OldRadioGuy
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Posts posted by OldRadioGuy
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You shouldn't need much of an antenna if the height is reasonable (like attic or second story) I reach a repeater 12 miles away with my 805G and a Smiley super stick or Nagoya 771. I think just a plain vertical in the attic would be great.
Arrow Antennas makes some portable take-down Yagis for Ham 70cm and I use mine on the 805G and it works fine. The match on GMRS is fine. It has huge gain... maybe too much... or too narrow. One of their antennas may interest you. Ham Radio outlet carries some of the Arrow antennas.
Vince
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The cable will not generally affect SWR - just the loss.
A foot or two of coax generally has almost negligible loss. So you can use anything half decent. RG141 or even RG316 is very thin and flexible. Check the power handling capacity of very thin coax to make sure it's adequate but should be fine for GMRS. Pasternack and Digikey both sell short cables with connectors installed.
The odd thing is that lossy coax will actually make your antenna SWR look BETTER.
SWR is based on return loss or reflected power. Loss reduces the reflected power and thus improves SWR.
I've heard a number of stories about hams who invested in better coax and it "made their antenna worse."
No, it just allowed the meter to see the reflected power better.
Vince
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Your own test seems to answer the question pretty well.
Trees don't absorb 450MHz that badly unless they are just loaded with snow or something. Maybe not even then.
Terrain is the dominant factor and higher power will just extend the fringe a small amount.
Of course there are different factors in different situations - like cars or houses blocking your signal. You could also have beneficial reflections of your signal that help you reach over the horizon. In these cases the high power could make a bigger difference. I suspect in the city the higher power may be a bigger factor. But it's very tricky to put a number on.
Vince
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As others have said, these cables are really easy to get at Office Depot or BestBuy.
If you are looking for something special like a right angle or shorty or whatever PCH cables is the mother load. They are also dirt cheap.
I used to go in the store and get BNC cables, USB, Power etc.. It's a handy place.
The quality seem OK on everything I've bought there.
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I use my ham mag mount 2M/440 or 2M/70cm antennas. There is a much greater selection of antennas for ham 70cm and in my experience they work fine on GMRS. Of course you'd want to check SWR but mine have all checked out fine. Since GMRS is shorter than 70cm you could always trim a little off. See Ham Radio Outlet.
Ham Radio Outlet also sells SMA-to-BNC or SMA-to-PL259 "pigtail" adapters that have a short section of thin, flexible coax. This is puts less stress on the radio connector and makes it easier to hold. Another option is to use a right angle adapter to give a better angle.
I got a really cheap speaker mic from Powerwerx and it works great on my 805.
Vince
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There are switching converters in just about everything electronic - especially anything with batteries. So you are already operating your radios in the presence of switching converters. Your vehicle probably has several switching converters in it already. I would be more worried about radiated interference than conducted interference. If you have issues consider locating the converter in an area that is shielded from the antenna.
Switching converters can be very clean but higher power converters will make more noise. I would by a quality brand. Cheaper brands are more likely to cheat.
Chances are you will be fine with it but there is some luck involved. Most switching converter noise (especially broad band noise) tends to be well below 400Mhz. So I would be optimistic. It'll probably be just fine.
Vince
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Another simple test that does not have the complications of high reflected power is to simply measure the loss of the coax by putting the meter at the antenna end and directly on the radio and comparing. No worries about your radio seen a high SWR this way.
Vince
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Here's a way to test your coax.
Use a low power source that will not be damaged by high SWR or pad the source (radio output) with an appropriate power rated 6dB pad so it will not see the bad SWR.
First put a dummy load at at the antenna end and look for a good low SWR - maybe 1.1 or better.
If this passes this test leave the end open and look for a very high SWR.
Then short the end and look for also a bad SWR.
The short is more reliable than the open so put more weight on that test.
You can figure out how bad your SWR should be with the short and open as follows.
Look up the loss of your line for the length you have and double it. This should be your return loss.
Find a table to translate return loss to SWR.
