Poor Performance of new Repeater...

[n4gix]

I have been having some poor receive sensitivity with my new Bridgecom repeater system, and I'm trying to narrow down just where I might take some action to improve things. Beginning with the antenna system seems a good place to start.

 

The antenna is a monoband Comet CA-712EFC mounted on a roof tripod on a 10' mast. With the combined height of the roof the base of the 8' antenna is at 52' AGL. The feedline is 60' of new 1/2" Comscope heliax, which terminates in a new MFJ-270 Lightning Surge Protector (Gas) just outside my office/shack exterior wall. It is brought into the repeater with 6' of RG-213.

 

I've done a sweep of the entire antenna system with a Surecom SA-250 Antenna Analyzer. The lowest SWR is 1.09 @ 461.275 MHz. At the receive frequency of 467.675 MHz the SWR is 1.32 (see details in next image) :

http://puu.sh/or8Lw.jpg

 

Averages on a single frequency, 10 pass sweep are shown in the next image. The camera didn't focus too well for this image, but it should still be readable.

SWR 1.32

Zx 50.1 ohms

Rs 57.5

jX -28

 

http://puu.sh/or9sa.jpg

 

The final image is at the transmit frequency of 462.675 MHz. This image is crystal clear so I won't transcribe the results. I cannot spot anything that stands out as a possible problem.

 

http://puu.sh/or9Kn.jpg

 

The last image is a composite trace of the duplexer. Note that the insertion loss at the receive frequency is -1.42 dB, which isn't all that bad! The reject of the transmit frequency isn't all that spectacular, but should be acceptable at -70.81 dB.

 

http://puu.sh/ora4W.png

 

The transmitter is limited to 20 watts output in an attempt to better balance the system. It is capable of a full 50 watts continuous duty.

 

Range testing with a 4 watt Motorola XPR7550 shows full quieting at 1 mile, 70% quieting at 2 miles, but unreadable at 3 miles. With the antenna height and average 5' portable/mobile height, I should be seeing around 10 miles for 70% HT coverage by my calculations.

 

Does anyone have any suggestions as to where next to look?

[coryb27]

i am shocked a company that markets repeaters with duplexes has to order one.... 

[n4gix]

i am shocked a company that markets repeaters with duplexes has to order one....

So am I Corey, so am I...

 

...I'm also a bit shocked that apparently I know more about duplexers (which isn't all that much) than the engineer who designed and built the repeater.

[coryb27]

This is the reason I run all Motorola gear

[Logan5]

This is why I didn't go with the internal mobile duplexor.

[n4gix]

UPDATE: I received an email from Ron this morning. The new duplexer was installed and...

With Squelch at 1, the unit stays locked in decode all the way down to 0.25 uV. The unit is putting out around 30-32 Watts. It looks very very stable and it's working like it should.

 

As I suspected, I believe the previous duplexer was the source of grief. I'm terribly sorry about this. I don't know what happened.

Unit has been shipped this morning and should arrive Thursday by end of day. I'm looking forward to putting it through its paces.

 

In the meantime, I've placed a bid on a Decibel DB4076W-A bandpass/reject duplexer to keep on hand in case it's needed. That with a receiver preamp and my Henry amp should solve any future issues I should think!

[Logan5]

UPDATE: I received an email from Ron this morning. The new duplexer was installed and...

Unit has been shipped this morning and should arrive Thursday by end of day. I'm looking forward to putting it through its paces.

 

In the meantime, I've placed a bid on a Decibel DB4076W-A bandpass/reject duplexer to keep on hand in case it's needed. That with a receiver preamp and my Henry amp should solve any future issues I should think!

Now your talkin....

[n4gix]

Okay, final update on this saga. I received the BCR-40U back yesterday afternoon, which was remarkably good timing since a fellow on eBay won the bidding on the unit in the picture above and I needed to box it up for shipment later today.

 

The new duplexer has made a not insignificant difference (note the use of syntax and qualifiers). While it is better, it's still not as good as I'd like, but it is as good as it's going to get with my limited antenna height and HAAT of a mere 22' on average.

 

I was awakened this morning by the sounds of two friends chatting on my repeater, which was a pleasant surprise. One was mobile (meaning his HT was connected to a mag mount antenna, and the other was just using his HT.

