Monthly Archives: July 2008

Electronics Flea Market and Inline Amplifiers

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On Saturday morning I headed over to the monthly Electronics Flea Market over at the De Anza College parking lot.  My main reason for going was to pick up a few more of the $1 LED Keychain flashlights I got there a few months back, mine broke and Ellen wanted one.  Of course I wanted to check out the other “toys” there as well!

On the last row just as I was getting ready to leave I saw a brand new Mirage B-34 linear power amplifier sitting on a table.  They are hooked up in-line between a 5 watt handheld radio and the antenna, boosting the signal output up to 35 watts.  I’d never used one, but I know I could definitely benefit from some additional power.  Thought about buying it, the price was $40, then wandered away.

Before leaving, I pulled out my iPhone and checked Google and eBay for the prices of these things… saw prices ranging from $89-$120 for them, so $40 was a great deal, figured I could just sell it and make a profit.

Well, as soon as I got home I quickly talked myself in to at least “trying it out” which led to a long afternoon of playing with cables, connectors, and soldering irons.  I checked the max power consumption of my cigarette lighter adaptor for the car, saw it was good enough, so I soldered a lighter adaptor to the power cables on it.  Bought an antenna cable at radio shack, cut off the end, and soldered on another PL-259 to the end of it and got everything running.

I pulled out my second HT so I could test the audio differences with it on and off, and quickly learned about desensing a receiver… The HT would hear the “roger beep” style tone of the repeater, but I couldn’t hear the audio of my own transmission at all.  I even separated it from the antenna a ways and had it recording on my laptop so I could review the audio later, but still wasn’t able to get much.

It wasn’t until tonight when I was talking with Craig, W6WL, and he told me it was definitely just desensitizing the receiver, and after a quick test with him we proved both radios really were transmitting properly.  Sitting in my driveway with my mag-mount antenna he said he could receive me about 70% signal.  Then I flipped on the 35 watt amplifier and he said he could hear me at 104% hehe.  We chatted for a bit and my signal was quite strong to him, so long story short, I’m very pleased with my purchase!

In addition to that, while I was working on getting that wired up, I also did some additionall installation to get my RTrack APRS tracker wired up in a more permanent installation.  I’ve got it running to my old hershy kiss mag mount antenna.  We’ll see how often I make it to a digipeater now, and if I don’t get great results, I may toss the 35W amp inline for that transmitter for a little while and see if that brings about great improvement.

The tracker of course was primarily for the airplane, and I think the lower power of the unit will work just great.  Driving around this mountainous tree filled area with a small antenna some extra wattage might be beneficial!

Commercial use of Family Radio Service (FRS) Frequncies

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FRS RadioI work for a non-profit organization and over the years I have spotted more and more of our staff groups using Family Radio Service (FRS) radios as a part of their jobs. While I knew it is an unlicensed band, I also assumed that business use would have been prohibited since it was called the “Family” radio service.

I inquired with two of our staff who probably authorized their purchase and use to see if they knew the legalities of it, and both admitted they were not absolutely sure if it was legal or not, but also commented on the truth that they are such short range devices it probably would not cause any harmful interference to any other users of the frequencies.

I decided to do a few minutes of research which I shared with them, and now I also share with you in case your might also be interested.  The short story is… yes, it’s legal. 

The longer version follows:

The last sentence of the FCC introductory paragraph on the service is of most interest to us in this case:

Family Radio Service (FRS) is one of the Citizens Band Radio Services. It is used by family, friends and associates to communicate within a neighborhood and while on group outings and has a communications range of less than one mile. You can not make a telephone call with an FRS unit. You may use your FRS unit for business-related communications.http://wireless.fcc.gov/services/index.htm?job=service_home&id=family

It does appear in 2002 that a petitionReleased by the FCC as RM-8499 in WT Docket No. 95-102 to amend Part 95 of the FCC’s rules, ITA’s petition specifically seeks to prohibit daily business communications on FRS frequencies. was given to the FCC by the ITASource: http://mrtmag.com/business/industrial/radio_exclude_business_family/ requesting business use be prohibited from the frequencies, but with quick review of the FCC comments on that petition it looks like they dismissed it as a money-making attempt by business band radio manufacturers :-)

So for businesses who do use FRS as a part of their day-to-day operations I would just recommend always keeping in mind that this is shared radio spectrum, and if ever our use interferes with anyone else’s use of the frequency we need to be willing to move and not assert any “rights” to those channels. Personally I believe that if push ever came to shove, I think families and occasional users have more right to “family” spectrum than do businesses, but currently it is completely legal to use it.

My only other brief comment is that if you ever create an emergency communication plan or disaster plan, I recommend including FRS Channel 1 with Privacy Code 0 (no tone transmitted) as that frequency to be used for staff responding to such an emergency.

Channel 1 is casually recognized across the country as the emergency frequencyhttp://www.f-r-s.org/inside/homepage.htm, and turning off all privacy tones ensures more radios from various manufacturers would actually be able to communicate with each other since the tones selected don’t always match across brands.

If you have any additional information or correction to this post, please let me know in the comments, I’d be glad to update my text with any details you may point out.