8569B随机杂散噪声

您好论坛，我最近购买了8569B。
通常使用这些旧设备固定所有旋钮/金属接触刮水器。
清洁所有开关，连接器，触点等。该装置经过良好校准，并在过去一周内一直运行良好。
今天我开始注意到来自输入的随机尖峰时，我正在监控900MHz ISM频段的一些信号。
我断开了天线，噪音仍在那里。
我将Span / Div改为100MHz并注意到这个噪音都在频段上下。
我已经通过其全范围调整了每个控件。
完全衰减，无衰减。
全波段扫描，窄扫描。
RBW。
参考电平，视频滤波器，频段。
一切。
噪音是持久的。
- 通常情况下，使用最大保持，迹线将会很好（大约一分钟）（没有噪音），突然噪音很快就会开始积累......有时甚至只有一次扫描。
它让我想起有人在画布上扔了一桶油漆，因为噪音只是“溅到”屏幕上，如附图所示。
我也在其他乐队中获得噪音。
我想知道DSP部分或RF部分是否更多。
- 当我将“跟踪部分”按钮设置为“存储空白”并将扫描设置为大约1mS / Div时，我仍然可以看到迹线上的噪声。
我现在打开设备，打开服务手册。
但我必须承认我现在很难过。
任何想法从哪里开始？



     以下为原文

  Hello Forum,

I recently purchased a 8569B. Fixed all the knobs/metal contact wipers as usual with these older units. Cleaned all switches, connectors, contacts, etc. The unit is well calibrated and has been working great for about the past week.

Today I was monitoring some signals in the 900MHz ISM band when I started to notice random spikes that were not coming from the input. I disconnected the antenna and the noise was still there. I changed the Span/Div to 100MHz and notice that this noise was all up-and-down the band.  

I've adjusted every control through its full range. Full attenuation, no attenuation. Full Band sweep, narrow sweep. RBW. Ref Level, Video Filter, bands. Everything. The noise is persistent.  -  Usually, using Max Hold, the trace will be fine for about a minute (no noise), and suddenly the noise will quickly start building up ... sometimes in as little as one sweep. It reminds me of someone throwing a bucket of paint at a canvas, as the noise just "splatters" across the screen, as shown in the attached image. I'm getting the noise in the other bands as well.

I'm wondering if this is more in the DSP section or the RF section. - When I set both 'trace section' buttons to 'Store Blank,' and set the sweep to around 1mS/Div, I can still see the noise on the trace. I have the unit open now and my service manual open. But I must admit I'm stumped at the moment. Any ideas where to begin?   
附件

• IMG_0673.JPG4.1 MB