[Mobile-Portable] IC706

[K0DAN]

----- Original Message ----- 
From: "K0DAN" <k0dan at comcast.net>
To: "Mobile-Portable Reflector" <mobile-portable at mailman.qth.net>
Sent: Wednesday, January 17, 2007 9:37 PM
Subject: Re: [Mobile-Portable] IC706


> Paul I hope your comments were indeed tongue in cheek. The "actual facts" 
> (a joke?) fly in the face of real world performance of FM in general, and 
> particularly with do-it-all rigs such as the 706.
>
> Most amateur rigs which do FM at 2M and 70M are extremely vulnerable to 
> adjacent channel QRM, desense, and storng signal overload at 15 khz 
> separation.
>
> Capture effect occurs after the front end filtering, which is basically 
> nil on most amateur and even commerical rigs. Squelch action (and PL/CTCSS 
> for that matter too) occurs after the filtering, so any strong signals 
> which get through the front end have already done their damage. This also 
> happens to include intermod. Even the old Motorola MICOR's, which had 
> about as tight a front end as could be found on any VHF/UHF radio, could 
> be blown away by too much signal too close to the on-center frequency. In 
> such cases, 15 khz spacing is not laughable, and capture effect doesn't 
> easily override anything.
>
> In the case of the 706 (and I do love this rig), the front end 
> capabilities on VHF, UHF, and even HF are fair to poor.
>
> If you were joking, sorry, I missed it...just trying to help those who 
> need assistance trying to enhance their operations.
>
> 73
>
> Dan
> K0DAN
>
>
> ----- Original Message ----- 
> From: "Paul Goble" <goblefam at swbell.net>
> To: "Mobile-Portable Reflector" <mobile-portable at mailman.qth.net>
> Sent: Wednesday, January 17, 2007 1:18 PM
> Subject: Re: [Mobile-Portable] IC706
>
>
> To whom it may concern,
>
> Putting my toungue securely into my cheek, the following actual facts 
> apply:
>
> The situation you describe is why God invented squech.
>
> Additionally, if you look at your Bessel functions, the energy out at 
> 16KHz is so low as to be laughable.
>
> On top of that, look at the FM quieting curve of any FM receiver and you 
> will see that the weakness of the FM "sidebands" that far out means, 
> clearly, that the FM capture effect will easily override any adjacent 
> channel "stuff".
>
> FM is, by definition, a strong-signal mode - who worries about weaksginal 
> characteristics of a strong signal mode?  Enquiring minds are curious - 
> HIHI!
>
> um, "FM" satnds for "forbidden mode", doesn't it?
>
> Another "gem":
>
> "REAL mobile antennas are omnidirectional!" (You ought to see the fire in 
> some folks eyes when I say this UNTIL they realize I'm kidding! - HIHI!).
>
> Enjoy!
>
> Paul ND2X/5
> http://www.nd2x.net/pix/new.jpg
>
>
> Gary Pearce KN4AQ <kn4aq at arrl.net> wrote:
> This is straying off-topic from purely mobile-portable, but I'd like to
> note that EVERY radio will be unable to completely reject strong signals
> from a 15 kHz adjacent channel.  That's because the actual spectrum used 
> by
> a properly operating narrow-band FM transmitter is 16 kHz, so there will 
> be
> some RF within the receiver pass band of even the tightest receive 
> filters.
>
> 15 kHz channel steps were a "necessary evil" when ham repeaters filled up
> all the available 30 kHz channels in metro areas back in the
> 70's.  Repeater councils in the eastern half of the country decided to
> "split" the channels to 15 kHz, and use about 50 miles of physical
> separation between repeaters, which theoretically makes the adjacent
> channel signal weak, to reduce the overlap problem.  Repeater councils in
> many western states (plus Michigan and Alabama in the east) bit the bullet
> and went to 20 kHz steps, requiring many repeaters to shift to a new
> frequency.  In the repeater band from 444.5-145.5 MHz, which was developed
> after many 15 kHz "split" repeaters were on the air, the entire country
> decided to go with 20 kHz channels.
>
> 15 kHz channel steps for simplex are a bad idea, since there's no way to
> provide physical separation.  3 miles between 50 watt base stations with
> good outdoor gain antennas is "nothin'."  Repeater owners debate to this
> day which plan, 15 or 20 kHz, works best for repeaters.
>
> Some receivers have narrower IF filters than others, so some get hit worse
> than others.  I'm not sure about the Icom 706.  You can see the specs in
> ARRL equipment reviews.
>
> Interference from paging and other out-of-band signals is a separate
> problem.  Adjacent channel rejection is provided by a filter in the IF
> chain.  "Out of band" signals are rejected by filters in the RF or
> "front-end" area of the receiver.  "Out of band" is a bit of a misnomer in
> most radios, as they are designed to receive signals across a wide
> spectrum.  They rely on tunable filters to keep from having the "barn 
> door"
> front-ends some hams complain about.  Some tunable filters are better than
> others, and out of band rejection is quiet variable between makes and
> models (Kenwood 733: bad.  Yaesu 8900: good).  Good, fixed band-pass
> filters are better than tunable filters and will stop all but the 
> strongest
> out of band signals cold.  But they also prevent you from listening to 
> NOAA
> weather, the local police and fire departments, etc.
>
> If you're bothered specifically by paging transmitters, PAR sells notch
> (and band pass) filters that will take out several common VHF and UHF
> paging channels while allowing the rest of the public-safety and business
> spectrum to pass through.  They go in your antenna line and can handle 50
> watts of transmit power, so you don't need switching.
>
> You can buy an "on channel" crystal filter for limiting the RF stage of
> your receiver to a single narrow channel.  It's a solution for some
> repeater problems, but not your home station.  And it won't keep out the
> on-channel RF from an adjacent 15 kHz signal.
>
> 73,
> Gary KN4AQ
>
> At 11:30 PM 1/14/2007, you wrote:
>>----- Original Message -----
>>From: "Larry Comden"
>>Sent: Sunday, January 14, 2007 4:44 PM
>>Subject: [Mobile-Portable] IC706
>>
>>
>>We just ran our club 2M simplex contest with 50 to 100 stations in the 
>>local
>>area.. I was mobile with my IC706 MkIIG. Strong signals on adjacent 
>>(15KHz)
>>FM channels were bleeding thru so badly that weak signals (the life blood 
>>of
>>a contest like this) were swamped. We were definitely not operating side 
>>by
>>side. My competitors were 3 or more miles away - some mobiling some fixed.
>>All stations limited to 50W.
>>
>>I've also noticed this effect in other locations near paging, radio and TV
>>transmitters. Does anyone on the list know what front end VHF/UHF 
>>filtering
>>is done in this rig?
>>
>>At home on HF I can use the RF gain to reduce the effect.
>
>
>
>
>
> ARVN: Amateur Radio//Video News
> Gary Pearce KN4AQ
> 508 Spencer Crest Ct.
> Cary, NC 27513
> kn4aq at arvidnews.com
> 919-380-9944
> www.ARVidNews.com
>
>
> ----
> Your Moderator: Dick Flanagan K7VC, mobile-portable-owner at mailman.qth.net
>
> ----
> Your Moderator: Dick Flanagan K7VC, mobile-portable-owner at mailman.qth.net
>
>