Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old June 13th 19, 07:27 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jun 2018
Posts: 10
Default Noisy repeater output

Hi, my old HT DMM is still abandoned, but...
I must repair a Vertex VRX-7000 repeater that has a noisy output:

https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg

Do you know how can generate this noise, also UNDER the trasmitting
frequency?
The receiver frequency falls in the noisy area, and when I connect a
duplexer, the sensitivity of receiver is blanked.

I still must begin to investigate, but if someone know something, I will
much appreciate any suggestion.
Thanks.

  #2   Report Post  
Old June 13th 19, 09:04 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jul 2006
Posts: 3,362
Default Noisy repeater output

In article ,
says...

Hi, my old HT DMM is still abandoned, but...
I must repair a Vertex VRX-7000 repeater that has a noisy output:

https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg

Do you know how can generate this noise, also UNDER the trasmitting
frequency?
The receiver frequency falls in the noisy area, and when I connect a
duplexer, the sensitivity of receiver is blanked.




Go here and ask the question , Many repeater owners are here.

https://groups.io/g/repeater-builder


It could normal for the transmiter. How many notch cavities are you
using for a duplexer


  #3   Report Post  
Old June 14th 19, 04:09 AM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jul 2007
Posts: 3,896
Default Noisy repeater output

On Thu, 13 Jun 2019 20:27:52 +0200, Eremita Analogico
wrote:

Hi, my old HT DMM is still abandoned, but...
I must repair a Vertex VRX-7000 repeater that has a noisy output:

https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg


Argh. You're overdriving the spectrum analyzer. Most of the junk
looks like it's coming from intermod mixing between the harmonics
produced in the now non-linear spectrum analyzer input states.

The SA shows that your input signal is 4.52dBm (about 3mw) into an
internal 10dB attenuator. What model HP spectrum analyzer are you
using and will it tolerate a +5dBm input signal level?

Put some external -10dB attenuators in line and see if the junk
(noise) decreases. If it decreases more than -10dB, then it's being
generated in the SA by your overload. If it drops exactly -10DB, then
it's real.

Do you know how can generate this noise, also UNDER the trasmitting
frequency?
The receiver frequency falls in the noisy area, and when I connect a
duplexer, the sensitivity of receiver is blanked.


Duplexer tuning and cabling are somewhat of an art. For example, the
coax cables between the duplexer and the receiver input, and between
the duplexer and the transmitter output MUST be an odd multiple of 1/2
wavelength electrical long, as measured from the pickup loop in the
cavities, to the receiver front end device or transmitter RF output
transistor. Use the wrong length, or wrong connectors, and you'll
never get the rated isolation.

I agree with Ralph Mowery. Go to:
https://groups.io/g/repeater-builder
and ask the same question, but also include what radio and duplexer
you are using. Also what test equipment you have available. Most
important, exactly what problem you are trying to solve that required
troubleshooting.

I still must begin to investigate, but if someone know something, I will
much appreciate any suggestion.


There a many articles and videos on the web on "duplexer tuning". I
would recommend one, but need to know the details of your repeater to
find something appropriate.
https://www.google.com/search?q=duplexer+tuning

Good luck.



--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #4   Report Post  
Old June 14th 19, 01:16 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jun 2018
Posts: 10
Default Noisy repeater output

Il 14/06/2019 05:09, Jeff Liebermann ha scritto:
On Thu, 13 Jun 2019 20:27:52 +0200, Eremita Analogico
wrote:

Hi, my old HT DMM is still abandoned, but...
I must repair a Vertex VRX-7000 repeater that has a noisy output:

https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg


Argh. You're overdriving the spectrum analyzer. Most of the junk
looks like it's coming from intermod mixing between the harmonics
produced in the now non-linear spectrum analyzer input states.



I don't think so. The repeater TX has an output of 10W. Prior to enter
in the spectrum analyzer, the signal is reduced by a 20 dB in line
attenuator.


The SA shows that your input signal is 4.52dBm (about 3mw) into an
internal 10dB attenuator. What model HP spectrum analyzer are you
using and will it tolerate a +5dBm input signal level?


The SA input tolerate 1W (30 dBm)
The model is 8590B



Put some external -10dB attenuators in line and see if the junk
(noise) decreases. If it decreases more than -10dB, then it's being
generated in the SA by your overload. If it drops exactly -10DB, then
it's real.

Do you know how can generate this noise, also UNDER the trasmitting
frequency?
The receiver frequency falls in the noisy area, and when I connect a
duplexer, the sensitivity of receiver is blanked.


Duplexer tuning and cabling are somewhat of an art. For example, the
coax cables between the duplexer and the receiver input, and between
the duplexer and the transmitter output MUST be an odd multiple of 1/2
wavelength electrical long, as measured from the pickup loop in the
cavities, to the receiver front end device or transmitter RF output
transistor. Use the wrong length, or wrong connectors, and you'll
never get the rated isolation.


We have tryed with Procom and Motorola duplexers, both with 3 adjustable
cavities for RX path and another 3 adjustable cavities for TX path.
The same duplexers work perfectly with a repeater built with two
separate Simoco SRM9000, without any desensization of RX unit when the
TX is operated.
Thus, I think that the PA of Vertex VRX7000 has some issues, but I never
seen noises of that type. I wolud expect some harmonics.
The internal supply can do this noise?



I agree with Ralph Mowery. Go to:
https://groups.io/g/repeater-builder
and ask the same question, but also include what radio and duplexer
you are using. Also what test equipment you have available. Most
important, exactly what problem you are trying to solve that required
troubleshooting.