Vince
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After thinking about it..... a better way to put it is that there is no point in treating very short lines as T-lines. There is no benefit in treating it that way. In PCB and chassis design it's mainly the delay of the T-line that has any meaning
When you design on a PC board, even at 1GHz you measure the S-paramterters on the PCB or at the PCB interface. So all the parasitics related to the packaging and PCB interface are absorbed into the S-Parameters. Matching network components are generally treated as discrete impedances - and this is pretty accurate. Everything is surface mount today and the traces are typically as short as the pads. Once we got past the matching network we would try to keep our microstrip in the ballpark of 50 ohms but in many cases you are only going an inch or two. So if your microstrip is off 15% it's probably still better than your matching network.
Even at a GHz PC boards have become too small to economically use stubs and T-lines for on board for matching. You can buy an 0402 1pf cap or 1nH inductor for next to nothing. PC board space is too valuable for stubs or T-lines of meaningful length.
The only way to really see this is to plot it out on a Smith chart. When the rotation is so small it just doesn't do anything.
Vince
- mbrun, overrulecaratmutt, axorlov and 1 other
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Not true. When the transmission line is shorter than about .1 Lambda (wavelength) it no longer behaves as a transmission line.
I used to design RF probes and test gear for Maxim who made chips for cell phones etc. I spent a lot of time on network analyzers and sim tools. You don't treat every chip lead, pad, and bond wire as a transmission line... and you can't. Chip designers do not treat anything like a transmission line.
Certainly you can call it what you like but as a practical matter it's not a transmission line anymore when it's a small fraction of a wavelength.
Vince
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Here's something to ponder.
If a 2:1 SWR antenna were connected directly to the radio with no coax at all there could be no standing wave. Standing waves need transmission line in order to exist. A mismatch is still a mismatch even without a transmission line to allow standing waves.
You will still have the same loss of radiated power due to the same mismatch. The standing wave itself is only a symptom of the mismatch. The coax is just the middle man.
When you have a "matching box" at the radio end of the coax things get really complicated. There is still a mismatch between the antenna and the coax but the mismatch at the match box makes a "reciprocal" reflection that cancels out most or all of the bad reflection at the antenna. The length of the coax will affect the match in this case. This is why is it best to have the matching unit right at the antenna. The icom AH4 does this for the HF bands and works very well with terribly mismatched wire antennas. You do not see these things on the VHF/UHF bands where antenna size is not much of a problem. Better to just make the antenna the right length.
Just some
Vince
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MacJack is right. That "line of sight" tool is amazing and highly useful for site surveys.
You can probably tolerate a grazing contact with the soil but not much more.
My path to the repeater 15 miles from here shows that I am almost line of sight with just a glancing blow to a hill between here and there.
It's so marginal it makes a definite difference whether I am upstairs or downstairs.
Also, the antenna makes a difference. So it's a close call just like the tool says.
Now if it would only shade all the areas that are LOS from my location. Probably have to pay extra for that feature.
Vince
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The reason antenna (and therefor radio outputs) were designed to be 50 ohms is largely the coax.
50 Ohm coax is practical to make in manageable diameters and will carry decent amounts of power. They determined that 50 ohm coax for a given size could carry more power than other impedances. It was deemed optimum by some military research study. Also, with low voltage solid state radios it works out very well.
Once you choose 50 ohm coax for your radio system it makes sense to have the radio and antenna made to match it.
Of course there is 300 and 400 ohm twin lead transmission line (ladder line) and some radios used to be designed for it. It made far more sense in the tube days to design higher Z finals on radios. But that's mostly history - at least for our portable 12v radios.
Most radio outputs are predominantly resistive impedance with little reactance (inductance or capacitance).
Vince
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Impedance is the ratio of current versus voltage that a source can generate when producing maximum power. You want a load that uses current and voltage
A low Z source can make lots of current but not so much voltage. Car audio systems often use 4 ohm and even 2 ohm speakers because the stereo is limited to 12V of the car battery. So you need to "take" more current to get more power out of the 12V source. Switching power converters have changed this more recently.
A hi Z source can make lots of voltage but not so much current. As soon as you draw some current the voltage will drop. You want a load that can make use of higher voltage but not need a lot of current.
