Newly Purchased ICOM FR4000

[SDS]

Hello Wizards of GMRS,

 

I have been bitten by the GMRS bug and have even gone as far as to purchase a repeater (ICOM FR4000).

 

Currently, I am using a Comet C-712EFC on a 20 foot mast with 50 feet of DXE-400MAXDX050 coax.

The issue I am having is the repeater works fine within a 1/8 of mile, but beyond that I only hear the repeater kurchunk (nothing is transmitted).

 

I have contacted the seller and they said that maybe the duplexer wasn't tuned correctly and offered to reprogram the repeater.

 

Have any of you run into something similar or have any other ideas what might be the problem?

 

Thanks in advance!

[berkinet]

...The one weak link you have in my opinion is that knock-off LMR-400 coax cable. ...

Do not use LMR 400 between the duplexer and your antenna. There are reports that the new versions of the top quality cable no longer are subject to the bi-metallic problem of the old versions. But unless you are buying a cable you know to be OK for use in a repeater, stay away from LMR 400 altogether.

 

Simply put, if you cannot be heard by the repeater when you are 1/8 of a mile away, why worry about a DB difference in signal loss. You have much bigger problems to solve.

[tweiss3]

All components appear to be excellent choices.

 

1) So your 10' antenna is on top of a 20' mast, for a total height of 30'? or is the 20' mast on your roof? Many places, houses can be 30' tall and would be blocking your signal. 

 

2) If the seller is offering to reprogram the duplexer, I'd let him give it a look.

 

3) What frequency are you using? Have you checked to see if there is local interference on this channel? Is there FRS using adjacent frequencies that could be causing problems.

 

All three items could simple or difficult, but need to be addressed.

[WRAK968]

Its the duplexer. I have an antenna about 20 feet up and had the same issue until I replaced the duplexer. Easy way to tell is to turn the repeater to low power (This is one of the things that increased range for me) If you get a little more range then you know for sure, but of course this doesnt make up for the duplexer being installed backwards, or if it is way out of tune.

As you have just started I do not know your skill level so Ill explain what the problem is:

A duplexer separates the transmitter and receiver signals, thus anything the transmitter is putting into the antenna shouldn't be able to get to the receiver. When the duplexer is damaged, out of tune, or installed improperly, the receiver can still hear local signals through general proximity and even by using the jumper as a sort of antenna. This would be why you can use the repeater when you are close up. However when you leave the signal fades away, just as it would if you placed a portable next to the repeater.

The transmitter doesn't help as its signals also overpower any other signals and causes what we call "De-sense" which is a situation where the transmitters signals are blocking any other signals from getting into the receiver. De-sense usually occurs when no or a slightly out of tune duplexer is used. It would seem from what your explaining that the RX side of the duplexer is out of tune causing your de-sense.

The other cause would be crapily built duplexers. China has flooded the market with these stupid things and I've been a victim of their lower prices. Since I upgraded to a DB BPBR duplexer I have not had an issue with de-sense.

Check to see what duplexer the seller has sent you. if you have a flat-pack (Notch type duplexer) perhaps he can upgrade you to a BPBR (Band pass/Band reject) type duplexer for a small fee. Never hurts to ask and made a world of difference for me.

[Radioguy7268]

I'd be concerned with anyone who let a repeater go out the door & didn't check the duplexer the first time. If he didn't get it right then, what's the chances he's going to get it right this time? It sounds like you bought it from the seller as a working package.

 

Before you send it back - make sure you've got the cables hooked up correctly  - the High side should be to the Receiver, low side for the Transmit. I've seen too many jumpers crossed up not to ask.

[gortex2]

Also connectors ? N ? Adapters ? What cables are on the duplexer inputs from the repeater  ? 

[SDS]

Thank you all for taking the time to reply.  As this is all new to me, I really appreciate it

 

As an update, I took the seller up on his offer to check the duplexer.  The seller tested the duplexer and I was told the duplexer is tuned correctly.  When the duplexer was sent back, I reinstalled the duplexer and made sure all the connections were correct.

 

The repeater frequencies used are not active frequencies in this area.

 

At this point, the repeater will work on occasion (repeater worked well with a very clean signal little over 4 miles out) and the later when I tried I just heard the repeater kurchunk (nothing is transmitted).  Then, when I get about 1/8 mile from the house I can hit the repeater again.

 

There is no real pattern when the repeater works and when it doesn't.  I leave the repeater on (don't turn it off at night) and the repeater doesn't appear to be overheating. 

 

Do duplexers go bad and if so is what I am describing a symptom?  If not, has anyone experienced anything similar?  Any other ideas?

 

Thanks again for you time!

[Jones]

I still think you are describing de-sense.  The one weak link you have in my opinion is that knock-off LMR-400 coax cable.  I also still wonder what you are using for jumpers between the radios and the duplexer.  Cheap CB coax jumpers will NOT work for that purpose.

