Posted: 12/29/2008 5:22:16 PM EDT
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Recently have decided to get an Am radio license, exam is in a couple of weeks... so.. obviously, now I am thinking through various options of where to start, equipment wise.
I need to equip 3 vehicles first... me, the wife and a very mobile college age daughter... the wife and I are simple... the question is regarding the daughter... Curious about the performance differences in these two setups. 1 - a simple 2m mobile unit, like a Yaesu FT-2800M with a decent antenna, similar to a Comet SBB-5 NMO... her car might make the unit placement a challenge.... and, she isn't going to want it in her car... 2 - a HT, like a Yaesu VX-170, similar external antenna with a concealed amplifier (under a seat) like a Mirage B34G... this setup I can pretty much hide in her car for her use when she actually needs it. The 2800 has almost twice the wattage of the HT (with the amp)... so the question is... for a mobile unit, does anyone have a guestimate of what I should expect the usable difference to be in a suburban envirnment? Not a city, no mountains, just normal suburbia and assuming the repeaters are down??? Is effective range a simple linear relation to wattage, given a common antenna? Thanks in advance for any input!!! eta: yes, all 3 will have a license... :) |
The issue with the daughter's vehicle could be solved with that type of solution but a mobile will perform much better than a handheld even with an amplifier. You could go the route of a detachable head radio and put the head in the glove box and when she needs it give her instructions on how to use it and put the head back in the cradle. I ran the mobile amp with a handheld at first and was miserable. The front end of the radio overloaded all the time and it was just a general pain in the ass. 
Personally I would go with 7800's or an 8800 for your vehicle and 7800's for the rest. Yes they do cost more but 70cm is usually a popular band and sometimes more popular than two meters in a given area. With the 8800 you can have the ability to cross band repeat if you need to be away from the vehicle and need to use the radio. Ten miles is easy with two meters without repeaters being flat ground. It can be greater but I am factoring a suburban environment with obstructions. |
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With the 8800 you can have the ability to cross band repeat if you need to be away from the vehicle and need to use the radio. I don't yet understand the issue / benefit of cross band repeat..?? I assume using the mobile as a repeater to a HT? Yes. You can repeat your 2m mobile transmission to a 440cm repeater, for instance. Might be handy if you're away from your vehicle, and the only local repeater is 440. |
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You did well to get your wife and daughter to test with you. It took me a long time to get my wife to get her license and then she left town with my best Icom WT, newest 357 mag revolver and newest car. Of course, I have accumulated much more good stuff since then.
Good Luck. RS |
| I use the Yaesu 7800R for both base and mobile ops. I'd rather have an 8800 for base ops but I can tell you that the 7800 is great for mobile ops. The 7800 has backlit keys on the the control head and the 8800 does not. This makes a big difference when operating at night. |
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I use the Yaesu 7800R for both base and mobile ops. I'd rather have an 8800 for base ops but I can tell you that the 7800 is great for mobile ops. The 7800 has backlit keys on the the control head and the 8800 does not. This makes a big difference when operating at night. I've got a 7800 for my vehicle, and an HT w/ external antenna for the house. I'd like to get an 8800 for the car so I can use the 7800 for the base. The backlit keys do make a difference, but I think I'd rather have the dual recive and crossband repeat. |
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To double the range you have to increase power 4x (+6 db). So, a 1:2 ratio or effective range to output wattage?? To double the wattage would quadruple the range... so... if you can get 20 miles out of a 50W mobile, a 25W mobile should have an effective range of 5 miles? In suburbia, that sounds not "out of the ball park"... |
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For your first 2M rigs go with a 45W 2 mobile rig - skip the HT's. The HT rubber duckie antenna's are nothing more than a resonant dummy load (very in-efficient).
