paluzzi@pioneer.arc.nasa.gov (Peter Paluzzi ZeroOne) (06/01/90)
This is a followup summary of the replies I received concerning
the Kenwood TH-26AT receiver interference problems I've experienced
recently.
Before listing the replies, I should mention that while tuning around
the 2m band with the external J-Pole attached I was able to determine
the the source of the interference was a nearby Radio Shack Room
monitor. I went over to my daughter's room (I said it was nearby didn't
I?) and turned the transmitter off and voila, the interference
disappeared. Checking the documentation on the room monitor I found out
that the frequency used was about 49 mHz. The third harmonic fell right
on top of the 147.570 mHz channel I was trying to receive. This still
does not explain the commercial FM program also heard. I suppose that
there could have been intermod with an FM broadcast station in the 98-99 mHz
range.
With the room monitor transmitter off, there is still some activity with
the S-meter even without a signal present. Also there are locations
while operating mobile where bunches of stations leak through on an
"empty" channel. Consequently I would still like to try a bandpass
filter or preselector of some sort. BTW, does anyone know of any
"brick" style linear amps with receive preamps/preselectors which are
more immune to interference than the TH-26AT?
Anyway, here are the replies I got, other than the phone calls. I want
to take this opportunity to thank all those who took the time to
respond. I was re-assured that I wasn't the only one who was having
this problem.
73s
Pete N6YEO
Peter Paluzzi, Sr. Graphics Analyst, Sterling Software, ZeroOne Group
Advanced Computing Facility, NASA/Ames Research Center
Mail Stop 233-3, Moffett Field, CA 94035
(415) 604-4589 paluzzi@ames.arc.nasa.gov N6YEO (FTS) 464-4589
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Begin Replies~~~~~~~~~~~~~~~~~~~~~~~~~~~~
From: miker%porkface2.wv.tek.com@RELAY.CS.NET
Helical resonators are nice cause they're small. IF you're not
strapped for space, use a full length resonator or a loaded one.
I had same problem with my IC3AT. Made a filter out of two soup cans
soldered end to end with copper pipe up the middle. Cap from top to
can to tune. Loop couple near the bottom. Worked like a charm.
Lots of articles exist in old QST etc for filters.
One of the major selling points for newer radios is wide frequency
coverage. Probably can't buy a good front end any more. Sigh!
miker
From: Skip La Fetra <fel@hpcuhb.cup.hp.com>
/ hpcuhb:rec.ham-radio / paluzzi@pioneer.arc.nasa.gov (Peter Paluzzi ZeroOne) / 10:18 am May 24, 1990 /
> I am looking for some information on the new Kenwood TH-26AT 2m
> handheld transceiver.
>
> When I disconnect the "rubber ducky" antenna and attach a roof mounted
> American Legion J-Pole at the QTH, I get a minimum S5 to S9 +30 reading
> across the 2m band on what sounds like background noise! Most repeaters
> still come in loud and clear although I seem to lose some of the more distant
> stations in this "noise" (receiver desensing?). I also noticed that some very
> channel). Again, with the rubber ducky, the errant S meter readings go away.
>
>
> Peter Paluzzi, Sr. Graphics Analyst, Sterling Software, ZeroOne Group
Peter:
I've noticed much the same thing with my (2-week old, I got it as a
"reward" for passing my Extra) TH-26AT, but it seems to affect the S-meter
only (i.e. the audio is fine, although I haven't checked for desensing).
The noise is definitely correllated with RFI, since it is most pronounced
in RFI-dense environments (San Francisco, next to pager transmitters, or
computer rooms, 'nuff said). It also comes through with the magmount
in my car, although I haven't noticed it much with the American Legion
J-pole at 25ft on the roof (QTH near Vallco Shopping Center).
I just ignore the S-meter in such sitiations, since I find I don't use
it much while "waiting for signal" anyway. Transmit audio & power level
seems fine (but boy does the sucker get hot at 5W with 13.8V in the
auto!)
Let me know if you find anything interesting.
- Skip KK6HK
From: stevew@wyse.com (Steve Wilson xttemp dept303)
In article <50106@ames.arc.nasa.gov> you write:
>When I disconnect the "rubber ducky" antenna and attach a roof mounted
>American Legion J-Pole at the QTH, I get a minimum S5 to S9 +30 reading
>across the 2m band on what sounds like background noise! Most repeaters
>still come in loud and clear although I seem to lose some of the more distant
>stations in this "noise" (receiver desensing?). I also noticed that some very
>wide band interference (10s of kHz) which carries what sounds like either a
>FM Broadcast Program or TV center about 147.570 (local ARES simplex
>channel). Again, with the rubber ducky, the errant S meter readings go away.
Your having problems receiving leakage from the cable company lines.
Over here in Milpitas that section of the band is almost unusable
due to leakage. Look at 145.25 roughly for the center of the
disturbance.
