TF144 Turret Tuner

During my experiments with reception of long waves it was clear that the best coils are wound with Litz wire. The chief reason being that their overall quality was better.... meaning less signal loss and you can tune to a sharper peak thus minimising interference. The reason for this has been known for many decades and is that alternating currents flow chiefly in the skin of a conductor. That means the least resistance to AC is achieved if one uses a good electrical conductor having the best surface area. One way to meet this requirement is to use a large diameter copper wire, but as the centre of the wire isn't really used much by the AC the majority of the expensive copper content is wasted. A long time ago someone realised that a better alternative was to use a large number of very thin insulated copper wires bundled together and joined at their ends. This "Litz wire" provided the maximum surface area for the weight of copper.

I spotted this coil assembly carrying loads of coils and bought one. It turned out to be a New Old Stock spare turret tuner for the TF144H signal generator.

One potential project is to use it as a preselector for an SDR or even as the basis for a simple signal generator. Either case will involve some tricky metalworking and construction to use the turret tuner feature although, if the design was limited to HF and lower frequency ranges a rotary selector switch might be a much simpler option. Below are pictures of the coil assembly...

The first step is to evaluate exactly what's present and examination of the TF144 manual supplies some information. For example the signal generator has no less than 12 ranges using three different tuning condenser and coil connections as listed below. The three gang tuning condenser C101/102/103 has 200pF sections and the trimmers C152 etc are 4-20.5pF, usually with a fixed capacitor across it as shown below. Using these figures the tuning coil inductance can be worked out. Not too easily I might add because large coils can have a sizeable self-capacitance. To work out the coil inductances I assumed the tuning condenser minimum plus miscellanous strays were about 20pF and trimmers were set at 12pF. Given all these numbers I worked out the likely self-capacitance of each coil, Cs as shown below. I didn't bother with effects of mutual inductance because this won't materially affect re-use of the coils and I assumed the effects of dust cores are included in the coil inductances shown below.

RANGE	Min	Max	Tuning condenser configuration	Fixed	Fixed pF	Trimmer	Tuning coil	Cs pF	Inductance
A	10KHz	20KHz	C101+C102 in parallel with C103	C153	82	C152	L114	72	323mH
B	20KHz	40KHz	C101+C102 in parallel with C103	C156	91	C155	L115	64	80.4mH
C	40KHz	80KHz	C101+C102 in parallel with C103	C159	82	C158	L116	72	20.2mH
D	80KHz	200KHz	C101+C102 in parallel with C103	C193	10	C161	L117	60	5.6mH
E	200KHz	535KHz	C101+C102 in parallel with C103	-	-	C164	L119	54	925uH
F	535KHz	1605KHz	C101+C102 in parallel with C103	-	-	C167	L121	31	133uH
G	1MHz	2MHz	C101+C102 in parallel with C103	C171	91	C170	L123	62	32.5uH
H	2MHz	4MHz	C101+C102 in parallel with C103	C174	91	C173	L125	62	8.1uH
I	4MHz	8MHz	C101+C102 in parallel with C103	C177	82	C176	L127	52	2.1uH
J	8MHz	16MHz	C101+C102 in parallel with C103	C180+C194	100+10	C179	L129	40	0.51uH
K	16MHz	32MHz	C101+C102 in series with C103	C183	10	C182	L131	20	0.51uH
L	30MHz	72MHz	C103	C198	10	C184	L133	12	0.11uH

Click on the picture below to see detail.

pending

TF144 Turret Tuner

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