[OZAPRS] Setting up TT4 Tx on 2m

Fri Feb 19 23:27:24 EST 2010

Thanks
I've located the problem/s through some testing
Tracker Antenna mostly and digipeater Rx tuning

David


On 19 Feb 2010, at 22:20, Michael Wain wrote:

> DEV = Audio
>
> VK3HAU
>
>
> ----- Original Message -----
> From: "David and Justine Olsen" <davejust at bigpond.net.au>
> To: "Australian APRS Users" <ozaprs at aprs.net.au>
> Sent: Friday, February 19, 2010 8:00 PM
> Subject: Re: [OZAPRS] Setting up TT4 Tx on 2m
>
>
>> Ray
>>
>> Thanks for that info. I can do all of that except the last step (7).
>> The MT8000 has a TT3 chip and Tx on the same board and there is no
>> adjustment of audio to the Tx from the TT3 chip.
>> The only adjustments available are PWR and DEV.
>>
>> David
>>
>> On 19 Feb 2010, at 18:51, Ray Wells wrote:
>>
>>> David,
>>>
>>> This is what I would do with just a CRO as available test equipment.
>>>
>>> 1. Monitor your rx with the CRO
>>> 2. If you have a handheld or other 2m rig and, with it on the  
>>> correct
>>> frequency, produce some loud Shhshhing noise into the microphone.
>>> Generally higher frequency audio produces the maximum deviation,  
>>> hence
>>> the shhishing. Most commercial amateur rigs will produce close
>>> enough to
>>> 4.5/5khz deviation, the standard level in the amateur service in Oz.
>>> 3. Establish a reference point on the CRO from the shhishing.
>>> 4. Connect your TNC and if you can switch between tones, feed the
>>> 2200Hz
>>> tone into the tx at a reasonably high level, and adjust the  
>>> deviation
>>> control for a tad under the reference level you established on the
>>> CRO.
>>> 5. Don't touch the deviation control after this is set.
>>> 6. Reduce the output of the TNC to its minimum value and enable
>>> both TNC
>>> tones
>>> 7. Increase the audio input to the tx until you again see the
>>> reference
>>> level on the CRO and then back it off just a tad.
>>>
>>> Provided the tx has "standard" preemphasis characteristics you
>>> should be
>>> pretty close to ball park settings and, the decoded tones as seen
>>> on the
>>> CRO should appear at approximately the same level, if you're
>>> looking at
>>> deemphasised audio (say the top of the volume control) If you're
>>> looking
>>> at pre-deemphasis audio the high tome should be approximately twice
>>> the
>>> level of the low tone but this is not important here. What's  
>>> important
>>> is that you set the maximum level to just a tad below your CRO
>>> reference
>>> level.
>>>
>>> I usually set packet rigs for 4.0khz deviation on the high tone.  
>>> Since
>>> you have no way of measuring deviation with just a CRO, the  
>>> reference
>>> point minus a tad method should be reasonably satisfactory.
>>>
>>> Don't confuse deviation with tx power, there is no relationship. A
>>> given
>>> tx will produce the same deviation regardless of whether it's power
>>> output is 1mW or 1KW. Only the range of that tx will change, not its
>>> "loudness".
>>>
>>> Ray vk2tv
>>>
>>> David and Justine Olsen wrote:
>>>> Thanks Ray
>>>>
>>>> It seems the MT8000 has just PWR and DEV adjustments. So it was  
>>>> DEV I
>>>> was adjusting.
>>>>
>>>> After adjusting deviation by listening to change in audio, I've now
>>>> managed 1 kilometer range out of the 8 watt tracker with rubber
>>>> antenna, sitting on the dashboard of my car. I am not sure how much
>>>> better I could expect with this set up, but I was hoping for  
>>>> quite a
>>>> bit better. My digi is picking up mobiles from 20k away.
>>>>
>>>> David
>>>>
>>>> On 19 Feb 2010, at 17:32, Ray Wells wrote:
>>>>
>>>>
>>>>> David,
>>>>>
>>>>> I don't know the rig or the tx audio circuit so my only thought is
>>>>> that
>>>>> the audio limiter/compressor is being badly overdriven and its
