Realistic DX-302 - UK Vintage Radio Repair and Restoration Discussion Forum

darren67 · 21st Feb 2016, 12:47 pm

hi
I have always enjoyed shortwave listening, and own a Trio 9R-59DS and a Heathkit SW717 as well as a portable Sony ICF-SW55, but I have recently acquired a Realistic DX-302, which performs well on my 60t foot longwire. I have monitored several ham stations from Europe the US and one from Brazil.
The Realistic does have two niggles though, and not having owned one before I was hoping for some advice, as I'm not sure if either can be classed as normal. Although it works, operating on USB the sound quality seems rather too high pitched and harsh, so I'm wondering if there is a fault in USB, LSB is fine. The MHz selector control, although smooth, does require some effort to rotate. I appreciate that if it was too loose you would be constantly adjusting the control, again as having never owned one before I'm just not sure.
any thoughts and advice would be greatly appreciated.

Best regards Darren.

Radio Wrangler · 21st Feb 2016, 2:40 pm

Sounds like the usb carrier insertion oscillator is off frequency.

I don't imagine Tandy fitted crystal oscillators, so there is likely to be a twiddler needing a tweak.

David

Skywave · 21st Feb 2016, 2:52 pm

The MHz selector control may just need some lubrication: a close inspection should reveal. On the other hand, the mechanics of that control may be poor. I found a similar situation with a Yaesu FR-50B upon its initial acquisition: loose, floppy operation of the main tuning control and with some hysteresis. By re-engineering the mechanics - fitting a proper bearing, sleeve, etc., - that main tuning control operation was substantially improved. I also installed a few electronics modifications in places where the design left quite a lot to be desired. As a S/W AmRad radio, it now works very well.

Al.

darren67 · 22nd Feb 2016, 1:28 pm

hi,
thanks for the replies allways nice to have some advice from someone more knowledgeable it's greatly appreciated.
i have found and downloaded the user manual and more importantly the service manual and after a quick look through the manual, it looks like usb/lsb can be tweaked up with the signal generator i will have a proper study of it this evening.
the mhz control i agree a closer inspection is needed but any thoughts on lubrication? i admit to the use of 3 in 1 it has solved many a problem with vintage variable capacitors in the past.
i'll look at both and be back later.

best regards darren.

Radio Wrangler · 22nd Feb 2016, 2:40 pm

The tuning of the local oscillator is the main player in determining where the stations appear on the dial. Adjustment of the IF has a much smaller effect on this, but has a big effect on the IF bandwidth and on the flatness of the audio received. Expensive receivers use highly stable quartz crystal filters to fix the IF very accurately. Lower cost boxes use ceramic filters, which are almost as good. Basic radios use IF transformers and capacitors to do all the selectivity. These are much more adjustable.

It's usual for radios with crystal or ceramic filters to have some IF transformers in the IF, but the block filters dominate and the IFTs are just peaked up for best gain.

So the selectivity in the IF determines where you tune to get the maximum signal = loudest sounds. When receiving SSB, a further oscillator is needed, offset from wherever the centre of the IF happens to be, to convert the signal down to audio. On some sets these are crystal-controlled oscillators, on some ceramic resonators are used, and some sets have a tuneable LC oscillator (often called a BFO) Tuning the BFO doesn't change the station being heard, but it does shift the entire audio spectrum coming from it up and down. Quite amusing when you first come across it. So you would tune the main tuning for max audio level, then tune the BFO to put the pitch wher sounds right to you.

Some basic sets have BFOs with switched trimmer capacitors to set the BFO a set amount above and below the IF for lower and upper sideband reception. These can be a bit prone to drifting and give frequency-shifted speech when you've tuned onto the signal. This sounds to fit your description.

David

ms660 · 22nd Feb 2016, 3:19 pm

For USB a fixed capacitor is shunted across the BFO's tank so far as I can make out.

Lawrence.

orbanp1 · 22nd Feb 2016, 4:38 pm

I just wonder if people are aware that this receiver is a "Wadley-loop" receiver.
Apparently it uses the same frequency conversion scheme as the Yaesu FRG-7.
Here is some info on that:
http://www.televideo.ws/wadley.html

Best to follow the tune-up instructions given in the service manual, including for the BFO.

