whip shares a feedpoint with the horizontal disc elements, adding lots of capacitance to ground and reducing efficiency. At 39 or 42 or 45MHz for CHP these Discones are about as good as a random length coat hanger.
I just installed an older European Nevada brand Discone with typical 50MHz top whip and wanted CHP coverage at a mountain cabin and replaced the top whip with a longer one, specifically tuning it to the local 42MHz frequency and it really perked up reception over the stock length that resonated at 50MHz. I have a couple of surplus CHP NMO broad band vehicular whips and will probably make a dedicated ground plane for CHP in the future. One of these CHP whips on my vehicle in the driveway works better than the modified Discone on the roof, so that should tell you how bad a stock Discone would be on CHP freqs.
HappilyRetired
Member
If you want the best performance on CHP the antenna I use is made by Childs and is an absolute solid performer. All you need is the ability to hear the repeater output. Those vary between 39-45 megahertz. So you want one tuned in the middle which is 42.5. It's what I use at my home up on top of the hill and I pull in Border, Southern, and Inland.
A cheaper approach is to get a layered VHF low band antenna which is what CHP uses. They make a ground plane kit for it. So you get the antenna which runs about $70 and then the ground plane kit and you're in it for just over $100. Since just about all of CHP in Southern California is on a repeater you may not need something as big as the Child's. I like the child because the units do like to use "direct" and talk to one another on the repeater output frequency. The funny thing is that the dispatcher can still hear them and will sometimes respond. It's my understanding that they have a special microphone on their radios that when they press the top they're on the repeater and when they press on the bottom there on direct. Or the other way around but I don't think it matters. With the Child's I can hear them on "direct" for quite a ways.
A cheaper approach is to get a layered VHF low band antenna which is what CHP uses. They make a ground plane kit for it. So you get the antenna which runs about $70 and then the ground plane kit and you're in it for just over $100. Since just about all of CHP in Southern California is on a repeater you may not need something as big as the Child's. I like the child because the units do like to use "direct" and talk to one another on the repeater output frequency. The funny thing is that the dispatcher can still hear them and will sometimes respond. It's my understanding that they have a special microphone on their radios that when they press the top they're on the repeater and when they press on the bottom there on direct. Or the other way around but I don't think it matters. With the Child's I can hear them on "direct" for quite a ways.
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oldradioguy2010
Member
Or, when all else fails, try a wire dipole.
40/50 mhz. Which is 6 meters approximately.
So if I am correct each arm is 58 inches.
Then invert the V and you have a low cost dedicated low band antenna.
As always, give it a shot.
DW
So. Cal
40/50 mhz. Which is 6 meters approximately.
So if I am correct each arm is 58 inches.
Then invert the V and you have a low cost dedicated low band antenna.
As always, give it a shot.
DW
So. Cal
HappilyRetired
Member
468 / 42 = 11.1428571429 feet.
An inverted the antenna is slightly longer than a normal dipole. The full length of an inverted V is 11.560 feet. Divide that in half and you get 5.7802 feet per leg. The ends need to be elevated above ground by at least 5 ft which means you're going to come down 45-60° on each leg. But there's easier ways to do this then and an inverted v.
On the rocker PT-T switch when you pushed down on the rocker switch they are Tx on the 42 MHz freq to Dispatch called the "S" channel and when they push up they are TX on either the 39 or 45 Mhz freq which is the freq they receive dispatch and communicate car-to-car direct which is known as the "C" channel. The rocker switch first came out in 1977 on the Micor radios.
oldradioguy2010
Member
I am sorry Happy My thought was for RX only.
A near cut might work fine.
Even a end fed random cut of wire would work like what we use on HF.
DW
So. Cal
A near cut might work fine.
Even a end fed random cut of wire would work like what we use on HF.
DW
So. Cal
If you want something "multi-banded" I've had excellent results with the Comet GP-15. Although tuned for the 50-54/144-148/440-450 bands, it works great for me on the equivalent VHF public service bands. Only downside is they have increased in price lately.
A coaxial dipole, like the Childs, referenced above, would be the kind of antenna found in commercial 2-way establishments (those that are left on low-band, that is).
A coaxial dipole, like the Childs, referenced above, would be the kind of antenna found in commercial 2-way establishments (those that are left on low-band, that is).
HappilyRetired
Member
Thank you, but I cannot put up an exterior antenna. This is an office building.
But if your happily retired, why would you be in an office building?
HappilyRetired
Member
Great question! I was wondering if anybody was going to think it through and ask. 🤣
Because I have started a business in the Inland Empire and monitoring fire departments is important.
I use a Tram CB antenna, model NH-4-M5-HC. Not sold anymore. It's very sturdy, strong magnetic base. Previously used indoors, now moved to the car. I hold the end down with small magnets. It gets very good CHP reception as well as local PD and Sheriff (P25) in the 470-480 Mhz range. Hooked up to an SDS100.
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