QRZ! Ham Radio 3/QRZ Ham Radio Callsign Database - Volume 3.iso/digests/homebrew/930085.txt

Internet Message Format | 1994-06-04 | 16KB

Date: Wed, 27 Oct 93 04:30:29 PDT
From: Ham-Homebrew Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Homebrew Digest V93 #85
To: Ham-Homebrew


Ham-Homebrew Digest         Wed, 27 Oct 93       Volume 93 : Issue   85

Today's Topics:
                    8 pin Mic. connectors source?
                       How to do CW with a cb?
                          INTERMOD (2 msgs)
                            QRP Mail List
                     What's this cable? (2 msgs)

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Archives of past issues of the Ham-Homebrew Digest are available
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We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party.  Your mileage may vary.  So there.
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Date: 26 Oct 93 14:10:28 GMT
From: sdd.hp.com!col.hp.com![e-mail]
Subject: 8 pin Mic. connectors source?
To: [e-mail]

Jeffrey D. Angus ([e-mail]) wrote:
:  Here we go again.

:  I need to find a source of the Microphone Connectors used with most of
:  todays equipment. This is the 8 Pin connector with a threaded sleeve.
:  The female cord mounted connector is a Radio Shack 276-025 listed on
:  page of the new (coupon enhanced) catalog. They used to stock the mating
:  male chassis receptical. Philco carries them in some electronics and
:  HAM stores, as part number T-700 and P-700 as well.

:  If you want to tell me that your Radio Shack store still has them, fine,
:  let me know who much and how many and I'll arrange to buy them through you.

:  If you have a vendor source for these (like Allied or Newark and yes I
:  aready checked with them and they don't have them) let me know as well.

:  73 es GA from Jeff

:  (Note, Newark does stock the old Motorola series 3/4" dia mic connectors)

 I bought mine from HRO although you won't like the cost, I'll bet.
 I think they cost me about $5.00 each, plus their shipping and handling-
 about $4.00.  I bought 5 or 6 and averaged out the shipping/handling.
 HRO advertises in QST, CQ, and, I'll bet, 73 magazines.

 Good luck.  Mike, K0TER

------------------------------

Date: Tue, 26 Oct 1993 01:21:54 GMT
From: csus.edu!netcom.com!netcom![e-mail]
Subject: How to do CW with a cb?
To: [e-mail]

If he transmits a constant carrier, keys an audio oscillator to produce
CW-like sounds, and identifies by voice, code practice over CB should
be legal anywhere, even in the US.  Strikes me as being a good way to
get some practice.  Keeping on legal frequencies may save you some
hassles, and is much more polite.
73, doug

------------------------------

Date: 26 Oct 93 13:12:01 GMT
From: rosevax!animal![e-mail]
Subject: INTERMOD
To: [e-mail]

>
>     Hi everyone, This question should concern every soul that ever attempted
>to operate an H.T. in a mobile using a Mag Mount or other type of external
>'gain' antenna in a large city: >>>>> INTERMOD !  The solution seems quite
>simple ... I noticed that when I'm swamped with intermod, going back to the
>'ducky' usually solves the problem at least partially. If one could attenuate
>the incoming signals from the external antenna on receive only and not affect
>anything during transmit, you would have the perfect combination for an H.T. in
>a car ... So what is really needed for so many of us is a "variable rf in-line
>attenuator" that would be rf-switched-out during transmit.
>
>        Any ideas out there?
>
>                                Thanks & 73 de Denis.


I have a Heath HW2P that is terrible on an external antenna in the city
with intermod.  I also used an amplifier in the car to get it from 2.5
watts (save a bit of battery) up to around 10 watts.  This is a home
brew amp.

My solution to the intermod was to build a helicoil front end for the
reciever inside the amplifier.  The relay switching made connecting the
coil bandpass filter easy.  Normaly on an amp relay, two leads are shorted
togather to pass the recieve signal.  I just added my filter in the place
of the short.  I also added a switch to disable the filter for out of
band recieving.  With this, I also found that I had very low loss thru
the filter (weak signal increase was barely changed with the circuit
switched in or out).  Intermod is GREATLY reduced!!!

I found a suitable circuit in "The VHF Manual" by Jesop (English Author,
book sold in many Ham Radio stores) that gives a low loss (you don't need
great sensitivity in the city anyway) during receive and the circuit is
switched out during transmit.

Tuning is done on low power out of the rig thru the filter.  Tune for max
output.  I found less than 1db loss.

