Improving a Degen / Kaito 1103 or Redsun 2100

[mitaux8030]

I've been doing a bit of AM broadcast band DX'ing and have found that my Degen DE1103 is superior to the Redsun 2100 due to its much narrower filter... where I am in this part of the world, 9 kHz seperates AM stations, and I like to sniff out the 10 kHz stations from the USA, so a narrow filter is a must.

And this got me thinking... how easy would it be to retrofit a better filter to the two portables I have?
The Degen / Kaito 1103 doesn't need a lot of help, but fitting a genuine 3 kHz (or less) SSB filter would be nice, and it would help with digging out those 10 kHz AM broadcast stations in between the 9 kHz locals. Problem is that the Degen uses a 450kHz filter, not a 455kHz type which dramatically limits narrow filter options. Also real estate - finding the space to mount a new (larger) filter inside could be a factor too.
Perhaps a good quality Murata CFWLA450KJFA-B0 would be better than the Chequers CQ R50J filter? But thats only speculation, they're the same specified bandwidth after all, anyone know for sure if the Murata product would offer better performance?

The Redsun 2100 (locally sold as a Jaycar AR1747) desperately needs help though - its 'narrow' filter sounds like its about 10kHz barn-door-wide, despite using a 455 "I" (4 kHz) filter. The 'wide' filter is far far too wide! I feel like swapping the 'narrow' filter to the wide position, and using a CFS455J or even a CFJ455K5 filter for the narrow one.

Just thinking out loud... perhaps someone might pick up the ball and give these ideas a go. If you do, let us know how it all goes...

 

[k9rzz]

I'll bite.

Have you taken either apart? Got any photos to show how much room there is inside? I don't own either one, but you could remotely mount a different filter inside, if there's room. I recall reading somewhere that it's been done before with other radios, can't think off hand where I found that though. Neat little project though. While you're on the topic, perhaps the FM filter could be swapped out for a 150 or 110khz bandwidth for better performance there. I've done that to the GE SR3 and a Subaru car stereo, both mods worked great. I don't see why you couldn't do it for AM and SW.

Pop the covers and post a few pix if you can.

 

[mitaux8030]

I've seen reference to an Italian who has modified their Degen 1103 with more narrow FM filters, though I don't speak Italian so I can't understand the text and the results of the mod. I have a girl friend who can speak Italian, might have to ask her to translate.
Generally speaking, it should just be a case of removing one MCF and installing another. I don't really have the need to go for a better MCF (FM filter) in my situation, but if I can find the parts easily enough then I might give it a go.

As for AM filters, the Murata CFWLA appears to be the same size as the CQ R50 series, perhaps not quite the same pinout... will have to find out.

The main problem with internal space is going to affect the Degen / Kaito 1103... not a lot of room in there. But looking at the picture:

there appears to be some room to fit a larger (better) filter like the Murata CFJ or CFS series in place of the CQ R50J.

I've done a similar trick to my old AR3000 and my Kenwood TS2000 roofing filters, courtesy of InRad. So long as the connecting wires from the filter to the board are kept short as possible, then it doesn't have any significant impact.

As for the Redsun / Kaito 2100 / Jaycar 1747 - there's lots of room, except around the AM filters!

Both radios have one characteristic in common: they're both mechanically a little tricky to take apart! Yes, I've 'looked under the hood' of both while I was reviewing both units for a local scanning website.

Time - or lack of it - and parts availability (being in Australia) mean that it'll be unlikely that I'd have much opportunity to do much experimenting... but if anyone else wants to have a go and share the resutls, you're more than welcome to

 

[Bill_White]

Moving the narrow filter to wide filter position and replacing the narrow filter…
Back when I thinking about doing the same thing to my RS DX-390, which also has a second IF of 450 kHz.
Looking around I found my PCR-1000 has a third IF of 450 kHz and the SSB/CW filter with a bandwidth of 2.8 kHz
is in the third IF. Anyone with a PCR-1000 will tell you how great this filter is for MW DXing. Without looking,
I think the 1500 and 2500 use the same filter. The filter is FL5, CFWS450K3.
Sorry but the scan of the service manual I have is incomplete so I cannot give you Icom part numbers.

