Skipp- Everything you say below is correct. But I would still argue that it simply isn't worth it to do all the modifications you suggest to a scanner when you can pick up a good receiver from a Motrac/Micor/MastrII/MastrPro for $25 at a hamfest or ebay and have a receiver that is still better than the modified scanner.
------ Original Message ------ Received: Sun, 17 Aug 2008 04:15:47 PM PDT From: "skipp025" <[EMAIL PROTECTED]> To: [email protected] Subject: [Repeater-Builder] Re: Scanner as repeater receiver? > I posted the following reply to the group on Aug. 13th > and it doesn't appear on the group (although Jeff received > my email direct). Here it is again to the group... > > Re: Re: Scanner as repeater receiver? > > Hi Jeff, > > There are some conditions where a scanner receiver could be > modified for use in repeater and base station applications. > > First you can throw away the label/word "quality"... it's all > about the actual circuit design and construction of the scanner > in question. > > Scanners as a general rule are very, very, very wide frequency > range receivers with very modest/light/non existent front-end > protection, which often leads to other problems you don't > normally run into with true communications grade receivers. > > **** > > Some scanners have pretty much the exact same back-end circuit > design (with minor differences) as kit communications receivers > made and sold for repeater operation. Let me try to quickly talk > about one common example. > > Some older crystal controlled scanners make semi fair repeater > receiver candidates with the following considerations: > > 1. The receiver front-end (pre-selection) should be improved. > In most cases the receiver front-end is not usable as-is/found. > There are also cases where the antenna input jack is not a true > 50 ohm antenna port. The more practical fix is improve the receiver > front end protect with an additional filter or seriously modify > any usable original circuit. High-Q Helical front-end circuits > are/were made and sold, which do work for the cause. I used to > like and use the HRA units sold by Hamtronics, but they no longer > offer that exact product. Still the HRA Preamp Pre-selector Manual > is available on the Hamtronics web-site if you want to see an > example. > > 2. The receiver IF Filter might be wider than the best value for > your application. > > If the scanner IF filter (often referred to as the Crystal Filter > but not always a crystal type device) is really a generic/default > wide value chosen for typical consumer grade scanner operation. > You/I/we can often replace the stock IF Filter with much improved > after-market IF Filter products sold by Comm-Spec and other sources. > > 3. The Squelch circuit might not be the best operational situation > for your application. > > Scanner receivers more often than not have a very mushy consumer > grade squelch circuit, which is sometimes easily modified with > a common parts value changes. Since many scanners and some > communications receivers have similar trailing circuits... it's > not hard to find a very similar squelch circuit layout to > copy into your application. > > 4. You would need to "tap into" the receiver to obtain audio > sources and usable COS/COR logic levels. Not hard and that > information is available as mentioned just above. The IF and > Audio Sections of a receiver are fairly easy to deal with > when you have a circuit diagram in hand and the resources > of this group available to help you. > > 5. Some synthesized (programmable) Scanners might not have a > stable enough VCO operation for use as a serious receiver. You > could often hear hum, warble, noise and Selection D (all the > above) in the recovered audio. Once again since many scanners > and some communications receivers have similar circuits, it's > not super hard to find a comparable VCO layout/circuit to help > improve your receiver operation. It would be more of a question > of how practical all the parts and effort would be. > > Another issue is how some synthesized scanners lock/track onto a > received signal using common AFC (automatic frequency control) > operation. Sometimes you might be required to defeat or modify > the AFC Circuit operation. > > I have seen cases where synthesized scanners were easily stable > enough to use as repeater receivers when properly modified as > mentioned above. Just a generic overview of what you might be > up against when trying to use a Scanner as a candidate for a > repeater receiver. > > Hope this helps a bit... > > > cheers, > > skipp > skipp025 at yahoo.com > www.radiowrench.com/sonic > > > > "jstechnicalservice" <[EMAIL PROTECTED]> wrote: > > Has anyone used a good quality scanner as a receiver for > > a repeater and if so, how well did it work? I'm contemplating > > a Radio Shack PRO-2055 as it seems to have good receive > > capability and picks up signal better than some of our > > mobile radios. > > Jeff Skaggs > > Concord-Greene FD > > > > >
