Tag Archives: Radio Modifications

SI473x Receiver Firmware Update and Internal Photos

Many thanks to SWLing Post contributor, Robert Richmond, who writes:

Hi Tom,

Ricardo (PC2CLR) recently published an excellent firmware update for the SI473x kit-based receivers flooding AliExpress, eBay, etc.

I purchased a preassembled SI473x model, and it has a much better user interface following the update IMO. Other changes include being able to tweak or disable soft mute, finer grained attenuation, and a few options being moved to the encoder instead of multiple button presses.

The update including directions and a list of features can be found here:

https://github.com/pu2clr/SI4735/tree/master/examples/SI47XX_KITS/AliExpress

Best Regards,

Robert Richmond

Internal Photos

Robert also kindly shared the following internal photos of the SI473x receiver:

Robert, thank you so much for sharing the information and your SI473x photos/mods!

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Tecsun PL-330 tip: Using the telescopic antenna for the LW & MW bands

Many thanks to SWLing Post contributor, Mad Radio DXer, who writes:

Hi,

I want to let you & your readers know of a Tecsun PL-330 trick that I saw mentioned in the comments section of your blog some time ago which does not seem to have a lot of awareness. This is for using the telescopic antenna for the LW & MW bands, & it works for the 3305 version of the PL-330 which I understand is the export version. The original comment I saw said this also works for the Chinese version of the PL-330, before firmware 3305.
It is very easy to do & instructions are the following…

1. Turn on the radio.
2. Select either the MW or LW band.
3. Press the number 3 key down for a few seconds, until the display shows “CH-S”.
This means the MW & LW bands can now be received with the telescopic antenna.
4. To use the ferrite bar again, press the number 3 key until “CH-A” appears on screen.

I also did a YouTube video showing this trick in action…

This reminds me of the trick used for the Degen DE1103 PLL version which allows reception of the telescopic antenna for the MW band. However, in my opinion this is much easier to use on the PL-330 than the DE1103 PLL which could be very fiddly. Also this trick is most effective on the LW band, as I find Chinese portables are usually very weak on this part of the band which is good news for LW DXers. I hope you & everyone reading find this trick very useful & that it works.

Thank you so much for the excellent tip!

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How to effectively disable transmit on the Icom IC-7300 via Settings menu

Many thanks to SWLing Post contributor, Justin (N2UJZ), who shares the following Icom IC-7300 tip:

I was looking for a way to completely disable the TX (to share an antenna) on a IC-7300 and found this article. I didn’t get any answers saying “yes” but I just figured it out and yes it can be done.

Press ‘Menu”, then press “Set”, then “Function” to bring up a menu starting with “Beep Level.” The fourth item down is “Band Edge Beep.” You want to set that to “ON (User) & TX Limit”

Then once that is turned on, there will be a “User Band Edge” option in the Function menu. Under that select and delete all of the band edges. The radio will now not TX at all from any button on any band. To re-enable TX, change the “Band Edge Beep’ anything other than TX Limit.

[IMPORTANT] Don’t forget to save to the SD card before deleting the band edges or you might have to re-enter them.

I was just disconnecting the mic until today but this way I’m a little more at ease now with the 7300 sharing an antenna with the HackRF. 73, Justin N2UJZ.

What a brilliant tip, Justin. Thank you for sharing this!

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How to install a mechanical SSB filter on the Yaesu FRG-7

Many thanks to SWLing Post contributor, Kostas (SV3ORA), for sharing the following guest post which originally appeared on his radio website:


How to install a mechanical SSB filter on the Yaesu FRG-7

by Kostas (SV3ORA)

The Yaesu FRG-7 is a general coverage MW/SW receiver that uses the Wadley Loop system for stabilizing the frequency tuning. The receiver has a good sound on AM mode, that reminds me the tube receivers sound. However, on sideband mode, it is pretty much useless. The IF ceramic filter that is used, does not have enough selectivity to reject the opposite sideband. No matter if the front panel mode selector switch states USB/CW and LSB, these just shift the BFO, nothing more. The receiver is a DSB set not SSB. A cheap way you can accomplish single signal sideband reception with the FRG-7 is described in this link. Whereas it works, it increases the audio bandwidth of the signals to the high pitch.

A better approach is to install an additional mechanical filter to the receiver. This of course requires expensive 455KHz mechanical filters, but if you have one in hand or if you are willing to pay for the improvement in performance, then this is the recommended option. But you can’t just desolder the ceramic filter of the receiver and solder a mechanical filter in place. On AM mode, you need wider bandwidth, but on SSB mode you need narrower. So both filters must be in place and a selection must be done in each mode. Thankfully, this modification is pretty easy on the FRG-7 and it does not require any modification of the external appearance of the radio.

The schematic of the FRG-7 is shown above. Everything with red color, are part of the modification. The modification is pretty straight forward. You have to desolder the original ceramic filter from the FRG-7 PCB and install it on a separate PCB along with the new 455KHz mechanical filter. To select between the two filters, a 9-12v DPDT relay can be used and it must be connected as shown in the schematic. The power for the relay coil is derived from one section of the mode switch (S3d). On USB or LSB modes, the BFO is energized and this power is also used to energize the relay, which in turn switches to the narrow mechanical filter on these modes.

A good place for the new PCB that accommodates the filters, is just below the main tuning dial of the receiver. There is a hole there and three screws, which can be used to also hold this PCB in place. I needed to replace these screws in mine with longer ones, because I used spacers to prevent the PCB from touching the chassis. But this is optional.

Two small pieces of coaxial cables are used to connect the new PCB to the pads of the ceramic filter, that has been now removed from the original PCB of the receiver. Ground these cables on both ends.

