Extend Regeneration - UK Vintage Radio Repair and Restoration Discussion Forum

staples1 · 29th Mar 2012, 11:23 am

Hi All

I hope you can help. I have almost completed a transistor regenerative RX based on the HAC T-Twin but with added attenuation, untuned RF amp, switchable wavebands using mix of Denco Green and homemade coils plus audio amp. This excellent site was a great help - http://www.mds975.co.uk/Content/trfradios02.html. Always wanted to build similar as a kid & results much better than my recent valve regens. I get continuous coverage from MW through 160m, 80m and down to 30m. SSB resolution very clear. Only using a small attic longwire but once I get to my new house I can experiment with external wires etc! My question. Regeneration occurs when VR set to about 1/3 way round on MW, 1/2 way on 160m and over 3/4way when on 30m. I get no regeneration with coils for higher frequencies. Can I extend the regeneration range, ideally by a switch for when over 10MHz? I assume it may be a case of altering VR1 or C1, see here for basic circuit http://vintageradio.me.uk/kits/hac%20twin/circuit.jpg

I could experiment more but can someone explain theory or how it might be possible.

Thanks very much.

Regards
Rob

G8HQP Dave · 29th Mar 2012, 1:00 pm

As the first transistor has an untuned load its gain will fall with increasing frequency, due to stray and intrinsic capacitance. You could try changing the coupling winding on the HF coils - a few more or fewer turns. Experiment!

staples1 · 1st Apr 2012, 9:48 am

Thanks for getting back Dave.

On rereading the RF amp plans I saw the circuit isn't so suitable for higher frequencies due to the stray capacitances. I thus bypassed the amp and found a couple of faint signals became less faint but still no improvement in regeneration.

I am using a Denco 5 for this range so can't adjust coils. Will need to do further research but my plans for further experimentation are. 1. I'm using a 350pF VC whereas circuit calls for 170pF which might be a problem? 2. Build own coil so I can adjust couplings 3. Possibly a tuned RF amplifier but that would radically alter my design.

Regards
Rob

TrevorG3VLF · 2nd Apr 2012, 10:34 pm

As has been said, the gain of a transistor drops as the frequency rises. You do not say what transistor you used, but you could try one with, say, twice the Ft.

If you use one with super Ft, the layout will be critical.

staples1 · 6th Apr 2012, 9:56 am

Thanks Trevor . Been a few days but been so busy with work For the RF amp I'm using a 2N3819 FET which I think is sufficient ? Im using it in 'common source ' which my book says is less good for higher frequencies. I will try the 'common gate ' circuit.

Also want to experiment more with my coil . Another source says for 10-30 Mhz is to wind the aerial coil on top of the main tuning coil & have the reaction coil alongside . I have reaction coil on top of the tuning coil and the aerial coil alongside . Not so familiar with correct terminology but hope that makes sense. A few things to try over the bank holiday weekend

Any suggestions for the upper HF frequencies appreciated. I have never had good results with Denco 5 but determined this time to get the 10- 30MHZ working as best I can . My electronic theory is a bit limited which I hope to address !

Regards
Rob

29th Mar 2012, 11:23 am	#1
staples1 Retired Dormant Member Join Date: May 2011 Location: London Posts: 5	Extend Regeneration Hi All I hope you can help. I have almost completed a transistor regenerative RX based on the HAC T-Twin but with added attenuation, untuned RF amp, switchable wavebands using mix of Denco Green and homemade coils plus audio amp. This excellent site was a great help - http://www.mds975.co.uk/Content/trfradios02.html. Always wanted to build similar as a kid & results much better than my recent valve regens. I get continuous coverage from MW through 160m, 80m and down to 30m. SSB resolution very clear. Only using a small attic longwire but once I get to my new house I can experiment with external wires etc! My question. Regeneration occurs when VR set to about 1/3 way round on MW, 1/2 way on 160m and over 3/4way when on 30m. I get no regeneration with coils for higher frequencies. Can I extend the regeneration range, ideally by a switch for when over 10MHz? I assume it may be a case of altering VR1 or C1, see here for basic circuit http://vintageradio.me.uk/kits/hac%20twin/circuit.jpg I could experiment more but can someone explain theory or how it might be possible. Thanks very much. Regards Rob

29th Mar 2012, 1:00 pm	#2
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Extend Regeneration As the first transistor has an untuned load its gain will fall with increasing frequency, due to stray and intrinsic capacitance. You could try changing the coupling winding on the HF coils - a few more or fewer turns. Experiment!

1st Apr 2012, 9:48 am	#3
staples1 Retired Dormant Member Join Date: May 2011 Location: London Posts: 5	Re: Extend Regeneration Thanks for getting back Dave. On rereading the RF amp plans I saw the circuit isn't so suitable for higher frequencies due to the stray capacitances. I thus bypassed the amp and found a couple of faint signals became less faint but still no improvement in regeneration. I am using a Denco 5 for this range so can't adjust coils. Will need to do further research but my plans for further experimentation are. 1. I'm using a 350pF VC whereas circuit calls for 170pF which might be a problem? 2. Build own coil so I can adjust couplings 3. Possibly a tuned RF amplifier but that would radically alter my design. Regards Rob

2nd Apr 2012, 10:34 pm	#4
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Extend Regeneration As has been said, the gain of a transistor drops as the frequency rises. You do not say what transistor you used, but you could try one with, say, twice the Ft. If you use one with super Ft, the layout will be critical.

6th Apr 2012, 9:56 am	#5
staples1 Retired Dormant Member Join Date: May 2011 Location: London Posts: 5	Re: Extend Regeneration Thanks Trevor . Been a few days but been so busy with work For the RF amp I'm using a 2N3819 FET which I think is sufficient ? Im using it in 'common source ' which my book says is less good for higher frequencies. I will try the 'common gate ' circuit. Also want to experiment more with my coil . Another source says for 10-30 Mhz is to wind the aerial coil on top of the main tuning coil & have the reaction coil alongside . I have reaction coil on top of the tuning coil and the aerial coil alongside . Not so familiar with correct terminology but hope that makes sense. A few things to try over the bank holiday weekend Any suggestions for the upper HF frequencies appreciated. I have never had good results with Denco 5 but determined this time to get the 10- 30MHZ working as best I can . My electronic theory is a bit limited which I hope to address ! Regards Rob