>>>>> compression characteristics are frequency sensitive.
>>>>>
>>>>> I'd attack it from a different angle and start with as little
>>>>> audio as
>>>>> possible (certainly less than 50mV into the microphone input) and
>>>>> then
>>>>> raise the level, all the time watching the CRO. Then the
>>>>> limiting/compression point will become obvious on the CRO as that
>>>>> point
>>>>> where received high tone no longer increases whilst the low tone
>>>>> still
>>>>> increases.
>>>>>
>>>>> It's also worth checking the audio level into the tx  
>>>>> occasionally to
>>>>> make sure something stupid isn't happening there. Murphy is your
>>>>> constant companion when testing something.
>>>>>
>>>>> Ray vk2tv
>>>>>
>>>>> David and Justine Olsen wrote:
>>>>>
>>>>>> Ray
>>>>>>
>>>>>>
>>>>>> Thanks. I got that info from the previous link I posted.
>>>>>>
>>>>>> Now with the Microtrak8000, I am looking at the traces on a
>>>>>> software CRO
>>>>>>
>>>>>> I get the 8000 to transmit, and I have the audio from a receiver
>>>>>> going into my PC and viewing the trace of a software CRO
>>>>>>
>>>>>> Here is the interesting thing. As I decrease drive of the  
>>>>>> 8000, the
>>>>>> amplitude of high frequency tone becomes much smaller than  
>>>>>> that of
>>>>>> the low frequency tone.
>>>>>>
>>>>>>
>>>>>> David
>>>>>>
>>>>>>
>>>>>> On 19 Feb 2010, at 12:56, Ray Wells wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>> David,
>>>>>>>
>>>>>>> Put simply, the high frequencies (high tone for packet) are
>>>>>>> boosted in
>>>>>>> the tx at the (usual) rate of 6dB per octave, meaning that each
>>>>>>> time the
>>>>>>> audio frequency is doubled , the tx deviation is also doubled.
>>>>>>> If a
>>>>>>> 1khz
>>>>>>> tone produced, say, 2.5khz deviation, a 2khz tone would produce
>>>>>>> 5.0khz
>>>>>>> deviation.
>>>>>>>
>>>>>>> In the rx the reverse process takes place to restore the  
>>>>>>> audio to
>>>>>>> what
>>>>>>> it was prior to tx preemphasis. The effect of pre/deemphasis  
>>>>>>> is to
>>>>>>> improve the signal to noise ratio of the recovered audio.
>>>>>>>
>>>>>>> Television audio and FM radio both use pre/deemphasis for the  
>>>>>>> same
>>>>>>> reason.
>>>>>>>
>>>>>>> Ray vk2tv
>>>>>>>
>>>>>>>
>>>>>>> David and Justine Olsen wrote:
>>>>>>>
>>>>>>>
>>>>>>>> I am afraid preemphasis and deemphasis are beyond my present
>>>>>>>> knowledge
>>>>>>>> :-)
>>>>>>>>
>>>>>>>> David
>>>>>>>>
>>>>>>>>
>>>>>>>> On 19 Feb 2010, at 08:38, Richard Hoskin wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>> Ray / All,
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Several years I did some extensive testing on the effects of
>>>>>>>>> deemphasis on received AX25 signals at APRS digipeaters.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I found that the digipeaters reception and decoding of data
>>>>>>>>> worked
>>>>>>>>> best (1 to 2 db better) when the deemphasis was bypassed.
>>>>>>>>> This was
>>>>>>>>> the case for both preephasised and non-preephasised  
>>>>>>>>> transmitted
>>>>>>>>> signals. This is partly explained by the fact that most TNC
>>>>>>>>> (especially the MFJs) require the high tone of the received
>>>>>>>>> audio to
>>>>>>>>> be louder than the low tone for correct decoding.  
>>>>>>>>> Especially for
>>>>>>>>> weak
>>>>>>>>> signals.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I also looked at the output of the Kenwood D7 & D700 and found
>>>>>>>>> that
>>>>>>>>> they only used a 3db per octave preephasised / deemphasis  
>>>>>>>>> on the
>>>>>>>>> data
>>>>>>>>> TX / RX.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> All VK3 digipeaters have been modified to bypass the
>>>>>>>>> preephasised /
>>>>>>>>> deemphasis to obtain the better receive performance. The other
