On 2/2/07, *Kevin Custer* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
I don't know that any commercial manufacturer did, but that's not
the point. The point is if someone stuffs a new crystal in a 5C
element, it MAY NOT hold to its OEM specifications no matter the
temperature change. Are you going to guarantee that any
recrystaled 5C is going to be 2PPM in the 'normal range' if the
recrystaled ICOM was not temperature compensated? I didn't
think so.
Nate Duehr wrote:
Actually I'd have to think about that, and maybe even do some tests.
You just never know... there's always the possibility that no matter
what value of capacitor you stuff into an ICOM's compensation circuit
-- within a "normal" range of capacitors that would normally be used
for netting in a crystal -- the thing just might be designed from the
get-go to barely be 2PPM even in worst-case conditions.
All depends on the engineering on that one. (GRIN)
I think we need to ask some of the folks that have the facilities to do
this to comment. I think you'll find that with the crystals that are
being made today, that changing the main compensation capacitor with
every re-stuff is pretty common.
Dave Karr? Care to comment?
But I doubt I'll ever have time to test that possibility. However, it
might explain why a lot of people have fairly good luck just stuffing
crystals in ICOM's. There's probably a fairly small range of caps
used to bring "the usual" crystals into spec... and a good chance
that your new crystal behaves similarly enough to the original that it
will work some large percentage of the time.
I wouldn't say "a lot of people have good luck". Have you seen the
amount of posts on Repeater-Builder and the other radio branded lists on
the subject over the years? I have, because I've commented seemingly
hundreds of times. In my personal experience, it seems like the bare
crystals I bought years ago were generally better in quality, no matter
who I had bought them from. Now a days, it's pretty common to stuff a
crystal in a element (of any kind) (from any place) and have it not come
up on frequency. Recently I have had two such crystals that I couldn't
change the main ranging capacitor to even get it close. Even if I would
have gotten them to resonate on channel, would it have been stable
(within OEM specs?)
Your article is correct -- if you HAVE to know it's going to work...
have the whole ICOM worked on at the crystal shop... and pick wisely
on the shop.
So seriously, do you see a lot of folks complaining that their
un-compensated crystal elements aren't working after replacing a
crystal on the GE's? I'm genuinely curious? Or maybe you see it a
lot on some other different radio types?
Go back through the archives, or just pay attention from here on out.
And remember, these are the folks that have come to the end of their
string and have had to ask. Now with the article I presented, the need
for these types of postings will likely be less because of folks reading it.
It's -1.3 degrees F here (Friedens PA) as I write this. How many 'not
properly compensated' ham (or worse yet, commercial) radios are there
that are running out of spec? More than anyone would want to admit.
The crystal has to get pretty damn far off before distortion results,
and these are the folks that complain, think of the folks that don't
complain; that don't post - are quiet, read the posts, and send in their
botched attempt to have it 'done right'.
With the above-mentioned comment about there probably being a fairly
"standard" range of caps, for something that's not being used as a
"top of the mountain" repeater that is in a basement as a "back-yard"
system... if you had a small supply of 5C elements and were building
something out of GE MASTR II's on a severely limited budget... I
honestly don't think there's much harm in stuffing a crystal yourself.
This is plainly stated in an article I pointed you to earlier. You must
not have read it the whole way through? <grin>
http://www.repeater-builder.com/ge/mastrii/m2icoms.html
Look at the last paragraph after the pictures and before the horizontal
bar.
I'll post that text here, so you don't have to go to the article:
/There is one way to cheat if all you have is ECs. An EC will maintain
better than 5ppm from +32 degrees F to above 120 degrees F only if you
have a stable +5v DC voltage on the compensation line. This is plenty
good for a garage repeater (i.e. your test bed system), while you finish
it and burn it in. A voltage divider made from a pair of 1.0K, 2.2K,
3.3K or 4.7K 1/4w or 1/2w metal film resistors in series from the +10vDC
supply to ground, with the center point tied to the compensation line is
all that is needed (with suitable RF bypassing). The two resistors
must be the same value, and they and the bypass cap can be soldered onto
a base connector salvaged from a dead element - this allows you to leave
the exciter or receiver circuit board unmodified - and the voltage
divider plug can be removed easily when you find a 5C element (or
replace the ECs with 2Cs). Until then, use the ECs, install them in
the radio, and set the elements on channel with the radio in the 60 to
75 degrees F temperature range. It will work well enough while you
locate a couple of good (5C's or) 2Cs and have them rocked up on your
frequency pair.
/
Again, the new article is not intended to be a complete crystal 101,
many of the things you have brought to the table are covered already in
other articles. Maybe it would be a good idea for me to reference these
articles from the new one, and vice versa? But, will folks read all of
them?
I have found that if an article is too big, it looses its effectiveness.
But you'd want to carefully align and check everything (assuming here
that you have more time available than money) and watch for changes
over time. But also, if the thing wasn't behaving, grab a different
5C and try another. No harm in that at all, really.
Agreed....
I actually enjoyed your description of the Moto stuff... I had no idea
they weren't built as well. (HUGE GRIN)
Taking my toungue out of my cheek for a moment, your description
definitely makes it sound like the Moto elements need more up-front
work and TLC... if they're kinda "always compensating"? I believe
someone shared with me that the same element is used for TX/RX in a
MICOR design too, right?
That would make the "flatness" of the center band of the temperature
curve REALLY important.
Only on a MICOR UHF Mobile, all other MICOR's are conventional, and, a
few other Motorola designs on 800/900, as I remember.
Here is another article for you to read:
http://www.repeater-builder.com/rbtip/micoruhfmobile.html
Just in case... I hope you're not taking these comments personally?
Hard to tell tone over e-mails. I'm not mad, just discussing!
Emotion over email is difficult at best to decipher. No, I'm not mad.
It's my job ( I guess) to educate. I'm sure you aren't the only one
here that has been enlightened.
So you're right, there's not a warning, but a newbie coming in the
front door might assume that such a missive about 2 PPM vs 5 PPM means
that there are 5 PPM devices out there lurking, ready to pounce on
them if they put them in their brandy-spankin' new UHF repeater... you
know?
Not if they took the time to read all there is about the subject, which
they likely would have before they got to this new article.
Also, the comment about 2PPM *might* make them think about the
situation, and have them ask about it, or go and look for more information.
This whole thing has me insanely curious. (You probably agree with
the insane part by now.) I want to go find a 5C and figure out what
cap is changed to net the crystal in and put wildly variable values of
capacitance in there and see just how far it'll drift if stuck in a
freezer/heated up.
Here is some information on how GE did things on the MVP and EXEC II. I
don't know if it applies to the MASTR II, but I suspect it does.
This addition to the website came from Chuck WB2EDV, and it's his
comments that appear the end of the file.
http://www.repeater-builder.com/ge/mvp/pdf/temp-comp-mvp.pdf
There is no link to the file from the website yet. Maybe Bob M. can
place a link to it from somewhere on the MASTR Index Page under the MVP
information section, and EXEC II Index?
Kevin Custer
