RTL-SDR BLOG BROADCAST AM BLOCK HIGH PASS FILTER (HPF)
Official HamRadioShop Italy Distribution
FREE UP HF BANDS: BUILT TO BLOCK MEDIUM WAVE INTERFERENCE!
Are you a shortwave enthusiast or do you use SDR dongles in Direct Sampling mode? **HamRadioShop**, official **RTL-SDR Blog** distributor, presents the **Broadcast AM Block** high-pass filter. Specifically designed to eliminate overloading caused by very strong local Medium Wave (AM) broadcasters, this filter restores maximum sensitivity to your receiver on higher HF frequencies.
Why do Medium Waves (AM) block your SDR receiver?
The AM broadcast band (Medium Wave) extends from approximately 525 kHz to 1,705 MHz. Due to enormous transmission powers and the proximity of local repeaters, these signals can hit your shack's antenna with devastating energy. When commercial AM signals enter a wideband SDR receiver (or a traditional radio), they cause an immediate **overload of the gain stages**.
The result of this overload is severely degraded, dull, and noisy reception on the remaining useful HF bands (such as amateur radio bands or higher shortwave). This filter solves the problem at the root: it acts as an insurmountable wall, **attenuating all signals below 1.7 MHz by a good 60 dB** and drastically eliminating VLF, LF, and MW interference as well.
PRACTICAL TIPS FOR USE AND INTEGRATION
-- EXCELLENT FOR DIRECT SAMPLING (RTL-SDR V3)
If you use *Direct Sampling* (Q-Branch Direct Sampling) mode on the RTL-SDR V3 dongle, this filter is practically mandatory. Without it, powerful medium wave stations mirror themselves within the shortwave spectrum due to aliasing. Inserting the filter instantly cleans up the waterfall.
-- OPTIMIZATION FOR UPCONVERTERS (SPYVERTER AND SIMILAR)
Please note: if you use an external Upconverter, it is already capable of handling strong signals fairly well. However, adding the BCAM high-pass filter before the Upconverter helps to further linearize the input, significantly improving the S/N (signal-to-noise ratio) on extremely weak HF signals.
-- UNDERSTANDING THE CUTOFF POINT (ROLL-OFF)
As a true high-pass filter and not a simple band-stop filter, VLF, LF, and MW signals are entirely blocked. Due to the natural rolloff curve of the filter, the point of full operability and minimum loss starts from approximately **2.5 - 2.6 MHz and above**.
-- DC BLOCK (NO DC PASS)
Caution: the architecture of this filter does not allow DC voltage to pass. It therefore cannot be used in coaxial lines where power for masthead amplifiers (Bias-Tee) is transmitted. Designed for reception power only (RX: do not transmit!).
TECHNICAL SPECIFICATIONS
| RF Parameter | Construction Details and Rated Values |
|---|---|
| Filter Type | Concentrated constant type LC High Pass Filter. |
| Cutoff at -3 dB | Fixed between 2.5 MHz and 2.6 MHz (full efficiency and off-band linearity from this frequency upwards). |
| AM Band Attenuation | Deep attenuation of approximately 60 dB for all frequencies below 1.7 MHz. |
| Insertion Loss (I.L.) | In the useful passband, it is typically well below 2 dB. |
| Power Levels and DC | Usable exclusively for reception (RX). Does not allow DC current to pass (No DC Pass). |
EXCELLENCE FOR YOUR SDR RECEIVER
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Request Information or Technical Support on HF FiltersRTL-SDR Blog, Broadcast AM Block HPF are registered trademarks — Official distribution, sales, and support in Italy via HamRadioShop
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