[SDS]

Gentlemen,

 

Thanks again for your reply and patience with this rookie.  I really do appreciate it

 

I called the company I bought the cable from and they said ... yeah, the guy you spoke with shouldn't have told you to buy that cable .. argh.
 
At this point, what type of cable would you recommend? 
 
Also, the  jumpers between the radio and the duplexer look like cheap CB coax jumpers.  I would post a picture here, but don't know how. What connectors would you recommend?

 

Thanks again!!

[Radioguy7268]

Half the time I see people blaming a "bad duplexer" - it turns out to be the junk cables connecting the repeater to the duplexer. You should be using a good quality double shielded cable like RG400 with the correct ends (no adapters!).  Type N is the preferred connector, but if your repeater or duplexer has different connectors, you need to work with those.

 

Try someone like these guys  - avoid the cheap "tin" or nickel plated connectors - there's a few USA based sellers with similar products: https://www.ebay.com/itm/6-10-RG400-M17-N-Male-Clamp-Jumper-Silver-coated-RF-cable-USA/131269263466

[Jones]

...You should be using a good quality double shielded cable like RG400 with the correct ends (no adapters!). 

NOTE: RG-400u is NOT the same type of cable as LMR-400 or DX-400.  RG-400u is a smaller diameter, double-shielded cable, the size of RG-58u, for use as jumpers in a repeater system, or internal radio connections where signal leakage would be a problem.

 

LMR400 from TImes Microwave and its clone, the DX400 cable from DX Engineering is a larger cable, the size of RG-8u, that is supposedly rated for use up into the 400 MHz range with low-loss. It has its uses, and can be great for a GMRS base station, but not a repeater where it has to transmit and receive at the same time - that is where the trouble starts.

 

RG-400u, and its larger cousin RG-214u are Mil-Spec double-shielded, silver plated cables, specifically designed so that the signals between two closely-ran cables will not cross-talk into one another.  That's what you need is a repeater system.

[Jones]

Another pro-tip: Do not tape or tie-wrap the RX and TX cables together going into your duplexer to make them look neat and tidy.  Keep those cables as far apart as possible.  At UHF, those cables should also be a foot long or less, unless you are using Heliax or Superflex coax. (If you can afford them, pre-made Andrew Superflex jumpers would be even better than RG-400)

[berkinet]

BTW, it has not been directly suggested, but one possible explanation of your problem could be a very poor connector/cable connection that is actually radiating RF and desensing the receiver.

[Jones]

As for a recomendation for cable between your duplexer and your antenna, if you are going 100 feet, you really shouldn't go anything less than 1/2 inch semi-rigid transmission line, or "Hard-Line" such as Commscope/Andrew LDF4-50a Heliax.  That can be found for under $3 per foot. Expensive, but owning a repeater isn't cheap.  We've mentioned that before in other areas of this site.

 

An even better solution would be to jump up to 7/8 inch line, such as LDF5-50a, but that gets you close to $8 per foot.

 

In my opinion, Commscope/Andrew is the best, but there are also less expensive transmission lines out there, such as Eupen, which you may find at a better price.  Make sure to buy the correct connectors for whatever brand of transmission line you buy.  Those connectors are not interchangeable between brands or types.

[berkinet]

One thing to keep in mind is what kind of range you will actually need.  For example, if you live in the center of a valley surrounded by tall mountains 5 miles away in every direction, there is no point in spending a lot of money for extra power or to reduce cable loss.  For example 20 watts into a 6db loss feed line might still cover the entire area quite well.

 

Also consider the criticality of the system. Is this just for fun and maybe a backup for a cell phone. Or, is this your sole means of communications. Once you answer that question, budget accordingly.

 

And, also step back a bit and look to see if there is another way to organize your installation. For example, instead of locating the radio 50 feet from the tower, can you create a small enclosure and house the radio at the base of the tower.  A good quality weatherproof garden shed, or even a large tool-box, might cost a lot less that 100 feet of high-end feedline.

[n4gix]

If there is anyone close to NW Indiana who wants of needs 1/2" Andrews FSJ4-50B heliax, let me know. I have 678' of it which I got for free, so I'll be happy to share. I only need about 300' of it myself.

 

The connectors are inexpensive. I paid $19.95/each for two of them.

 

F4PNMV2-C Type N Male for 1/2 in FSJ4-50B cable, Knurled Nut, Captivated Pin, MFR: AndrewOne source for male N connectors: https://www.rfparts.com/connectors-heliax/connectors-12heliax/12helicon-fsj/f4pnmv2-c.html

https://puu.sh/G8TuS.png

[lougasp61]

Very old thread but in case anyone else has this issue, I would suggest that you check to see if you have your antenna connected to the Tx/Rx connector and not the Rx connector, assuming you are using a duplexer.

[gortex2]

That also depends on if the repeater has the internal duplxer or internal. Mine is internal and the TX RX Port is the TX RX Port. The manual shows the modification. 

https://www.manualslib.com/manual/867444/Icom-Ic-Fr3000-Series.html?page=24#manual