Noisy repeater output

[Eremita Analogico]

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.

[Ralph Mowery]

In article <qdu4j9$3ok$1...@gioia.aioe.org>,
LEDITApao...@DALNASOlibero.it 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 >

[Jeff Liebermann]

On Thu, 13 Jun 2019 20:27:52 +0200, Eremita Analogico
<LEDITApao...@DALNASOlibero.it> 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 je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Eremita Analogico]

Il 14/06/2019 05:09, Jeff Liebermann ha scritto:
> On Thu, 13 Jun 2019 20:27:52 +0200, Eremita Analogico
> <LEDITApao...@DALNASOlibero.it> 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.

[Eremita Analogico]

Thanks, please follow the answer to Jeff Liebermann

[Jeff Liebermann]

On Fri, 14 Jun 2019 14:16:05 +0200, Eremita Analogico
<LEDITApao...@DALNASOlibero.it> 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.

[Ralph Mowery]

In article <c8j7ge53nt8esk4tn...@4ax.com>,
je...@cruzio.com 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.

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

[Jeff Liebermann]

On Fri, 14 Jun 2019 15:32:53 -0400, Ralph Mowery
<rmower...@earthlink.net> wrote:

>In article <c8j7ge53nt8esk4tn...@4ax.com>,
>je...@cruzio.com 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.