Mike  WA0VNH
 [e-mail]

------------------------------

Date: 26 Oct 1993 09:49:49 +0200
From: agate!howland.reston.ans.net!pipex!sunic!news.funet.fi!butler.cc.tut.fi!lehtori.cc.tut.fi![e-mail]
Subject: INTERMOD
To: [e-mail]

Gregory Lapin ([e-mail]) wrote:

> A friend of mine (Rajiv AA9CH) suggested a solution that I tried but didn't
> get it to work.  I didn't really spend much time on this (intermod is
> almost non-existent for most of my operating area) and it seems logical so
> here goes:

> At the HT, place a T-connector with one leg going to the gain antenna.  The
> open leg should be connected to a shorted 1/4 wave piece of coaxial cable,
> which appears as an open circuit at the frequency it is cut for and as a
> short circuit at frequencies far away (such as the pagers that cause many
> of the intermod problems).  This seems like a pretty nifty little bandpass
> filter for the front end of the HT.

You seem to have mixed up things a bit. A shorted 1/4 wave stub acts as a
paralell resonance (open circuit). What you actually want is short circuit
at the offending frequency (series resonance) and this can be done with an
_open_  1/4 wave stub or a 1/2 wave _shorted_ stub at the offending
frequency.

As open stubs are not truely open, I would suggest a shorted 1/2 stub,
which is also easier to tune by a shorting needle.

Use low loss coax as this will determine the Q of the resonance and remember
to include the velocity factor of the coax in the calculation.

                Paul OH3LWR


--------------------------------------------------------------------
Phone   : [phone]
X.400   : G=Paul S=Keinanen O=Elisa-Tampere A=ELISA C=FI
Internet: [e-mail]
Telex   : 58-100 1825 (ATTN: Keinanen Paul)
Mail    : Hameenpuisto 42 A 26
          FIN-33200 TAMPERE
          FINLAND

------------------------------

Date: Tue, 26 Oct 1993 09:21:12 GMT
From: news.Hawaii.Edu!uhunix3.uhcc.Hawaii.Edu![e-mail]
Subject: QRP Mail List
To: [e-mail]

In article <[e-mail]> [e-mail] (karayannopoulos,george) writes:
>A couple of weeks ago, somebody posted a QRP construction article, where
>he mentioned the existence of a QRP mailing list. I lost that article and
>don't know who it was. Does anybody have any info on that mailing list?
>How do I get on it?
>
>
>___________________________________________________________________
>George Karayannopoulos              N2OWO
>[e-mail]             Bellcore, Red Bank, NJ
>Disclaimer: The opinions expressed here are mine and not my employer's.

George, to get on the QRP mail list send an email to: [e-mail]
and in the msg just ask to subscribe. The owner will add your email address
to the group; you'll get posts via email. Usually no more than 10 articles
are posted each day, although it's been a bit quiet lately. If you want
to post any questions or comments to the rest of the group, then just
use the email address: [e-mail]

There are some very famous folks who hang out on there: one of the
fastest CW ops in the country, Chuck Adams (70 wpm), is always
building one thing or another. In fact, that is an alternative
homebrew group! It seems everyone is building stuff either from
scratch or from kits (lots of cheap QRP kits available: the Northern
California QRP club is offering a 40M xcvr for about $75). Always
helpful advice is being passed about on there.

72 (the QRP'ers 73),
Jeff NH6IL

------------------------------

Date: 26 Oct 1993 13:03:47 GMT
From: olivea!inews.intel.com!ilx018-bb.intel.com!ilx049![e-mail]
Subject: What's this cable?
To: [e-mail]

Scrounging in the dump behind the local cable TV company,
I found a chunk of coax. It's labeled only "T-10" (or maybe T-12
if my memory is failing...).  It's a bit bigger than RG-8, and
has a shield consisting of two layers of aluminum braid and
two layers of aluminum foil.  From the outside in, they go:
braid-foil-braid-foil-dielectric-center.  The dielectric is foam.

This stuff looks like if mught have really low loss for UHF.
Does anyone know if this is a standard cable type?  It is 75
ohms?  Are connectors available?  Perhaps regular N connectors
for RG-8 might fit it?  If I knew anyone who worked at the
cable company, I would ask them.

--

-------------------------------------------------------------------
Doug Braun     Intel Israel, Ltd.      M/S: IDC1-41
               Tel: [phone]   [e-mail]

------------------------------

Date: 26 Oct 1993 22:54:15 GMT
From: sdd.hp.com!cs.utexas.edu!swrinde!emory!europa.eng.gtefsd.com!howland.reston.ans.net!wupost!crcnis1.unl.edu!unlinfo.unl.edu![e-mail]
Subject: What's this cable?
To: [e-mail]

[e-mail] (Doug Braun) writes:

>Scrounging in the dump behind the local cable TV company,
>I found a chunk of coax. It's labeled only "T-10" (or maybe T-12
>if my memory is failing...).  It's a bit bigger than RG-8, and
>has a shield consisting of two layers of aluminum braid and
>two layers of aluminum foil.  From the outside in, they go:
>braid-foil-braid-foil-dielectric-center.  The dielectric is foam.

>This stuff looks like if mught have really low loss for UHF.
>Does anyone know if this is a standard cable type?  It is 75
>ohms?  Are connectors available?  Perhaps regular N connectors
>for RG-8 might fit it?  If I knew anyone who worked at the
>cable company, I would ask them.