The Larsen 5/8th wavelength antenna's are the "standard mobile VHF antenna" for multiple good reason's. Dealing with a HT while operating mobile is a pain, inevidably you will add wires for a modile charger, then an coax cable adapter and coax cable for a perminate mounted 2M mobile antenna since the rubber duckie antenna sucks. Figure $200 for the radio and mobile antenna/per vehicle. To be honest with the teenager, go with a cell phone. Thru VerizonWireless I enabled parental tracking on my teenager's cell phone account, I can log in online and track him anytime I am worried about him. As she show's personal responsibility, reward her by adding features such as texting. Your wife will thank you. 73, Don |
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To double the range you have to increase power 4x (+6 db). So, a 1:2 ratio or effective range to output wattage?? To double the wattage would quadruple the range... so... if you can get 20 miles out of a 50W mobile, a 25W mobile should have an effective range of 5 miles? In suburbia, that sounds not "out of the ball park"... OK Guys, it is not that simple. Yes x4 power is a 6dB increase (in a 50 ohm system), but that will not double the range of a radio. For every wavelength from a isotropic antenna you will loose 6db. This is do to the propagation resistance of air being 377 ohms - not 50 ohms. Your communications ability within an urban area is largely dependent upon terrain and interferring structures. Most of the modern 2M mobile rigs have low (5W), Medium (20W), and High (45W). You will be pleasantly surprised how well you will do on simplex communications running 5W. Increasing from 5W to 20W will give you 6dB, and going to 45W will give just over another 3dB. Using a 5/8th wavelength will give about 2dB gain in ERP, going to one of fancy Comet antenna's might give you 4 to 6 dB in gain in ERP. If you are in the mid west (flat land), 5W to 20W and a decent mobile antenna will serve you very well. 73, Don |
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I get an easy 30 miles with a 1/4 wave with an icom 2100h running high power over relatively flat ground. In more urban areas, signal reports run good out to about 15 miles again high power. On one occasion my installation was noticeably superior to another hams "lets throw an antenna on the car and go" approach.
My mobile rig is installed on a 1993 suburban, consists of antennax 1/4 wave running into a permanent nmo mount with the icom powering everything. All family members are becoming hams right? Why not install nmo mounts on all the vehicles and experiment with antenna's? I suspect that the 1/4 waves which tend to be very discrete will work just fine in your scenario. If more range is needed or local geography demands it, carry 5/8 wave antennas with you as back ups and swap out. I would think that swapping antennas is easier than attempting to get an amp to run from a HT especially if some parts to connect are missing or not installed correctly. |
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To double the range you have to increase power 4x (+6 db). So, a 1:2 ratio or effective range to output wattage?? To double the wattage would quadruple the range... so... if you can get 20 miles out of a 50W mobile, a 25W mobile should have an effective range of 5 miles? In suburbia, that sounds not "out of the ball park"... No, to double the wattage would not double the range. You would have to increase wattage four time to double range. If you can get 20 miles from 50 w, to get 40 miles it would take 200 w. But there is an additional problem... it's that curvature of the earth, line of sight thing. While it is easy for me to hit a repeater 45 miles away with only 10 w, MY J-pole is 20' up. And the repeater's antenna is, I think, 500' up. This is flat country, no hills. Taking your example, cutting power from 50 w to 25 w would not cut range in half. It would only cut it by about 20%, from 20 miles to perhaps 16 or so. But a car, the antenna down low, power is not your problem. It is that line of sight thing. Power vs range is not linear. It is a squared relationship. |
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1 - a simple 2m mobile unit, like a Yaesu FT-2800M with a decent antenna, similar to a Comet SBB-5 NMO
I'm looking at the same antenna, Comet SSB-5 NMO for my truck. I want one of those door edge mounts that would hang on the top edge of the back driver side door on my Dodge 1500 Laramie. What Comet (or other) part number do I need? Is this the correct mount attach it to the lip of the back door on my truck? CP-5NMO 
––––- And power vs range... it is not ohms or resistance... it is the fact that you are trying to spread the power over twice the range, but 4 times the area. It is a squared relationship. 2 x range = 2 squared or 4 x power 3 x range = 3 squared or 9 x power 4 x range = 4 squared or 16 x power 10 x range = 10 squared or 100 x power This is the same relationship of sound progation, radiation, etc. Again, at 2 meters, antenna height is the problem, not power. |
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I'm looking at the same antenna, Comet SSB-5 NMO for my truck. I want one of those door edge mounts that would hang on the top edge of the back driver side door on my Dodge 1500 Laramie. What Comet (or other) part number do I need? Is this the correct mount attach it to the lip of the back door on my truck? that looks like it. ar-jedi |
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Again, at 2 meters, antenna height is the problem, not power. the limiting factor for ANY transmission path using FM is the link budget required to get to a nominal 12dB SINAD at the receiver's discriminator circuit. this link budget includes the transmitter's power output, the gain of transmitter's antenna (which could be negative) [aside: the combo of these two is the ERP], the path loss, the gain of the receiver's antenna (which could be negative), and the receiver's selectivity and sensitivity (the former helps reduce the ambient noise floor by eliminating sources of intermod). this is the reason you can only talk 3 miles from a 5W HT to another 5W HT, but 30 miles from a 5W HT to a repeater. HT to HT range is generally not limited by the radio horizon (about 1.4X the physical horizon due to refraction), but by insufficient signal at the receiver discriminator. ar-jedi |