I still must begin to investigate, but if someone know something, I will
much appreciate any suggestion.


There a many articles and videos on the web on "duplexer tuning". I
would recommend one, but need to know the details of your repeater to
find something appropriate.
https://www.google.com/search?q=duplexer+tuning

Good luck.




Ok, thanks, I will try also the repeater-builder forum, but if I can
obtain some useful tips without register me I will much appreciate.
Wednesday I will resume the repeater investigation.
  #5   Report Post  
Old June 14th 19, 01:16 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jun 2018
Posts: 10
Default Noisy repeater output

Il 13/06/2019 22:04, Ralph Mowery ha scritto:
In article ,
says...

Hi, my old HT DMM is still abandoned, but...
I must repair a Vertex VRX-7000 repeater that has a noisy output:

https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg

Do you know how can generate this noise, also UNDER the trasmitting
frequency?
The receiver frequency falls in the noisy area, and when I connect a
duplexer, the sensitivity of receiver is blanked.




Go here and ask the question , Many repeater owners are here.

https://groups.io/g/repeater-builder


It could normal for the transmiter. How many notch cavities are you
using for a duplexer



Thanks, please follow the answer to Jeff Liebermann



  #6   Report Post  
Old June 14th 19, 05:52 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jul 2007
Posts: 3,896
Default Noisy repeater output

On Fri, 14 Jun 2019 14:16:05 +0200, Eremita Analogico
wrote:


Put some external -10dB attenuators in line and see if the junk
(noise) decreases. If it decreases more than -10dB, then it's being
generated in the SA by your overload. If it drops exactly -10DB, then
it's real.


Please do the above test with a 10dB attenuator. If the spurious
noise drops 10dB, then you have a real problem. If the noise drops
more then 10dB, the noise is being generated inside the spectrum
analyzer.

We have tryed with Procom and Motorola duplexers, both with 3 adjustable
cavities for RX path and another 3 adjustable cavities for TX path.
The same duplexers work perfectly with a repeater built with two
separate Simoco SRM9000, without any desensization of RX unit when the
TX is operated.
Thus, I think that the PA of Vertex VRX7000 has some issues, but I never
seen noises of that type. I wolud expect some harmonics.
The internal supply can do this noise?


The spectrum analyzer picture shows that you are operating on 162.4
MHz.
https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg
In the USA, that's one of the weather stations broadcast frequencies.
http://weatherradios.com/stations-and-frequencies
I have no idea what 162.4MHz might be used for in Italy.

You haven't supplied any additional information on the equipment
you're using, duplex split frequency, and available test equipment.
The HP spectrum analyzer will survive the obvious overload, but I'm
not sure if it will produce usable measurements (without spurious
noise). As I mentioned, try reducing the input level with an
additional attenuator and see if the spurs disappear.
--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #8   Report Post  
Old June 15th 19, 12:55 AM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jul 2007
Posts: 3,896
Default Noisy repeater output

On Fri, 14 Jun 2019 15:32:53 -0400, Ralph Mowery
wrote:

In article ,
says...

You haven't supplied any additional information on the equipment
you're using, duplex split frequency, and available test equipment.
The HP spectrum analyzer will survive the obvious overload, but I'm
not sure if it will produce usable measurements (without spurious
noise). As I mentioned, try reducing the input level with an
additional attenuator and see if the spurs disappear.


I have used a HP 8924C for a SA and sometimes it is difficult to tell if
it is overloaded at first even though it has the high power option and
will handle 100 watts.


I've had the same problem with every spectrum analyzer I've used. When
brand new, the SA is probably quite linear throughout its specified
dynamic range. However, after getting overloaded with too much RF
causing components to fry, the dynamic range can be reduced somewhat.
It's difficult to tell if something is broken, but the 10dB attenuator
test I previously mentioned is a clear indication that either
something is wrong or burnt out.

Notice that the marker shows a signal level of 4.52dB (upper right of
screen), but shows about +10dBm on the graticule.
https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg
Kinda looks like the detector and/or the A/D converter that is
measuring the marker level has gone rather non-linear.

Sometimes to see the spurious RF you need to notch out the fundimental.


That works very well on UHF frequencies which have a 5MHz split
between transmit and receive. Unless you have a rather large cavity
handy, it works badly on VHF frequencies, where the split can be as
little as 0.6MHz. For the present situation, the SA shows a span of
almost 300MHz for a 161.4MHz center frequency. For all I know, the
spurious noise could be switching noise, AM/FM/SW/TV broadcasting,
other services, etc along with their intermod mixes. With a sweep
from 0 to 300MHz, that's about what I would expect with a cliplead
crammed into the antenna connector.


--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Wireless router as repeater Uncle Albert Electronics Repair 6 February 9th 13 07:27 PM
Video Monitor "Repeater" Over Network Jim Thompson[_3_] Electronic Schematics 38 November 3rd 10 01:34 PM
The three dial repeater of set 277 [email protected] Metalworking 0 March 28th 09 07:42 PM
how do you make a rubber band gun repeater [email protected] Woodworking 3 November 20th 06 01:38 AM
Rocking Horse Droppings - (10M USB repeater cable) [email protected] UK diy 9 February 6th 06 08:47 PM


All times are GMT +1. The time now is 12:56 PM.

Powered by vBulletin® Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2004-2019 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"

 

Copyright © 2017