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Faux Grid Dipper




 
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Author Topic: Faux Grid Dipper  (Read 10648 times)
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K9ACT
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« on: May 31, 2007, 12:41:09 AM »

My old Knight Kit GDR bit the dust and I am lost without it.

I now have an RF sig gen and a scope and it seems as though I should be able to work this into something better than the GDR but I am getting strange results.

Starting with a tank circuit (cap and coil), I put a loop at the end of the Sig Gen leads and around the coil.  I then connect the scope across the cap/coil and swish the sig gen around till I get a dip or peak.  I do not recall which but it is very sharp and well defined.

If I set the gen of some freq and tune the cap, I get the same result.

Great!  Unfortunately, when I put the tank in a circuit, it's not even close... like off by a mhz or so, nor does it agree with the calculated res freq.

What am I missing?

js
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KB2WIG
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« Reply #1 on: May 31, 2007, 01:38:09 AM »

Your faux dipper is interacting with the '"tank" ckt. The pick up coil is wound around the 'tank' coil and is reflecting your Signal Gen. ckt into the tank...  The scope Z In is probably having a very,very minor effect on the tank ckt. 1 MC off sounds like a lot...   Try moving your pick up coil away from the tank coil and see if this changes things.

Sri 'bote the Knite Kit.......

I finally got a Millen GDO after 30+ years... I'll never give it up.....   klc
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The Slab Bacon
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« Reply #2 on: May 31, 2007, 08:10:54 AM »

I have both griefkit and Eico GDO's. I'm lost without them!! I also have the "grid dip "adaptos for my mighty fine junk antenna anal izer.
It will also do the job as well.

You know, it is amazing how many hams dont even have a friggin clue what a GDO even is!! Itz definately nice to know that someone else besides myself still uses one!!

I have added pickups to mine to tie in a freaky counter, this really gives you an accurate indication of where your dip iz!! Lets face it these things do drift all ova the place. But none the less, an indispensable piece of test equipment if you still build things!!

                                The Slab Bacon
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K1MVP
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« Reply #3 on: May 31, 2007, 09:16:27 AM »

I have both griefkit and Eico GDO's. I'm lost without them!! I also have the "grid dip "adaptos for my mighty fine junk antenna anal izer.
It will also do the job as well.

You know, it is amazing how many hams dont even have a friggin clue what a GDO even is!! Itz definately nice to know that someone else besides myself still uses one!!

I agree Frank,--I also would not be without one,(a GDO) have used it for "teaking" the final tank circuits
in homebrew rigs, making antenna traps, neutralizing, etc, etc.
Other items I consider a "must", are a good scope, a frequency counter, VTVM, etc.
I dont see how any guy can build, fix ot troubleshoot without these "indispensible tools".
                                                 73`s, K1MVP
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K9ACT
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« Reply #4 on: May 31, 2007, 10:44:57 AM »

Your faux dipper is interacting with the '"tank" ckt. The pick up coil is wound around the 'tank' coil and is reflecting your Signal Gen. ckt into the tank...


Isn't that the point?  The tank circuit transfers max energy from the gen when it is resonant.  The scope just displays the amplitude which would be max or min depending on whether it is parallel or series tuned.

The coupling is very loose... just the clip leads hooked together and around the coil.  Moving it around makes no difference.

>Sri 'bote the Knite Kit.......

Me too.  I have had it since  a teenager.  The only coil I can find for it is the 80 meter one that was in it when I dug it out of mothballs.  Fortunately, that is all I really need.

I think the problem is "just" the meter itself so I could rig up an outboard one but the other idea seems so much better.

I like the idea of hooking a counter to it but for most purposes, the callibration is close enough for tank circuits.

js

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Pete, WA2CWA
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« Reply #5 on: May 31, 2007, 01:37:19 PM »

There's about a dozen of them for sale, starting around $5, on ebay right now.

I use a Measurements 59 and a solid-state Kenwood DM-81.




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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
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« Reply #6 on: May 31, 2007, 08:13:04 PM »

Repair the Knight Kit?

What's wrong with it???

Is it toobers or soylent state?
There are schetch-a-matiicks on "bama" for a lot of gear... maybe that one too.
And, they're all similar.

Not that much in a dippo... (famous last words from a guy who has a Griefkit Tunnel dipper DOA over there - but I did just find it in a dumpster! -true!- and it looks clean, but don't osckallate)

pete - those coils look like the coils that came with an Eico GDO that I just picked up at a hamfeast!!

                 _-_-Wbear2GCR
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Pete, WA2CWA
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« Reply #7 on: May 31, 2007, 09:47:46 PM »

Yep, good eyes. The site where the picture link is pointing to, describes the use of the Model 59 with Eico coils.
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K9ACT
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« Reply #8 on: June 01, 2007, 12:37:27 AM »

There's about a dozen of them for sale, starting around $5, on ebay right now.


Thanks for the heads up.  I bid on 2 of them including one just like I have including all the coils I am missing.

I also spent about an hour on the rest of that list and only got half way through it.

js
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K9ACT
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« Reply #9 on: June 01, 2007, 12:41:33 AM »

Repair the Knight Kit?

What's wrong with it???


The meter is fried.  I hooked up an outboard to day and it is usable.

However, the original problem with the scope and gen has been solved.  It was indeed interacting with the test equipment but it was the scope and not the gen.  When I switched to link coupling on both the gen and the scope, it works perfectly with super sensitivity.  A vast improvement over a dipper.

js
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« Reply #10 on: June 01, 2007, 10:41:08 AM »

A case of a Big Dipper vs. a Little Dipper??

