Pre-selection
 

Sorting through the junk box (50 years + and growing!) I am amazed at
the number of ex-valve-consumer-radio 2-gang tuning condensers (not
capacitors in them thar days!) that I have in the junk box, which was the
germ of an idea for preselection without coil switching - ie, one twin gang
condenser giving two tuned circuits for each band in the HF range.

Pre-selection
 

On Sat, 31 May 2014, gareth wrote:

Sorting through the junk box (50 years + and growing!) I am amazed at
the number of ex-valve-consumer-radio 2-gang tuning condensers (not
capacitors in them thar days!) that I have in the junk box, which was the
germ of an idea for preselection without coil switching - ie, one twin gang
condenser giving two tuned circuits for each band in the HF range.



It was covered in "73", at least, two articles, the same author, in "73".
One was definitely in 1964, but I can't remember which. The first one
used one of those large air variables, the other used one of those mylar
insulated cariables as seen in small transistor radios.

A websearch says the small one was in "73" in December 1964, W6SFM was the
author of that and the earlier article. Both definitely have an
explanation of how it works, two coils with quite different inductance,
one coming into use while the other is mostly insignificant as the
variable capacitor changes value, and vice versa.

I ahve definitely seen the technique in a QST converter article, so I
suspect the idea may date quite far back, but not sure. That article
didn't give any real explanation of how the tuner worked, as if we were
supposed to know from past experience.

That said, it's only one tuned circuit. Good for a lot of things, but
unless you cascade a few, you won't get very good bandwidth.

Michael

Pre-selection
 

In article ple.org,
Michael Black wrote:

Sorting through the junk box (50 years + and growing!) I am amazed at
the number of ex-valve-consumer-radio 2-gang tuning condensers (not
capacitors in them thar days!) that I have in the junk box, which was the
germ of an idea for preselection without coil switching - ie, one twin gang
condenser giving two tuned circuits for each band in the HF range.

It was covered in "73", at least, two articles, the same author, in "73".
One was definitely in 1964, but I can't remember which. The first one
used one of those large air variables, the other used one of those mylar
insulated cariables as seen in small transistor radios.

A websearch says the small one was in "73" in December 1964, W6SFM was the
author of that and the earlier article. Both definitely have an
explanation of how it works, two coils with quite different inductance,
one coming into use while the other is mostly insignificant as the
variable capacitor changes value, and vice versa.

That sounds a bit like the "single coil" Z-match antenna tuner
design. It uses a split-stator capacitor, one part in series with the
entire coil primary, and the other part in series with a tap at the
halfway point (halfway in windings, not in inductance).

http://users.tpg.com.au/users/ldbutl...CoilZMatch.htm

Pre-selection
 

"Michael Black" wrote in message
news:alpine.LNX.2.02.1406021612540.11397@darkstar. example.org...
On Sat, 31 May 2014, gareth wrote:
Sorting through the junk box (50 years + and growing!) I am amazed at
the number of ex-valve-consumer-radio 2-gang tuning condensers (not
capacitors in them thar days!) that I have in the junk box, which was the
germ of an idea for preselection without coil switching - ie, one twin
gang
condenser giving two tuned circuits for each band in the HF range.
It was covered in "73", at least, two articles, the same author, in "73".
One was definitely in 1964, but I can't remember which. The first one
used one of those large air variables, the other used one of those mylar
insulated cariables as seen in small transistor radios.
A websearch says the small one was in "73" in December 1964, W6SFM was the
author of that and the earlier article. Both definitely have an
explanation of how it works, two coils with quite different inductance,
one coming into use while the other is mostly insignificant as the
variable capacitor changes value, and vice versa.
I ahve definitely seen the technique in a QST converter article, so I
suspect the idea may date quite far back, but not sure. That article
didn't give any real explanation of how the tuner worked, as if we were
supposed to know from past experience.
That said, it's only one tuned circuit. Good for a lot of things, but
unless you cascade a few, you won't get very good bandwidth.

Interesting, and perhaps something akin to the Z Match ATU, but not
quite what I had in mind which was two ganged tuned circuits top
coupled by a capacitor.

Pre-selection
 

On Mon, 2 Jun 2014, gareth wrote:

"Michael Black" wrote in message
news:alpine.LNX.2.02.1406021612540.11397@darkstar. example.org...
On Sat, 31 May 2014, gareth wrote:
Sorting through the junk box (50 years + and growing!) I am amazed at
the number of ex-valve-consumer-radio 2-gang tuning condensers (not
capacitors in them thar days!) that I have in the junk box, which was the
germ of an idea for preselection without coil switching - ie, one twin
gang
condenser giving two tuned circuits for each band in the HF range.
It was covered in "73", at least, two articles, the same author, in "73".
One was definitely in 1964, but I can't remember which. The first one
used one of those large air variables, the other used one of those mylar
insulated cariables as seen in small transistor radios.
A websearch says the small one was in "73" in December 1964, W6SFM was the
author of that and the earlier article. Both definitely have an
explanation of how it works, two coils with quite different inductance,
one coming into use while the other is mostly insignificant as the
variable capacitor changes value, and vice versa.
I ahve definitely seen the technique in a QST converter article, so I
suspect the idea may date quite far back, but not sure. That article
didn't give any real explanation of how the tuner worked, as if we were
supposed to know from past experience.
That said, it's only one tuned circuit. Good for a lot of things, but
unless you cascade a few, you won't get very good bandwidth.