 

Eventually they switched to the "Munster 600" repeater, which with it's 4 bay DB antenna at the top of a 100' tower gave them both full quieting. Unfortunately that repeater's transmitter is slowly dying and gets quite noisy as it heats up.

 

I've got to route a new RG-214 jumper from the antenna's lightning protector into the shack and then I'm just going to leave it running until I find a new home for it.

[Logan5]

Did you win the Decibel DB4076W-A?

[coryb27]

I was concerned about this "the unit stays locked in decode all the way down to 0.25 uV" I have 16 year old MTR2000's that will hear down to .20uV and my XPR8400's still hear down to .18uV. Maybe that's just the spec on that repeater duplexer combo. Sounds a little def to me but again, that could be the best the receiver has to offer.

[n4gix]

The auction of the DB duplexer won't end for another 17 hours and a few minutes. I'm still the high bidder but have a max bid sufficiently high to probably get it. I'll keep my eyes on it just in case though. The specs on that model are outstanding -95dB reject, -1.2dB insertion loss:

http://www.repeater-builder.com/antenna/db/pdfs/db-4076-duplexers.pdf

 

I shouldn't need it, but I do have a 100 watt Henry amp I can drive up to 50 watts if necessary.

 

Corey, the mobile duplexer is undoubtedly the proximate cause of the performance, as it has about -2.5dB insertion loss. If I can at least get it to hear as far as it transmits, I'll be more satisfied. I just got home from shipping the dual CDM-1550 repeater to its new home in Boonsville, NC and was chatting with a fellow ham/gmrs user. He's running 4watts into a simple antenna up about 17' and was easily 95% full quieting into the repeater. He had solid copy from my 45 watt mobile up to around 10' miles from the repeater with the rear of my car (minor lobe) aimed at the antenna, so that's about what I expected. I could still copy the repeater at full quieting at 14 miles LOS from the repeater. Again, just about what we've projected.

[n4gix]

Update: I won the bidding war for the DB duplexer, but one SOB pushed the price up with six consecutive bids trying to hit my max limit, darn it! From $188 to $268 needlessly...

 

...ah well, it should arrive next Thursday.

[linboogy]

UPDATE: I received an email from Ron this morning. The new duplexer was installed and...

Unit has been shipped this morning and should arrive Thursday by end of day. I'm looking forward to putting it through its paces.

 

In the meantime, I've placed a bid on a Decibel DB4076W-A bandpass/reject duplexer to keep on hand in case it's needed. That with a receiver preamp and my Henry amp should solve any future issues I should think!

 I feel your pain in this. I have done everything wrong when I started my repeater. I still am to an extent. I noticed that you are getting a preamp? I started out with a Laird 4607 antenna that was not very good and was only 40 feet of the ground. I tried to cheat the system and installed an old Motorola Micor amp and a advanced receiver research preamp. Im not an expert by any means but I can tell you for sure that (height is might). I can also tell you my experience that seems similar to what you are doing is that the amp made it sound a little louder and better at penetrating the trees but made little difference for the distance the system would cover. The preamp actually hurt me more than anything. If you have even the slightest bit of desense, it will overload the RX. I still run it but I had to install an attenuator. I also got rid of the Laird 7db and installed a decible DB404-B that only has 3.8 db and it does circles around Laird and then some. I know you are running this out of your house but I would really consider a way to get the antenna as high as possible. I would bet even another 10 feet off the ground and a splice in your heliax would out do your new duplexer, preamp and amp

[n4gix]

The new duplexer is many times better that even a six can mobile duplexer, period. With both bandpass and reject that will dump -95dB, and only -1.2 dB insertion loss (compared to -2.2 dB loss with the mobile duplexer), it should boost my receive sensitivity quite a bit.

 

No splicing will be needed for the heliax either, since I seem to have overestimated how much I'd need by about 20' or possibly a bit more... <oops!>

 

The problem is that I cannot raise the antenna another 10' even without having to resort to guy wires.

[linboogy]

That's a shame on the antenna height. I was fortunate enough to find a tower on Craigs list cheap!

I cant hardly tell the difference between my Chines flat 6 pack that was tuned good versus my 4 oil can Celwave. It was only about 2 db of difference. Of course, I am not in a high RF site so there really is no need for the reject. I am curious how it works out for you