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Capacitor RF Measurements

I am still in search for the "optimal" replacement for the dreaded Hammarlund 10nF capacitors. High voltage types with axial leads, suitable for RF are rare nowadays. On the Hammarlund reflector and on other resources on the net mostly issues on reliability and leakage current are discussed, usually on types which seem completely unavailable in Europe. Therefore I decided to do some research on my own with an arbitrary set of 30 capacitors (including the original found in my SP-600-JX), some brand new, some NOS (New Old Stock) and some extinct. Hopefully others will find the results valuable.

For bypass purposes a certain maximum impedance must be maintained for the frequencies of interest only. Phase, dielectric loss and actual capacitance are irrelevant.
Coupling capacitors (esp. in frequency dependent circuits) should be fairly stable over temperature and time. Dielectric losses should not be too high. But in a feedback loop phase IS essential, which prohibits the use of different capacitances (when the capacitor's impedance is not negligibly small relative to the feedback path's impedance) . In the Hammarlund SP-600, as in most HF receivers before the advent of PLLs and synthesizers, all internal frequencies stay below 60MHz. The upper limit of 200MHz in the following measurements will therefore suffice for the 3rd harmonic at least.
The tests were performed with a network analyzer calibrated to 50 Ohm. Lead lengths were 2.5 cm for all capacitors.

Table Of Results

The diagrams (3rd column) show the magnitude of impedance in Ohm for 100kHz to 200MHz. A maximum impedance less than 1 Ohm up to 60MHz can be considered as usable, 0.3 Ohm or less as excellent. My personal favorites are nos. 6, 9, 22 and 30 for coupling and bypassing as well as no. 28 for bypassing. The ceramics fail due to excessive degradation at high temperatures (although I must confess 85 °C are a bit tough, 65°C would be probably more appropriate). If those designed for mounting on PCBs were not ruled out because of style issues, nos. 10, 11, 14, 18, 23 and 24 could be used.
The last column displays the manufacturer (M:), manufacturing date (D:), AC or DC voltage rating (V:) and the actual capacitance in nF for 22 and 85°C.
If someone recognizes the logo of an unknown manufacturer, please tell me!

Note: Diagrams for nos.29 and 30 were taken with the analyzer's "smoothing" feature switched off inadvertently.

3cmgrey tubular flat, <1 1
M:?
D:1950?
V:?
22°C:11n05
85°C:12n89
The original GLOD
3cmsmall yellow tubular flat, <1 2
M:Roederstein
D:?
V:630dc
22°C:3n47
85°C:3n57
Available, for comparison only
3cmyellow tubular resonance: >9 @120MHz, else <1.5 3
M:?
D:new?
V:1500dc
22°C:4n68
85°C:4n67
Available, "cheap" appearance
3cmblue ceramic disk resonance: >4 @160MHz, else <2 4
M:Murata
D:1980?
V:250ac
22°C:4n38
85°C:2n08
For comparison only
3cmbrown ceramic disk resonance: >10 @170MHz, else <1.5 5
M:?
D:1980?
V:400ac
22°C:4n87
85°C:1n28
For comparison only
3cmsmall yellowish tubular flat, <1 6
M:Philips
D:1950?
V:400dc
22°C:9n79
85°C:10n24
I found 12 NOS specimen
3cmtransparent tubular almost flat, <2 7
M:?
D:new
V:1500dc
22°C:9n58
85°C:10n15
Available, "cheap" appearance
3cmbig yellow-green tubular flat, <1 8
M:KONDUR
D:1960?
V:1250dc
22°C:10n35
85°C:10n77
For comparison only
3cmyellow tubular flat, <1.5 9
M:Plessey
D:1990?
V:630dc
22°C:9n45
85°C:9n28
Available, but out of production?
3cmblue, for PCB almost flat, <2 10
M:Philips
D:new?
V:250ac
22°C:9n73
85°C:9n81
Available
3cmred, for PCB almost flat, <2.5 11
M:WIMA
D:new
V:630dc
22°C:9n77
85°C:9n55
Available
3cmtransparent tubular resonance: >>10 @75MHz, else <1.5 12
M:?
D:?
V:630dc
22°C:10n09
85°C:9n95
Available
3cmlight yellow, for PCB resonance: 5 @100MHz, else <2 13
M:Arcotronics
D:new
V:1000dc
22°C:10n29
85°C:10n01
Available
3cmred, for PCB almost flat, <1.8 14
M:WIMA
D:new
V:1000dc
22°C:10n04
85°C:10n27
Available
3cmblue, big, for PCB resonances: 8 @85MHz, 3 @170Mhz, else <1.5 15
M:Siemens
D:1990?
V:1500dc
22°C:10n04
85°C:10n18
Available, but out of production?
3cmceramic disk resonance: 5 @140MHz, else <1 16
M:SGS-Thomson
D:1990?
V:3000dc
22°C:10n3
85°C:3n87
Out of production, but still available
3cmsmall ceramic disk flat, <0.7 17
M:?
D:new?
V:500dc
22°C:9n6
85°C:2n06
Available, for comparison only
3cmblue, for PCB almost flat, <2 18
M:Siemens
D:1990?
V:1000dc
22°C:11n84
85°C:11n6
Available
3cmblue, big, for PCB resonances: 7 @65MHz, 3 @135Mhz, else <2 19
M:Roederstein
D:1990?
V:1500dc
22°C:14n8
85°C:14n57
Out of production? For comparison only
3cmbig red tubular flat, <1.5 20
M:Roederstein
D:1960?
V:1250dc
22°C:23n6
85°C:24n6
For comparison only
3cmblue, for PCB resonances: >10 @60MHz, 3.5 @115Mhz, else <2 21
M:WIMA
D:new
V:1250dc
22°C:22n2
85°C:21n7
Available
3cmyellow tubular flat, <1 22
M:?
D:new?
V:630dc
22°C:22n1
85°C:22n6
Available, but "cheap" appearance
3cmblue, for PCB almost flat, <1.5 23
M:Philips
D:new?
V:250ac
22°C:20n2
85°C:19n9
Available
3cmbig, red, for PCB almost flat, <1.8 24
M:WIMA
D:new
V:1000dc
22°C:32n5
85°C:32n7
Available
3cmblue, for PCB resonance: 2 @55MHz, else <1.5 25
M:Siemens
D:1990?
V:1000dc
22°C:32n7
85°C:32n1
Available, but out of production?
3cma fat 'orange drop' resonances: >5 @18MHz, 2 @35Mhz, else <1.5 26
M:Sprague
D:1990?
V:800dc
22°C:100n5
85°C:99n8
For comparison only
3cmgreen tubular flat, <1 27
M:Roederstein
D:1970?
V:250dc
22°C:144n2
85°C:151n5
Out of production, but still available
3cmyellow tubular resonance: >1 @20MHz, else <1.3 28
M:?
D:1990?
V:630dc
22°C:147n3
85°C:153n9
Out of production, but still available
3cmyellow tubular resonance: 6 @100MHz, else <2 29
M:(for RS-Components)
D:new
V:1000dc
22°C:
85°C
"Cheap", wrapped in adhesive tape
3cmsmall yellow tubular flat, <1 30
M:Roederstein
D:1987?
V:400dc
22°C:
85°C:
Out of production, but still available

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Corrections (content and spelling) are welcome!
Last update: 2003-07-02, Gottfried Ira ira@oe1ira.at
http://www.oe1ira.at/hc/hammarcapac.html