Need Help with PRC-128 Problem

Radio Telephone and Telegraph Transmitting and Receiving Equipment
Post Reply
User avatar
FKAM
G-Staff Sergeant
G-Staff Sergeant
Posts: 60
Joined: Mon Oct 17, 2016 2:41 pm
Location: Utah

Need Help with PRC-128 Problem

Post by FKAM » Tue Aug 07, 2018 7:43 pm

I have a PRC-128 that I think has issues, but I am unsure if it might not just be operator headspace and timing. It has a high band RF/IF module in it, but the radio only allows me to enter low band frequencies. From what I have read in the manuals the radio should automatically recognize which module is installed and allow the proper freq's to be entered. Does anyone know if this is correct? If so, I definitely have problems. Or does someone know of a way to switch the way freq's are entered? When I enter any of the low band freq's, the antenna match fails in any position, which would make sense with the High Band Module installed. I didn't read the manual word for word and just focused on the parts that I thought applied. Military manuals always seem to leave me lacking the information I need and I spent 42 years in the Army. Any info someone might be able to pass along would be much appreciated.
Thanx
Fred KI7YCK
AoUS Retired


snock
G-Sergeant First Class
G-Sergeant First Class
Posts: 77
Joined: Fri Jul 30, 2010 9:11 pm
Location: Loudonville, Ohio

Re: Need Help with PRC-128 Problem

Post by snock » Fri Aug 10, 2018 7:46 am

It sounds like it's fine. The antenna switch needs to be on the 50 ohm position for all frequencies when using the high band module. As far as the frequency goes, you need to mentally put a "1" in front of what's entered on the display. There aren't enough digits to display the full high band freqs.
1989 M998
1964 M151 w/1967 M416
1986 M1009

User avatar
FKAM
G-Staff Sergeant
G-Staff Sergeant
Posts: 60
Joined: Mon Oct 17, 2016 2:41 pm
Location: Utah

Re: Need Help with PRC-128 Problem

Post by FKAM » Fri Aug 10, 2018 10:29 am

snock
Roger that, I knew about the 50 ohm setting but had no idea about the "Mental 1 before.." concept. You would think that would be pointed out in the programming sections of the manuals (might be tho, and I just missed it.). I'll give it a try. and see what happens.
Thanx
Fred KI7YCK
AoUS Retired

User avatar
FKAM
G-Staff Sergeant
G-Staff Sergeant
Posts: 60
Joined: Mon Oct 17, 2016 2:41 pm
Location: Utah

Re: Need Help with PRC-128 Problem

Post by FKAM » Fri Aug 10, 2018 12:29 pm

snock
Hot Dawng success! That was it. Thanx for the info. But....I have another question if you don't mind. The squelch is always open. According to what I have read in the manual and what little I remember from using these, long ago that it should automatically squelch unless you pressed and held the squelch disable button. Is there another thing I am missing here?
Thanx
Fred KI7YCK
AoUS Retired

User avatar
pvtwinger
G-First Sergeant
G-First Sergeant
Posts: 133
Joined: Thu Oct 03, 2013 5:21 am
Location: USA

Re: Need Help with PRC-128 Problem

Post by pvtwinger » Tue Aug 14, 2018 3:33 am

The Squelch may need adjusting. I think there is a screw on a pot on the module to adjust the Squelch threshold.

Also, you can easily determine which module is installed. When you turn it on (and or push the Squelch button I think) if the high band module is installed the display will read HI, and if the low band module is installed the display will show LO.
1979 AM General M151A2 "Barstow"
1972 AM General M151A2 (Sold 2020)
1987 AM General M1026 HMMWV (Sold 2012)
1986 Chevy M1009 CUCV Blazer (Sold 2006)
2 M416 Trailers (Sold)

K3YYZ

snock
G-Sergeant First Class
G-Sergeant First Class
Posts: 77
Joined: Fri Jul 30, 2010 9:11 pm
Location: Loudonville, Ohio

Re: Need Help with PRC-128 Problem

Post by snock » Tue Aug 14, 2018 6:17 am

Yeah, either your squelch needs adjusted or you are receiving enough noise to break it. You might try another frequency before you start messing with it. When using the high band module the squelch is received signal strength based and not tone based like is used on the low band module. Actually, that may be wrong, I can't remember. The low band module might also use RSS squelch as well but transmit the 150Hz tone for PRC-25/77 and VRC-12 compatibility.

PRC68.com is a good site to peruse for these radios.
1989 M998
1964 M151 w/1967 M416
1986 M1009

User avatar
FKAM
G-Staff Sergeant
G-Staff Sergeant
Posts: 60
Joined: Mon Oct 17, 2016 2:41 pm
Location: Utah

Re: Need Help with PRC-128 Problem

Post by FKAM » Tue Aug 14, 2018 7:30 pm

Roger all, snock & pvtwinger,
Thanx for the info. I'll try different freqs before I start messing with things. I was wondering if the "HIGH" I saw meant High Band. I knew there was a high band installed. I had opened it up to see what was inside for a module. I also have an issue of the internal mike/speaker not going silent like the manual says when you attach a handset. So It looks like I have some more experimenting/learning to do. I have found that more often than not it's me not understanding how to work things. I knew about PRC68's web site. It has been my go to site for all things mil radio for a while now. Couldn't find anything about my problems on his site, one of the reasons I turned to this place for help. Just wish more of his links were still functional. But appreciate you telling me.
Thanx for all the help!!!
Fred KI7YCK
AoUS Retired

snock
G-Sergeant First Class
G-Sergeant First Class
Posts: 77
Joined: Fri Jul 30, 2010 9:11 pm
Location: Loudonville, Ohio

Re: Need Help with PRC-128 Problem

Post by snock » Wed Aug 15, 2018 4:50 am

Try a different handset. There's a circuit that mutes the speaker on these when it detects a minute current through the handset speaker element. I've certainly had a few faulty H-250s over the years.
1989 M998
1964 M151 w/1967 M416
1986 M1009

User avatar
FKAM
G-Staff Sergeant
G-Staff Sergeant
Posts: 60
Joined: Mon Oct 17, 2016 2:41 pm
Location: Utah

Re: Need Help with PRC-128 Problem

Post by FKAM » Wed Aug 15, 2018 7:37 am

Roger that, I thought that might be the issue when I first noticed it and I've tried a couple, no change. I plan to try a few more. All the handsets I've tried fit pretty sloppy so I night have a worn out connector on the radio.
Thanx
AoUS Retired


Post Reply

Return to “Radio's and Communications”

Who is online

Users browsing this forum: No registered users and 39 guests