Thoughts on the "spy radio" that never was. - UK Vintage Radio Repair and Restoration Discussion Forum

neon indicator · 2nd Jul 2011, 1:27 pm

I started getting sub-miniature Russian Pencil valves (tubes) because I wanted a better GDO than my Ambit/Circuit G3PO model and a valve DC/AF/RF millivoltmeter (harder to wreck than IC version). Also they intrigued me.

Then my "local" electronics/radio friend suggested a Radio. I'd always fancied having a "lady Margaret" style battery radio like we had when I was a kid in shorts. I remembered the small suitcase (not much bigger) than those radios and a little like the "spy radio" suitcases of WWII/Early Cold War. My grandfather used it for packed lunches in at least the 1960s when he went fly fishing.

I've built 1MHz to 30MHz linear Class AB RF PA using low voltage MOSFET and 1MHz to 4MHz using ex PC SMPSU MOSFETS (rated to 900V!) on back of Pentium II heatsinks using 24V to 48V HT.

So I thought why not a "spy type" transmitter + broadcast reception dual superhet receiver that might have been built but never was. So no transistors or ICs. I'll allow myself SAW and Ceramic filters though. And diodes. Hence the thread on battery boxes. https://www.vintage-radio.net/forum/...ad.php?t=71256 Might as well use a "standard" battery box stuffed with NiMH I thought. (In practice there are problems with that and an inverter isn't just "cheating", it makes RF noise and you have then a shortage of running time unless you use 10 x 10AH D cells!).

So Suitcase is Internal size is 11 x 23.5 x 37.5 cm (4.25" x 9.2" x 14.75"), with inside of lid rest on edge when closed. It's tan coloured leather and looks about 5 years old not 45+ or 50+ He was born 1898 and remembered the 1st phone he saw, getting installed where he worked as an apprentice. He was about 93 or 94 when he died. He kept very good care of everything, so the suitcase could even be from 1930s!

I picked 32.9 MHz for 1st IF as it's Nicam IF, so flat and narrow enough (< 800KHz) to avoid images with 455kHz 2nd IF filter. It's readily available filter (from old VCRs and TVs if not new), Above Broadcast Bands and outside Amateur bands. Only really used for Cable TV upstream. Higher is more difficult for valves. (Modern radios use 68MHz to 1.2GHz for 1st IF).

I considered first a 34MHz to 39MHz VFO, but a +/- fine tune capacitor is less than 0.2pF per 100kHz! Stability needs to be about 0.000025%! for +/- 100Hz

Traditionally Collins, FT101 series, most "pre" synthesiser Communications receivers use around 5MHz to 6MHz. So about 0.002% for +/- 100Hz. But they typically have only 500kHz per band.

Next I analysed 6.5 to 11Mhz approx VFO, This gives a 50 turn 0.275" coil for about 6.2MHz and 200pF Then a 10pF tuning capacitor is about +/- 100kHz. Main tuning by screwing a brass bolt in a captive nut on hollow shaft with knob. As you rotate, the dial cord is driven by shaft and the brass 1/4" bolt will move in/out of coil arranged to reduce inductance from 3uH to 1uH. Maybe the brass needs a slot to improve Q. I'm not sure.
Tuning scale can be 5mm per 100kHz, about 230mm long including "blank" at each end, and case is over 370mm long. (Small fluorescent tube as optional back light? What is minimum volts for 190mm tube?)

Scale printed from PC and glued to clear plastic pipe on Wavechange 8 way rotary switch with edge of disc/knob beside end of scale, so 230mm long window only shows current band.

Figures in (brackets) are 1.2V max filament currents

The VFO (6.5MHz to 10.6MHz approx using 1j24b (17ma) or 1j18b (24mA) Colpits ) is added or subtracted from crystal osc/mixer using a 1j37b (55mA) dual control grid pentode to give local oscillator. This is filtered and drives a 2nd 1j37b as 1st Mixer. There is optional 1j17b(55mA), 1j24b (17mA) or 1j29b (60mA) RF preamp, no amp, 10dB attenuator or 20dB attenuator. Aerial is multi-turn loop glued on lid or external. The mixer feeds the 32.9MHz filter and followed by IF amp(s), 1 or 2 1j17b(55mA), 1j24b (17mA) or 1j29b (60mA) then we have another crystal osc/mixer with a 32.445 crystal (custom? It's 32.900 - 32.445 = 0.455MHz). Then switchable wide or narrow 455kHz filter (Crystal or Ceramic or whatever). More IF amp(s), this time the 1j18b (24ma) is a choice as well as the others (it's got g3 internally connected to cathode/filament, so not as good for higher frequencies, though wired with g2 as Anode it works over 100MHz as an oscillator!).