This particular problem isn't Kenwood, but rather the cable company.
73's de Steve KA6S
OO Co-ordinator, SCV section
From: mbutts@mentor.com (Mike Butts)
>From article <50106@ames.arc.nasa.gov>, by paluzzi@pioneer.arc.nasa.gov (Peter Paluzzi ZeroOne):
>
> While talking on one of the local repeaters, one ham encouraged me to get a
> helical resonator filter to limit out of band signals which may be causing
> intermodulation interference from other services. He further said that
> he uses one on his ht and hasn't had a problem since.
>
> Are there any suppliers of 2m helical resonators which can be used for both
> transmitting and receiving? If so any info on contacting them would be
> appreciated since I cannot think of another solution. I noted there was
> some discussion of helical resonators on this new category recently but
> I didn't follow it (I had neither license or ht at the time). Was this
> discussion archived or can someone summarize. BTW the Kenwood guy said an
> external helical resonator wouldn't work because it wouldn't be inside the
> ht!
I am also quite interested in this subject, but for a different reason. I just
got an OSCAR-13 setup on the air, and I've got real bad intermod on the 2 meter
receiver, being in a major city (Portland) with very strong broadcast and land
mobile. This is even though the rig (Ten-Tec 2510) has an LC-tuned GaAsFET
front end. I have an image from Channel 2 TV + FM broadcast = 2 meters, and
other loud ones that come and go very much like land mobile. By the way, my
IC-u2AT HT on a 1/4-wave magmount goes crazy with junk when I'm downtown.
I'm making a coax stub filter. Also, I have spotted the 3-section 145 MHz Toko
helical resonators in the DigiKey catalog, 1-800-344-4539, $22.92 each:
Toko 272MT-1006A, 2.8 MHz BW, 25 dB@+-6 MHz, 8 dB loss, DigiKey TK3506
Toko 272MT-1008A, 1.2 MHz BW, 30 dB@+-6 MHz, 8 dB loss, DigiKey TK3504.
I've ordered a surplus 2M coaxial resonator from Fair Radio. The June QST has
their ad for a 2-section tunable resonator with vernier dials, gold plating and
Type-N connectors, all for $30, so I figured what the heck. I am unsure
whether these filters will work correctly looking into the GaAsFET front end,
which I don't think is 50 ohms. Maybe I'll need a balun. I'm also unsure
whether the insertion loss will be too much for the satellite signals. We'll
see.
Finally, maybe it's just the preamp? I haven't had a chance to call Ten-Tec
yet to see what they say (I will), but I am wondering whether a different
preamp (maybe one with helicals designed in) will work better. Do any of the
commercial preamps (ARR, Landwehr) use helicals? Anyone know of such a
homebrew design?
Any discussion on the above, past or present will be appreciated.
73 DE KC7IT
--
Michael Butts, Research Engineer KC7IT 503-626-1302(fax:1282)
Mentor Graphics Corporation, 8500 SW Creekside Place, Beaverton, Oregon 97005
!{ogicse,sequent,tessi,apollo}!mntgfx!mbutts mbutts@pdx.MENTOR.COM
Any opinions are my own, and aren't necessarily shared by Mentor Graphics Corp.
From: tad@ssc.UUCP (Tad Cook)
In article <50106@ames.arc.nasa.gov>, paluzzi@pioneer.arc.nasa.gov (Peter Paluzzi ZeroOne) writes:
>
>
> When I disconnect the "rubber ducky" antenna and attach a roof mounted
> American Legion J-Pole at the QTH, I get a minimum S5 to S9 +30 reading
> across the 2m band on what sounds like background noise! Most repeaters
This is a common problem with using external antennas with a handheld
radio. These radios are designed to be used with the "rubber duck"
antenna, and anything else may overload the front end in some areas.
>
>
> Any information on how to deal with this problem other than returning
> the unit will be appreciated.
You might try the LC filter (144 or 220 MHz Bandpass Filter) in the
recent issues of the ARRL Handbook. It is on page 31-29 of the 1990
edition. This is not as sharp as some more exotic filters, but
is easy to build. It would be easiest to tune with a spectrum analyzer.
>
Tad Cook
Seattle, WA
Packet: KT7H @ N7HFZ.WA.USA.NA
Phone: 206/527-4089
MCI Mail: 3288544
Telex: 6503288544 MCI UW
USENET:...uw-beaver!sumax!amc-gw!ssc!tad
or, tad@ssc.UUCP
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~End Replies~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Peter Paluzzi, Sr. Graphics Analyst, Sterling Software, ZeroOne Group
Advanced Computing Facility, NASA/Ames Research Center
Mail Stop 233-3, Moffett Field, CA 94035
(415) 604-4589 paluzzi@ames.arc.nasa.gov N6YEO (FTS) 464-4589