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Mehdi

@MehdiHacks

Mar 22

Book thread: to make it easier to find all the books I have introduced so far, I will link them under this thread.
They are about: RF, radios, satellites, SDR, electronic warfare, radars, wireless communications, and electronics. (And related topics)

0/n

https://x.com/MehdiHacks/status/2018385023326412920?s=20

1. Oscilloscopes

https://x.com/MehdiHacks/status/2018385023326412920?s=20

https://x.com/MehdiHacks/status/1919032572887072868?s=20

2. Planar Microwave Engineering

https://x.com/MehdiHacks/status/1919032572887072868?s=20

Read 26 tweets

Mehdi

@MehdiHacks

Mar 3

https://twitter.com/te3ej/status/2028602455211053411

Here's my 2 cents:
First of all, if you don't know, a numbers station is usually a radio signal where a sequence of numbers are read by a machine voice.
It's a way to send a one-way message to your assets (spies) who are in dangerous territory and can't communicate back.
1/4

https://twitter.com/te3ej/status/2028602455211053411

This is the first time I hear a number station in Persian.
There are 3 main possibilities:
1. An intelligent unit (e.g. MOSSAD) is sending info to their asset inside Iran.
2. The asset is sending this info.
3. IRGC members are sending to each other.
I believe the scenario 1 is what's happening here.
Here's why:

2/4

1. You usually use this approach to send data or commands to your assets where they could be in danger and/or don't have access to communication devices.
2. Although HF signals are not as easy or straightforward to locate as VHF/UHF, it's still possible, and also dangerous to operate in the current state of Iran.
3. The frequency used (7910 KHz) is not a ham radio frequency, which means the usual ham radio transceivers can't transmit on this frequency (it's not impossible of course. Someone can modify their transceiver or even build a new one that can transmit on any frequency they want)
4. If Iranian army members needed to communicate with each other, they have other mechanisms. Even on HF radio, they could've for example used digital data or even voice, instead of numbers.
5. Weaker argument: the recipient of the signal only knows Persian (although you can say the same about the transmitter too)

3/4

Read 4 tweets

Mehdi

@MehdiHacks

Feb 25

دوستان داخل ایران: یکی از روش های دریافت اطلاعات در زمان جنگ، رادیوی موج کوتاه (short wave) هست. امواج رادیویی در این محدوده فرکانسی (٣ تا ٣٠ مگاهرتز) امکان طی مسافت طولانی در حد هزاران کیلومتر رو دارن.
تو این رشته کمی اطلاعات در این زمینه میدم که امیدوارم مفید باشه.
1/14

چرا رادیوی موج کوتاه حتی در قرن ٢١ استفاده میشه؟ یکی از دلایلش، ساده بودن نسبی ارسال و دریافت این سیگنال ها هست، به شکلی که حتی شما امکان ارسال سیگنال به یک قاره دیگه رو با یک رادیو و آنتن دست ساز هم دارید! (در ادامه بهش اشاره می کنم)
با توجه به اینکه امکان قطع برق و زیرساخت مخابرات در بحران هایی مثل جنگ یا زلزله هست، رادیو تنها جایگزین وسایل ارتباطی مثل موبایل و ماهواره و استارلینک هست.

محض اطلاعتون من یک رادیو آماتور مجوزدار هستم (دو کال ساین آمریکایی و آلمانی دارم) و کلی تماس بین المللی از طریق امواج کوتاه داشتم. اینجا هم صرفا از دستگاه هایی اسم خواهم برد که شخصا دارم یا قبلا استفاده کردم ازشون.
2/14

من این رشته رو به ٢ قسمت تقسیم می کنم. توی بخش اول به کلیت موضوع می پردازم. توی انتهای رشته، به مسائل فنی تر می پردازم که شاید مورد علاقه همه مخاطبان نباشه.
تمرکزم هم بر دستگاه های قابل حمل و باتری دار هست.

احتمالا اولین سوالی که خیلیا جوابشو می‌خوان اینه که چه رادیویی بخریم؟
با تجربه ای که شخصا از برندهای مختلف دارم، و با توجه به موجود بودن در بازار ایران، من ٣ دسته رادیو رو توصیه می کنم که در پست بعدی معرفی می کنم.
توجه کنید که این رادیو ها چند بانده هستن (یعنی هم موج متوسط، هم موج کوتاه و همچنین اف ام رو دریافت می کنن) ولی تمرکز ما در این رشته فقط بخش موج کوتاه هست.
3/14

Read 16 tweets

Mehdi

@MehdiHacks

Sep 22, 2025

I wish I could write more about the challenges we face at work.
I manage 3 core domains: IT (administration and help desk), security, and cloud infrastructure.
We face many challenges with running a reliable, secure, and available infrastructure for a safety critical system.

