Kenwood NX1700 - adjusting analog squelch threshold for weak signal working

[g8tzl2004]

I have a VHF Kenwood NX1700 DMR/NXDN/Analog radio which I have successfully programmed initially on analog channels.

The radio is working well with excellent sensitivity. The minimum user adjustable squelch threshold (level 1 using front keys) is ALMOST perfect for weak signal working. The threshold just needs to be slightly lowered so that the squelch opens on slightly weaker but still just readable signals.

I have lowered the squelch threshold on many other Kenwood radios such as the TK7180, TK8180, TK2180 and TK3180.

With my analog only Kenwood radios, the original "factory set" minimum squelch threshold is usually set relatively high eg. with my UHF TK8180, I have lowered the squelch threshold values from around 170 to around 130 at the 3 test points...so the radio now opens on really weak but just copyable signals.

The squelch threshold adjustment procedure for the NX1700 is similar to a TK8180 BUT it is done slightly differently as it includes squelch adjustment for DMR and NXDN as well as analog.

I understand that the "User Adjustable" squelch threshold ( 0 - 9 ) is fixed at level 5 for DMR and NXDN mode but is adjustable in analog mode from 0 - 9. I have set the user adjustable analog squelch to level 1 and it is OK but just needs to be slightly lowered.

Analog squelch alignment is done at level 5 and uses a -120dBm carrier to set the threshold. I assume I will just need to inject, say, a -123 dBm carrier rather than -120dBm in order to lower the minimum squelch threshold by 3dBm.

Before I start experimenting, I just wanted to get any views from others who might have already lowered the squelch threshold on a Kenwood DMR/analog radio. I don't want to start messing with the analog squelch threshold if it might effect DMR/NXDN squelch threshold operation. My understanding is that the Kenwood DMR/NXDN squelch threshold is aligned separately from the analog threshold so it should not be a problem?

I'm also wondering what happens if I lower the squelch threshold for DMR mode? Is the "default" DMR level 5 setting (which is not adjustable from the front keys) set in the factory at the absolute minimum for DMR weak signal working before the signal "disappears"? Does DMR mode actually need a "squelch" setting...there is no "white noise" problem? If I lower the DMR squelch threshold, do I hear brief "fragments" of audio rather than nothing if the squelch threshold is set higher?

At least its possible to experiment with squelch threshold levels using Kenwood DMR/analog radios...unlike my Motorola DMR/analog radios which just have 2 fixed squelch levels for both analog and DMR and no apparent way to adjust the squelch threshold!!

Thanks

 

[kd4efm]

Remember, in theory, -124 dBm is theoretical noise floor. These radios are commercial in their uses, so using it in the ham realm
for weak signal work, is not really ideal. HOWEVER, if your experimenting, you need a service monitor to fine tune the thresholds
but I say this with caution, write down ALL SETTINGS in the TUNE SECTION BEFORE YOU ADJUST ANYTHING!!!!

 

[g8tzl2004]

Yes, I always carefully write down all the tuning settings...as well as saving the tuning file if this is possible.

I find that my commercial radio "collection" works as well if not better than my dedicated ham radios for weak signal working once the SQ threshold has been lowered!!!

Lowering the SQ threshold on my analog Kenwood radios was not as easy as on Motorola radios. With Motorola radios, its possible to "manually" lower the SQ threshold using the tuner software and the up/down keys (or whatever)..but with a Kenwood TK8180, for example, setting the SQ threshold involves injecting a weak carrier and then clicking on "Apply" (or whatever). Its not possible to manually set the SQ threshold using up/down keys. But with the TK8180 it is possible to note down the previous SQ threshold value which I think is displayed on the radios LCD NOT in the software? I like to get the "Level 1" SQ threshold set for very weak DX...and then I can always increase the SQ to "Level 3 or 4" if I don't want to hear really weak signals. The "Level 1" SQ on my TK8180 and 7180 now both open on really weak signals which is great for DXing.

However, before I start experimenting with the NX1700 I want to see if anybody else has already lowered the NX1700 SQ threshold and whether any issues where encountered. Presumably the original SQ values at the 5 test points will be displayed on the LCD or software screen? Also do I need to manually set the SQ threshold to Level 5 before I start any alignment? Analog SQ threshold is aligned at Level 5 officially at -120dBm..but then the threshold can be lowered down to Level 1 which is likely around -123dBm. The NX1700 DMR SQ threshold alignment is also done at Level 5 at -123.5dBm BUT the SQ level is FIXED at Level 5...although the manual suggests that the SQ can be "opened" but I'm not sure what effect that actually has on RXing weak signals in DMR mode? For narrow 6.25 KHz NXDN, the level 5 SQ threshold is officially set at -125dBm so this suggests that narrow NXDN can work at lower signal levels than DMR??

 

[kd4efm]

The NX1700 DMR SQ threshold alignment is also done at Level 5 at -123.5dBm BUT the SQ level is FIXED at Level 5...although the manual suggests that the SQ can be "opened" but I'm not sure what effect that actually has on RXing weak signals in DMR mode? For narrow 6.25 KHz NXDN, the level 5 SQ threshold is officially set at -125dBm so this suggests that narrow NXDN can work at lower signal levels than DMR??

6.25 NXDN is a theoretical 3dB lower noise floor, compared to DMR. Why? Because DMR is TDMA 6.25e (12.5 but half).
6.25 NXDN FDMA operates better than DMR. I have proved this many years ago when I started the NXDN Ham Network (nxdninfo.com)
and have real world results where VNFM NXDN has anywhere from 5 to 15 miles further range RX than DMR. 12.5 (9600 baud) has the same range as DMR being 12.5 bandwidth.

Therefore, I wouldn't mess with the rx on 6.25 at all, because I can use a monitor with NXDN 6.25, and decode down to -126 dBm out of the box. this is at 5-7% BER or CM-2 (circuit maintenance 2 or broken, missing words but got the jest)
CM1 and CM0 are no copy or 15%< BER.

SO, I'd be cautious about stretching any more than NEEDED. at .015uV your in the noise floor as is, your not going to increase your decode anymore than at 0.018uV, the vocoder fails off in this area.

 

[g8tzl2004]

I read an article that stated that the theoretical noise floor in an analog FM radio system is around -125dBm...although there was no mention of whether this applied to low band, VHF or UHF (Receiver Sensitivity and Equivalent Noise Bandwidth by Dennis Layne).

Sensitivity was calculated as a function of band limiting thermal noise (-134dBm), receiver noise figure for analog FM (5dBm) and the required carrier to noise ratio for 12dB SINAD using analog FM with a 10KHz BW (4dBm).

Sensitivity = -134dBm +5dBm+4dBm = -125dBm = 0.12uV

One of my most sensitive 2m radios has a sensitivity of 0.10uV for 12 dB SINAD or -127dBm

That radio is able to resolve exceptionally weak VHF FM signals slightly better than another radio with a sensitivity of 0.12uV or -125dBm...which suggests that the VHF noise floor is lower than -125dBm??

On 10m FM, using a full size 10m dipole and monitoring an exceptionally weak stable FM signal, switching in 9dB of attenuation does not effect signal readability...so extra sensitivity on 10m FM does not improve reception due to the higher noise floor on 10m??