 

[k9rzz]

I've got an R-71a that I need to repair first, but I might be up for this challenge!

 

[mitaux8030]

I found some information on the Icom filter. Apparently the CFWS450K3 filter is the same as the CFWLA450KL6A002-B0 filter (whatta mouthful!) and the Icom part number is 2020001470. I'm going to contact the local Icom agent and see if they can order one in for me.

I was also looking at some filters on eBay, a CFJ455K5 and others like them... but they're either from non-english speaking countries or refuse to sell outside the USA. Does anyone know of a place that sells these sorts of 'mid range' filters? eg Murata CFS / CFR / CFK / CFL / CFJ types?

 

[Bill_White]

I found a source in The Netherlands
Barend Hendriksen HF Electronics
when looking for a filter for another project back in 2002.
They list mostly filters for 10.7 & 455.
I never ordered from them because “back then” we
Didn’t trust on-line banking and it wasn’t “that” important to me.
Funny how things change in a few short years.
We do all our banking on-line now.
I also remember reading someplace that someone
contacted a supplier on Global Sources or another
import site and asked for samples, which he received.
It has been a while since I looked but it wouldn’t hurt to check at
Mouser Electronics: Mouser Electronics - Electronic Component Distributor and
Digi-key Electronics: Digi-Key Corporation - USA Home Page
I think the best chance of obtaining, and choice, for the 450 IF filter is the Icom.
You may even want to order an extra one (or two). If it works,
I don’t think you would have a problem selling them. :wink:
Thanks for the update and keep us posted.

 

[DaveIN]

You may want to check Kiwa also:
Kiwa Electronics

I've had success with the Sony 2010.

 

[mitaux8030]

I've managed to find a few CFS455 and CFK455 type filters locally, so I'll have a try of these in the 2100, and Icom will be sending a narrow filter for the 1103 - 2 month lead time, but at least the price was agreeable. Will let everyone know how it goes.

 

[k9rzz]

Please do keep us informed. Maybe a YouTube video demonstrating the audio before and after? YouTube video of your actual mods? I'm sure that would be quite popular.

 

[mitaux8030]

OK well here is a preview.
I managed to find a spare hour today and modded the AR1747 (Redsun RP2100 clone).
Another ham kindly donated their MuRata CFJ455K14 filter - this is an 11 element ceramic filter with a total bandwidth of about 2.4 kHz, meant for SSB. Quite a bit tighter than the stock 6 kHz (supposedly) narrow filter, but remember the aim of my modification is to assist in my hunting AM broadcast band stations from the USA where 10 kHz increments are the norm, and I have to deal with local 9 kHz increments... that means that at best I'm dealing with 4.5 kHz between centre frequencies. So something tight is just what I needed.

I decided to replace the ridiculously wide "wide" AM filter - this is the one with LTM 455FW printed on it. My 'wide' setting is now my ultra-narrow filter. Using this physical position also made it much easier to mount the filter.

So, here's the first look at the RF board, showing the two filters (the little black squares):

Then on the underside of the board, here's the positions that you'll need to unsolder:

Back to the top side of the board again, I simply soldered in some stiff 0.7mm tinned copper wire for the three earth connections, and some more pliable 0.5mm tinned copper wire for the filter input and output.

And I'm afraid that's all the photos I have, as my camera batteries died at this point. So what's my impression of the modification so far? Well it's too early to tell... I'm waiting for the rest of the family to go to bed and turn off all the noisy TVs, DVDs etc. So the real test is yet to come, sniffing out the 10 kHz channels that happen to fall in between the 9 kHz channels locally.

But a few things have become apparent already:
1) the 1747 / 2100 I have is about 0.5 kHz low in frequency. Not a big deal when you're using wide filters, but when you're using very narrow filters, and only have a 1 kHz tuning step at your disposal, it can make a difference.
2) the new narrow filter is a bit more lossy than the others - knocks off about an S-point off the scale on an average weak AM station.
3) the new filter's audio is very muddy - as you'd expect for something so narrow. Partially eased by tuning slightly off frequency to emphasise the treble content a bit.
4) the RP2100 seems to have a bit of filter 'blow-by' - making the stock filters sound wider than what they really are. The 455IW filter is supposed to be 4 kHz wide, but sounds more like 6 or even 8 kHz wide. Similarly, the new CFJ455K14 filter sounds a touch wider than it really is too... so when 2.4 kHz sounds like it should be too narrow for AM mode, it probably is... but in the RP2100 it seems to work fine.

