Subject: glowbugs V1 #220
glowbugs Thursday, January 8 1998 Volume 01 : Number 220
Date: Wed, 7 Jan 1998 15:01:15 -0500
From: "Ornitz, Barry L" <ornitz@eastman.com>
Subject: Grid Dippers, was C and L meters
All the talk about capacitance and inductance meters brings up some
interesting points. The inexpensive C and L meters do a fairly good job
of measuring capacitance and inductance respectively, but they usually
do not measure the dielectric losses in capacitors (power factor, loss
tangent) or the resistive losses (Q, dissipation factor) in inductors.
This may not be much of a problem with well characterized capacitors and
inductors, but for "hamfest specials" it can be. Small mica capacitors
usually have very low dielectric losses, whereas these are higher in
ceramic capacitors, higher yet in most plastic film capacitors, and
exceptionally high in electrolytics. This relationship is fairly well
known and documented. Inductors are a different matter. With the rise
in popularity of switching power supplies, surplus inductors are
plentiful. But do you know if they will work at RF? Most will not, the
ferrite cores are designed for much lower frequencies. These C & L
meters give values at whatever frequency they are designed for, but they
tell you very little about the suitability of that particular component
in an RF circuit. Often too, the values of capacitance and inductance
generally needed at RF are well below the full-scale reading for the
most sensitive ranges of these meters.
Unless you are building audio filters from design formulas, knowledge of
the actual value of capacitance or inductance is rarely needed. For
bypass or coupling applications, for example, capacitor values can vary
considerably without affecting circuit performance much. In tuned RF
circuits, values are generally more critical but either an inductance or
capacitance or both must be varied to get the circuit "on frequency".
So measurement to high accuracy is not needed either.
What I am getting around to is that if you have a few extra dollars to
spend on test equipment, and you want to work at RF, a grid-dip
oscillator (GDO,
grid dipper, and variations like solid state versions, a.k.a. Heath
tunnel dipper) is a better buy. These can act as a simple signal
generator or absorption wavemeter (not terribly stable or accurate but
still useful). They can measure the resonant frequency of a tuned
circuit, a transmission line stub, or an antenna. AND, they can be used
to measure low values of capacitance and inductance. All you need is
one or two known values of capacitance, and an inductor whose value can
be measured with the unit.
Check out many of the older ARRL handbooks for GDO use. With a little
experience, you can judge from the depth and width of the meter dip how
well the capacitor or inductor will work in the frequency range of
interest - something those inexpensive C & L meters cannot.
At home, I have two General Radio bridges, one for capacitance only, and
the other for L, C & R. They are rarely used. At work, I have an old
GenRad bridge that I can read capacitance (accurately) to 5 o 6
significant figures.
It is great for studying dielectric materials but useless for ham radio!
I have a rather large number of signal generators too. But with a new
hamfest "goodie" (receiver or transmitter) to test, my handy old Allied
GDO is easiest to use. In fact, I got along for many years with only a
VTVM and GDO and a reasonably well-calibrated SWL receiver for test
equipment.
So if you see a GDO for sale at a reasonable price, go for it. For home
brewing radio gear, it will one of the most handy things you will ever
use.
73, Barry L. Ornitz WA4VZQ ornitz@tricon.net
Date: Wed, 07 Jan 1998 15:58:10 -0800
From: Jim Conn <jconn@gte.net>
Subject: Re: C and L meters
I purchased the AADE kit, and have been totally satisfied with it. It is
an LC meter. Mighty handy for building glowbug LC circuits! The web
site is http://www.aade.com The owner is a ham. The kit is not much less
cost than the Tenma unit, and doesn't do resistance, but you get the fun
of building it. I didn't need the resistance function anyway, I already
had a multimeter for that.
Regards,
Jim - AD4VL
Dexter Francis wrote:
>
> I recently bought a Tenma 72-875 LCR meter, after
> having bought and returned two other types from TechAm,
> because they lacked a zero capability or weren't able
> to measure capacitance below 40 pf accurately. The
> Tenma has been the best $100 I've spent in a long
> time.
>
> Ranges:
>
> 0 to 200pf, 2 nf, 20 nf, 200 nf, 2 uf, 200 uf, and 2000 uf
> 0 to 200 uH, 2 mH, 20 mH, 200 mH, 2H, 20 H, 200H
> 0 to 20 ohms, 200, 2k, 20k, 200k, 2M, 20M
>
> -df
> ----------------------------------------------------
> Need to Buy or Sell Tubes, Parts or BA Gear?
> Visit our Web site at http://www.xmission.com/~cwest/
> e-mail to: tubes@usa.net -or- cwest@xmission.com
> P.O. Box 22443, Salt Lake City, Utah 84122
Date: Wed, 07 Jan 1998 17:49:38 -0700
From: Steve Lords /WA7ISL <sklords@sprynet.com>
Subject: Re: C and L meters
is the tenma meter a stand alone unit??
and where do you get one???
thanks
steve
wa7isl
Dexter Francis wrote:
> I recently bought a Tenma 72-875 LCR meter, after
> having bought and returned two other types from TechAm,
> because they lacked a zero capability or weren't able
> to measure capacitance below 40 pf accurately. The
> Tenma has been the best $100 I've spent in a long
> time.
>
> Ranges:
>
> 0 to 200pf, 2 nf, 20 nf, 200 nf, 2 uf, 200 uf, and 2000 uf
> 0 to 200 uH, 2 mH, 20 mH, 200 mH, 2H, 20 H, 200H
> 0 to 20 ohms, 200, 2k, 20k, 200k, 2M, 20M
>
> -df
> ----------------------------------------------------
> Need to Buy or Sell Tubes, Parts or BA Gear?
> Visit our Web site at http://www.xmission.com/~cwest/
> e-mail to: tubes@usa.net -or- cwest@xmission.com
> P.O. Box 22443, Salt Lake City, Utah 84122
Date: Wed, 7 Jan 1998 19:46:30 -0600 (CST)
From: Kevin Pease <hamradio@mm1001.theporch.com>
Subject: Re: Grid Dippers, was C and L meters
I'll second Barry on the GDO topic. I have twon and havn't been without
one for years and would never be without one. So if you can get a GDO go
for it.
Kevin Pease
WB0JZG
Mount Juliet, TN.
Date: Wed, 07 Jan 98 22:51:54 PST
From: "C-W Crystals" <cwxtal@u-n-i.net>
Subject: WTB T-368 Xmtr. cabinet
Hi gang,
Does anyone know where I might locate a cabinet for the T-368 drawer
unit's? I have the drawer's, and manual and am in need of the cabinet.
73 John
Date: Thu, 8 Jan 1998 16:45:31 -0500 (EST)
From: lee1@digital.net
Subject: Antenna
>To: GB
>From: lee1@digital.net
>Subject: Antenna
>
>Hi Gang
>Thanks to all who responded to my last email asking about a 2meter ant.
>HOWEVER I got a scanner and when using it did something dumb
>which loaded up my hard drive and it crashed. So there went all the good
> info you sent me. The rig arrIved in fb shape and now I need the info.
>SO PLEASE THOSE OF YOU WHO SENT ME INFO ON HOW TO BUILD ONE
>WILL YOU PLEASE SEND IT TO ME AGAIN SORRY!!!!
>
>
Thank the good LORD for all that you have!!!
67yr old semi disabled senior trying to get code speed to 13wpm
(stroke got my eyesight, balance & coordination) SO ONLY BA'S NO SOLID STATE
Leon (lee) Wiltsey 4600 Lake Haven blvd Sebring fl. 33872 KF4RCL TECK+
End of glowbugs V1 #220
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