URC-200 ISsues

[BondTech]

Good Morning!

I just obtained a nice URC-200 that transmits per spec but the receiver has an issue. The sensitivity is per spec on the 10 frequencies
listed in the manual for performance testing but once programmed off of these frequencies it is stone deaf - like 1000uV even does not get through. Any help would be much appreciated. Also, are schematics available somewhere?

 

[K4EET]

Good Morning!

I just obtained a nice URC-200 that transmits per spec but the receiver has an issue. The sensitivity is per spec on the 10 frequencies
listed in the manual for performance testing but once programmed off of these frequencies it is stone deaf - like 1000uV even does not get through. Any help would be much appreciated. Also, are schematics available somewhere?

Welcome to Radio Reference!

My first question would be what frequencies are you trying to program that are “stone deaf” on receive?

 

[K4EET]

Here is the Operation and Maintenance Manual for a General Dynamics URC-200 (Version 2) VHF Transceiver:

https://www.manualslib.com/products/General-Dynamics-Urc-200-V2-13314404.html

That should have the information that you are looking for.

 

[AM909]

You're sure you have the correct modulation (AM or FM) and bandwidth programmed? Does it transmit on-frequency?

 

[BondTech]

Thanks for the replies!

I have read through the GD Manual. Unfortunately, it does not contain schematics. The 10 frequencies I mentioned are those the manual says to program into the radio for testing.

It is not in Aviation Mode and both the radio and signal generator were programmed for AM for FM Modes as appropriate.

The transmitter checks out using my AMM2002Q Modulation Analyzer (frequency, modulation percentage/bandwidth, distortion & power) It also draws the specified currents for both receive and transmit (internal readings were verified using an Agilent DMM).

Again, thanks for the comments!

 

[K4EET]

<snip> The sensitivity is per spec on the 10 frequencies
listed in the manual for performance testing but once programmed off of these frequencies it is stone deaf - like 1000uV even does not get through. <snip>

<snip> My first question would be what frequencies are you trying to program that are “stone deaf” on receive?

The desired frequencies you want to use that are not the ten frequencies that are listed in the manual, are they in the same sub-band? Based on the model number and any included options, are your desired frequencies within the operational sub-band that your General Dynamics URC-200 is configured for? It is odd that the “factory frequencies” function properly per specs for both transmit and receive, your desired transmit frequencies all function properly per specs, but all of your desired receive frequencies are “stone deaf” not even “hearing” a 1,000uV input signal.

Out of curiosity, what kind of readings are you getting on your Wayne Kerr AMM2002Q Modulation Analyzer for other receive frequencies between one of the ten receive frequencies that is within spec and one of your desired receive frequencies that is “stone deaf”? Through that range, take ten to twenty test frequencies, equally spaced, to see what a signal level versus frequency plot looks like. This may shed some light on what is causing your desired receive frequencies to be “stone deaf”. Worth a shot…

 

[BondTech]

Thanks, I'll do that. BTW - Do you or anyone else have leads on obtaining schematics?

 

[K4EET]

Thanks, I'll do that. BTW - Do you or anyone else have leads on obtaining schematics?

You're welcome!

As for the schematic(s), that seems to be a well-kept secret. One thing that you might try is to contact General Dynamics at

8220 E Roosevelt Rd​

Scottsdale, AZ 85257​

to see if somebody may be able to help you out.

If you cannot find a Scottsdale, Arizona telephone number for them, you might try their Headquarters in Virginia.

General Dynamics Mission Systems Headquarters​

15036 Conference Center Drive​

Chantilly, VA 20151​

tel: 1-877-449-0600​

 

[AM909]

I have read through the GD Manual. Unfortunately, it does not contain schematics. The 10 frequencies I mentioned are those the manual says to program into the radio for testing.

Where in the manual?

At what freq and mode is it deaf?

 

[PACNWDude]

Even working for an organization with many URC-200's, GD seems to only talk to those buying the current URC-300 radio. And then, it is like pulling teeth from a chicken. Good luck.

 

[BondTech]

The 10 Chanel Presents I am using are those found in Table 21 (FM) on Page 77 and Table 22 (AM) on Page 82.

