Realistic DX160: bad osc. tracking - UK Vintage Radio Repair and Restoration Discussion Forum

Skywave · 27th Jun 2009, 12:15 am

Not my usual type of comms. radio, but it came my way cheap; I've always been interested in evaluating the performance of these 'entry-level' comms. receivers; and it makes a change from the traditional valved comms. radios that I usually tinker with.

On first inspection, it does 'work' - sort of

. A quick listen round on band C (1.8 to 4.0 MHz approx.) soon told me that things weren't right here. A quick check with the sig. gen. confirmed this - sensitivity was way down. (The sensitivity on the other bands seems about right; the IF is 455 kHz and is 'on the nose'). The reason turns out to be bad osc. tracking on this range. The osc. is a Hartley (FET), adjustable ferrite core in the coil with the usual trimmer & fixed padder: 1000pF 'suflex' type; it measures 900 pF on test.

Assuming that the osc. is on the 'high side', (confirmed by testing the other ranges), when the LF end of the osc. is about right (coil core adjustment), the HF end of the osc. is about 700 Khz too low - even with the osc. coil trimmer right out. That is a large error for a RF tuning range of 1.8 to 4.0 MHz (approx.). Experimenting with the value of the padder (including replacing it with one of the original value) doesn't 'help enough' - but I can't see any other osc. components that exist for this range only that are frequency dependent. Overall, it's just got that feel of 'too much capacity' in the osc. on this range only; strange.

So, anyone else here familiar with this box of tricks - and its idiosyncracies?

Al. / Skywave.

Herald1360 · 27th Jun 2009, 8:59 am

You might get some help here: http://groups.yahoo.com/group/realisticdx/ if you haven't already found it......

Chris

Skywave · 27th Jun 2009, 9:17 am

Thank you, Chris - I hadn't spotted that.

Al.

Skywave · 1st Jul 2009, 10:30 pm

Interim report.

Progress is being made - there is light at the end of the tunnel - but it's been an uphill struggle. Since I've never seen one of these radios featured on this Forum before, I will make my concluding report in the Success Stories section of this Forum; see you there.

Al. / Skywave.

Skywave · 3rd Jul 2009, 10:56 am

This repair is now complete.

The work is now detailed in the 'Success Stories' section of the Forum.

Al. / Skywave.

Skywave · 3rd Jul 2009, 12:10 pm

Re: the above; this Thread can now be closed.

Al.

27th Jun 2009, 12:15 am	#1
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Realistic DX160: bad osc. tracking Not my usual type of comms. radio, but it came my way cheap; I've always been interested in evaluating the performance of these 'entry-level' comms. receivers; and it makes a change from the traditional valved comms. radios that I usually tinker with. On first inspection, it does 'work' - sort of . A quick listen round on band C (1.8 to 4.0 MHz approx.) soon told me that things weren't right here. A quick check with the sig. gen. confirmed this - sensitivity was way down. (The sensitivity on the other bands seems about right; the IF is 455 kHz and is 'on the nose'). The reason turns out to be bad osc. tracking on this range. The osc. is a Hartley (FET), adjustable ferrite core in the coil with the usual trimmer & fixed padder: 1000pF 'suflex' type; it measures 900 pF on test. Assuming that the osc. is on the 'high side', (confirmed by testing the other ranges), when the LF end of the osc. is about right (coil core adjustment), the HF end of the osc. is about 700 Khz too low - even with the osc. coil trimmer right out. That is a large error for a RF tuning range of 1.8 to 4.0 MHz (approx.). Experimenting with the value of the padder (including replacing it with one of the original value) doesn't 'help enough' - but I can't see any other osc. components that exist for this range only that are frequency dependent. Overall, it's just got that feel of 'too much capacity' in the osc. on this range only; strange. So, anyone else here familiar with this box of tricks - and its idiosyncracies? Al. / Skywave.

27th Jun 2009, 8:59 am	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Realistic DX160: bad osc. tracking You might get some help here: http://groups.yahoo.com/group/realisticdx/ if you haven't already found it...... Chris

27th Jun 2009, 9:17 am	#3
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Realistic DX160: bad osc. tracking Thank you, Chris - I hadn't spotted that. Al.

1st Jul 2009, 10:30 pm	#4
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Realistic DX160: bad osc. tracking Interim report. Progress is being made - there is light at the end of the tunnel - but it's been an uphill struggle. Since I've never seen one of these radios featured on this Forum before, I will make my concluding report in the Success Stories section of this Forum; see you there. Al. / Skywave.

3rd Jul 2009, 10:56 am	#5
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Realistic DX160: bad osc. tracking This repair is now complete. The work is now detailed in the 'Success Stories' section of the Forum. Al. / Skywave.

3rd Jul 2009, 12:10 pm	#6
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Realistic DX160: bad osc. tracking Re: the above; this Thread can now be closed. Al.