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Author Topic: FT-8900 Front Alignment After MARS Mod Required?  (Read 32685 times)

Posts: 227

« Reply #60 on: February 26, 2009, 12:08:57 AM »

Jim and David,

Thank you for your polite and well thought out comments that added in a positive way to the discussion. In my initial post of the incident I forgot to mention that the OP even telephoned American Towers and got permission to deploy the repeater on their roof, and, telephoned the EOC and relayed the approving authority information. It is amazing how there are those that will attempt to rip apart such a simple situation where ham radio was used in a manner that positively reflected upon the hobby.

David mentioned that even if a radio was MARS mod'd, most hams would use an alternate method of communication first. You are correct and we have a specific policy. As volunteers we attempt to use our ham repeaters for assistance first, our simplex net second, then our type accepted radios to go direct to the fire department, and then cell phones (which are useless in most places up here.) We are required to have type accepted radios in order to come up on the fire channel and ham radio equipment cannot be used as a replacement for a type accepted radio. In spite of the rampant speculation and making up of "facts" we have specific policies in place that deal with this. Ironically, I am the one that put them into motion. A scoflaw? Hardly.

Jim stated that the OP (as well as myself) might actually be in a position that would bring about this type of radio use and you are correct. The OP, whom I am not naming deliberately, and myself are SAR team members attached to the Sheriff's Department, and we are also ARES-like operators attached to the Fire Department. In fact, our vehicles have either red and blue lights and siren and say Sheriff on the side, or just red lights and a siren and say Fire on the side. Hardly amateurish. Those of you that minimize us fail to recognize that many of us, myself included, are Fire Fighter II and EMT certified. I just happen to be a ham radio operators as well.

We are regularly in situations that some of you consider non-emergencies that in fact, cause an antire crew to roll out. Some of you are blatant idiots and I pray that you never go camping or hiking. We've had 11 feet of snow already this season and numerous lost persons. We've had numerous avalanches that closed down a key road through the mountains with vehicles trapped in the slide zone and rescues that took place. None required the use of ham radio. But what do we know about radios. We just studied, got our tickets, and upgraded to at least General Class. Our own fire chief recently wrote:

"The mission that you provide to our communities regardless of government affiliation (city or county) is irreplaceable. Local government simply can't afford to replace the services you provide and we cannot supply the radio network you tirelessly maintain.

The funny part is that we know our systems will fail. With our high tech 800 MHz and VHF radio networks in place, microwaves, cell phones, satellite phones and any other type of communication devices available, we know they are all subject to failure. Your mission to support emergency communications is vital for our operations during disasters and to help us return our citizens to their normal lives after disasters."

Our fire chief is now ready to take the Technician Class test, he's that impressed. He takes great joy in saying, "Call the hams in. They'll get it going." And we do.

We're proud of what we do.

This incident isn't covered in a policy. It fell into the "Crap happens" category. Crap happening is covered in 97.403.

Posts: 618

« Reply #61 on: March 10, 2009, 07:21:04 PM »


On Robert's QRZ page:
"I first became involved in radio back in the 70's, but after returning home from military service I concentrated more on commercial radio repair and installation for a bit."
Sounds to me as though you could answer your own question.

As for those that started this fiasco:
Bet you're real proud of yourselves.



Posts: 227

« Reply #62 on: March 10, 2009, 07:58:16 PM »


I asked a serious question and was attacked needlessly. No, I did not have the answer already or I would not have asked. THIS is why we lose hams every year and don't fill their places with young talent -- they don't want any of this crap any more than you or I.

With commercial Yaesu's the software retunes for optimum performance based on frequencies loaded. But the 8900 doesn't have that kind of software and my original question remains unanswered. If you don't like the soap opera, why did yu join the cast?

Posts: 618

« Reply #63 on: March 10, 2009, 09:02:53 PM »

"I asked a serious question and was attacked needlessly."
Absolutely agreed but to keep it going for this long???

I'm not going to wallow into this fiasco that should have died two years, five and a half months ago but to address your original question:

First of all, by cutting the jumper or diode or adding one or whatever was required to extend the synthesizer range, you are only extending the range of a divide by "n" counter which is the usual way of programming the frequency in a non DDS synthesizer.  You are not affecting any tuning specifically by doing this.  However, in addition to dividing the VCO's output to the phase comparator by a specific number mathematically related to the desired frequency, the uproc also sets a reference voltage (usually through a DAC) which tunes varactors in the receiver's front end.  Now, as long as this output voltage tracks the selected frequency set by the synthesizer, the radio will work fine.  But, when you select a frequency too far from the normal operation of the specific radio, this tuning voltage can no longer follow the synthesizer's frequency and tune the front end stages.  At that point, RF sensitivity (and, no doubt, selectivity) suffers and you lose range.  The radio CAN USUALLY be tuned to compensate for the loss at one point but will lose sensitivity at another point depending on the specifics of the particular circuit.  It's difficult to compare various models and, even, specific radios of the same model due to component tolerances.  The example I've given is one of many ways to accomplish a broad band receiver and varies widely between makes and models but it is one of the more common ways in inexpensive ham gear.

"With commercial Yaesu's the software retunes for optimum performance based on frequencies loaded. But the 8900 doesn't have that kind of software..."

The principle is the same.  These operations are performed through FIRMWARE, not the programming software, which ham radios have as well.  Just picture "tuning" the radio with the tuning knob instead of RSS (tm)  Doesn't matter what you use to set that number (corresponding to the channel freq), the result is still the same.

NOW the experienced hams among you can pick my explanation all apart (and probably will) because I left a lot out and shortened other things to try to keep this post short(!!!)  Don't bother.  I am only trying to explain something, not write an engineering treatise.  By the way, DDS is the same, only different!

Posts: 3

« Reply #64 on: March 20, 2013, 10:38:02 PM »

My FT-8900 arrived <glee> and after testing it briefly locally I performed the MARS/CAP mod required for our SAR team. Went fine, but I'm clearly blind as a bat these days. At any rate, today I had and opportunity to go mobile. I live in a mountain area and signal strengths vary somewhat. I noted that receive on the 8900 seemed weak using the same mag mount antenna that previoulsy was connected to my VX-7 (also with the MARS/CAP mod.) I don't have anything to compare against and no service monitor to check sensitivity.

Does the 8900 need to be realigned after this mod?

Okay, so this is an old post, but I thought I'd join in on the fun!  What you are talking about is a wise choice and I for one applaud your efforts in helping the community.  However, if you look at my FCC history, you will see an administrative action filed and ultimately dismissed. Here is why.   I was in the mountains.  My friend and I were shot at and returned fire.  Not able to call 911, I used my ham to contact the local sheriff.  Spoke with dispatchers and responding LEOs.
After the smoke cleared I was contacted by the Sheriff as well as FCC.  I had to explain to both of the about the rules of using whatever frequency and power, etc ect.  Once they had a clear understanding of that, they moved on to the other topic.  "having out of band fqs programmed in the radio for transmitting".  Apparently that in itself is a violation.  Luckily, I was able to rattle off 6or 7 other agency fqs, tones and offsets.  This showed them that I knew the fqs and was able to face program my radio.  Problem solved.

Good luck and 73s.  Keep up the work!
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