> "William E. Janes" <weja...@...> wrote: > A couple of points here if I may .. > 1) The narrow-banding kit sold by Communications Specialists > will narrow the receiver bandwidth, but will not take into account > modifications needed in the discriminator to deliver full rated > audio output.
Which in reality should be just the addition to, or modification of the trailing detected audio output stage. One might also change some of the discriminator part values to the more practical NB values. > Most later models use a discriminator IC that usually cannot > be modified. In addition to the IF bandwidth... The bandwidth should normally be limited or restricted by the IC's adjacent connected parts. In many cases just changing the typical IF crystal filters is not a complete narrow band conversion. An interesting look is how Kenwood does NB/WB in their TKR-750 and TKR-850 repeaters... electronically switching two IF sections after the first DB Mixer. > If you get what you need by just turning the volume up higher, > OK no problem... BUT... Some receivers kick in an additional or higher gain stage after the detector to restore (increase) the recovered audio level. In some cases where the receiver audio output is connected to an off-board device (a repeater controller audio input), the input audio level pot on the repeater controller board can/does often cover the difference for the required audio level to the controller. > 2) Narrowband transmitters have to be designed AND FCC type > accepted to work in the narrow-band mode. This has to do with > the overall emission envelope. Just turning down the deviation > circuitry to 2.5 kHz will reduce the amount of deviation, but > not the bandwidth of the emission overall. > Turning down the deviation is simply not a legal option. If > it isn't type accepted for Narrow Band it can't be used to > transmit. I really, really, really don't want to debate this... but I will say the responsibility of the transmitter operation is to the actual license holder. A converted one time type accepted radio operating with the proper deviation/bandwidth should be just fine. The question of its legality (as told to me by some officials) will probably never come into question. > There is a second caveat to turning down the deviation. since > a lot of transmitters encode either digital or tone squelch > injected without components (pots) allowing adjustment of > the level, the transmitter will be sending those at +\- 600-800 > Hz before narrowbanding. That equates to approximately 15% of the > available modulation. When you narrowband, the transmitter > will still be cranking out tone or digital signals that will > now be at about 30% modulation. Obviously this is gonna have > a horrible effect on transmitted audio quality. Doesn't read like you've heard many of the narrow band LTR (trunking) systems on the air with "red-hot" signaling deviation. Oh they are terrible... So the mod for the fixed value part deviation transmitter encoder levels (like the MSR-2000) is to change out one resistor. > Any radio type accepted after February 14(?) 1997 was required > to be capable of narrowband. In the case of the HT1000 for > example, several versions were type accepted before, and did > not include a narrow-band mode while those type accepted > afterward did. That is true for many radios from all manufacturers. > The only tried and proven method is too 'read' each radio, and > see what it can do. My experience is that most manufacturers > have not been too enthusiastic in trying to compile lists model > by model. I suppose I can understand that to a degree (ducking > the rotten tomatoes) as they have long since discontinued support > on a lot of these radios, and the task would be monumental > considering the number of individual model variations /numbers > for each individual series (HT1000 is the SERIES and H01RDC9AA3BN > is the model number for one specific radio with a unique > combination of options including frequency, band split, channels > etc). Agreed... However, if you have someone running around checking radio model numbers just to point out one specific radio model doesn't appear on a list somewhere... that person has way to much time on their hands. Especially since the radio may be converted and operating in narrow band. > In the case of the Midland ST1 radios, as I recall, the narrow > band units were special order options. The basic 'normal' radio > was not capable. Yep... they are old enough in time that narrow band was just an optional blip on the radar screen. > January 1, 2011 will bring some interesting consequences. On > that date it will be illegal to manufacture or import any radio > with a wide band mode. Like Digital TV... a cluster yet to rear it's full size ugly head. > There are some that say mixing w/n on the same channel will > be detrimental to communications, others say it won't be a > problem.. I guess we will see. The w/n mix on the same channel is not nearly the grief caused by conventional users (with high power transmitters) who simply don't monitor the frequency before transmitting. > Regardless, the adventure is just beginning... > Bill > N9SII Enjoyed reading and responding to your post Bill... Onward... > > I am one that says there won't be a huge flood of radios > > hitting the surplus market. Everything sold in the past > > 10 (or more) years has been narrow band capable right > > out of the box. > > Chuck > > WB2EDV Most of the "kick out radios" might be from Local/State Government Surplus... "because the radios are old", reportedly "no longer legal to use" in narrow band systems and the "techs can't fix them any more". A few years back I ended up with a large stack of Surplus Midland Radios from Oregon State Surplus. Turned around and put them back into service. Didn't have to fix a one... Your tax dollars at work... cheers, skipp skipp025 at yahoo.com www.radiowrench.com
