Are all CB Amps built the same?

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Auldgeek
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Re: Are all CB Amps built the same?

Post by Auldgeek »

ghost123uk wrote:
Marky-boy wrote:one with a hard-switched PTT would be nice,
+ one on that !!! Image

I would not personally trust SS switching if using SSB.
+1 :thumbup:
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ghost123uk
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Re: Are all CB Amps built the same?

Post by ghost123uk »

kilimax wrote:
ghost123uk wrote:When mine arrives I will have a play, looking at the SWR between the radio and the L200, using different length patch leads. Also to see if it does affect the power out of the amp.
Would be interested in your findings!
Here we go then.

Using a Cybernet Beta 1000 with 4W full and 1W on low power. All tests done using a 60W dummy load. All tests done with 20A(ish) power leads, about 3 feet long, and going to the main "feed bus" of the fuse box and to a good solid earth point, to feed the Amp, and with a short lesser (~5A) cable feeding the rigs power socket, so unlikely any voltage drop to speak of (I know, I should have measured voltage drop, will do next time !!)

The SWR "seen" by the rig with a good quality RG58 patch lead of 12" was a standing needle. I then tried various other patch leads, including the recommended ( :roll: ) 90cm one, another of about 12 feet :o (Mini 8 there). At all times the SWR into the Amp (RM KL200) remained at a standing needle :)

Next power out from Amp.
Voltage = 12.8V (engine not running) 4W in = 65W out / 1W in = 15W out. This did not change regardless of what length patch lead I used.
Voltage = 14.1V (engine running) 4.5W in = 70W out / didn't test for 1.xW in :oops:

All in all, just what I expected, and in my case, with that Amp, the patch lead length made no discernible difference to either the rig to Amp SWR, or the power output.
John, on the S. Cheshire / N. Shropshire border. 26TM953 / muppet handle "Grey ghost"
Don't just monitor, key up and talk, otherwise everyone thinks no one else is out there !!!
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Auldgeek
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Re: Are all CB Amps built the same?

Post by Auldgeek »

ghost123uk wrote:

All in all, just what I expected, and in my case, with that Amp, the patch lead length made no discernible difference to either the rig to Amp SWR, or the power output.
Interesting result and tells us that with your particular setup, it doesn't seem to be influenced by coax length.
I notice that RM specify 90cm patch lead for "all" of their mobile CB amplifiers.

Off topic as not a CB amp, but I carried out a test with an old Daiwa 2m amplifier and my Yaesu FTM-100 set to 10 watts output. The Daiwa amp will produce around 150 watts out for 25 watts input power and about 90 watts at 10 watts input. I tried three lengths of RG213 I had lying about. I measured their lengths at 50cm, 1m & 3m. I added a swr bridge in circuit with a further 30cm lead to the amp input and tried each lead.
Connecting the 50cm or 1m lead showed no difference in power output but the input swr to the amp rose from 1.1:1 to 1.5:1 and when I connected the 3m lead, the input swr had reached over 2:1 and the amp had started to reduce its output.

So while not on 27Mhz, my test on 144Mhz produced differing swr readings for given coax lead lengths.

2m is likely to be more sensitive given the shorter wavelength but just shows you it "does" make a difference, at least in this non scientific test.
Auldgeek - Drew

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ghost123uk
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Re: Are all CB Amps built the same?

Post by ghost123uk »

Aye, I suppose at 2Mtrs, the percentage of a wavelength difference in a patch lead length is obviously much greater than at 11Mtrs.

I have always been one to trust my own real life findings, rather than trust just on the basis of something you have read. I'm also happy the my new amp shows the rig a nice 50 Ohm input, as I do like things to be "just right" ;)
John, on the S. Cheshire / N. Shropshire border. 26TM953 / muppet handle "Grey ghost"
Don't just monitor, key up and talk, otherwise everyone thinks no one else is out there !!!
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dt307
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Re: Are all CB Amps built the same?

Post by dt307 »

just sold the magnum 257 and thought ahh lets put a bit of class in there so in goes the globephone
same magmount same power connections same everything .
the kl203 working fine no rf feedback locking up the amp
from 26.965-28.8 mhz even with the swr @ close to 2 on the band edges
but the magnum and the globe work fine in the house with the kl203
i give up lol
163dt307-chris




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