GMRS Radio Question?

[shooting4625]

The low power output also could be the result of reflected RF power coming back into the radio because the antenna could be deteriorating at the connection or the cable could be faulting, thus cable loss. What is your VSWR reading? How much of reflected RF power do you have.

Also, make sure that your antenna mount has a chassis grounding connection and that you are not getting the antenna grounding through the coax connection.

Checked, mounts and antennas are new, I also have two one front one rear, both SWR are at 1.03 at higher power channels.
Midland flat out told me they lose power after a couple of years !!!!!

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[Mark75H]

I would be suspicious of a SWR reading that low. Might indicate bad coax.

 

[Mark75H]

Yeah, I was thinking Midland while typing Motorola or the other way around. Speaking of aged coax….LOL

Same here. I have to double check myself

 

[shooting4625]

I would be suspicious of a SWR reading that low. Might indicate bad coax.

A bad coax causes high SWR, a perfect SWR is 1.00, I have installed many off them and that is what I like about midland out of the box there SWR is almost always perfect. and the power on the 50 watt models has varied from 45-48 now it is 35-36.
I will be checking friends' radios to see if they are having the same power drop,

 

[Mark75H]

A dummy load always shows 1:1. Likewise partially shorted coax returns less reflected wave, ie SWR

 

[Nokones]

I would be suspicious of a SWR reading that low. Might indicate bad coax.

If the coax was bad the VSWR would be extremely high. It is not hard to get low readings if the antenna is properly tuned for the frequency.

 

[Nokones]

I have a Midland MXT500 that is almost three years old and as a coincidence, I checked the RF output power today, and the radio is still putting out 49 watts.

 

[Nokones]

The Midland Antennae are tuned strictly for GMRS freqs and will reflect good readings for both 462 and 467 freqs because the antenna bandwidth is narrow.

 

[Mark75H]

I have a Midland MXT500 that is almost three years old and as a coincidence, I checked the RF output power today, and the radio is still putting out 49 watts.

Good capacitors

 

[bd100]

Our Midland 275 has separate channels for repeater or non-repeater use. I.e. there is a channel 16 and a separate channel 16R. I have noticed a difference in reception between them, so there may be different circuits involved somewhere. Maybe recheck the transmit power for both the regular and the r channel.

 

[Nokones]

Unless, your antenna is practically tuned perfectly and you have near perfect VSWRs, with practically zero reflected power, the only way to check your RF output power of any radio is to use a 50-ohm Load Terminator (Dummy Load), and the 50-ohm Load Terminator has to be measured with near perfect 50 Ohm. Cheap POS "C" Load Terminators have known to be no way near 50 ohms.

 

[Nokones]

Our Midland 275 has separate channels for repeater or non-repeater use. I.e. there is a channel 16 and a separate channel 16R. I have noticed a difference in reception between them, so there may be different circuits involved somewhere. Maybe recheck the transmit power for both the regular and the r channel.

The Repeater Ch. 16R transmits on 467 Megs and the simplex Ch. 16 will transmit on 462 Megs. If you are checking the output power while the radio is connected to the antenna, your reading may be significantly different on each channel. Depending on the VSWRs and the reflected power of each channel, the RF Power measurement may be nowhere near being accurate because of the possible mismatch of the antenna tuning and if there is any cable loss along the way.

The power needs to be checked with a known 50-ohm Load Termination environment.

 

[bd100]

your reading may be significantly different on each channel

Which could explain their thought that the radio is weaker than it used to be. Perhaps it was the other channel, repeater vs regular.

 

[Nokones]

I would be suspicious of a SWR reading that low. Might indicate bad coax.

Um, no, not really.

For example, at 462.575 MHz, an open circuit 9-foot RG-58/U Low Loss cable will show a VSWR at 9.84:1 and the same cable that is short circuited will show a VSWR of 6.37:1. And 18 feet of the same cable will an open circuit cable with a VSWR of 4.5:1 and a short, circuited cable will show a VSWR of 4.62:1. It just takes one of those little itty bitty braided wire strands to short out a cable.

A low VSWR reading will indicate virtually very low reflected power and a near perfect antenna system match with the radio for the power being transmitted to the antenna.

 

[Nokones]

Which could explain their thought that the radio is weaker than it used to be. Perhaps it was the other channel, repeater vs regular.

The radio requires a 50-ohm load with the antenna system. If the loading is not near a perfect 50 ohm load, either with the antenna system and/or a Load Termination Device (Dummy Load), the measured RF Output Power will reflect in an inaccurate reading.

For an example, I have a commercial quality Load Termination Device and it measures 50.1 Ohms, not considering in any inaccuracies with the ohm meter. I also have a Cheap POS Dummy Load that came from a far-away land that you can't get there by a car, and it measures out at 49.1 ohms. I used a Kenwood TK880-1 that is spec'd at 25-watts transmitting on 462.575 MHz and I measured 26 watts with a recent calibrated Bird 43 In-Line RF Watt Meter and 200-500 MHz 100 Watt Slug, into the 50.1 Ohm Dummy Load. Transmitting the same freq into the Cheap POS 49.1 Dummy load, and using the same RF Power Meter and Slug, it measured 24 watts.

In this case using a radio that specs at 25 Watts, One ohm can make a difference in taking accurate readings when measuring the RF Output of a radio. Taking power readings when connected to the antenna system is a good idea to check it with the antenna so you know how the radio is performing connected to the antenna, but you need to know how the antenna is tuned and if it is matched to the radio, for the full picture.

With a radio that puts out at 51 watts into the 50 Ohm commercial grade dummy load also reflects the same 2-watt difference as compared with the cheap POS 49 Ohm dummy load.

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