EMRFD Message Archive 8505

Message Date From Subject
8505 2013-04-11 19:48:54 101 Device to read a resonant frequency directly & accurately?
I'm building a very steep (very high L/C ratio series tune) HF
preselector.

1. Is there a (digital readout) device that can read what the
resonance is directly & accurately (not as a dip meter)?

2. What I can think of is an antenna analyzer. Does it work &
accurately?

Best regards.
8506 2013-04-11 20:07:52 Jerry Haigwood Re: Device to read a resonant frequency directly & accurately?
Hello 101,

How about using a RF frequency generator with a frequency counter and a
scope or low power wattmeter. You will also be able to determine the width
of the preselector. Actually a grid dip meter and a frequency counter would
work. A sweep generator with a frequency readout and a scope would also
work. There are several ways to skin this cat.

Jerry W5JH

"building something without experimenting is just solder practice"







8507 2013-04-11 20:34:29 101 Re: Device to read a resonant frequency directly & accurately?
Thanks Jerry,

That's what I've been doing i.e. I use a Signal Generator (with digital readout applied) and a homebrew power meter.

But it is a many-step process. I need to see the resonant frequency reading instantly every time I retune the dial (or changing receiving station). I cannot fully rely
8508 2013-04-11 20:54:00 Jerry Haigwood Re: Device to read a resonant frequency directly & accurately?
There are other methods. I think I misunderstood your application. It
sounds as though you want to do this as you operate the receiver. If that
is the case, you could do some design work and end up with a custom readout
for your preselector. For instance, you could turn a linear pot at the same
time you turn your tuning capacitor thru a gear or belt arrangement. Place
a voltage across the pot and read it with a PIC or Arduino and convert the
voltage to a frequency either by formula or lookup table. Display the
frequency on a LED or LCD display. There are also other methods. Such as,
use a dual capacitor and tune an oscillator with the second variable cap.
Use a frequency counter to display the frequency which should match the
preselector frequency if done correctly. Just some food for thought..

Jerry W5JH

"building something without experimenting is just solder practice"







8509 2013-04-11 21:29:37 101 Re: Device to read a resonant frequency directly & accurately?
Dear Jerry,

Thanks for your suggestion. It'll take a long way for me to achieve what
you suggest cos I know nuts about PIC or Arduino! Anyway, I must start
from somewhere.

Do you have any good web site on PIC/Arduino tutorial?

Best regards.


8510 2013-04-11 22:09:06 Bob L Re: Device to read a resonant frequency directly & accurately?
This suggests it is a high Q circuit that has to be tuned to the incoming frequency. If so you might measure the resonant frequency at each tuning capacitor setting and use a dial to match the preselector to desired input.

Back in the old days it was common to use a multi-section tuning capacitor. One section would tune the VFO and the other secti
8512 2013-04-11 22:09:07 Kirk Kleinschmidt Re: Device to read a resonant frequency directly & accurately?
I swept the front-end tunable band-pass filter from the IRK-ZOI Progressive Receiver with a mini-VNA as shown here:

http://i50.tinypic.com/1zn28ap.jpg

http://i49.tinypic.com/2e39v79.jpg

I am definitely not an expert when it comes to using the thing, but it does work well as a filter sweeper. BTW, the tunable peak (double hump) is normal for this design.

73,

--Kirk, NT0Z

 
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)


>________________________________
>
8517 2013-04-11 22:53:29 101 Re: Device to read a resonant frequency directly & accurately?
Hi Bob,

I like this idea.

What is the maximum bandwidth that can be use as an oscillator? Normally
they use quartz (rather than LC circuit) which has a very very narrow
bandwidth. My LC circuit should have about 10 khz bandwidth.

Regards.

8518 2013-04-11 23:10:20 101 Re: Device to read a resonant frequency directly & accurately?
Hi Kirk,

Can I have a Table of Contents of your book - Stealth Amateur Radio?

8519 2013-04-12 00:30:20 101 Re: Device to read a resonant frequency directly & accurately?
Hi Bob,

It seems that I cannot convert (temporarily) my preselector into an
oscillator because oscillator circuit needs a parallel tuned LC whereas
my preselector is a series tuned LC.

Regards.

8520 2013-04-12 03:33:56 Roelof Bakker Re: Device to read a resonant frequency directly & accurately?
Hello all,

Such a system has been implemented in a series receivers of JRC.
E.g. the JRC NRD525 and JRC NRD535.
It might be worthwhile to look at how they made it work.

Instead of a kind of tracking generator, it will be easier to employ a
noise generator.
For tuning switch off the antenna and measure the noise increase at the IF.

Twenty years ago, I used the output of a crystal calibrator to peak the
front end filters manually.
This worked very well. The output of the crystal calibrator was at 25 kHz
intervals.

