Illinois State Police - Extenders on 151.16

[Starcom21]

I've previously reported ISP is using 155.505 again in southern IL with an NAC code that also displays the Starcom21 talkgroups.

Now, on I-55 near Litchfield (ISP District 18), I've found 151.16 in use as mobile extender. Previously this was a DNR/SOS frequency.

Detected 151.16 P25 NAC 204 (was carrying talkgroup 17000 traffic, which is D11 Dispatch A).

I'm not sure which unit was using it (whether an ISP, DNR, or SOS unit), but I did previously hear a D18 unit requesting an SOS unit for a traffic stop at Scale 82.

 

[scanman1958]

Nice info but I have to ask, how is a VHF frequency used within a 100% 700/800 MHz system? And was it a low power transmission similar to a walkie going through a car repeater? It sounds interesting.

 

[MikeyC]

Nice info but I have to ask, how is a VHF frequency used within a 100% 700/800 MHz system? And was it a low power transmission similar to a walkie going through a car repeater? It sounds interesting.

I imagine it's an in-car repeater taking the VHF input. In California the CHP used to use a VHF-Hi system as an in-car repeater for their VHF-Lo system. They're using a 700 MHz system to their VHF-Lo car radios now.

Here in LaSalle County the sheriff's use a conventional 800 MHz repeater to their MotoTRBO digital trunked radio.

 

[Starcom21]

ISP (at least some) have switched to Dual Band Portables (VHF and 700/800 MHz). Previously they were using 700 MHz extenders, but maybe they were interfering with 700 MHz sites?

Before SC21 they used some of these VHF frequencies (155.505 and some others) with their 42 MHz dispatch system. Base and Mobile radios were low band, portable radios were VHF. I think many cars had VHF radios, especially for ISPERN and DNR/SOS/Drug Task Force.

Nice info but I have to ask, how is a VHF frequency used within a 100% 700/800 MHz system? And was it a low power transmission similar to a walkie going through a car repeater? It sounds interesting.

 

[scanman1958]

Thanks that's what I was guessing. Did not know they switched to dual band handhelds. I remember those low band days and the VHF car repeaters. Those were some good times.

 

[N9JIG]

Before SC21 came along ISP had 42/44 MHz ("Low band") radios in the car and a VHF handheld to carry on the belt. One channel on the handheld was the "Extender" frequency, which was on 155.505 and transmitted PL (varied thruout the years and by district eventually). Channel 2 was 155.505 with no PL transmitted, this allowed person-to-person communications at a scene without activating the extender. Other common ISP VHF channels were also in the radios like ISPERN, HF4 etc. (Indiana State Police had a similar system and called F2 "Disable" as the lack of PL effectively disabled the retransmission to the Low Band radio).

When SC21 was instituted Downstate districts were provided "In Band" extenders that transmitted on specific 700 MHz. channels to activate the extender on the SC21 mobile radio. These were chosen since it was less expnsive than the dual-band radios at the time. These portables were also capable of using SC21 directly by themselves when in range. Most cars in the Chicago area (and perhaps Metro East as well) did not get equipped with extenders as they were not needed due to the better SC21 portable coverage.

Although I have been away for a while it appears that the In Band extenders were not working out so well and the price of dual-band radios have come closer to that of the single band. An APX7000 is not that much more than an APX6000 these days, even with the second band enabled.

The advantage of the dual-band (with VHF-Hi) radios is that in case of a failure of the SC21 system they can be used on legacy VHF channels as well. Most districts retained their old VHF-Hi channels after they switched to SC21 and some continued to use them for special situations such as details and outages. Now the troopers have portables on these same freqs.