Finally a 4th 1j37b (55mA) as detector/BFO etc.

Then 1j18b (24ma) (or two) and a pair of 1p24b as push-pull audio driving small 110/220V transformer for 4 Ohm 8" speaker.

Pye style sunrise & clouds grill done freehand with router.

For Transmit, the BFO / mixer is used as AM modulator and SSB created by suitable 455MHz IF filter. AM is possible. The pair of 1p24b are RF PA using 2 x capacitors and common mode choke balun to aerial TX/RX change over, power via audio transformer.

Anyone conversant with FT101, Swan, Collins etc can imagine all the various switching of direction of amplifiers and mixers. All same frequencies on TX and RX.

Bands and crystals

Code:

Band	min		max	Crystal
1;	0.02	-	1.7	24
2;	1.4	-	5.7	28
3;	6.6	-	10.9	20
4;	13.998-	18.298	12.602083
5;	20.6	-	24.9	6
6;	26.6	-	30.9	0
7;	49.2	-	53.5	10
8;	67.2	-	71.5	28

Band 6 doesn't need a crystal mix
Some bands use same crystal but different 1st IF Mixer or band crystal mix products.
12.602083 is a crystal from a Radio. in stock
all the other band crystals I have I think.

The following Amateur bands covered (ones needing special permission)

1: 0.1357-0.1378 (0.500)
2: 1.810-2.000 3.500-3.800 (5.000-5.500)
3: 7.000-7.200 10.100-10.150
4: 14.000-14.350 18.068-18.168
5: 21.000-21.450 24.890-24.990
6: 28.000-29.700
7: 50.000-52.000
8: 70.125-70.450

The between the aerial and rest of radio are 7 elliptical low pass filters for the amateur bands to block harmonics on Transmit. They help receive a little
Very Approx
2: 6MHz (no transmitting on less than 3.5MHz without external filters)
3: 12MHz
4: 22MHz
5: 30MHz
6: 40MHz
7: 60MHz
8: 85MHz

Will I add Broadcast FM-VHF band II RX? I'd like to. Even air band if possible.

So lots of testing of the Russian valves and built each section and debug separately.

RX and most TX HT is 40V to 48V, nominal 43.5V (diode drop)
(36V = flat and 48.6V fresh, scary 53V just disconnected charger)
Use 3 x 45V packs in parallel on Receive (inc the 1j24b PAs) via diodes and T/R relays when energised put them in series for about 10mA to 80mA @ 120V to 140V depending on power out. Maybe 1.5W AM and 6W SSB/FM/CW
What can go wrong? What have I forgotten?

maybe 3 way switch on LT supply for "fresh" (a resistor), "normal" (1/2 resistance), no resistance according to LT state.

Meter to measure LT, HT1, or RF. On RX it's S-Level, on TX a separate switch selects HT2 current (only feeds 1p24b so allows "dipping"), RF out or Reflected RF in the 1st switch's "RF" position. Also RF TX has "plate" (anode RF tuning) and "loading" tuning (simple PI) like FT101.

Thoughts?

neon indicator · 2nd Jul 2011, 1:31 pm

I already had a long discussion on the Transmit/Receive relays re: 1.5V, 24V in pairs or 48V.

It seems a cost advantage and slight power saving compared to 48V to go for 24V
(48V work 33V to 96, 24V work 16.5V to 48V)

neon indicator · 2nd Jul 2011, 5:16 pm

Experimenting with 0.5" / 12mm approx coil with 25t approx 3.2uH
solid alloy rod or brass (snib taken apart) maybe 6.5mm to 7mm reduces inductance to 2.7uH.
Testing with Alloy tube with Slot about 2.8uH and alloy tube (no slot) about 1.6uH

That's about 6.3MHz to 8.7MHz = 2.4MHz band size.

I suppose I could either:

Have smaller bands, may need some more. At least it's enough to cover 10m and 6m in one band. Maybe 2MHz bands are a better idea anyway. 100kHz is 10mm of main scale instead of 5mm
Have plunger with ferrite, gap, alloy to have greater change
Different coil design? Would it make any difference?

or?