73,
Roelof Bakker, pa0rdt
8521 2013-04-12 04:44:10 101 Re: Device to read a resonant frequency directly & accurately?
Hi Roelof Bakker,

A very good idea.

Is there a noise generator that covers HF spectrum?

With this, we can amplify the signal (until the threshole of Digital
Readout) and inject into the preselector, Digital Readout can be taken
off the output of the preselector immediately!

Please advise me a noise generator that covers HF spectrum.

Regards.


8522 2013-04-12 05:06:42 Roelof Bakker Re: Device to read a resonant frequency directly & accurately?
Hello 101, (not 409 or 412)

I have build the one from EMRFD page 7.39, which is simlar to the one on
page 168 of Solid State Design.
The output derates linear from -69 dBm @ 1 MHz to -79 dBm @ 30 MHz.
It is -73 dBm (S-9) at about 17 MHz.

Current draw is 35 mA @ 12 volt.

Best regards,
Roelof, pa0rdt
8523 2013-04-12 05:16:08 101 Re: Device to read a resonant frequency directly & accurately?
Hi Roelof,

Thank very much.

I read that page this morning, but it does not imply the frequency
range. In fact, I thought it generates AF rather than RF noise. Thanks
again.

Best regards.

8524 2013-04-12 05:35:03 William Carver Re: Device to read a resonant frequency directly & accurately?
Like the "noise bridge" so popular decades ago.......
W7AAZ



On Fri, 2013-04-12 at 12:33 +0200, Roelof Bakker wrote:
> Hello all,
>
> Such a system has been implemented in a series receivers of JRC.
> E.g. the JRC NRD525 and JRC NRD535.
> It might be worthwhile to look at how they made it work.
>
> Instead of a kind of tracking generator, it will be easier to employ a
> noise generator.
> For tuning switch off the antenna and measure the noise increase at the IF.
>
> Twenty years ago, I used the output of a crystal calibrator to peak the
> front end filters manually.
> This worked very well. The output of the crystal calibrator was at 25 kHz
> intervals.
>
> 73,
> Roelof Bakker, pa0rdt
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
8525 2013-04-12 05:53:38 Lasse Moell Re: Device to read a resonant frequency directly & accurately?
Was thinking the same...
I remember an atenna tuninging unit that had such a device built in, so
the noise bridge would allow for silent ATU operation.

SM5GLC



On 12 apr 2013 14:35 "William Carver" <bcarver@safelink.net> wrote:

>
>
> Like the "noise bridge" so popular decades ago.......
> W7AAZ
>
> On Fri, 2013-04-12 at 12:33 +0200, Roelof Bakker wrote:
> > Hello all,
> >
> > Such a system has been implemented in a series receivers of JRC.
> > E.g. the JRC NRD525 and JRC NRD535.
> > It might be worthwhile to look at how they made it work.
> >
> > Instead of a kind of tracking generator, it will be easier to employ
> > a
> > noise generator.
> > For tuning switch off the antenna and measure the noise increase at
> > the IF.
> >
> > Twenty years ago, I used the output of a crystal calibrator to peak
> > the
> > front end filters manually.
> > This worked very well. The output of the crystal calibrator was at
> > 25 kHz
> > intervals.
> >
> > 73,
> > Roelof Bakker, pa0rdt
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
>
>
>
>
>

[Non-text portions of this message have been removed]
8526 2013-04-12 06:41:51 Kirk Kleinschmidt Re: Device to read a resonant frequency directly & accurately?
Howdy!

You can see the TOC and part of all of the first chapter here:

http://www.amazon.com/Stealth-Amateur-Radio-Operate-Anywhere/dp/0872597571#reader_B004PYDPLS


It's kinda goofy and seems to be laid out bass-ackwards, but it's viewable :)

If that doesn't work out, let me know and I'll dig one up.

Thanks,

--Kirk, NT0Z


 
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amaz
8527 2013-04-12 07:23:48 William Carver Re: Device to read a resonant frequency directly & accurately?
Yes, I have a mobile 40m rig with internal tuner....and internal noise
bridge. I had not thought about using noise to check tuning of a front
end preselection filter, but it would be good for that, too.

