A question for anyone more qualified than I. I have a http://shop.ebay.com/i.html?_nkw=di...=CR8900&_osacat=0&_trksid=p3286.c0.m270.l1313CR8900 quad band antenna mounted on my pickup truck which is connected to a Yaesu FT-8900 in the cab. A couple weeks ago I noticed that one of the repeaters which usually comes in at full quieting had a lot of noise on it and barely registered on the signal meter. When I also got a bad signal report on another nearby repeater I suspected that something was up. When I got a chance this past weekend, I checked the VSWR and it is 1.5 or less on !0 meters, 6 meters and 70cm but is around 8 on 2 meters. I removed it from the truck, cleaned out all the joints and made sure that the set screws had not loosened. there was as little moisture in the base coil but everything else seemed fine. when I rechecked the SWR it was still high on 2 meters. Adjusting the 6/2 meter element does not make much difference in the 2 meter SWR either. Can it be a bad coil? If so, how would I check it with out any test equipment other than an SWR meter and why wouldn't the 6 meter SWR be affected? Any input will be appreciated before I spring for another antenna (looking at a Comet SBB15).
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CR8900 funkyness
- Thread starter Nursecosmo
- Start date
Never owned that particular radio or antenna. But if it was me having this problem, I would immediately suspect either the connector or a flaw with the coax.
The antenna itself probably isn't a problem - unless you might have smacked it hard somewhere down the line.
The antenna itself probably isn't a problem - unless you might have smacked it hard somewhere down the line.
Hard to say why it doesn't haven't a problem on 440mhz and does on 144mhz.
But since it is having a problem with VHF or UHF - which are prone to coax and connector maladies due to the high frequency being used - I will still look there first.
Can't get a real diagnosis without a careful examination first.
Routing coax in a car can create dilemmas for coax. If it gets pinched, flattened, torn, stretched, frayed, or it has an sharp bend or kink that deviates the distance of the core conductor and the shield inside - the coax is compromised.
If the coax connector is a poor quality crimp-on type rather than a solder-on type, it can also be considered suspect too. Even though they are mfd with this kind of crimp-on connector; they have histories of being less than flawless and have a higher failure rate than solder-on types.
Suspect everything; and then eliminate each possibility until the fault is found.
After that, I would go over the antenna itself with the same thought in mind. You might consider taking it completely apart - if possible - and thoroughly cleaning it too.
The eHam review on this antenna isn't so great. I would read it here:
http://www.eham.net/reviews/detail/3478
You might consider running a duplexer in the output of this radio and using two antennas; one for 2m/440mhz and another for 10m/6m (that is - if such a duplexer exists!). Seems that many people that bought this radio are stuck with antenna tuning problems with it. That is why I bought a Yaesu FT-8800R instead of the 8900 - read the reviews on it. But if you had this antenna tuned properly for all four bands at one point; then something has changed. Do you have a counterpoise wire for it/tried that? What happens to the SWR's when you run it on the roof? Is it mounted in the trunk? I wouldn't do that.
But since it is having a problem with VHF or UHF - which are prone to coax and connector maladies due to the high frequency being used - I will still look there first.
Can't get a real diagnosis without a careful examination first.
Routing coax in a car can create dilemmas for coax. If it gets pinched, flattened, torn, stretched, frayed, or it has an sharp bend or kink that deviates the distance of the core conductor and the shield inside - the coax is compromised.
If the coax connector is a poor quality crimp-on type rather than a solder-on type, it can also be considered suspect too. Even though they are mfd with this kind of crimp-on connector; they have histories of being less than flawless and have a higher failure rate than solder-on types.
Suspect everything; and then eliminate each possibility until the fault is found.
After that, I would go over the antenna itself with the same thought in mind. You might consider taking it completely apart - if possible - and thoroughly cleaning it too.
The eHam review on this antenna isn't so great. I would read it here:
http://www.eham.net/reviews/detail/3478
You might consider running a duplexer in the output of this radio and using two antennas; one for 2m/440mhz and another for 10m/6m (that is - if such a duplexer exists!). Seems that many people that bought this radio are stuck with antenna tuning problems with it. That is why I bought a Yaesu FT-8800R instead of the 8900 - read the reviews on it. But if you had this antenna tuned properly for all four bands at one point; then something has changed. Do you have a counterpoise wire for it/tried that? What happens to the SWR's when you run it on the roof? Is it mounted in the trunk? I wouldn't do that.
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I took a look at the installation instructions for this antenna here:
http://www.rfparts.com/diamond/pdfdocs/CR8900.pdf
It says that the base coil is the adjustment that will affect 6m and 2m. What I would do to troubleshoot this antenna is to remove everything from the Lower Phase coil up and take a reading. If I understand the antenna design properly, this should leave you with just a 1/2 wave 2m antenna. If you still can't get an acceptable VSWR with that, then you know the problem has got to be in that lower matching coil.
http://www.rfparts.com/diamond/pdfdocs/CR8900.pdf
It says that the base coil is the adjustment that will affect 6m and 2m. What I would do to troubleshoot this antenna is to remove everything from the Lower Phase coil up and take a reading. If I understand the antenna design properly, this should leave you with just a 1/2 wave 2m antenna. If you still can't get an acceptable VSWR with that, then you know the problem has got to be in that lower matching coil.
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