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Difference between 5/7/12mi range radios and leveling the playing field...


Guest 65ShelbyClone
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Guest 65ShelbyClone

I have not yet ripped apart my Motorola T5700s because I am frankly worried about wrecking a $40 pair of radios. The fact that I got the $40 5-mile range model instead of the $110 12-mile pair got me thinking.....whats the difference? My cynical mind got to thinking that maybe it's like families of computer processors; they essentially are the same except for minimal internal performance changes that drastically increase price.

With that out of the way, does anyone know how hard it would be to "upgrade" a pair of two-ways and what is involved? Would it dig into power consumption even when not transmitting?

I realize modding them over a certain power(or at all) is illegal and thus this discussion is purely for the acquisition of knowledge.  8)

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For sake of discussion only?

The EASIEST way to increase the range is to change the antenna!!!

As a ham operator, an antenna is called "the poor man's amplifier", regardless of output power.  Here's why:

If your antenna has a 3db gain your ERP (Effective Rated Power) is about 2x the amp output (5w in, 10x out).  If you attach a 10db antenna, you get 10x the input power.

I was able to build a "Quaggi" antenna (combo cubical and yagi) to produce a 14db gain antenna, which gave my 5w handheld 2m radio (144mHz) a ERP of about 60watts).  I was able to talk to different repeaters in countys 30-50 miles away.  When the conditions were right, I was able to Akron, Ohio, from Pontiac, MI.  (CB'ers called it "skip")

This antenna is way too big for portable use, bit the theroy is still the same.  If you can build or buy a high gain antenna for your rig, you can achieve the same output as the higher distance rig.

Besides antenna's, check the frequency difference between the rig's.  You may find that there is a difference between them.  My 10 meter mobile ham rig can talk to Europe on 10 watts, where my 2 meter handheld can't talk more than 25 miles, with manufacturer's antenna's.  I hear people who run QRP rigs (less than 10w) on 20 meters, from around the world.

Modifying your output power, on the frequency you are using, MAY get you in trouble if caught.  This is why I becam a ham.  The options to modify and use rigs is more allowable because of the frequency's used and the license I hold. And depending on the frequency I use, I can legally run 200-1500 watts maximum output power.  (add a 10db antenna to a 1500 watt amp and your ERP is now 15,000 watts) 

Hope this helps, since it is for discussion purposes. 

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That's the whole truth oldgrandpainmi :)
Use of an external antenna with higher gain is probably the easiest way to increase the range.
If the antenna connector on these radios is BNC or TNC it's easy to make something that fit, to increase the transmitting power you need to dig into the radio and as oldgrandpainmi said you could do something that FCC don't like  ;D
Number of batterys, driver and power amp transistor will set the maximum power you can get from your radios, to increase the power you probably have to replace the power amplifier transistor and modify the output circuit which match the antenna impedance so it is not that easy 65ShelbyClone they might even use a small pa module as power amplifier.
oldgrandpainmi what is your call sign?

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Guest 65ShelbyClone

I guess I should have been more specific: the Motorola T5700 is one of those consumer grade 2-way FRS/GMRS you can get nearly anywhere, mine came from Target. It is hardly profssional or even amateur grade. They are totally limited by line-of-sight, but even then I've had trouble at the limits of the 5-mile rating(mevon the side of a mountain talking to another on the floor of a valley). They transmit at 500mW and run on three AAs. I do have an old 23-channel automotive CB, though.  ;D

This is very similar to my radios:
ProductHome_Main_T5500R-2.jpg

All the great info from both of you further supports my theory that the power differences are purely internal. There are higher and lower range 2-ways from Motorola in the same exact package as mine, so the antenna isn't what does it. I'm just exploring the viability of them to being comparable with the more expensive radios minus the fist full of dollars(more like just a few dollars more, hehe.....bad joke/movie reference 8) ).

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65ShelbyClone I guess we need a schematic to be able to investigate if it is possible to increase the power, we don't know if they use transistors or a PA module.
The only thing I know about these radios is that the frequency they cover can be changed on some models
Would be interesting to see a schematic on one of these :)

oldgrandpainmi I'll look out for you on the bands :)

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Guest 65ShelbyClone

I doubt I'll be able to procure a schematic, but most likely pictures of the inside if it will help. They were tricky, though; the case halves are held together not with normal screws, but Torx-head fasteners. They underestimate my abilities.... 8)

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These torx heads are quite common but there's some heads that are especially made for screw driver wizards  ;D they are a real pain if you don't got right tools.
Well, why not take a snap shot of both sides of the pcb I've always been curious about how they look like inside.

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Guest 65ShelbyClone

Well, here they are. They are about 100k each, so dialuppers(are there any left?) might have to wait. If anyone wants the 230dpi originals for easier component I.D., just hollar.

Battery(and business) side first:

radiocircuit-rearsmall.jpg

And the front/LCD side:

radiocircuit-frontsmall.jpg

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:) Nice photo!
SF465 K is a saw filter for the front-end of the receiver, there is two black two legged components, one is located to the right of the "tied to the antenna" hole and the second one just above SF465 K2, I guess these are pin diodes used as transmit/receive switch.
My second guess is that the UDF is the power amplifier and the SMD transistor just below is the driver.
Just guessing but think it's pretty close  ::)

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....and not very easy to modify from the look and size of things.


It is not that hard to work with SMDs.  You need a thin tip soldering iron, a good light, a clear table, and solder wick.  Just remove the solder using the wick(be carefull not to accidently pick up adjacent small components with it), and if it doesn't come off apply more solder to get the flux in there to loosen the connection then use the braid again.  Trying to remove the component without getting all the solder off all pins can result in lifted/broken traces or broken pins on components, so use a very light hand if you are doing any prying.   
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Hello all,

Just my 2/100 of a dollar!

If a small enough soldering tip can't be found or made, what I've done in the past is to get a cheapy, dual wattage, iron from Radio Shack.  It has a screw in tip with a set screw to lock it.  Remove the tip and insert an leather sewing needle.  Break it to length, to fit your needs.  The shorter the better.  I have found that running at 30w is sometimes needed, as it now has a terribible heat transfer ratio, so you will loose a lot of heat, but for chip resister, caps, etc., and small SMT devices, it works reasonable.  You can also try different needle diameters or the other 15w setting to get different results

I have also found that when trying to desolder a SMT, 555 timer, with wick, it is a bit easier to float solder over all 4 pins (on one side) at once, then use the wick.  Doing one pin at a time, like a dip package, can be tough.

Food for thought, although a bit off of the origonal subject!

oldgrandpainmi

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Guest 65ShelbyClone

No, its all very helpful. I actually have one of those cheap 15/30w Radio Shack irons. The tip in it is worn out already(I have a new spare also), so I wouldn't worry about modifying it. I have access to a machine shop and could drill a small hole down the middle of the old tip and press in the needle you mentioned. This way it could have a short needle point and lots of area in the copper tip to stay hot. That or I could just grind the old tip and dress it as it erodes. And I would do all that, but I don't know where to make the modifications in the transmission circuit nor if doing so would affect the life/reliability of the radio.

I should have taken a picture of the antenna and how it mounts in the radio and on the board. It actually looked like a simple task to make a jack for plugging in a larger external antenna. The original was basically just a small coil of wire attached to metal tap and glued to the inside of a rubber case.

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