Peter

22nd Feb 2016, 4:44 pm

C345 from here http://www.freeinfostuff.com/dx300-3..._schematic.pdf I think, with a bit of luck it is too small so a 'gimmick' (a couple of short lengths of insulated wire twisted together) capacitor https://en.wikipedia.org/wiki/Gimmick_capacitor may do the trick, if not change the cap for a 33pF and then add the gimmick.

Jon_G4MDC · 22nd Feb 2016, 6:21 pm

Some back of the envelope scribbles with the values shown in the schematic, it does look like the 43pF for USB is way too big - suspect shift is about 10kHz.
33pF possibly still too big depending on the main filter bandwidth.

I would be tempted to try around 15-22 pF which should give a more normal shift for USB/LSB BFO.

Maybe replace C345 by a ~30pF trimmer? Then L309 will adjust LSB for correct pitch (adjust first) Use the new trimmer to balance USB for the same pitch on opposite sideband.

Just throwing in 2p/worth. Best of luck

Have now noticed OP has a model DX302 not a DX300.
Schematics differ in BFO.

Good to see in that model they added a BFO pitch control and the USB shift capacitor is now 18pF. They also added a narrow filter for SSB which is probably the reason for pulling in the BFO points.

The likely problem with this set is then probably only adjustment of L309 - now numbered L312 in the DX302!!

Radio Wrangler · 22nd Feb 2016, 7:05 pm

Yes, some proper improvements in the DX302. They weren't bad receivers. One member in the old Dunfermline RS got going with one of them. Yes, I know it's a Wadley. I've got the original mil-spec transistor Wadleys kicking around, an RA1217, and one of its designers was a lecturer at uni, many years ago. Nice to look at, but easily overloaded.

David

neutronic · 5th Mar 2016, 11:55 pm

Quote:

Originally Posted by darren67

The MHz selector control, although smooth, does require some effort to rotate. I appreciate that if it was too loose you would be constantly adjusting the control, again as having never owned one before I'm just not sure.
any thoughts and advice would be greatly appreciated.

Which one do you mean?
The large round ring around then kHz adjustment, that also should be used as a fine tuning for max.reception?
Or the range selector at the left?
That knob on my DX302 makes a loud click and feels a little bit ¨stiff¨,but mine had that already from the beginning.

Jard N.

Radio Wrangler · 6th Mar 2016, 9:41 am

The DX302, can be seen as a fairly basic 2 to 3 MHz receiver with 2 'RF' tuned circuits one 'RF' amplifier stage between them, and a VFO-driven mixer converting signals down to a 455kHz IF. There are indeed ceramic filters at 455kHz, and the BFO seems to be tuneable, free running.

Then there is a Wadley converter on the front of the 2-3MHz receiver to extend the coverage in MHz chunks, so the 'RF' stage of the 2-3MHz rx is really the second IF of the whole machine. The VFO, going into a counter doesn't need the same amount of care in its adjustment as is needed in the RA17 with its mechanical scale, but there is as much a need to get the VFO and the second IF tuned circuits tracking well as there is in any ordinary radio structure. Racal did away with the tracking tuned circuits in the RA117 and RA1217 by adding an extra (fixed-tuned) IF stage and mixer.

There is a preselector on the front of everything and this needs twiddling everytime you change frequency by more than a little. It's a nuisance, but a lot of radios have this irritation (RA17, 117, 1217, 1772 from Racal and my Eddystone EA12) Collins bust a gut designing the R390 family with dozens of cam-operated permeability tuners to make a true tracking preselector.

The MHz set ring is intentionally stiff to stop it turning when you move the kHz knob. With the smallish amount of rotation for each active patch per MHz, it is a bit iffy in use.

David

darren67 · 10th Mar 2016, 9:20 pm

hi all,

many thanks for the useful info everyone good advice is allways welcomed.
also apologies for delays, she who must be obeyed has had me doing work around the house and i have not had much opportunity to do anything radio related.
neutronic the mhz ring around the khz is very stiff not the preselector, having not owned one before i wondered if it was intended to be as stiff.
merlinmaxwell the circuit diagram you pointed me to is much clearer than the one in the 302 service manual though i could not find L312 but figured it out comparing the two diagrams the parts are numbered slightly differently L309.
the 43pf capacitor i think i might experiment with lower values at jon's suggetsion when i get a chance to look at the radio at the weekend but i will check out the BFO adjustment with the signal generator first.
the radio is triple conversion and does have it does use a 4mhz crystal oscillator and a wadley loop so as this is new to me further reading is required to help give me a better understanding of the radio.
once again many thanks for the advice i will get round to having a look at it over the weekend.

best regards darren.