TrevorG3VLF · 2nd Jul 2011, 7:45 pm

Slug tuning.
There has been some discussion recently on slug tuning aerials. For best Q the slug should not connect end to end so should be made from a stack of insulated washers. Sticking the metal slug to a ferrite slug widens the inductance range.

neon indicator · 2nd Jul 2011, 8:29 pm

I made a little match box super-regen once with a straw poked in to tune. One end had ferrite and the other a brass screw. Did Mobile, Band II and Airband. I still have it (made in 1990), no idea if it still goes. Single AAA cell and 5 or 6 transistor audio amp for 32 Ohm headphones. Miniature volume control

Anyway, smaller bands is easier to tune and more stable:

The coil will only do about 1.6 to 3.2uH, so

Code:

IF1	VFO min	VFO max	IF 2	Mixer 2
32.9	6.3	        8.7	       0.455	32.445


Band		min		max	Crystal	Lo min	Lo max	Low Pass
1	:	0.02	-	2.4	26.6	32.92	35.3	2.97
2	:	3.5	-	5.9	25	29.4	33.7	5.78
3	:	6.5	-	8.9	22	26.4	30.7	11.55
4	:	8.5	-	10.9	20	24.4	28.7	16.67
5	:	12.5	-	14.9	16	20.4	24.7	23.10
6	:	15.898	-	18.298	12.602	17.002	21.302	29.81
7	:	20.5	-	22.9	8	12.4	16.7	34.65
8	:	24.5	-	26.9	4	8.4	12.7	41.07
9	:	27.5	-	29.9	1	5.4	9.7	46.20
10	:	49.902	-	52.302	12.602	17.002	21.302	82.50
11	:	69.248	-	71.648	31.948	36.348	40.648	115.71
12	:	87		108	none	54.1	75.1	(direct L.O)

Band 12 will be direct mixer/osc at RF in, without the band mixers/crystals and the high stability 6.3 to 8.7 VFO

Not continuous coverage, but quite a lot of broadcast bands as well as Marine/aeronautical HF, Cadets and all the Amateur band below 2m. From my existing tests I'm confident of a direct mixer/osc with the 1j37b 54MHz to 75MHz L.O. and Band II in. Won't be very sensitive.

Since a band is 2.4MHz approx, every 1mm of linear scale is 10kHz (except on Band II, which is 100kHz per mm), assuming a 240mm long scale and separate +/- 100kHz approx geared 10pF capacitor. .

Is that correct?

