Batboard

I picked up a couple of nice MTX9000's recently that will not receive near 927.0. The VCO as observed on a spectrum analyzer is looking for lock. They do appear to lock OK when programmed near 928.0. Has anyone had this issue and solved it? This is different than the 927 transmit talk-around problem.

Thanks
Mike / W5JR
Milton GA (a suburb of Alpharetta)
902/927.0125 - 146.2 - Sweat Mt
902/927.0625 - 151.4 - Buckhead (Atlanta)
902/927.6500 - 100.0 - Milton

And I have several other MTX9000 that lock just fine even down in the 926 range.

-Mike / W5JR

Yes, it's a VCO lock problem that varies from radio to radio. The MTS2000 exhibits the same problem. Many radios will lock just fine but others will have the VCO unlock on the lower end of the band. This varies from radio to radio, and is often tied to temperature, battery voltage, and other conditions.

Here in Northern California, we run a linked repeater system that uses 902.0125 as the input and 927.0125 as the output. I found that the VCO would often unlock at 927.0125 (which is pretty far below the lower end of the spec'd RX range). However, the VCO would lock at 927.100 and above.

The solution to the problem is to try to hack the VCO settings with Lab RSS, to replace the board with one that works, or to buy an MTX9250.

Thanks

The main focus of that thread is TRANSMIT in the 927-928 range. However, there are two references to RECEIVE in the 927-928 range. The first is sell it if it won't RX. The second indicates that if the TX fractional synth values are adjusted too low, the RECEIVE VCO will unlock.

Well, I've moved the RX values from the default FFFF down in 1000 numbers with absolutely no change. I've also moved the TX and TX AUX numbers around with absolutely no change to the RECEIVE VCO lock performance. It locks for 927.9875 and is unlocked for 927.0125 (and 926.7500) regardless of the settings.

Anyone else with experience regarding the RECEIVE VCO?

Thanks
Mike / W5JR

JPOPatents wrote:Yes, it's a VCO lock problem that varies from radio to radio. The MTS2000 exhibits the same problem. Many radios will lock just fine but others will have the VCO unlock on the lower end of the band. This varies from radio to radio, and is often tied to temperature, battery voltage, and other conditions.

Here in Northern California, we run a linked repeater system that uses 902.0125 as the input and 927.0125 as the output. I found that the VCO would often unlock at 927.0125 (which is pretty far below the lower end of the spec'd RX range). However, the VCO would lock at 927.100 and above.

The solution to the problem is to try to hack the VCO settings with Lab RSS, to replace the board with one that works, or to buy an MTX9250.

Thanks John.

Are you aware of any starting point values for hacking the RX VCO. I systematically tried quite a few and didn't appear to have any effect on how it worked.

73
Mike / W5JR

Mike,

It sounds like you have tried what can be done. My only suggestion would be to start at the original setting, and then move each way in smaller increments. It's possible that the "sweet spot" is in between the increments that you tried. IT's also possible that you just have one of the radios that will not lock for receiving down that far. Usually the MTX9000 works in most cases, unlike the MTS2000 which is more finicky.

You might also try contacting KA3IDN over in Odessa, TX - he has played with the MTX9000 quite a bit.

w5jr wrote:

Are you aware of any starting point values for hacking the RX VCO. I systematically tried quite a few and didn't appear to have any effect on how it worked.

73
Mike / W5JR

Did you try the values listed in the link that I posted? They have always worked for me on both MTX, and MTS2000's.

Jim

n7maq wrote:

w5jr wrote:

Are you aware of any starting point values for hacking the RX VCO. I systematically tried quite a few and didn't appear to have any effect on how it worked.

73
Mike / W5JR

Did you try the values listed in the link that I posted? They have always worked for me on both MTX, and MTS2000's.

Jim

All of the values in the posts I saw in the link you provided were for TRANSMIT. I have varied these numbers previously on a few MTX9000 that did not transmit on 927 with success. Varying them had no effect on RECEIVE for the two units I have that do not receive in the low end of 927. If there were values for adjusting the received window down, I missed them.

-Mike