I recently got an ht750. There is a bad buzzzzz in the background of the receive audio. It is present on both the internal speaker and the speaker mic - other tones are clear - so I don't think that the speaker is blown. It is much more severe on one channel versus others, although it is always present at least a little bit. I've checked all of the settings that I can think of, i don't have expansion on or anything....soooooo.....
Any ideas or suggestions are appreciated.
HT750 Audio Problem
Moderator: Queue Moderator
There is a known issue with the Professional series radios when using an MDC1200 receive signaling system on a channel with CTCSS / TPL
With MDC enabled, the radio uses the MDC/DPL baseband offset instead of the PL offset, and you get a charming hum on the received audio.
The solution is to use Global Tuner to change the MDC/DPL baseband offset frequencies.
Under Utilities/Update Baseband Offset change the value for the MDC/DPL offset to match the appropriate PL value. I've had very good results using 57Hz.
Note that you have to change the offset for all three channel spacings, and click the "update" button after each change, before changing between spacings.
The isssue is documented fairly thoroughly in the Global Tuner ReadMe or help file.
With MDC enabled, the radio uses the MDC/DPL baseband offset instead of the PL offset, and you get a charming hum on the received audio.
The solution is to use Global Tuner to change the MDC/DPL baseband offset frequencies.
Under Utilities/Update Baseband Offset change the value for the MDC/DPL offset to match the appropriate PL value. I've had very good results using 57Hz.
Note that you have to change the offset for all three channel spacings, and click the "update" button after each change, before changing between spacings.
The isssue is documented fairly thoroughly in the Global Tuner ReadMe or help file.
Baseband offset frequency adjustments may be required to prevent PL hum in some customer radios. The most common reasons for this is the customer is listening to radio transmitting TPL and the customer radio is programmed for CSQ operation, or the customer is receiving TPL with either MDC or QCII signaling. Both of these situations will require BBO adjustment.
There are six different BBO frequency offsets, CSQ, DPL and four TPL. You will rarely have to adjust the TPL offsets. In most cases you will be adjusting the CSQ and/or DPL offset frequencies. The most common adjustment you will be making is for when a carrier with a TPL is being received on a mode set for CSQ. Please refer to chart 1 and you will see 115 Hz. is the default BBO frequency for CSQ receive. If the TPL being received is within 20 Hz. of 115 then the buzz will occur. 110.9 Hz. TPL is one example. In a case like this you would most likely find that a BBO frequency of 86 Hz. will improve the receive audio. However, if the customer's radio is using a TPL close to 85 Hz. on another mode, such as 85.4 Hz. the receiver will now buzz on that mode. Make a list of the different TPL frequencies used in the radio on modes set for CSQ receive. Try to select a BBO offset frequency from chart 1 that is at least 20 Hz. away from all the TPLs in the radio.
Hex Code BBO Freq. Note:
0 234
1 204
2 174
3 144
4 115 CSQ ,TPL RANGE 1 AND 4 DEFAULT
5 86 TPL RANGE 3 DEFAULT
6 57 TPL RANGE 2 DEFAULT
7 28
8 1500
9 1370
A 1215
B 1066
C 921
D 781
E 646 DPL DEFAULT
F 512
The other case is if the radio is receiving TPL on a mode programmed for MDC or QCII signaling. In this case the BBO frequency being used is NOT the TPL BBO. The BBO offset used for MDC and QCII signaling is the DPL offset. Refer to chart one and you will see the DPL default is 646 Hz. If buzzing is heard on a signaling mode you must change the DPL offset to correct the problem. Choose a BBO frequency from chart 1 and change the DPL offset from 646 Hz. to 57, 86, or 115 Hz., which are the defaults for TPL.
The last thing you may encounter is a signal with DPL even though the mode is programmed for DPL receive. Choose a DPL BBO frequency other than 646 Hz., such as 86 Hz. and try that offset.
The Global Tuner has 3 selections for Bandwidth, 12.5, 20, and 25/30 kHz. It is recommended that any adjustment to BBO be made for all 3 bandwidths.
There are six different BBO frequency offsets, CSQ, DPL and four TPL. You will rarely have to adjust the TPL offsets. In most cases you will be adjusting the CSQ and/or DPL offset frequencies. The most common adjustment you will be making is for when a carrier with a TPL is being received on a mode set for CSQ. Please refer to chart 1 and you will see 115 Hz. is the default BBO frequency for CSQ receive. If the TPL being received is within 20 Hz. of 115 then the buzz will occur. 110.9 Hz. TPL is one example. In a case like this you would most likely find that a BBO frequency of 86 Hz. will improve the receive audio. However, if the customer's radio is using a TPL close to 85 Hz. on another mode, such as 85.4 Hz. the receiver will now buzz on that mode. Make a list of the different TPL frequencies used in the radio on modes set for CSQ receive. Try to select a BBO offset frequency from chart 1 that is at least 20 Hz. away from all the TPLs in the radio.
Hex Code BBO Freq. Note:
0 234
1 204
2 174
3 144
4 115 CSQ ,TPL RANGE 1 AND 4 DEFAULT
5 86 TPL RANGE 3 DEFAULT
6 57 TPL RANGE 2 DEFAULT
7 28
8 1500
9 1370
A 1215
B 1066
C 921
D 781
E 646 DPL DEFAULT
F 512
The other case is if the radio is receiving TPL on a mode programmed for MDC or QCII signaling. In this case the BBO frequency being used is NOT the TPL BBO. The BBO offset used for MDC and QCII signaling is the DPL offset. Refer to chart one and you will see the DPL default is 646 Hz. If buzzing is heard on a signaling mode you must change the DPL offset to correct the problem. Choose a BBO frequency from chart 1 and change the DPL offset from 646 Hz. to 57, 86, or 115 Hz., which are the defaults for TPL.
The last thing you may encounter is a signal with DPL even though the mode is programmed for DPL receive. Choose a DPL BBO frequency other than 646 Hz., such as 86 Hz. and try that offset.
The Global Tuner has 3 selections for Bandwidth, 12.5, 20, and 25/30 kHz. It is recommended that any adjustment to BBO be made for all 3 bandwidths.
This describes what Motorola said they did to several of my JT1000s’. Originally I had this buzzing problem when RXing a PL signal while in CSQ. I mailed them the codeplug image and they modified and returned it to program the radio with. It worked other than that now it buzzed on a different PL.
I use a JT in order to select different PLs’ and frequencies on the fly as needed for the job.
Nand.
I use a JT in order to select different PLs’ and frequencies on the fly as needed for the job.
Nand.