The power cables for the relay coil (shown with red and black in the picture above), are passed below the PCB to the chassis opening and through a hole to the bottom of the original PCB of the receiver. The ground wire is soldered to the filter ground point and the red wire is soldered to the mode selector switch S3d. S3d is the outer wafer onto the switch. Use a multimeter to find the contact of the switch that has VCC when the mode is switched to USB or LSB. This is the point where you want to connect the red wire.

After installing everything, you should perform an alignment of the TC404 and the T406 in the BFO section as described in the manual. This requires a frequency counter, but I did my alignment by simply adjusting the two controls by ear, until I got roughly the same pitch on LSB and SSB audio bandpass. These controls interact, so you have to do a bit of back and forth in both of them. It is very easy.

After installing the modification and aligning the receiver, the result is pretty obvious. No more DSB reception, SSB signals are received just once in the dial and their bandwidth is limited as it should on SSB. The mechanical filter I had, was a bit narrow (2.1KHz) so I can also hear a bit os “seashell” sound on SSB, but SSB voice signals are perfectly understood. It is interesting that the audio volume between the ceramic filter and the mechanical filter was just about the same, which indicates that there is no additional loss in the newly installed filter. Another interesting thing is that there was no need for any impedance matching using active devices or transformers on the mechanical filter. It worked just by directly connecting it. Neither it’s loss, not it’s response seems to be affected by any possible impedance mismatches.

Note that Collins produced both symmetrical and asymmetrical mechanical filters (yes they used two filters, one for USB and one for SSB in some of their gear). My filter is a symmetrical one (same roll-off response curve on both sides of the filter passband). If you use an asymmetrical filter, expect a bit different pitch when switching from LSB to USB and vice versa. Not a huge problem, but just a note.

By performing this simple modification, you will end up with an FRG-7 receiver that is trully selective, allowing for real SSB reception. Most importantly you do not ruin the appearance of your precious FRG-7, but just improving it’s performance. This modification would probably be appreciated much when deciding to sell your FRG-7 to someone else.


Thank you for sharing this practical and affordable project with us, Kostas!

Post Readers: Check out this project and numerous others on Kostas’ excellent website.

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Kostas’ Yaesu FRG-7 adjustment that improves opposite sideband rejection

Many thanks to SWLing Post contributor, Kostas (SV3ORA), who shares the following video and writes:

In this 7.8Mb video (attached) is my solution for “converting” the Yaesu FRG-7 for single signal reception on SSB:

Not a mod actually, no additional filters, no soldering of any kind. Just tune the BFO on USB and on LSB a bit far away from the 455KHz ceramic filter (using the transformer for LSB and the capacitor for USB, as the manual states). As the video shows, this provides the near to
carrier selectivity to cut off the unwanted sideband.

The price you pay is more high frequencies (but in the wanted sideband) and a bit attenuated low frequencies as the filter is effectively shifted to higher frequencies. Very high frequencies cut-off is helped by the tone control of the receiver to some point.

This is a cost-free mod and requiring even no soldering skills, neither any mod to the receiver. Now as you tune the bands in SSB and CW, you do not hear the same signal twice. On AM mode nothing changes, since the BFO is switched off in this mode.

Many thanks for sharing this, Kostas! This seems like a simple adjustment for one of my all-time favorite receivers!

Post readers: Check out Kostas’ website for more modifications, ideas and radio projects.

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You’ve Been Warned: Emilio just brought a Grundig Frankenradio to life–!

Many thanks to SWLing Post contributor (and certified mad scientist), Emilio Ruiz, who writes:

Recently I was given a broken Grundig G8 Traveler II.  This radio had an accident–the case, speaker, tuning knob, and volume controls were all broken or damaged.

I discovered that the tuning and volume controls are not potentiometers, they are a rotary encoders, so I substituted the tiny and broken original controls with rotary encoders (typically used for Arduino projects), but I needed to remove the 10 kiloohms resistor to work properly (only used the CLK, DT, and GND pins).

All materials were reused from other things, the result is like a “Frankenstein radio”.

The “telescopic” antenna is a tape measure/flexometer which was broken too. I replaced the original speaker (which I think was another impedance) with a proper 8 ohms speaker which produced low volume, so i decide add a Pam8403 amplifier module for best performance. The total current drain is 0.10 amp for a regular “loud” audio level.

So the Grundig Frankie is alive!!… It’s alive!!

Click here to view video in new window.

This is brilliant, Emilio! Although this radio is quite scary–and, let’s face it, “post-apocalyptic”–I think it’s absolutely amazing! I love the handle and the tape measure antenna. You, sir, are a mad scientist and I look forward to your next creation! (I’ll just take shelter first!) 🙂

Anyone else ever created a Frankenradio? Please comment!

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Video: Antonio’s Kenwood R-2000 Modifications

Many thanks to SWLing Post contributor, Dan Robinson, who shares the following:

Antonio Fernandez, who is in Spain, posted this on the Extreme page. Very interesting R-2000 mods:

Major modifications are adjustable RF GAIN (using the former TONE control), BFO Pitch control (former AM Squelch, FM Squelch is retained) and DSP Audio filtering for SSB and CW. Internal DSP module is SOTABEAMS Laserbeam Filter Module. The former DIMMER and NB push switches are used for switching on (bypassing) the DSP module and bandwidth (CW, SSB) selection.

Click here to view on YouTube.

Those are brilliant modifications on a classic receiver!  Thank you for sharing, Dan!

Check out more videos from Antonio Fernandez on his YouTube channel.

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