W7AAZ




On Fri, 2013-04-12 at 14:53 +0200, Lasse Moell wrote:
>
> Was thinking the same...
> I remember an atenna tuninging unit that had such a device built in,
> so
> the noise bridge would allow for silent ATU operation.
>
> SM5GLC
>
> On 12 apr 2013 14:35 "William Carver" <bcarver@safelink.net> wrote:
>
> >
> >
> > Like the "noise bridge" so popular decades ago.......
> > W7AAZ
> >
> > On Fri, 2013-04-12 at 12:33 +0200, Roelof Bakker wrote:
> > > Hello all,
> > >
> > > Such a system has been implemented in a series receivers of JRC.
> > > E.g. the JRC NRD525 and JRC NRD535.
> > > It might be worthwhile to look at how they made it work.
> > >
> > > Instead of a kind of tracking generator, it will be easier to
> employ
> > > a
> > > noise generator.
> > > For tuning switch off the antenna and measure the noise increase
> at
> > > the IF.
> > >
> > > Twenty years ago, I used the output of a crystal calibrator to
> peak
> > > the
> > > front end filters manually.
> > > This worked very well. The output of the crystal calibrator was at
> > > 25 kHz
> > > intervals.
> > >
> > > 73,
> > > Roelof Bakker, pa0rdt
> > >
> > >
> > > ------------------------------------
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> >
> >
> >
> >
> >
>
> [Non-text portions of this message have been removed]
>
>
>
>
>
8529 2013-04-12 17:07:36 blumu Re: Device to read a resonant frequency directly & accurately?
One feels a warm glow to note that the lowly noise bridge
and noise generator have been resuscitated :-)

Michael

----- Original Message -----------------------------------------------

8531 2013-04-12 18:17:01 Kerry Re: Device to read a resonant frequency directly & accurately?
> One feels a warm glow to note that the lowly noise bridge
> and noise generator have been resuscitated :-)
>
> Michael

************************************

Agree; one of my favourite instruments.

I built my version of the ARRL/John Grebenkemper design quite some years ago. It was, for me, the first step from scalar measurements to vector measurements.

An amateur here in VK makes & sells very nice ones;

http://www.vk3aqzkits.com/

Kerry VK2TIL.
8556 2013-04-16 14:35:13 Tim BandTech.com Re: Device to read a resonant frequency directly & accurately?
Try a wideband amplifier with your preselector at the input, and a small piece of wire to couple the output of the amplifier back to the preselector input. This forms an oscillator and by feeding the amplifier output to a frequency counter a frequency can be measured without the need to use an external oscillator.

This is handy for developing LC tuned circuits or for testing crystals.
I'm sure there will be plenty of criticism due to the lack of attention to phase response, but so long as your preselector works well then only a narrow frequency band will be getting fed back.

My amplifier's input is an open gate BF998 so has about 2.5 pF input capacitance. It has three stages, the tail end of which is a J310 source follower for low output impedance. It does not detune low frequency circuits, but the output must be loosely coupled to prevent detune. High Q circuits do well with almost no feedback, which basically means that feedback is finding its way due to my unshielded amplifier.

It is good to verify results occasionally by sweeping with an external oscillator. I even measure the self resonant frequency of coils alone with this setup, at which point things are pretty subjective, but it gives sensible values. If your C is real small then I suspect you are in for some misleading results no matter what system you use: you are basically dealing with the self resonant response of your inductor coupled with whatever input capacitance is down the line, which may have a large impact
8560 2013-04-17 17:32:10 101 Re: Device to read a resonant frequency directly & accurately?
Hi Tim,

Thank very much for your advice.

8561 2013-04-18 09:12:15 Nick Kennedy Re: Device to read a resonant frequency directly & accurately?
Coincidentally, I'd just finished building a broadband "utility" amplifier,
50 in / 50 out, with about 38 dB of gain the day before your post. It uses
three MMICs cascaded. I'd wondered what might happen with a resonant
circuit from output to input.

First I tried an inductor wound on a film coil with a 100 pF capacitor in
series, coupled back to the to the other port with a gimmick wire. I
expected something in the 5 to 20 MHz range. What I got was something over
200 MHz, so as you suggested I was apparently seeing the SRF of my coil.

Next I decided to try a length of coax as the "resonator". I had something
over 10 feet with BNCs on each end so I hooked it from output to input with
a homebrew step attenuator before the input and a tee at the output for the
scope or counter. I had to fool with the attenuation a little before
getting a fairly steady 27.9 MHz. I was using about 30 to 34 dB of
attenuation, I think.

Tried a crystal in series with a couple RG174 jumpers having connectors on
one end and bare wires on the other -- where I inserted the crystals. Also
still had the attenuator in line. Results in the 100 MHz or higher range
for crystals of 3.579 and 7.68 MHz made me conclude that the shift from the
coax was dominating and the crystals were being bypassed via their holder
capacitance. Maybe a fixture with no coax would give better results.

This little project started out with a desire to have a high impedance, low
capacitance probe for my scope, followed optionally with a bunch of gain.
For the front end, I have a J310 follower with a voltage gain of about
0.5, but I haven't tied the whole thing together as yet.

73-

Nick, WA5BDU


8566 2013-04-20 11:55:52 Tim BandTech.com Re: Device to read a resonant frequency directly & accurately?
8567 2013-04-20 17:42:38 Nick Kennedy Re: Device to read a resonant frequency directly & accurately?
8570 2013-04-21 07:17:54 Tim BandTech.com Re: Device to read a resonant frequency directly & accurately?