70's SCANNING QUESTION: Pre-amps and antennas??

[Archie]

Noticed many VHF and UHF scanner indoor/ outdoor antennas and a Pre amp in a 1973 Lafayette catalog.

Were these items really needed back then due to either weak general reception and/or low signal strength common with older radio systems??

Repeaters: If frequencies are changed from VHF to UHF or whatever, does it require an entirely new repeater or can existing repeaters be modified for new frequencies???


Many Thanks

 

[ScannerSK]

In my area back then most of the radio communications were in the VHF range and most of the scanners back then could handle an outdoor antenna without overloading. The higher the antenna the better the reception. These days our local police and fire are in the 800's which require a small antenna and also many of the scanners overload easily today so that may explain in part what you are seeing.

I believe most repeaters are kept to a rather tight bandwidth of reception to maximize sensitivity. Changing to a different band would almost certainly require a new board/equipment tailored for that frequency range.

Shawn

 

[wyShack]

Scanners have gotten much more sensitive since the 70's. At that time UHF was 'high tech' and 2-3 microvolts was great. Now it is more like .1. Unfortunately the selectivity seems to have gone downhill and is now the main feature to look for.

Most repeaters can 'cover' a 'band' (VHF (148-174) or UHF) although some models cover less. Moving a repeater in frequency generally would involve some time with a operator or technician adjusting the receiver, transmitter and other parts (like the duplexer) to the new frequency-the process is more than just dial and go. This allows the repeater to operate more effectively.

 

[scanmanmi]

Ahhh the 70's! Loved it.

Growing up in NW indiana my rig went nonstop. FBI, DEA, Chicago police, tv news crews, helicopters. All with a 1/4 wave on a 10' pole. No amp. In the 80's I was an EMT and our abulance freq was the same as some school bus company so faw away I never heard of it and they came in.

 

[ofd8001]

It's kind of a "On the one hand, but on the other. . . " situation.

"Back in the day" when VHF was used versus 800, the VHF signals used to go a long way. A VHF radio wave travels farther than UHF or 800 and the FCC allowed more powerful transmitters. So an outside antenna with or without pre-amp, might not have been "needed".

"These days" a lot more 800 trunking is used. The 800 radio waves don't go as far and the FCC reduced transmitter power so as to avoid frequency congestion.

So a guy could make an argument that an outside antenna is needed presently to pull in distant signals.

Having said that, "back in the day" a lot of state police/highway patrol agencies were using VHF low band. This was often an arrangement where the cars would transmit on one frequency to the district headquarters and the district headquarters would transmit to cars on an another. So as to "pull in" more mobile units, outside antennnas were helpful.

 

[DJ11DLN]

In my area back then, repeaters were few and far between. So you heard the base stations, but not the units in the field. If you wanted to hear the cars (forget the H-T's unless they were right on top of you), you needed something to get more gain. So people who wanted to hear both sides of the convo put up an outdoor antenna, added a pre-amp, or did both. We only had one repeater back then, the Terre Haute PD...everybody else was strictly Simplex (same freq or TX/RX splits, a lot of the latter). Hearing a unit in the field respond to a base at all on just the indoor telescopic antenna that came with the scanner meant that he was pretty close by. And living out in the boons as I did/still do, having those be that close was the exception rather than the rule. So you bought co-ax and an antenna to hang up near the TV antennas everybody had back then...or got creative with a coat hanger, and if done right that worked just as well for a fraction of the cost.