Chris1978 · 10th Mar 2016, 10:45 pm

IIRC on the DX-302 there is a nylon gear wheel behind the MHz adjustment knob which often cracks with age. It has been a while since I opened one of these sets but pretty sure it was a similar size to those readily available from radio controlled model shops.

Great sets on the whole although the tuning on the one I had used to drift a little when it was cold but it normally stabilised itself within 10-15 minutes of being switched on.

Chris1978 · 11th Mar 2016, 12:10 am

Just read the original post again. The outer MHz ring should have some slight resistance, whereas the inner kHz knob should turn with ease. As long as there is no notchy feel I'd say that all is well.

Jon_G4MDC · 12th Mar 2016, 8:07 pm

Hello darren67,

Please don't be misled by the two circuit diagrams even if one is clearer and easier to read.

The set you have is a DX-302 and the BFO coil is L312.
There are also other changes in the BFO.

If you use the earlier diagram where BFO coil is L309 it will lead you down the garden path, wrong values and things which are/are not there in the later version.

To be honest I really think your set should only need a tweak of L312.

Best.

darren67 · 11th Apr 2016, 10:10 am

hi all.

at last i have got round to tweaking the bfo pot L312 with the signal generator as per the service manual and now usb is much more readable (resloved) than before.

thanks jon i was comparing the two circuit diagrams and the differences so wont be misled.

the outer MHz ring does have quite a bit of resistance chris but is not at all notchy so i will leave this alone the gear wheels must be in good order and i dont want to mess with it as it's working maybe at a future date if it cant be rotated.

many thanks for the advice everyone it's very much appreciated

best regards darren.

21st Feb 2016, 12:47 pm	#1
darren67 Tetrode Join Date: Jun 2014 Location: Plymouth, Devonshire, UK. Posts: 70	Realistic DX-302 hi I have always enjoyed shortwave listening, and own a Trio 9R-59DS and a Heathkit SW717 as well as a portable Sony ICF-SW55, but I have recently acquired a Realistic DX-302, which performs well on my 60t foot longwire. I have monitored several ham stations from Europe the US and one from Brazil. The Realistic does have two niggles though, and not having owned one before I was hoping for some advice, as I'm not sure if either can be classed as normal. Although it works, operating on USB the sound quality seems rather too high pitched and harsh, so I'm wondering if there is a fault in USB, LSB is fine. The MHz selector control, although smooth, does require some effort to rotate. I appreciate that if it was too loose you would be constantly adjusting the control, again as having never owned one before I'm just not sure. any thoughts and advice would be greatly appreciated. Best regards Darren.

21st Feb 2016, 2:40 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	Re: realistic dx-302 Sounds like the usb carrier insertion oscillator is off frequency. I don't imagine Tandy fitted crystal oscillators, so there is likely to be a twiddler needing a tweak. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

21st Feb 2016, 2:52 pm	#3
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: realistic dx-302 The MHz selector control may just need some lubrication: a close inspection should reveal. On the other hand, the mechanics of that control may be poor. I found a similar situation with a Yaesu FR-50B upon its initial acquisition: loose, floppy operation of the main tuning control and with some hysteresis. By re-engineering the mechanics - fitting a proper bearing, sleeve, etc., - that main tuning control operation was substantially improved. I also installed a few electronics modifications in places where the design left quite a lot to be desired. As a S/W AmRad radio, it now works very well. Al.

22nd Feb 2016, 1:28 pm	#4
darren67 Tetrode Join Date: Jun 2014 Location: Plymouth, Devonshire, UK. Posts: 70	Re: Realistic DX-302 hi, thanks for the replies allways nice to have some advice from someone more knowledgeable it's greatly appreciated. i have found and downloaded the user manual and more importantly the service manual and after a quick look through the manual, it looks like usb/lsb can be tweaked up with the signal generator i will have a proper study of it this evening. the mhz control i agree a closer inspection is needed but any thoughts on lubrication? i admit to the use of 3 in 1 it has solved many a problem with vintage variable capacitors in the past. i'll look at both and be back later. best regards darren.