I'll let you know how my real world on-air experiences go with it.

Oh, what about the Degen? I'm waiting for the Icom filter to come from Japan... 2 month wait apparently. Stay tuned (pun intended)

 

[k9rzz]

Cool! That filter fits in there just fine.

This is the radio?

Very nice pictures. Grab some audio one way or another if you can.

 

[mitaux8030]

Yes that's the radio - I took that pic while reviewing the AR1747 on another website. Interesting to compare it with the Degen... and the TecSun loop sitting beside it is an excellent little loop for the money... highly recommend one if you're DX'ing on a budget or can't have outdoor antennae.
I'll get some audio bites later today and in the evening once I can showcase it's adjacent channel seperation abilities.

 

[mitaux8030]

Just an update: Icom have come back to me, and said they're now shipping my filter for the Degen.
I did try to grab some audio bites, but the noise induced into the 2100 from the laptop (running on battery) was overwhelming! I'll have to record it to ye olde audio tape, then sample it - or use a microphone placed in front of the 2100.

 

[mitaux8030]

OK, the Icom 450kHz SSB / narrow AM filter CFWLA450KL6A002-B0 has been fitted to my Degen DE1103. When you take apart the Degen DE1103, you must be patient and careful. You'll need a very fine and long needle nose soldering iron tip, mainly to assist removing the fine wires of the ferrite rod antenna from the main PCB. Some fine needle nose pliers will also be very handy to have. Anyway, on to the mod: here's some photos:

The stock CQ marked Chequers filter:

Here's the solder pads you'll need to unsolder... this isn't a job to be rushed. It took me a good 30 minutes of patient desoldering with braid/wick and a fine tipped soldering iron. You'll also have to lift a tin shield to access one of the solder pads. (you can see this shield out-of-focus, lifted up out of the way, in the bottom of this picture)

And lastly, the new filter is fitted. Its slightly larger, but the pins are exactly the same and it drops right in.

So how does it compare to the old filter? Well its definitely tighter than the stock narrow filter... not dramatically so, but noticable. As usual, this will make recovered AM audio sound muddy, but this can be partly offset by tuning 1kHz off frequency. I'll give it a bash later this evening and see how much of a difference this makes for my hunting of in-between 9kHz channels.
I did make a 'before' audio recording of the narrow filter setting, but have had trouble getting a suitable programme source to show the 'after' result - I need to find a timeslot on my test radio station that has a female announcer to compare 'apples with apples' so to speak.
What about SSB? The end result is better - it doesn't sacrafice much audio quality, but does cut down on noise a little bit. For example a mobile phone charger in the house used to make a faint zzzt...zzzt...zzzt noise. Now, with the new filter, this disturbance is reduced perhaps 50%.

So my initial overall impressions? Well, I actualy think that unless you're into hunting the in-between channels (eg 9kHz channels when you're in the USA, or 10kHz channels in parts of the world that use 9kHz), or if you use SSB a lot, then I don't actually think its worth the trouble - the performance gains are minor, and you do lose some fidelity on AM narrow.

I'll do some DX'ing over the next few nights and also capture some audio of the after-mod result and add those in a few days, to let you all know how this turns out.

 

[k9rzz]

Sweet. It's always fun DXing with a hot-rodded radio. LOL Yeah, would love to hear some audio sometime. I've got a little $20 digital voice recorder that does a nice job, or maybe even video record it ala Ridgescan.

 

[ka3jjz]

mitaux, this would make a fine addition to our wiki. As this radio is relatively low cost, it's a natural for the modifications area. It would be helpful to know precisely which pads have to be unsoldered.

Contact me via RR email or ka3jjz@netscape.com and I can guide you through the steps. We're definitely going to want to capture those pix as well...73 Mike

 

[mitaux8030]

Sure Mike, I'll email you later about this.
For anyone who can't wait... in the second picture where I say "Here's the solder pads you'll need to unsolder..." - look in the middle of the picture, there's five solder pads that I've desoldered there - conspicious by the lack of solder, you can see the PCB holes as black centres to the pads I've unsoldered. The five holes form an L shape.