2nd Jul 2011, 1:27 pm	#1
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Thoughts on the "spy radio" that never was. I started getting sub-miniature Russian Pencil valves (tubes) because I wanted a better GDO than my Ambit/Circuit G3PO model and a valve DC/AF/RF millivoltmeter (harder to wreck than IC version). Also they intrigued me. Then my "local" electronics/radio friend suggested a Radio. I'd always fancied having a "lady Margaret" style battery radio like we had when I was a kid in shorts. I remembered the small suitcase (not much bigger) than those radios and a little like the "spy radio" suitcases of WWII/Early Cold War. My grandfather used it for packed lunches in at least the 1960s when he went fly fishing. I've built 1MHz to 30MHz linear Class AB RF PA using low voltage MOSFET and 1MHz to 4MHz using ex PC SMPSU MOSFETS (rated to 900V!) on back of Pentium II heatsinks using 24V to 48V HT. So I thought why not a "spy type" transmitter + broadcast reception dual superhet receiver that might have been built but never was. So no transistors or ICs. I'll allow myself SAW and Ceramic filters though. And diodes. Hence the thread on battery boxes. https://www.vintage-radio.net/forum/...ad.php?t=71256 Might as well use a "standard" battery box stuffed with NiMH I thought. (In practice there are problems with that and an inverter isn't just "cheating", it makes RF noise and you have then a shortage of running time unless you use 10 x 10AH D cells!). So Suitcase is Internal size is 11 x 23.5 x 37.5 cm (4.25" x 9.2" x 14.75"), with inside of lid rest on edge when closed. It's tan coloured leather and looks about 5 years old not 45+ or 50+ He was born 1898 and remembered the 1st phone he saw, getting installed where he worked as an apprentice. He was about 93 or 94 when he died. He kept very good care of everything, so the suitcase could even be from 1930s! I picked 32.9 MHz for 1st IF as it's Nicam IF, so flat and narrow enough (< 800KHz) to avoid images with 455kHz 2nd IF filter. It's readily available filter (from old VCRs and TVs if not new), Above Broadcast Bands and outside Amateur bands. Only really used for Cable TV upstream. Higher is more difficult for valves. (Modern radios use 68MHz to 1.2GHz for 1st IF). I considered first a 34MHz to 39MHz VFO, but a +/- fine tune capacitor is less than 0.2pF per 100kHz! Stability needs to be about 0.000025%! for +/- 100Hz Traditionally Collins, FT101 series, most "pre" synthesiser Communications receivers use around 5MHz to 6MHz. So about 0.002% for +/- 100Hz. But they typically have only 500kHz per band. Next I analysed 6.5 to 11Mhz approx VFO, This gives a 50 turn 0.275" coil for about 6.2MHz and 200pF Then a 10pF tuning capacitor is about +/- 100kHz. Main tuning by screwing a brass bolt in a captive nut on hollow shaft with knob. As you rotate, the dial cord is driven by shaft and the brass 1/4" bolt will move in/out of coil arranged to reduce inductance from 3uH to 1uH. Maybe the brass needs a slot to improve Q. I'm not sure. Tuning scale can be 5mm per 100kHz, about 230mm long including "blank" at each end, and case is over 370mm long. (Small fluorescent tube as optional back light? What is minimum volts for 190mm tube?) Scale printed from PC and glued to clear plastic pipe on Wavechange 8 way rotary switch with edge of disc/knob beside end of scale, so 230mm long window only shows current band. Figures in (brackets) are 1.2V max filament currents The VFO (6.5MHz to 10.6MHz approx using 1j24b (17ma) or 1j18b (24mA) Colpits ) is added or subtracted from crystal osc/mixer using a 1j37b (55mA) dual control grid pentode to give local oscillator. This is filtered and drives a 2nd 1j37b as 1st Mixer. There is optional 1j17b(55mA), 1j24b (17mA) or 1j29b (60mA) RF preamp, no amp, 10dB attenuator or 20dB attenuator. Aerial is multi-turn loop glued on lid or external. The mixer feeds the 32.9MHz filter and followed by IF amp(s), 1 or 2 1j17b(55mA), 1j24b (17mA) or 1j29b (60mA) then we have another crystal osc/mixer with a 32.445 crystal (custom? It's 32.900 - 32.445 = 0.455MHz). Then switchable wide or narrow 455kHz filter (Crystal or Ceramic or whatever). More IF amp(s), this time the 1j18b (24ma) is a choice as well as the others (it's got g3 internally connected to cathode/filament, so not as good for higher frequencies, though wired with g2 as Anode it works over 100MHz as an oscillator!). Finally a 4th 1j37b (55mA) as detector/BFO etc. Then 1j18b (24ma) (or two) and a pair of 1p24b as push-pull audio driving small 110/220V transformer for 4 Ohm 8" speaker. Pye style sunrise & clouds grill done freehand with router. For Transmit, the BFO / mixer is used as AM modulator and SSB created by suitable 455MHz IF filter. AM is possible. The pair of 1p24b are RF PA using 2 x capacitors and common mode choke balun to aerial TX/RX change over, power via audio transformer. Anyone conversant with FT101, Swan, Collins etc can imagine all the various switching of direction of amplifiers and mixers. All same frequencies on TX and RX. Bands and crystals Code: Band min max Crystal 1; 0.02 - 1.7 24 2; 1.4 - 5.7 28 3; 6.6 - 10.9 20 4; 13.998- 18.298 12.602083 5; 20.6 - 24.9 6 6; 26.6 - 30.9 0 7; 49.2 - 53.5 10 8; 67.2 - 71.5 28 Band 6 doesn't need a crystal mix Some bands use same crystal but different 1st IF Mixer or band crystal mix products. 12.602083 is a crystal from a Radio. in stock all the other band crystals I have I think. The following Amateur bands covered (ones needing special permission) 1: 0.1357-0.1378 (0.500) 2: 1.810-2.000 3.500-3.800 (5.000-5.500) 3: 7.000-7.200 10.100-10.150 4: 14.000-14.350 18.068-18.168 5: 21.000-21.450 24.890-24.990 6: 28.000-29.700 7: 50.000-52.000 8: 70.125-70.450 The between the aerial and rest of radio are 7 elliptical low pass filters for the amateur bands to block harmonics on Transmit. They help receive a little Very Approx 2: 6MHz (no transmitting on less than 3.5MHz without external filters) 3: 12MHz 4: 22MHz 5: 30MHz 6: 40MHz 7: 60MHz 8: 85MHz Will I add Broadcast FM-VHF band II RX? I'd like to. Even air band if possible. So lots of testing of the Russian valves and built each section and debug separately. RX and most TX HT is 40V to 48V, nominal 43.5V (diode drop) (36V = flat and 48.6V fresh, scary 53V just disconnected charger) Use 3 x 45V packs in parallel on Receive (inc the 1j24b PAs) via diodes and T/R relays when energised put them in series for about 10mA to 80mA @ 120V to 140V depending on power out. Maybe 1.5W AM and 6W SSB/FM/CW What can go wrong? What have I forgotten? maybe 3 way switch on LT supply for "fresh" (a resistor), "normal" (1/2 resistance), no resistance according to LT state. Meter to measure LT, HT1, or RF. On RX it's S-Level, on TX a separate switch selects HT2 current (only feeds 1p24b so allows "dipping"), RF out or Reflected RF in the 1st switch's "RF" position. Also RF TX has "plate" (anode RF tuning) and "loading" tuning (simple PI) like FT101. Thoughts?