22nd Feb 2016, 2:40 pm	#5
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	Re: Realistic DX-302 The tuning of the local oscillator is the main player in determining where the stations appear on the dial. Adjustment of the IF has a much smaller effect on this, but has a big effect on the IF bandwidth and on the flatness of the audio received. Expensive receivers use highly stable quartz crystal filters to fix the IF very accurately. Lower cost boxes use ceramic filters, which are almost as good. Basic radios use IF transformers and capacitors to do all the selectivity. These are much more adjustable. It's usual for radios with crystal or ceramic filters to have some IF transformers in the IF, but the block filters dominate and the IFTs are just peaked up for best gain. So the selectivity in the IF determines where you tune to get the maximum signal = loudest sounds. When receiving SSB, a further oscillator is needed, offset from wherever the centre of the IF happens to be, to convert the signal down to audio. On some sets these are crystal-controlled oscillators, on some ceramic resonators are used, and some sets have a tuneable LC oscillator (often called a BFO) Tuning the BFO doesn't change the station being heard, but it does shift the entire audio spectrum coming from it up and down. Quite amusing when you first come across it. So you would tune the main tuning for max audio level, then tune the BFO to put the pitch wher sounds right to you. Some basic sets have BFOs with switched trimmer capacitors to set the BFO a set amount above and below the IF for lower and upper sideband reception. These can be a bit prone to drifting and give frequency-shifted speech when you've tuned onto the signal. This sounds to fit your description. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

22nd Feb 2016, 3:19 pm	#6
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Realistic DX-302 For USB a fixed capacitor is shunted across the BFO's tank so far as I can make out. Lawrence.

22nd Feb 2016, 4:38 pm	#7
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: Realistic DX-302 I just wonder if people are aware that this receiver is a "Wadley-loop" receiver. Apparently it uses the same frequency conversion scheme as the Yaesu FRG-7. Here is some info on that: http://www.televideo.ws/wadley.html Best to follow the tune-up instructions given in the service manual, including for the BFO. Peter

22nd Feb 2016, 4:44 pm	#8
Guest Guest Posts: n/a	Re: Realistic DX-302 C345 from here http://www.freeinfostuff.com/dx300-3..._schematic.pdf I think, with a bit of luck it is too small so a 'gimmick' (a couple of short lengths of insulated wire twisted together) capacitor https://en.wikipedia.org/wiki/Gimmick_capacitor may do the trick, if not change the cap for a 33pF and then add the gimmick.

22nd Feb 2016, 6:21 pm	#9
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Realistic DX-302 Some back of the envelope scribbles with the values shown in the schematic, it does look like the 43pF for USB is way too big - suspect shift is about 10kHz. 33pF possibly still too big depending on the main filter bandwidth. I would be tempted to try around 15-22 pF which should give a more normal shift for USB/LSB BFO. Maybe replace C345 by a ~30pF trimmer? Then L309 will adjust LSB for correct pitch (adjust first) Use the new trimmer to balance USB for the same pitch on opposite sideband. Just throwing in 2p/worth. Best of luck Have now noticed OP has a model DX302 not a DX300. Schematics differ in BFO. Good to see in that model they added a BFO pitch control and the USB shift capacitor is now 18pF. They also added a narrow filter for SSB which is probably the reason for pulling in the BFO points. The likely problem with this set is then probably only adjustment of L309 - now numbered L312 in the DX302!! Last edited by Jon_G4MDC; 22nd Feb 2016 at 6:51 pm. Reason: further info

22nd Feb 2016, 7:05 pm	#10
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	Re: Realistic DX-302 Yes, some proper improvements in the DX302. They weren't bad receivers. One member in the old Dunfermline RS got going with one of them. Yes, I know it's a Wadley. I've got the original mil-spec transistor Wadleys kicking around, an RA1217, and one of its designers was a lecturer at uni, many years ago. Nice to look at, but easily overloaded. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