It is almost an exact analogy to torque and RPMs in the mechanical world. Transmissions are impedance matching devices. They behave exactly like a transformer in the electrical world - trading torque for RPMs the way transformers trade voltage for current. Torque being voltage and RPMs being current.
Vince
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A couple internet sites said truckers/travelers use channel 7 but I've never tested it.
I've heard that truck drivers now use an internet based thing with their cell phones. It uses the GPS in the phone to determine what general area they are in and even which interstate they are on. ( I believe they can specify some of these things.) Then it puts them all in a chat room of sorts with other drivers in their area. So it's like virtual CB radio. I believe it is a subscription service that they pay for. So not just wide open to anyone..... and of course you have to have cell service.
Here's another data point..... If you go to a truck stop and look in the display case they still have quite a few CB radios but I have not noticed any GMRS radios. If they had any GMRS it was just one or two. It's been over a year since Ive been in a truck stop though. So it may be changing. When you see truck stops carrying more GMRS radios you'll know they are changing over.
I also checked Camping World to see what they sell. They have a bunch of little FRS hand-held sets and one pair of GMRS hand-helds. They do not sell any GMRS mobile rigs. I think this is a good indicator of what people are NOT using out on the highway.
Vince
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This is a cool demo but there is a simpler way to look at SWR.
Bad SWR is almost exactly like having your car (or bike) in the wrong gear.
It means your engine (or legs) will not be as effective and you won't get the full horsepower from it.
If your gear is just a little high or low it's just not optimum. It's not a big deal.
If your gear is way off it could either stall out or over-rev your engine or break your bike chain or whatever.
So you could break something but it has to be an extreme mismatch.
With more power it becomes a bigger deal but even 50W is not a lot of power.
Vince
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As others have said SWR is the same as "return loss" which means how much power is reflected.
An SWR of 1:1 which is a very high (technically infinite) return loss or no reflected power.
Coax with more loss allows less power to be reflected and therefor a better SWR.
Adding a 3dB attenuator to your antenna cable will improve the SWR.
Of course, that would reduce your radiated power so no one would likely ever do that.
You can look up a table of SWR versus return loss and see the impact of cable loss on SWR.
Vince
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Like one of the other posters, I just use a Wouxun 805G for everything and use a mag mount when in the car.
I don't talk enough to even require a batt. eliminator.
I do have a speaker mic to make it more convenient.
I think GMRS is mostly for talking with people "in your group" who your are traveling with.
So you don't need a lot of range or power. Just an external antenna.
I have never found much general activity "out there" - but our highway travel is somewhat rural.
I don't think you will find a lot of "strangers" to talk to along the highway.
Vince
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I got my extra class ham license in 1985 and live out here in Spokane.
I often monitor the ham repeater system here that covers essentially the whole eastern half of Washington state.
I also belong to the Spokane VHF Club.
I find that most of the hams are surprisingly receptive to GMRS and many (or most) of them have their GMRS license.
They talk about GMRS on the ham repeater now and then.
They also have discussed it on the VHF club net and at meetings.
The reason is that most hams have family members and fishing buddies who are not hams.
So ham is pretty useless for communicating at camps and family outings.
Most hams love all kinds of radios.
Also, hams believe that GMRS brings people into ham radio.
So they don't see it as competition. They see it as something that promotes amateur radio.
Of course there will always be some delicate egos out there.
A few guys see ham radio as a religion.
They worked very hard to get a license and don't like people who just "wrote a check".
I almost like GMRS better than ham sometimes because it is less exclusive.
Ham is sometimes just too quiet.
Vince
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There are quite a few "board stuffers" here in the US since it is almost totally automated.
They just load the reels of parts and set up the stencil and align/orient it.
The CAD files give all the part locations.
So there is more board assembly here than you might think.
Most of the products I designed were all built over here... with some or many foreign parts of course.
Most of our low-mid volume boards were populated right in Oregon.
The blank boards themselves were more often fabricated in Asia.
Caps and resistors are almost free but the boards themselves can get expensive... $2-$15 depending on size, # of layers, etc.