It's not just the infrastructure, but also designing a secure system (and subsystems), making sure they are properly tested, doing the traditional things (e.g. vulnerability management), compliance, etc for a system that has hardware, cloud, firmware, mobile app, ECU, wireless communications, payments etc.

On a personal level, hardware and wireless comms are the most interesting parts to me. But then in real world scenarios, main risks usually are elsewhere.
But still very happy to work with hardware teams on security.

Read 4 tweets

Mehdi

@MehdiHacks

Aug 3, 2025

🧵 RF basics: How to read a SDR’s datasheet.
You’ve probably seen terms in a SDR or spectrum analyzer’s datasheet, like IIP3, phase noise, noise figure, dynamic range, etc.
In this thread I’ll give a short intro on what they mean.
I’ll use these 3 products' datasheet.

1/10

https://twitter.com/mehdihacks/status/1920582579758989507

Before we start, I have to clarify that this is for beginners and I have to oversimplify a few things.

Also: if you’re not familiar that much with SDRs, or you need a refresher, check out my thread on SDRs here:

2/10

https://twitter.com/mehdihacks/status/1920582579758989507

For the first example, let’s look at HydraSDR RFOne’s datasheet.

Every SDR or spectrum analyzer has a start and stop frequency where they can receive (or transmit, in case of TX SDRs). Here, it’s 24MHZ to 1.8GHZ. This means the product either can’t receive below 24MHZ and above 1.8GHZ, or even if it can, the performance would be poor and not guaranteed.
The next one is Noise Figure (NF). Noise figure is the amount of noise a system adds to its input. It applies to receivers, amplifiers, mixers, etc. Basically any device that receives a signal at the input, and processes it and gives us another signal at the output. The unit is dB. We usually desire the lowest noise figure possible (I say desire, because sometimes it’s not practical due to many reasons like cost). The stated 3.5-4.5dB noise figure is very good. As (apples and oranges) comparison, USRP B200’s NF is <8dB.
Tracking RF filters: this means the filters used in the RF section of the device are not fixed. They change, based on the tuned frequency, to reject out-of-band undesired signals.
IIP3: third-order intercept point. I will write about this separately later, but the short summary is that it’s a measure of how well a receiver can handle strong nearby signals, and avoid intermodulation products when multiple signals are present. The unit is dBm (here, it’s 35dBm which is very good. For comparison, USRP B200’s IIP3 is -20dBm, which means it’s more suitable for lab use rather than in presence of strong real world signals)

3/10

Read 10 tweets

Mehdi

@MehdiHacks

Jun 9, 2025

🧵How to get into the RF world: a short thread for beginners.
As promised, here’s my tips to get into RF as a hobbyist/beginner.
Disclaimer: RF/Radio are my hobbies, but I'm not a professional RF engineer (My profession is “security”, and I studied computer science; I use RF/SDR for my job as well) so these tips may not be for you if you want to pursue it academically/professionally, or if you are already into RF.

1/8

Like any other hobby or field, you have to ask yourself what you want to achieve by getting into it.
If your goal is to get a PhD in communications, then this thread is not that useful. But if you want to learn to play with SDRs, get your ham radio license, build a hobbyist RF lab at home, learn wireless hacking, etc, then read on.
People who have “ham radio” or “RF” as a hobby, have very wide interests. Not everyone does the same. For example there are people who love receiving and listening to shortwave stations (even very distant ones) and they invest lots of time and money in their equipment. Some others like designing and building RF circuits like antennas and amplifiers. Some people are not RF experts, but use RF equipment (like SDRs or spectrum analyzers) in their job (example: using SDRs for wireless security and signal analysis, as part of security pen test).
I can go on and on with these examples, but my point is that you have to take parts of my advice that suit your goals/needs. And of course, this is my advice. Another person might have a totally different (and valid) approach.

2/8

One of the best ways to get into the RF world is to study for a ham radio exam, and get your license. Even if you never do any ham radio stuff, this is useful for 2 reasons:
1. You will learn a lot of useful RF basics, while studying for the exam (different frequency bands, antenna basics, signal propagation, regulations, basic measurements, etc)
2. After getting the license, you are allowed to legally transmit as well (whether you want to communicate with other amateurs or you want to do lab experiments, having a license is necessary/useful)
Here’s a thread on ham radio you can read for more details:
3/8

x.com/MehdiHacks/sta…

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