Many thanks to SWLing Post contributor, Paolo Viappiani (SWL I1-11437), who shares the following guest post. Note that, as with any radio modification, perform this operation at your own risk. This is a very simple mod, but if you feel it might be beyond your skill level, consider hiring a radio technician to perform it on your behalf:
Unblocking the YAESU FRG-8800 Frequency Coverage Limitations
by Paolo Viappiani
Figure I: An unblocked FRG-8800 receiver tuned to 29.999.9 MHz.
It is well known that some receivers produced in the last decades of the last century suffered from a limited frequency coverage due to legislative restrictions in force in some countries (Germany, Australia, etc.).
In particular, in Germany it was forbidden to listen to HF frequencies higher than 26.1 MHz, while in other Countries shortwave were not allowed to receive frequencies below 2 MHz.
These restrictions led most radio manufacturers to produce “blocked” versions of their HF receivers in order to satisfy the various national requirements; almost classical examples are the world renowned SONY ICF-2001D and the PHILIPS D-2935/D-2999 portables.
The blocking/unblocking procedure of some frequency bands was quite simple in microprocessor-governed synthesized radios: usually it was sufficient to add (or remove) proper jumpers in the vicinity of the microprocessor to perform the task, and the correct procedure was often covered in the Service Manuals or in specific Technical Bulletins; in any case plenty of information can be found on the Internet. Continue reading →
Many thanks to SWLing Post contributor, Robert Richmond, who writes:
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:
Many thanks to SWLing Post contributor, Brian, who writes with the following inquiry:
I found a pic of a printed circuit board, based on Mr. Carlson’s Sony CRF-320 panel light mod, on the Yahoo 320/330 fan page but no board dimensions or component values.
I plan to order a bunch of these so if anyone can sort out some measurements on this board or are interested in obtaining a board, please comment. I am a novice in this and am unsure of the component values. I have wired up an electric guitar, so this I anticipate will be less complicated.
Post readers: If you can help Brian with this info, please feel free to comment!
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!
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!
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.
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!) 🙂