We made educational science equipment so had all different volumes of products.
Some things were almost entirely US made and other things entirely Chinese or Thai.
It's a very complicated business.
If you buy parts in the US then send them to China for assembly and bring them back the import duties get very complicated.
You can end up paying duties twice on the same part.
Then the finished products were sometimes sold to China and charged another duty.
So we started keeping stock in China for sales there.
(Yes, there are American companies selling electronics devices to China.)
I would guess that hand held consumer radios are entirely made in Asia.
The designs could be done either here or Asia... but likely China.
The chip makers do most of the radio design since it entirely revolves around the chip for that function.
Only the support circuits (power, control, etc.) are done by the maker.
When I worked at Maxim (chip maker) many wafers were made in the US then tested and packaged into chips in the Philippines.
I trained a couple of Filipino engineers in RF test back in the late 90's.
We made a lot of cell phone chips back then.
The chip designs were mostly done in the US
Basically, I'm just saying its a very complicated picture.
Hopefully somebody found this interesting. :-)
Vince
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I think Smiley antennas and Arrow antennas are substantially made in the US.
MFG makes meters analyzers and antennas over here.
Cushcraft makes some antennas here.
Elecraft makes their ham radios "substantially" over here.
If you build it as a kit the assembly will surely be here.
Electronics can be very hard to pin down origin the of.
(I'm not necessarily talking about radios here - just any electronics.)
The design could be done here.
The bare boards may be fabricated in Asia then "stuffed" or assembled over here.
Or the boards entirely made in Asia and then assembled into the case over here.
Even for the products that I designed myself I would have trouble saying what percentage American they are.
Some of our products were almost entirely designed and built in China - only the software done here.
Others were mostly done here with sheet metal and machined parts in addition to electronics.
With consumer grade "walkie talkies" or mobile radios I'd be surprised if there was much US involvement other than the styling and specs.
Companies like Cobra and Midland probably have a couple engineers overseeing the work and contributing at least minimally.
But at least that is some contribution. Better than nothing.
Vince
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I've had a VX5 for several years which is very similar to the VX6.
I'm not exactly thrilled with it.
The buttons and labels are very very small and hard to read and use.
I find Yeasu's menu system kind of quirky and non intuitive.
Once you learn it it's OK but just kind of puzzling why they do certain things.
The VX does not have easy access "hot keys" for the tone etc.
I would opt for a larger and simpler radio with bigger buttons if possible.
The VX crams too much into too small of a space.
My old Yaesu 209RH was a great radio and very easy to use.
The VX was a real step down in usability.
My Yaesu mobile radio is better than the VX.
Same strange menu system but easier to access.
I'm just not a fan of Yaesu's menu system and tiny buttons aggravate the whole the situation.
I've learned to live with it but just don't like it at all.
I would take a good look at Kenwood and Icom and really study the manuals before buying.
Vince
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Usually in VHF UHF the long distance propagation phenomenon is called "ducting".
It's cause by various layers of the atmosphere stacking up just right.
It only happens a few times a year or maybe once a month??
Back in 1986 I moved about 20 miles further north from Milford, NH to Greenfield, NH.
I plugged in the TV to check that I could still get the Boston and Manchester stations.
I did get my usual stations, just a little weaker...
But I was shocked to find that I got the Burlington VT station plain as day.
That would be over 100 air miles away with some mountains in between.
I wondered how far north did I move? Did I check the mileage right?
Well, the next day it was completely gone and I never got that station ever again.
Not even a snowy shadowy picture. Nothing.
It was just a rare case of ducting that happened at the right moment.
Vince
12v UPS power supply
in General Discussion
Posted
Harbor Freight has several "Jump Starter" battery packs with built in chargers. You can just leave it plugged in and charging.
I have one and it works great (I do not use it for radio stuff so much so you'll have to check the specs)
Mine was not very expensive but they do not make that model anymore.
You could also just get an AGM (sealed) 12V battery and keep it on a low amperage charger.
This assumes you don't talk continuously on the radio.
You have to do the math and see how much battery and what amperage charger you need.
Vince