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TK7180 - front end RX filters use fixed default values??

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g8tzl2004

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The TK7180 service manual states that you just input fixed default values for the front end softpots?

This suggest that NO further alignment is required.

Has anybody managed to obtain better sensitivity by adjusting the default values?

With other radios I have found that front end alignment is very broad so small changes in softpot values makes no difference...I guess this must be the same for the TK7180 otherwise why have fixed default values?

With my TK3180 hand portable it appears that the radio was set up for "exactly" 119dBm for 12dB SINAD and no attempt was made by the factory to get better performance. I obtained a good improvement when I actually aligned it for better than 12dB SINAD. But the TK3180 did not use 100% fixed default values as with the TK7180!!!

So can I get better RX performance from my TK7180 be doing a careful front end alignment or is it a waste of time?

Thanks
 

g8tzl2004

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Any ideas?

I've now programmed my TK7180 and its RX performance is good...only a few dB behind my Motorola MCS2000 which has a very hot front end.

One issue with the TK7180 is the squelch settings. Using the minimum User Adjustable level 1 (out of 9) weak signals are still missed. I have lowered the level using Test Mode but there is a high level of fixed hystersis ie. the SQ closes, say , 6dB below the level that the SQ opens. So if you set the SQ to open at a very low level, it will then not close. With Motorola stuff there is only a small amount of hystersis so you can get Motorola radios to open (and close) on exceptionally weak signals.

The TK7180 Test Mode SQ level adjustment is NOT manual..unlike other Kenwood and Motorola stuff..so you cannot just use a trial and error method to set the SQ level ie. lower level until SQ just opens (white noise) and then just keep going up by 1 unit until its opening and closing on a very weak but readable signal. With the TK7180 you need to inject an "accurate" dBm signal and then click on Apply..its impossible to do manually.....I think!!!!
 

g8tzl2004

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This was some time ago but I think the service manual stated that you just use fixed default values for the VHF front end rather than alignment for best sensitivity. The manual gives you the default values and I guess these values should be what is in your TK7180.

BUT I would try aligning the radio anyway and see if you get any improvement..you can always go back to the default values. I would be interested to hear if you get any improvement in sensitivity.

I've recently acquired a UHF TK8180 which was a bit deaf....as expected with Kenwood stuff (seems crazy for Kenwood not to align for best sensitivity in the factory!!!). I realigned the radio and got an improvement BUT I'm a bit disappointed with the overall sensitivity compared to my Motorola and other Kenwood stuff. Whereas my UHF TK3180 and VHF TK2180 handhelds ended up with excellent sensitivity (once aligned), the TK8180 ended up with better sensitivity but no where near as good as some of my other radios :( I'm wondering if my TK8180 was out of a repeater and there is an RX attenuator pad which has been enabled on the PCB...I think some Motorola radios have this feature so that the radio is NOT too sensitivity in a high RF environment.
 

g8tzl2004

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Jun 4, 2010
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The front end filters on my UHF TK8180 were originally 94, 122, 150, 172, 194 and the values after alignment were 70, 105, 130, 165, 190.

The service manual default values were more or less identical to the original values in my radio (there was actually a difference of 1 unit for some reason (95, 123, 151, 173, 195)...but tuning is so broad that 1 unit has no difference...its actually difficult to notice a sensitivity change on a 5-10 unit difference!!).

However, the optimum values in my TK8180 will not necessarily be the optimum values in your radio...you really need to align your radio using a very weak signal source..ideally a signal generator...then you can tune the front end filters for maximum quieting ie. less hiss.

A great source of a weak signal is the local oscillator of a HT or scanner. I use my Kenwood TH-F6 which has an IF of 57.6MHz. To get to a test frequency , say 400.05 MHz, you subtract 57.6 from 400.05 which equals 342.45MHz...so if I set the RX on my TH-F6 to 342.45, the RX local oscillator will put out a super weal signal on 400.05 MHz...which can be used to align the TK8180. Connect the TK8180 to, say, a mag mount antenna and then bring the TH-F6 close to the antenna so that you hear a super weak signal on the TK8180..and then align for maximum quieting. You need to repeat this for all 5 test frequencies.. 400.05 to 469.95 MHz.

Different HT's have different IF freqs so you will need to research the IF of your UHF HT. Also sometimes you need to add or subtract the IF freq to get a weak signal on a test freq. Experiment using two HT's - one on RX and the other as a weak signal source using the IF freq!!!
 
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