How much SWR is safe?

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DylanMadigan

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-sorry, not sure if this is the right area-

I have a Motorola CDM1550-LS+ transmitting at 48w on UHF. With a 5 foot cable, my SWR meter shows about 0.5. With my 25ft cable made out of some fairly cheap cable (RG58), I'm getting about 4 on the meter, just inside the red.

I don't need the signal to be too amazing, this is for a base station going to a repeater. I just want to know at what point should I worry about the equipment's safety? I'm quite new to radios (aside from some handheld stuff), but the needle is in red so i would assume I might have a problem lol.
 

Kb2Jpd

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You have a MAJOR problem. Stop transmitting. Change out your cable, check the cable for water egress. Check your antenna. Are you using a UHF SWR meter?
Borrow a real meter from someone. Program the same frequency but at low power for testing.


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DylanMadigan

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Yeah its a real UHF meter (i mean, its some $150 one). It seems to read very low untill i use either of the cables i made using this cheap RG58. It got the same high reading at 1 foot and 40 feet. Using 25ft of RG8 (i think) is when i got the low readings.
 

kf5bti

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If your SWR gets worse with a longer cable you must have a bad cable or connector. The loss in a longer cable will absorb some SWR, so the longer the cable the less the SWR will typically read on a meter. Check your cables and connectors.
 

majoco

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Do you own a 50ohm load? If not, then you should. Then you can put it on the end of the cable before you go connecting to an antenna. Then you will see where the fault lies.

RG58 can easily get squashed which will give you an impedance bump.
 

jaspence

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How much is safe?

Never more than 2:1 and 1.5:1 should be attainable on almost good antenna with decent coax. I have even used Radio Shack coax (go ahead laugh) with decent results when the connectors were installed properly and before it failed due to poor overall quality
 

vagrant

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Plenty of good advice on here. As you go higher in frequency, short coax runs and quality coax really helps. Also, turn down your power and work your way up. If you're full quieting into a repeater with five watts, there is no need for increased power.

Remember, quality coax improves TX and RX, especially in UHF.
 
D

DaveNF2G

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Ultimately, the "safe" SWR depends on the power dissipation ratings of your finals and how much power you are using. If the sum of forward and reflected power is within the capacity of the final stage to dissipate the heat without damage, then the SWR at that point is "safe".

Naturally, high SWR is connected to other issues and should be corrected in any event.
 

wb6uqa

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A friend has a 900 MHZ transceiver in his car. The radio has 30 watts. With 10 feet of RG 58 nothing came out 0 watts at the antenna
 
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