Jarred J. said:
so if you have a 5 watt handheld, and your using 2 connectors if they are "good" your losing .6% of your wattage. that's also that much in receive as well...
your 5 watt handheld is now doing 3 watts. even if your using a "High gain" Antenna.
this can be fixed with either getting a real mobile radio or a HT amp.
:hopeless: OK, stand back... let me drop some science on you. Forget that whole .6% number - that's totally bogus... and how .6% of your "wattage" gets you from 5 watts to 3 watts, I have no idea. Plus the fact that watts don't really matter anyway.
First, let's document some assumptions:
The HT in question produces a nominal 5 watts out and we're operating at 150.000MHz.
The existing portable antenna has a gain of -2.15dBd (that's 2.15dB below the "gain" of a dipole... yes, "negative gain" is possible)
We'll assume the HT antenna is in free space (not on your belt being attenuated by your donut storage area) but that the body of the vehicle attenuates all signals by 10dBm (in the real world it's a lot messier - a repeater you can see out the window will be attenuated less than one that has steel in between, but we're going for rough numbers here)
If you go to an external antenna (which you're going to do right - by drilling a hole, installing a mount, and attaching a real, properly tuned antenna... if you intend to use a mag-mount, there's no hope for you anyway) the coax run will be 15 feet of Belden 8259 RG-58A/U with a 1/4-wave
VHF antenna attached, which is properly tuned and resonant. Our coax loss is 1.021dB and we'll lose 1dB in the connectors and mount.
We are primarily concerned with the "talk in" capability of this system. Most repeaters are more powerful on the output side than the input (because most aren't very well engineered).
First, let's start out by putting our radio's output power into dBm. dBm is the power ratio in decibels to 1 milliwatt - 0dBm = 1 watt.
Pdbm = 10*log10(1000*Pw) where Pdbm is our power in dBm and Pw is our power in watts.
Going the other way, Pw = 10^(Pdbm/10)/1000.
Pdbm = 36.98970dBm
Now, it's important to remember that the dB scale is logarithmic. Doubling the output power results in a 3dBm increase in signal.
Now that we're in dBm, dealing with all the losses and gains is simple:
36.98970 - 2.15 - 10 = 24.8397.
Using our power equations, our 5 watt radio is now effectively 0.3 watts as soon as it leaves the car.
If we go with an external antenna (0dBd gain, minus the coax and connector loss)
36.98970 - 0 - 1.021 - 1 = 34.9867dBm or 3.1396W.
Now, let's take a step back and look at all those numbers.
Radio output: +36.98970dBm
HT antenna loss: -2.15dB
External antenna gain: 0dB
Coax loss: -1.021dB
Connector loss: -1dB
Vehicle attenuation: -10dB
Which number jumps out? The vehicle attenuation. Other than the output power, the vehicle attenuation is the big number... so if we just don't make things worse and we get that antenna onto the roof of the vehicle (some height advantage that we haven't accounted for) and eliminate that attenuation, we've tackled the biggest issue with our RF system. Without question, plugging a well-engineered/installed external antenna into your HT will net you significant results.
Now, why am I saying don't do it, when all this math says it will help?
1. Notice the assumption of well-engineered/installed. If you don't crimp a connector on properly, or you short the coax, etc., you can cause yourself all sorts of issues.
2. We're assuming the use of good antennas, coax, and adapters. If you buy a crap adapter that is intermittent or is a 20dB attenuator, you'll have a crap system.
3. The antenna connector on the top of an average portable was not built for hundreds of connections and disconnections. MIL-C-39012 says that an SMA connector (what's on top of the HT1000) meets spec if it does not suffer damage after 500 cycles at 12 cycles/minute maximum. These are not high cycle-count connectors like you would expect from a BNC, Type N, etc.
4. The connector on the top of the radio is mounted into plastic. If you have a flexible antenna attached and you drop the radio, most likely the antenna will flex and absorb the vast majority of the impact. If you have a rigid adapter attached, all of that force will be transmitted straight to the connector mounting. Yes, I've seen more than one Jedi-series radio (Ht1000, etc.) with the top connector broken out of the case.
5. I'm assuming that you want to be able to take the radio with you (drop in your bunker coat, etc.) Installing and removing an adapter every time is slow - time you don't want to spend.
From a technical perspective, yes, an external antenna will net significant benefits. From a usability perspective, it sucks. There are vehicular adapters built for both radio platforms, and a real mobile radio isn't that expensive (a Kenwood TK7180 will run you $200). Avoid a few trips to Dunkin Donuts and put that money toward a real mobile radio. You'll be much happier in the long run.