>--

>-------------------------------------------------------------------
>Doug Braun     Intel Israel, Ltd.      M/S: IDC1-41
>               Tel: [phone]   [e-mail]

People often confuse shielding with low loss. I don't know what
particular cable you have found but would be surprised if the loss
figures aren't beatable elsewhere. However, the shielding properties
of that cable should be hard to beat.

Gary

------------------------------

Date: 27 Oct 1993 00:13:41 +0200
From: sdd.hp.com!usc!howland.reston.ans.net!pipex!sunic!news.funet.fi!butler.cc.tut.fi!lehtori.cc.tut.fi![e-mail]
To: [e-mail]

References <2aikqt$[e-mail]>, <2ajm3n$[e-mail]>, <2ajpgb$[e-mail]>tle
Subject : Re: INTERMOD


Rajiv Dewan [e-mail] wrote:

> For a while I liked the simplicity and ease of construction of using
> a parallel tuned shorted stub for rejecting intermod.  After trying it
> and computing the impedance it became evident that it did not do much.

> The impedance presented by the shorted stub is
>      50*Tan(157.345/147.345 * Pi/2) = -467 ohms (capacitative)
> in parallel with the antenna.  This will may not do much to attenuate
> the offending signal at 157.345.

I had similar experiences when I tried to help a new ham, who had
severe intermods on his HT from a nearby FM (100 MHz) station.
First we tried a shorted 1/4 wave stub at 145 MHz without much
help. By calculating the impedance in the 87-108 MHz range, it was
clear why it did not work as expected.

A new shorted stub tuned to 1/2 wave of the unwanted frequency was
installed and this helped a lot, not only reducing the intermods
from the BC-station but also reducing intermods from a pager system,
which is only 600 kHz above our repeater output frequency.

The only explanation I could think of is that the HT had an untunned
front end and by reducing the level of the strongest signal in the
pre-mixer pass band, the mixer was no longer driven into gain compression,
thus reducing other intermod products too.

To sum up, if you have harmfull intermods from a frequency you can't
filter out, try to locate the strongest signal within the pre-mixer
bandwidt, even if that strong signal doesn't cause harmfull intermods
to those frequencies you are using. Make a shorted 1/2 vawe stub for
this strong signal and check if it also reduced the harmfull interference
you are trying to get rid off.

Of course, notch filters are only useful in fixed installations,
they are hardly usable in mobile installations.

                Paul OH3LWR


------------------------------

Date: 27 Oct 93 07:03:21 GMT
From: elroy.jpl.nasa.gov!grian![e-mail]
To: [e-mail]

References <[e-mail]>, <[e-mail]>, <[e-mail]>
Subject : Re: Need Louder PC Speaker for Code Practice.

[e-mail] (Michael Ardai) writes:

>In article <[e-mail]> [e-mail] (Alan Bloom) writes:
>-Richard L Barnaby ([e-mail]) wrote:
>-: I'd like to add a simple speaker to an IBM PC that is externally
>-: controlled.  Just an op-ap, a pot, and a speaker?  Tap into the
>-: pc's speaker "jack"?

>Friendly warning - on most PCs, one side of the speaker is tied to +5.  If
>you do add an external speaker jack, make sure it is insulated from ground!

On my machine it is hooked to +5, as you said.  I mounted a 1/8" stereo
headphone jack on the plastic case, and hooked up a small 2.5k volume
control.  this allows me to use a set of Walkman-style headphones for
code practice (or game-playing), with a volume control.  It is also
wife-friendly (she frequently goes to bed earlier that I do).  With
earphones an amplifier probably won't be needed.

--
Mike Morris   WA6ILQ   | This space intentionally left blank.
PO Box 1130            |
Arcadia, CA. 91077     | All opinions must be my own since nobody pays
818-447-7052 evenings  | me enough to be their mouthpiece...

------------------------------

Date: Tue, 26 Oct 1993 16:05:25 GMT
From: sgi!fido.asd.sgi.com!odin!chuck.dallas.sgi.com![e-mail]
To: [e-mail]

References <[e-mail]>, <2ahetv$[e-mail]>, <[e-mail]>
Subject : Re: INTERMOD

Jeff's post on the qrp mailing group is correct, except for one
small point.  I'm not famous and I am not the fastest CW op in
the country or the world.  But I might be in the top 50%.  :-)

The Northern California QRP Club kit, called the NorCal 40, is
history.  They made 100 kits and sold all of them in a hurry.
This kit, designed by Wayne Burdick, N6KR, famous for his Safari
multiband rig that appeared in several issues of QEX, is small
and well designed.  I own one and wouldn't part with it.

So, come on down.  Don, tell the people what they've won......

73 es cul de k5fo/qrp    dit   dit

--
SIG
------cut here----------
Chuck Adams, K5FO - CP60 (clocked at 70+wpm 10/25/93 receiving)
[e-mail]

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End of Ham-Homebrew Digest V93 #85
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