Something I forgot to mention... the only local AM broadcasting station in my vicinity now is a low power (250 watt) ethnic narrowcasting station on 1611 kHz. I noted that up on 1711 kHz on the wide filter I can hear a phamtom image of this station (though I don't think image is technically correct in that sense of the word). Switch in the (new) narrow filter and there's no trace of it. I'd say the new filter has less spurious response than the stock wide filter as a result. I only found this out after I'd fitted the new filter, so I can't say if the stock narrow filter also has this same spurious response too. Oh well.

Last night's DX'ing wasn't as good as I'd hoped. Logged on to the local lightning tracker - no lightning storms in this quarter of the hemisphere which was a good start. But my daughter and her boyfriend were watching DVDs and the DVD/TV are rather noisy all through the AM band... and signals seemed weaker than normal last night too. Will try again tonight and get a better impression of how the new filter will assist me in DX'ing.
I love this maximum bang-for-your-buck DX'ing thing. $80 Degen, $30 tecsun loop, and I'm DX'ing signals from all over Australia, New Zealand, and beyond... all from my bedside table.

 

[degenmodnut]

Advanced DEGEN/KAITO 1103 mods

Like this thread on a great radio; I have 2 now. The 450KHz ceramic filters supplied at 4 & 6 KHz are quite good, BUT no-one has noted that the switch for them also changes the AUDIO frequency response. I have also tried several AF capacitor upgrades (increasing values for better bass).

Looking at the only available schematic for an unknown (early, <4) version, from radioscanner.ru, find the switch S2, for NAR/WIDE. Find and remove C316 & C317 at 103P (0.01uF), which are SMT parts on the back of the main board - follow the traces from S2. There is already 0.01uF loading the L-OUT/R-OUT lines coming out of U2. Next, I noted that a DC control line switches C502 & C508 (3.3uF) in and out of the NF )Negative Feedback) filter pins of the stereo power amp IC5. To leave these larger parts on-line at all times, either short across Q9 & Q10 C-E, OR directly ground the - leads of these 2 caps.

The above will let you hear ONLY the filters BW changing, and depending on the version of your radio, add the shielding (insulating tape under copper tape or shield metal cut from a radio/TV shield) as described in the Russian translated mods for the radio. This improves filter blow-by as they measured in that excellent analysis. This is like a high-end radio.

I have also tried upgrading every Demodulator/Audio path signal coupling cap as well as main electrolytic filter/bulk capacitors up to 10X previous value. The result is less noise and better bass.

I have added a jack for the rod antenna, to access the preamp Q1, but it did not help with a long coax feed such as in the car, as it is a capicatance buffer only (source follower, x1 gain). This could be converted to a gain stage with a separate bipolar transistor for gain, with output connected to D3-Anode.

I do not have a later version schematic, so do not know if the FET protection diodes are fitted. If not, small SMD parts such as 1N5711WS could be installed back-to-back across R102 to protect Q1, and another pair across C134/B1 coil input.

Other ideas are improving the BFO stability by replacing Q17 with a enable-controlled Low Dropout 3V regulator such as LT1521CST-3#PBF. Connect the supply side to C407+, and not Q7-C. My second unit is off-alignment on the BFO, check by tuning 10.000MHz WWV and zero-beat; should be near middle of W701 SSB dial. I will swap out U8 resonator or alter C706 100pF to compensate.

For better line-out audio, possibly change out IC3 LM358AM (a crummy '741 OP-AMP) with lower current low distortion Audio IC Linear Tech LT1211CS8.

Finally, does anybody know about the KIWA mods for improving the AM (detector) distortion? It is very interesting how the AM/FM IC IC2 has either Audio or RF output at pin18 - and that gets filtered and routed as appropriate to the SSB mixer/demod IC7. This is a custom PCB glued-on chip board with inputs at pads 2 & 6 and output at pad 1 - also used for the 55.845MHz to 450KHz IF converter - and the only part with NO datasheets available.

I am working on lots of pix and measurements to document the mods if there is enough interest!

 

[k9rzz]

Anxiously awaiting some audio clips! Maybe a YouTube video?