6th Mar 2016, 9:41 am	#12
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	Re: Realistic DX-302 The DX302, can be seen as a fairly basic 2 to 3 MHz receiver with 2 'RF' tuned circuits one 'RF' amplifier stage between them, and a VFO-driven mixer converting signals down to a 455kHz IF. There are indeed ceramic filters at 455kHz, and the BFO seems to be tuneable, free running. Then there is a Wadley converter on the front of the 2-3MHz receiver to extend the coverage in MHz chunks, so the 'RF' stage of the 2-3MHz rx is really the second IF of the whole machine. The VFO, going into a counter doesn't need the same amount of care in its adjustment as is needed in the RA17 with its mechanical scale, but there is as much a need to get the VFO and the second IF tuned circuits tracking well as there is in any ordinary radio structure. Racal did away with the tracking tuned circuits in the RA117 and RA1217 by adding an extra (fixed-tuned) IF stage and mixer. There is a preselector on the front of everything and this needs twiddling everytime you change frequency by more than a little. It's a nuisance, but a lot of radios have this irritation (RA17, 117, 1217, 1772 from Racal and my Eddystone EA12) Collins bust a gut designing the R390 family with dozens of cam-operated permeability tuners to make a true tracking preselector. The MHz set ring is intentionally stiff to stop it turning when you move the kHz knob. With the smallish amount of rotation for each active patch per MHz, it is a bit iffy in use. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

10th Mar 2016, 9:20 pm	#13
darren67 Tetrode Join Date: Jun 2014 Location: Plymouth, Devonshire, UK. Posts: 70	Re: Realistic DX-302 hi all, many thanks for the useful info everyone good advice is allways welcomed. also apologies for delays, she who must be obeyed has had me doing work around the house and i have not had much opportunity to do anything radio related. neutronic the mhz ring around the khz is very stiff not the preselector, having not owned one before i wondered if it was intended to be as stiff. merlinmaxwell the circuit diagram you pointed me to is much clearer than the one in the 302 service manual though i could not find L312 but figured it out comparing the two diagrams the parts are numbered slightly differently L309. the 43pf capacitor i think i might experiment with lower values at jon's suggetsion when i get a chance to look at the radio at the weekend but i will check out the BFO adjustment with the signal generator first. the radio is triple conversion and does have it does use a 4mhz crystal oscillator and a wadley loop so as this is new to me further reading is required to help give me a better understanding of the radio. once again many thanks for the advice i will get round to having a look at it over the weekend. best regards darren.

10th Mar 2016, 10:45 pm	#14
Chris1978 Retired Dormant Member Join Date: Mar 2016 Location: Wednesbury, West Midlands, UK. Posts: 4	Re: Realistic DX-302 IIRC on the DX-302 there is a nylon gear wheel behind the MHz adjustment knob which often cracks with age. It has been a while since I opened one of these sets but pretty sure it was a similar size to those readily available from radio controlled model shops. Great sets on the whole although the tuning on the one I had used to drift a little when it was cold but it normally stabilised itself within 10-15 minutes of being switched on.

11th Mar 2016, 12:10 am	#15
Chris1978 Retired Dormant Member Join Date: Mar 2016 Location: Wednesbury, West Midlands, UK. Posts: 4	Re: Realistic DX-302 Just read the original post again. The outer MHz ring should have some slight resistance, whereas the inner kHz knob should turn with ease. As long as there is no notchy feel I'd say that all is well.

12th Mar 2016, 8:07 pm	#16
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Realistic DX-302 Hello darren67, Please don't be misled by the two circuit diagrams even if one is clearer and easier to read. The set you have is a DX-302 and the BFO coil is L312. There are also other changes in the BFO. If you use the earlier diagram where BFO coil is L309 it will lead you down the garden path, wrong values and things which are/are not there in the later version. To be honest I really think your set should only need a tweak of L312. Best.

11th Apr 2016, 10:10 am	#17
darren67 Tetrode Join Date: Jun 2014 Location: Plymouth, Devonshire, UK. Posts: 70	Re: Realistic DX-302 hi all. at last i have got round to tweaking the bfo pot L312 with the signal generator as per the service manual and now usb is much more readable (resloved) than before. thanks jon i was comparing the two circuit diagrams and the differences so wont be misled. the outer MHz ring does have quite a bit of resistance chris but is not at all notchy so i will leave this alone the gear wheels must be in good order and i dont want to mess with it as it's working maybe at a future date if it cant be rotated. many thanks for the advice everyone it's very much appreciated best regards darren.