 Grin
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K9ACT
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« Reply #11 on: June 01, 2007, 02:30:24 PM »

A case of a Big Dipper vs. a Little Dipper??



Could be.  I will have to take it out tonight and see if it points to the North Star.  Actually,it should point to the Knight Kit inside.

js
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Rob K2CU
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« Reply #12 on: June 01, 2007, 10:14:00 PM »

Hey Pete, It looks like your using a set of Eico GDO coils with your 59. Does that set up work well and is it accurate? I have a 59 with the normal set of coils. I understand there are two additional lower frequency coils. I guess I should look through my manual to see if there is mention of them. Very few newbies today know what they are let alone how to use them.

A related quiz: Iron core/ferrite slugs lower frequency, what do brass slugs do?
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« Reply #13 on: June 01, 2007, 10:58:40 PM »

Hi Rob,

Actually there is a complete lower frequency head which plugs into the power supply/meter and looks just like the standard HF head.  My 59 came with the additional manual for the LF head but unfortunately not the head itself.  I believe that there is also a third head which extends the UHF range a bit.  My 59 gets a lot of use but I also picked up a military AN/PMR-10 at a hamfest last year.  I didn't really need a second meter but at $5 I couldn't resist.

73, Rodger WQ9E
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Pete, WA2CWA
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« Reply #14 on: June 01, 2007, 10:58:58 PM »

Hey Pete, It looks like your using a set of Eico GDO coils with your 59. Does that set up work well and is it accurate? I have a 59 with the normal set of coils. I understand there are two additional lower frequency coils. I guess I should look through my manual to see if there is mention of them. Very few newbies today know what they are let alone how to use them.

A related quiz: Iron core/ferrite slugs lower frequency, what do brass slugs do?

It's not my site and not my Model 59. I was just referencing the Model 59 with the picture. It was the first site I found.
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« Reply #15 on: June 01, 2007, 11:02:25 PM »

Hi Rob,

Actually there is a complete lower frequency head which plugs into the power supply/meter and looks just like the standard HF head.  My 59 came with the additional manual for the LF head but unfortunately not the head itself.  I believe that there is also a third head which extends the UHF range a bit.  My 59 gets a lot of use but I also picked up a military AN/PMR-10 at a hamfest last year.  I didn't really need a second meter but at $5 I couldn't resist.

73, Rodger WQ9E


There's the Model 59, the Model 59-LF, and the 159RF. Without running down to look at all the manuals, I believe the 159RF is the UHF version.
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« Reply #16 on: June 02, 2007, 09:56:07 AM »

brass probably does nothing good.
since it has copper as a significant part, it may act like "shorted turns" and effect the flux path/eddy currents...  it seems to me.

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K9ACT
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« Reply #17 on: June 02, 2007, 12:24:36 PM »

brass probably does nothing good.
since it has copper as a significant part, it may act like "shorted turns" and effect the flux path/eddy currents...  it seems to me.

I think you win.  Here are the results of my Mr Wizard science project.

I took a slug tuned receiver type coil with  100 uH and 2.5 mH  nominal coils.

The 100 uH tuned DOWN to about 83 with a brass slug.

The 2.5 mH tuned Down to about 1.9 mH.

I also did a 3.3 uH which was 1.0 with the slug removed.

It tuned down to about .9uH with brass.

I then tried a steel slug and it tuned UP to about 1.1

So, brass has the same effect as shorting turns, viz., reducing inductance.

Not sure what makes this a bad idea.  Pushing in brass has the same effect as pulling a slug out of an inductor.

Thanks for the stimulating question.  It was a welcome relief from debuging my exciter.


js
 
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Ian VK3KRI
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« Reply #18 on: June 03, 2007, 01:04:36 AM »


So, brass has the same effect as shorting turns, viz., reducing inductance.

Not sure what makes this a bad idea.  Pushing in brass has the same effect as pulling a slug out of an inductor.

Thanks for the stimulating question.  It was a welcome relief from debuging my exciter.

js
 

Ive seen coils with brass slugs. I think they were mainly in old TV tuners. Possibly iron-powder for VHF wasn't so good 50 years ago and brass slugs were less lossy.

I don't think that shorted turns are in themselves bad if done properly. I've seen deigns for VHF power amps that tune the L in the pi coupler with a rotatable shorted turn made out of a piece of copper pipe. As long as resistive losses are low it shouldn't be lossy.

                                                Ian VK3KRI
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The Slab Bacon
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« Reply #19 on: June 03, 2007, 07:44:09 PM »

Brass slugs actually REDUCE the inductance of an inductor as they are screwed into the coil. This is typically found on higher frequency applications.

                                                                      the Slab Bacon
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Rob K2CU
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« Reply #20 on: June 04, 2007, 06:22:42 PM »

Well, you are all basically right! I have seen brass slugs in old turret type TV tuners, primarily for the lower channels. The brass slugs do lessen the inductance by creating shorted turns. I though it might be a good quiz question and give someone some possible solutions to problems when your circuit resonates too low and you want a quickie fix to see if retuning will fix a problem. I also remember seeing adds for "magic wands" that were small brass slugs on the end of a phenolic shaft to diddle tune a circuit.

I don't think they were too good for the Q of the circuit, but if it worked, why fix it? IN those days, you could see the Empire State building and only needed rabbit ears to pick up the 6 TV channels out of NYC.

ras

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Ian VK3KRI
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« Reply #21 on: June 11, 2007, 06:03:43 AM »

I forgot to mention in the previous post, that a handy tool is a stick with a ferrite slug on one end and a brass slug on the other. Stick ferrite end in a coil and inductance increases, stick in the brass end and inductance decreases.
                                         Ian VK3KRI                     
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