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R2670 RF In/Out Woes

Posted: Sun Jul 16, 2017 9:14 am
by jmfirefighter20
Hello All,

I have a "new to me" GD R2670 that I picked up a week ago. Came to me labeled "bad antenna port"....replaced the fuse and good to go.

I've been playing around with a few Quantars and have found that it seems the RF In/Out Port is NOT putting out what it should be, and is not letting RF pass as it should. A Quantar at 20 watts into the RF In/Out port causes the "PA LOW" to come on, if I put a "t" on the port and have a dummy load connected I get "PA FULL". My Bird shows about 20 watts, but the R2670 input numbers don't jive, they are too low, like -10 dBm.

Same thing if I generate out the port, both of the Quantars open up at -60 output....not jiving for sure.

I'm assuming something is wrong with the port. I don't have the service manual...is there a fuse hanging out in there too, or something I should check internally for connection?

Thanks gurus.

Josh

Re: R2670 RF In/Out Woes

Posted: Sun Jul 16, 2017 9:53 am
by mac1_131
Ohm out the port should read 50 ohms? I'm not really that familiar with the R2600s but most service monitors have a flat substrate 50 ohm attenuator maybe that's blown?

Re: R2670 RF In/Out Woes

Posted: Sun Jul 16, 2017 11:27 am
by jry
the RF I/O input pad is blown in most cases....about 99% sure just based on your issues.

$$$$$$$$

Re: R2670 RF In/Out Woes

Posted: Sun Jul 16, 2017 11:44 am
by jmfirefighter20
I should have gotten ambitious before I posted......

I took the screws off the RF I/O connector and the darn thing fell out. Looks like there is a little "ribbon" of metal that connects the center pin to the I/O unit, and it was broken. Took the bottom of the monitor off, and the cover of the I/O unit. A little solder, heat, and lining the pieces back up, and the RF I/O port is back in business. My Bird and the monitor jive, and the quantar now opens up at -120.

I noticed that the center pin of the RF I/O was sticking out too far, so I pushed it back in. My theory is that someone got a little rough with the unit, breaking that ribbon. Looks like I got lucky.

Thanks for the input...hopefully someone else can use this info!

Josh

Re: R2670 RF In/Out Woes

Posted: Mon Jul 17, 2017 5:39 am
by jry
you were very lucky ...I have only seen a broken input connection on an R26XX one other time.

Usually the input pad fails due to the duty cycle being exceeded and just the overall thermal stress on the device.

Be very careful on testing high powered devices ...my rule is to NOT connect them directly to any service monitor since it's easy to loose track of how much TX on time and in general these devices have aged and been thermally stressed to start with.

Most service monitor input pads are non standard values , difficult to obtain , expensive and require re-calibration after replacement. The R26XX is no exception and actually the worst when it comes to this situation.

Re: R2670 RF In/Out Woes

Posted: Mon Jul 17, 2017 9:40 am
by jmfirefighter20
I always turn down the power or use a pad into the monitor....no exceptions!

Re: R2670 RF In/Out Woes

Posted: Mon Jul 17, 2017 12:57 pm
by d119
jmfirefighter20 wrote:I noticed that the center pin of the RF I/O was sticking out too far, so I pushed it back in. My theory is that someone got a little rough with the unit, breaking that ribbon. Looks like I got lucky.

Josh
I have personally (recently) broken two RF I/O connectors on two separate R2600 monitors. It was due to using LMR400 type coax directly on the monitor with many connect/disconnect cycles in a very short amount of time. Same thing happened - Center conductor pulled out, everything broke. Sent them in for repair.

I'd HIGHLY suggest when using coax of any real thickness on one of these monitors, you throw a 90 degree connector on the RF I/O port and let THAT get broken.

Re: R2670 RF In/Out Woes

Posted: Tue Jul 18, 2017 7:15 am
by jmfirefighter20
d119 wrote:I have personally (recently) broken two RF I/O connectors on two separate R2600 monitors. It was due to using LMR400 type coax directly on the monitor with many connect/disconnect cycles in a very short amount of time. Same thing happened - Center conductor pulled out, everything broke. Sent them in for repair.

I'd HIGHLY suggest when using coax of any real thickness on one of these monitors, you throw a 90 degree connector on the RF I/O port and let THAT get broken.
During my inspection and repair of the RF I/O, it certainly appears to be a pretty "cheap" design. A super thin, fragile piece of metal connecting the center pin to the pad. Almost like it was set up for failure.......

Re: R2670 RF In/Out Woes

Posted: Tue Jul 18, 2017 10:11 am
by jry
the N connector and bracket are actually part of the input attenuator assembly which Motorola OEM'd from a couple of vendors.

The actual pad connections were really intended for a rigid PCB and not intended to tolerate any flex you get from the N connector.

Guess using an inline 20db pad would avoid both the flex issue and exceeding the duty cycle.

Better to blow or break the $40 pad than the RF I/O module

Re: R2670 RF In/Out Woes

Posted: Sat Jul 22, 2017 8:32 am
by d119
jry wrote:the N connector and bracket are actually part of the input attenuator assembly which Motorola OEM'd from a couple of vendors.

The actual pad connections were really intended for a rigid PCB and not intended to tolerate any flex you get from the N connector.

Guess using an inline 20db pad would avoid both the flex issue and exceeding the duty cycle.

Better to blow or break the $40 pad than the RF I/O module
Hence my suggestion of just using a 90 degree adapter (or two if necessary) to avoid working with the N connector too much.

Thinking about it, an N to BNC would be even more ideal, just deal with the required cable changes. That's what I do on my R2014D/HS.