（挂错了标签，重发一下） IC718，接HF-20A天线，天线的长臂从18层楼的5楼垂到地面，用钉子（不是很长）打到土里，短臂接到了电台的接地点，驻波很低1.1左右，能隐隐约约听到友台通联但是底噪非常大一直都有S9 ，开衰减也只是S7的样子，QTH在西安长安。手头没有其他设备对比，下表是三月15晚上9点各个频点的底噪，想问一下大家这合理吗，是底噪就这么大还是说电台坏了？另外这个718发射也有点问题，设定100W发射假负载测出来只有50W，这个台在仓库躺了10年，从买到现在基本没有发射过，这个会有关吗？谢谢🙏 [upl-image-preview uuid=f16ee888-486e-4c7b-be44-a851ede9be8d url=https://storage.hamcq.cn/2025-03-15/1742045641-717823-img-4688.jpg alt={TEXT?}] | **频率 / kHz** | 1800 | 3500 | 7000 | 10100 | 14000 | 14250 | 18068 | 21000 | 24890 | 28000 | |-|-|-|-|-|-|-|-|-| |**底噪** | S8.5 | S8.5 | S9.5 | S9 | S8 | S8.5 | S7 | S2 | S4 | S1 | |**SWR**| 2.3 | 2.0 | 1.1 | 1.15 | 2.5 | 2.5 | 2.1 | 1.5 | 1.6 | 2.0 |

我在老家自家楼顶上架正V，基本上天天晚上都是S9的底噪....... 😵

很合理~ 去周围看看有没有电瓶车在充电或者LED灯牌。。。~

太合理了，我在家里晚上40米都是+10的

家里别玩语音了 cw和FT 8首选

40米底噪高，在城市里挺正常的。我这个频段也就打算玩一下FT8，以及和邻近的HAM SSB通联，其他的都不指望。

这个频段我的qso个数还没超过50，我这儿40m底噪s4-s7，无奈用的加感gp效率太低，15w出去也所剩无几了

低波段底噪比较高是正常现象，注意排查周围干扰源

曾经在单位的一个类似仓库作用的厂房上面拉了一根20米端馈，接ic-7300驻波尚可，接收噪音59+，频谱一片红色，于是试着分别断电看看哪里的干扰，当断开不远处的电动自行车充电电源时，整个世界清净了，底噪不超过53-55，7050等频率的通联也都听到了，第一次感受到电动自行车的劣质充电器的厉害。记得多年前单位同事把用不上的充电器送我，沉甸甸很重，里面竟然是做工精致的R型变压器，再看现在的充电器，搁手上比纸盒重不了多少，一小片电路连散热器都不舍得用。

@"BG3AE"#p57109 按理来说现在技术进步了，东西可以做的更小更轻，比之前的辐射值更小，但是现在很多商家为了省钱，根本不管这些的，所以买通过认证或者有品牌的产品更好一些

Is a 40m band noise floor of S9 reasonable?

BH9DFB_AI6YY

(Incorrect tag, re-sending)
IC718, connected to the HF-20A antenna. The long arm of the antenna extends from the 5th floor (18 stories) down to the ground, and is secured with nails (not very long) into the soil. The short arm connects to the radio's grounding point. The SWR is very low, around 1.1, allowing for intermittent communication with other stations, but there is a significant amount of noise. There is always S9 noise.
The S7 also experienced a decline, and QTH was located in Xi'an, Chang'an.

I don't have any other equipment to compare with, so the following table shows the background noise at each frequency point at 9 PM on March 15th. I was wondering if this level of background noise is normal, or if the radio is malfunctioning?

Additionally, there seems to be an issue with the 718 transmitter. When I set it to transmit at 100W with a dummy load, I only measured 50W. This equipment has been sitting in storage for about 10 years and hasn't been used much since I bought it. Could this be related? Thank you.🙏

Frequency / kHz	1800	3500	7000	10100	14000	14250	18068	21000	24890	28000
Background noise	S8.5	S8.5	S9.5	S9	S8	S8.5	S7	S2	S4	S1
SWR	2.3	2.0	1.1	1.15	2.5	2.5	2.1	1.5	1.6	2.0

BA7NNC-JOE

I have a high-end stereo system installed on the top floor of my family's house. It generates a significant amount of background noise, especially at night, which sounds like S9. 😵

BG2EFX

That makes sense. Check if there are any electric scooters charging nearby or LED streetlights...

BG7TVF

Anything below S9 is unreasonable.

BG4IDK

That makes perfect sense. I have a range of +10 at home, even up to 40 meters.

BG7NOD

BG4IDK Yes, and not to mention that all the charging stations are now located downstairs.

bg2kud

Please don't use voice communication at home. CW and FT-8 are preferred.

BH9DFB_AI6YY

bg2kud Then I arranged for the FT8 to be used.

BD8DLV

The noise floor at 40 meters is quite high, which is normal in an urban environment. I plan to experiment with FT8 and communicate via HAM SSB with nearby stations; I don't expect much success with other modes.

BG5VLI

In this frequency band, I haven't made more than 50 QSOs. The noise floor on my 40m band is S4-S7, which makes it difficult to use a low-power (15W) transmitter effectively.

BG2EWI

It's normal for low-frequency noise to be relatively high; pay attention to identifying and eliminating potential sources of interference.

BG3AE

I once connected a 20-meter end-fed antenna to a building that served a similar purpose as a warehouse at my workplace. The SWR was acceptable, with a noise level of 59+ dB and a spectrum dominated by red. I then tried disconnecting different sources of interference one by one. When I disconnected the power supply for an electric bicycle charger located nearby, everything became quiet, with a background noise level below 53-55 dB. I was also able to hear communication on frequencies such as 7050. This experience made me realize the extent of the problems caused by cheap and poorly designed electric bicycle chargers. I remember that several years ago, a colleague at my workplace gave me an unused charger. It was heavy and bulky, but inside it was a well-made R-type transformer. Looking at the chargers available today, they are much lighter and smaller than the one I received, and some even don't have a heatsink.

BA4SFW

BG3AE Therefore, with current technological advancements, products can be made smaller and lighter, with lower radiation levels compared to the past. However, many businesses prioritize cost savings and often ignore these factors. As a result, it's better to purchase certified or branded products.

BH9DFB_AI6YY

BG3AE It seems like… there's a row of electric scooters parked downstairs, and I suspect they've been cheaply made without proper EMI shielding.

BG9CHE

It's perfectly normal. Try checking for background noise between 6 AM and 9 AM, or take your equipment outside to a quieter location – you'll notice a significant improvement.

dxs660

To measure the machine's power output, set it to RTTY mode for transmission. If you are using SSB mode without voice compression, an output of 50W is normal.

BH9DFB_AI6YY

dxs660 Okay.😐I tested it under RTTY, and the actual output power could consistently track the set power. I also tried adjusting the potentiometer on the main control board, but it didn't work. It seems like there might be a problem with the amplifier itself.

BH4GQD

Perfect to an unbelievable degree.

Harunanana

The best way to measure power is to use FM or CW mode.

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