Repeater Testing

[MarkInTampa]

I picked up a Vertex VXR-7000u repeater for a heck of a deal without a duplexer that I would like to test to make sure it works. It does power up fine. I need to order up a programming cable to find the frequency it's set at and ordered one last night. For testing since I don't have a duplexer, can I run the repeater WITHOUT a RX antenna since I'm sitting right next to it with the TX antenna hanging 40ft directly above me? Would not connecting a RX antenna provide enough isolation to test? Hate to buy a duplexer if the repeater doesn't work.

[MarkInTampa]

37 minutes ago, Sshannon said:

Even though the receiver is tuned to a 5 MHz offset, without filtering on the receive side the 5 MHz offset ceases to be meaningful. The receiver front end will receive it.  I don’t know whether it will overload it.

I've got a local Motorola dealer/shop 5 miles from me that also supports the ham radio community and usually has a table setup at any hamfest in the area. Guess I could call him and see if he could check it out. Again, I plan on donating it and don't mind spending another $100 or so to get it up to snuff but if there are issues with it I'll flip it for parts.

[tweiss3]

Typically you test it with a dummy load on the output, and you can leave the RX unattached. Just keep your duty cycle down (in accordance with your dummy load rating) and watch out, it will get hot.

[MarkInTampa]

21 minutes ago, tweiss3 said:

Typically you test it with a dummy load on the output, and you can leave the RX unattached. Just keep your duty cycle down (in accordance with your dummy load rating) and watch out, it will get hot.

Thanks for the reply. Unfortunately I don't have a dummy load handy. My thought was to use the low power mode on the repeater with no RX antenna for a quick test. My favorite local repeater (30 miles away) on .600 is being ran by a couple of old Johnson mobiles converted to a repeater with a power amp at 400ft and is getting a bit noisy. I wanted to test and make sure the repeater I bought works. If it does I'll program it for .600 and do a surprise donation to the owner of the existing repeater. I have no interest in running a repeater of my own but got the Vertex for $100 bill so couldn't turn it down, figured one of the local repeaters could use it.

[BoxCar]

IMO it would be against the regulations to key the transmitter without knowing the output frequency. It could have been set to use a licensed frequency where you would then be an unauthorized transmitter and/or possibly interfere with a current user of the frequency.

[Flameout]

55 minutes ago, markskjerve said:

Thanks for the reply. Unfortunately I don't have a dummy load handy. My thought was to use the low power mode on the repeater with no RX antenna for a quick test. My favorite local repeater (30 miles away) on .600 is being ran by a couple of old Johnson mobiles converted to a repeater with a power amp at 400ft and is getting a bit noisy. I wanted to test and make sure the repeater I bought works. If it does I'll program it for .600 and do a surprise donation to the owner of the existing repeater. I have no interest in running a repeater of my own but got the Vertex for $100 bill so couldn't turn it down, figured one of the local repeaters could use it.

I did a similar testing with my IC-FR4000, to be sure it was within the specs. No antenna on the RX side and a power meter and antenna on the TX side. A dummy load should be best to test and I have a dummy load, but it is a cheap $50 piece of crap from Amazon and was getting about a 1.70 SWR using it. I was getting a 1.03 SWR on low pwer and 1.11 on high (Comet 712EFC)

You definitely got a heck of a deal on that repeater! There were just 2 of the RFS UHF duplexers for sale on QRZ for $100 each but they sold very quickly

this is what my test looked like. Power was much lower going through a duplexer

 

[Sshannon]

@markskjerve

First, I applaud your wish to help the repeater owner.  In a world where generosity sometimes seems to be lacking it’s refreshing to see someone perform an altruistic act.

I think there’s an easy way forward.  You can use incandescent light bulbs or heating elements as a dummy load if you really want to surprise the repeater owner or you can surprise the repeater owner with an untested repeater and he/she can come up with a dummy load.  At the lowest power setting you don’t really need to worry about power damage to your finals as a result of impedance mismatch.

[MarkInTampa]

30 minutes ago, Sshannon said:

@markskjerve

First, I applaud your wish to help the repeater owner.  In a world where generosity sometimes seems to be lacking it’s refreshing to see someone perform an altruistic act.

I think there’s an easy way forward.  You can use incandescent light bulbs or heating elements as a dummy load if you really want to surprise the repeater owner or you can surprise the repeater owner with an untested repeater and he/she can come up with a dummy load.  At the lowest power setting you don’t really need to worry about power damage to your finals as a result of impedance mismatch.

It's not the impedance mismatch on the transmitter I'm worried about. For testing I plan on using my base antenna connected to the TX of the repeater and nothing connected to the RX of the repeater and use a HT on 1watt without an antenna right next to it to key it to keep from overloading the RX. I was just wondering since there is no duplexer or coax connected to the input of the repeater if there was enough separation with the base antenna 40ft directly above me to keep the transmitter from bleeding 5MHz away back into the input since it's not shielded or connected to anything.

Don't have a clue what frequency the repeater is currently on, have to wait for the programming cable to do much more testing.

[Sshannon]

8 minutes ago, markskjerve said:

It's not the impedance mismatch on the transmitter I'm worried about. For testing I plan on using my base antenna connected to the TX of the repeater and nothing connected to the RX of the repeater and use a HT on 1watt without an antenna right next to it to key it to keep from overloading the RX. I was just wondering since there is no duplexer or coax connected to the input of the repeater if there was enough separation with the base antenna 40ft away to keep the transmitter from bleeding 5MHz away back into the input since it's not shielded or connected to anything. 

Even though the receiver is tuned to a 5 MHz offset, without filtering on the receive side the 5 MHz offset ceases to be meaningful. The receiver front end will receive it.  I don’t know whether it will overload it.

[gortex2]

Take it to the shop. You stated you have no idea how its programmed. It could be on GMRS, or public safety or Land Mobile frequencies. A shop can put in on proper test equipment and possibly read out whats in the repeater.

[MarkInTampa]

3 hours ago, gortex2 said:

Take it to the shop. You stated you have no idea how its programmed. It could be on GMRS, or public safety or Land Mobile frequencies. A shop can put in on proper test equipment and possibly read out whats in the repeater.

I've got a programming cable for it on the way and already have the software. In looking through the software it appears to be one of the most simple repeaters/radios I've seen compared to my DMR HT's to program. There are examples of this repeater setup for GMRS here on this forum as well. For the most part everything is on one page and unlike Wouxun software the help menu actually works. I'll pull the config off of it when I get the cable to see where it sits now. If it's in the 450-470MHz range now I'll swap it over to GMRS and do a quick test. If it's tuned currently for something below 450MHz or so it may not work for GMRS or will need to be tuned for it. Guess if that's the case I can set it up on 70cm to test it (yes I hold a Tech license). Just don't want to put money into a paperweight if it doesn't work at all.

[MarkInTampa]

Got the programming cable today and pulled the config. It's already programmed for GMRS! Ran a quick test and it appears to work so I guess it's worth a trip to the radio tech to have him check it out. Although it's programmed for GMRS it's CW ID shows a ham callsign that lives around 30 miles from me, don't know what that's about.

 

[Guest]

1 hour ago, markskjerve said:

Got the programming cable today and pulled the config. It's already programmed for GMRS! Ran a quick test and it appears to work 

Congrats on your catch