2nd Jul 2011, 1:31 pm	#2
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: Thoughts on the "spy radio" that never was. I already had a long discussion on the Transmit/Receive relays re: 1.5V, 24V in pairs or 48V. It seems a cost advantage and slight power saving compared to 48V to go for 24V (48V work 33V to 96, 24V work 16.5V to 48V)

2nd Jul 2011, 5:16 pm	#3
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: Thoughts on the "spy radio" that never was. Experimenting with 0.5" / 12mm approx coil with 25t approx 3.2uH solid alloy rod or brass (snib taken apart) maybe 6.5mm to 7mm reduces inductance to 2.7uH. Testing with Alloy tube with Slot about 2.8uH and alloy tube (no slot) about 1.6uH That's about 6.3MHz to 8.7MHz = 2.4MHz band size. I suppose I could either: Have smaller bands, may need some more. At least it's enough to cover 10m and 6m in one band. Maybe 2MHz bands are a better idea anyway. 100kHz is 10mm of main scale instead of 5mm Have plunger with ferrite, gap, alloy to have greater change Different coil design? Would it make any difference? or?

2nd Jul 2011, 7:45 pm	#4
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Thoughts on the "spy radio" that never was. Slug tuning. There has been some discussion recently on slug tuning aerials. For best Q the slug should not connect end to end so should be made from a stack of insulated washers. Sticking the metal slug to a ferrite slug widens the inductance range.

2nd Jul 2011, 8:29 pm	#5
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: Thoughts on the "spy radio" that never was. I made a little match box super-regen once with a straw poked in to tune. One end had ferrite and the other a brass screw. Did Mobile, Band II and Airband. I still have it (made in 1990), no idea if it still goes. Single AAA cell and 5 or 6 transistor audio amp for 32 Ohm headphones. Miniature volume control Anyway, smaller bands is easier to tune and more stable: The coil will only do about 1.6 to 3.2uH, so Code: IF1 VFO min VFO max IF 2 Mixer 2 32.9 6.3 8.7 0.455 32.445 Band min max Crystal Lo min Lo max Low Pass 1 : 0.02 - 2.4 26.6 32.92 35.3 2.97 2 : 3.5 - 5.9 25 29.4 33.7 5.78 3 : 6.5 - 8.9 22 26.4 30.7 11.55 4 : 8.5 - 10.9 20 24.4 28.7 16.67 5 : 12.5 - 14.9 16 20.4 24.7 23.10 6 : 15.898 - 18.298 12.602 17.002 21.302 29.81 7 : 20.5 - 22.9 8 12.4 16.7 34.65 8 : 24.5 - 26.9 4 8.4 12.7 41.07 9 : 27.5 - 29.9 1 5.4 9.7 46.20 10 : 49.902 - 52.302 12.602 17.002 21.302 82.50 11 : 69.248 - 71.648 31.948 36.348 40.648 115.71 12 : 87 108 none 54.1 75.1 (direct L.O) Band 12 will be direct mixer/osc at RF in, without the band mixers/crystals and the high stability 6.3 to 8.7 VFO Not continuous coverage, but quite a lot of broadcast bands as well as Marine/aeronautical HF, Cadets and all the Amateur band below 2m. From my existing tests I'm confident of a direct mixer/osc with the 1j37b 54MHz to 75MHz L.O. and Band II in. Won't be very sensitive. Since a band is 2.4MHz approx, every 1mm of linear scale is 10kHz (except on Band II, which is 100kHz per mm), assuming a 240mm long scale and separate +/- 100kHz approx geared 10pF capacitor. . Is that correct? Last edited by neon indicator; 2nd Jul 2011 at 8:40 pm.