I have attached two PDF files of some sensitivity measurements I made using an HP8648B set per the manual. As can be seen, the UHF AM is per spec up to about 355MHz. The VHF FM has 'groups' of 'good' frequencies surrounded by out-of-spec groups. The transmitter has been on frequency with specified RF output on both ranges.

 

[prcguy]

The 10 Chanel Presents I am using are those found in Table 21 (FM) on Page 77 and Table 22 (AM) on Page 82.

I have attached two PDF files of some sensitivity measurements I made using an HP8648B set per the manual. As can be seen, the UHF AM is per spec up to about 355MHz. The VHF FM has 'groups' of 'good' frequencies surrounded by out-of-spec groups. The transmitter has been on frequency with specified RF output on both ranges.

There could be a couple of things going on. The input band pass filters appear to be full band but the receiver is track tuned across each band. It could be a chip that outputs BCD data for track tuning voltage where a bit is stuck as in it might output 0000 then 1000 then 0100, etc and a mid range bit is stuck like 00X0 causing wrong data every so often on the tuning voltage. Or they may be switching from high side to low side injection on an LO and one of the sides is not functioning properly.

If there is a BCD device feeding the tuning voltage you could scope the LSB through MSB and make a truth table as you program frequencies every MHz or so to see if a bit is stuck. For checking high or low side injection you would need to sniff the LO with a spectrum analyzer and program a bunch of frequencies to see if anything looks unusual with the LO signal.

 

[prcguy]

And another thing, it shows 6.5KHz deviation used in the FM-PT sensitivity testing. For "normal" FM voice channels you should use 1KHz tone at 3KHz deviation, otherwise SINAD or 20dB quieting tests would be off. And SINAD is measured at the 12dB point.

 

[prcguy]

Looking over the data again I see the actual sensitivity is not really changing over the entire VHF band and its the point where the receiver gets unsquelched that may be a problem. Since the receiver is about the same sensitivity through the entire VHF ranges I wonder if its the excessive deviation that may be causing the squelch to act strange. You might repeat the squelch test at lower deviation like 3KHz.

On UHF it looks similar with the same sensitivity across the entire band and only the squelch break point changing above 355MHz. You might tune the signal generator a few KHz high or low on some problem frequencies to see if the squelch acts more normal when off frequency.

 

[RFI-EMI-GUY]

Some thoughts:

1) This radio apparently has some "aviation mode" (Page 5-5, section 5.3.3) which invokes some wacky tuning scheme where your display and the receiver operating frequency intentionall disagree. I would recommend monitoring the LO by tapping it with a frequency counter and taking note of the LO when transitioning from a Pass to a Fail frequency. Try tuning to the side of a failed channel either up or down to see if the Fail becomes a Pass.

2) The preselector of the receiver uses Varactor tuning. If the tuning voltages are wrong then the receiver will have poor sensitivity.

3) Monitor Varactor tuning voltage when transitioning from a Pass to a Fail frequency. If the channels are adjacent, there should be little variation.

4) Without a detailed schematic it is near impossible to see how the radio really "is supposed to work". I would suggest that it could be a power supply voltage problem where the varactor tuned preselector circuits are getting wrong or unstable reference voltages. It could be some D/A convertor that takes digital channel or factory tuning data to set the Varactor voltage. It could also be a broken or corrupted data transfer between the main processor and the Preselector module.

5) If you haven't already done so, inspect for physical damage to the internal wireing and connections. Disconnect and reseat the connectors and use some CRC or De-Oxit electronic connector cleaner.

A better more concise manual at SCRIBD link below:

URC-200 VHF Transceiver User Manual | PDF | Frequency Modulation | Power Supply

The document is a user's manual for the General Dynamics VHF URC-200 Transceiver, detailing its operational and maintenance procedures. It includes sections on product requirements, installation, operation, and system maintenance, along with customer support information. The manual also outlines...

www.scribd.com

 

[RFI-EMI-GUY]

Is it a (V2) radio as all the documentation we have so far is (V2) and if you have some earlier or later vintage, the specs may be different. For example aviation mode might be cooked into the ROM as opposed to user selectable.