Interesting, and perhaps something akin to the Z Match ATU, but not
quite what I had in mind which was two ganged tuned circuits top
coupled by a capacitor.

Ah. So how do you expect to get this to be multiband without
bandswitching?

As any general coverage shortwave receiver will tell you, you can
generally get 2:1 tuning range, so of course on the upper bands fewer
coils are needed. I always assumed receivers that could tune the whole sw
band but needed crystals every 500KHz just relied on that.

Michael

Pre-selection
 

"Michael Black" wrote in message
news:alpine.LNX.2.02.1406022006130.12068@darkstar. example.org...
On Mon, 2 Jun 2014, gareth wrote:

Interesting, and perhaps something akin to the Z Match ATU, but not
quite what I had in mind which was two ganged tuned circuits top
coupled by a capacitor.

Ah. So how do you expect to get this to be multiband without
bandswitching?

Of course, there has to be bandswitching of the antenna input and
the filtered output, but otherwise, for as many band as you wish
to cover, you have that many tuning condensers (and knobs!)

Apart from LF where you'd likely have a LPF rolling off at 300kHz





As any general coverage shortwave receiver will tell you, you can
generally get 2:1 tuning range,

500pF = 3:1

Pre-selection
 

"Michael Black" wrote in message news:alpine.LNX.2.02.1406021612540.11397@darkstar. example.org...
On Sat, 31 May 2014, gareth wrote:

Sorting through the junk box (50 years + and growing!) I am amazed at
the number of ex-valve-consumer-radio 2-gang tuning condensers (not
capacitors in them thar days!) that I have in the junk box, which was the
germ of an idea for preselection without coil switching - ie, one twin gang
condenser giving two tuned circuits for each band in the HF range.



It was covered in "73", at least, two articles, the same author, in "73".
One was definitely in 1964, but I can't remember which. The first one
used one of those large air variables, the other used one of those mylar
insulated cariables as seen in small transistor radios.

A websearch says the small one was in "73" in December 1964, W6SFM was the
author of that and the earlier article. Both definitely have an
explanation of how it works, two coils with quite different inductance,
one coming into use while the other is mostly insignificant as the
variable capacitor changes value, and vice versa.

I ahve definitely seen the technique in a QST converter article, so I
suspect the idea may date quite far back, but not sure. That article
didn't give any real explanation of how the tuner worked, as if we were
supposed to know from past experience.

That said, it's only one tuned circuit. Good for a lot of things, but
unless you cascade a few, you won't get very good bandwidth.

Michael

Many of my two gang condensers were from early Superhetrodyne's where one gang tuned the local oscillator, and the other tried to tune the antenna input circuit. This resulted in major engineering headaches, trying to get the oscillator tracking the antenna........ or was it the other way around? Anyway, the gang used for the local oscillator was much smaller (in fully meshed capacitance) and with strangely shaped plates. In fact one of the outboard plates on each gang, was cut into multiple "fan" shaped segments, for adjusting resonance of it's stage in mid band. Little "padders" were quite often part of the assembly, for tracking on the open or closed ends of travel.
A hot radio repairman could achieve reasonable tracking in a few minutes with a Hickok Analyzer, and fiber screwdriver. Less than hot repairman were advised not to just "tighten up all the screws" Heehaw.
Some of the old collectables had multiple "gangs" with the same number and shape of plates in each gang. These were often extracted from (now priceless) "TRF" radios with several stages of tuned RF stages.... (OK, I know, TRF means that.. grin) They tried everything!

Old Chief Lynn, W7LTQ

Pre-selection
 

"coffelt2" wrote in message
...
Many of my two gang condensers were from early Superhetrodyne's
where one
gang tuned the local oscillator, and the other tried to tune the antenna
input circuit.
This resulted in major engineering headaches, trying to get the oscillator
tracking
the antenna........ or was it the other way around? Anyway, the gang used
for
the local oscillator was much smaller (in fully meshed capacitance) and
with
strangely shaped plates.

Then, with a sufficiency of supply, use as a single gang condenser, and
have more of them in sequence (with more knobs to twiddle)

Any real radio amateur worth his salt is quite capable of tweaking lots
of knobs to get the best performance, as, indeed, we all had to do once.

On that front, a few years back a family member wanted to buy me a present
so I
opted for an FT817 so as not to impact heavily on his finances, but with
nothing for
me to do, the FT817 palled into ennui very quickly, seemingly being little
removed
from a CB set, and so with his approval , sold it on again and
returned the cash to him.