>>>>>>>>> advantage of this is that we bypassed the audio volume
>>>>>>>>> control and
>>>>>>>>> squelch circuitry which makes the digi on the hill less  
>>>>>>>>> prone to
>>>>>>>>> accidentally adjustments.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Cheers
>>>>>>>>>
>>>>>>>>> Richard
>>>>>>>>>
>>>>>>>>> VK3JFK
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> -------------------------------------------------------------- 
>>>>>>>>> --
>>>>>>>>> --
>>>>>>>>> --
>>>>>>>>> ----
>>>>>>>>>
>>>>>>>>> *From:* ozaprs-bounces at aprs.net.au
>>>>>>>>> [mailto:ozaprs-bounces at aprs.net.au] *On Behalf Of *Ray Wells
>>>>>>>>> *Sent:* Thursday, 18 February 2010 1:15 PM
>>>>>>>>> *To:* Australian APRS Users
>>>>>>>>> *Subject:* Re: [OZAPRS] Setting up TT4 Tx on 2m
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> David/All,
>>>>>>>>>
>>>>>>>>> I'm not suggesting your problem is tone level related but
>>>>>>>>> failure to
>>>>>>>>> grasp the following is arguably responsible for more TNC  
>>>>>>>>> decode
>>>>>>>>> issues than any other cause.
>>>>>>>>>
>>>>>>>>> The need for "twist" adjustment depends on the radio hardware
>>>>>>>>> involved so a brief discussion is probably in order.
>>>>>>>>>
>>>>>>>>> The "norm" for an FM/PM radio is to apply 6dB (x2) per  
>>>>>>>>> octave of
>>>>>>>>> preemphasis in the transmitter. For packet, this results in  
>>>>>>>>> the
>>>>>>>>> high
>>>>>>>>> tone (2200Hz) having twice (near enough) the deviation as the
>>>>>>>>> low
>>>>>>>>> tone (1200). In the receiver deemphasis is applied which
>>>>>>>>> restores
>>>>>>>>> the
>>>>>>>>> audio to a "flat" condition, i.e. both tones going to the TNC
>>>>>>>>> have
>>>>>>>>> the same level.
>>>>>>>>>
>>>>>>>>> If TNC audio is fed into the microphone socket you can depend
>>>>>>>>> on 6dB
>>>>>>>>> per octave preemphasis. However, if the TNC audio is fed in
>>>>>>>>> further
>>>>>>>>> down the tx audio chain, such as the audio injection point for
>>>>>>>>> tone
>>>>>>>>> signalling, preemphasis will not be applied in the tx and
>>>>>>>>> should be
>>>>>>>>> applied externally - with twist, in the case of the TT4.
>>>>>>>>>
>>>>>>>>> Going to the receiver again, if it receives a signal without
>>>>>>>>> preemphasis, it will still apply deemphasis (assuming audio is
>>>>>>>>> taken
>>>>>>>>> after deemphasis), resulting in the high tone being just half
>>>>>>>>> the
>>>>>>>>> level of the low tone when fed to the TNC. FSK demodulators
>>>>>>>>> based on
>>>>>>>>> the the  exar pair 2206/2211 will not decode if the high  
>>>>>>>>> tone is
>>>>>>>>> lower in amplitude than the low tone, by even a very small
>>>>>>>>> amount.
>>>>>>>>>
>>>>>>>>> If rx audio is taken from the demodulator in the radio, i.e.
>>>>>>>>> before
>>>>>>>>> deemphasis, the preceding is not a problem because audio  
>>>>>>>>> that is
>>>>>>>>> transmitted "flat" will be decoded "flat".
>>>>>>>>>
>>>>>>>>> The exar chip set (found in genuine TNC2 TNC's)  is not
>>>>>>>>> disturbed by
>>>>>>>>> high tone being considerably higher in amplitude than the low
>>>>>>>>> tone.
>>>>>>>>>
>>>>>>>>> In summary, every tx should employ preemphasis, regardless  
>>>>>>>>> of it
>>>>>>>>> being generated internally, or externally. That will
>>>>>>>>> eliminate any
>>>>>>>>> decode problems in TNC's with finicky chip sets because high
>>>>>>>>> tone
>>>>>>>>> will always be the same level as, or higher than, the low tone
>>>>>>>>> coming
>>>>>>>>> out of the rx.
>>>>>>>>>
>>>>>>>>> David, is TXD 60 60mS or 600mS? Although TXD provides time for
>>>>>>>>> your
>>>>>>>>> tx to stabilise before valid data is sent, it can also have an
>>>>>>>>> impact
>>>>>>>>> on the remote rx in cases where muted audio is being used for
>>>>>>>>> the
>>>>>>>>> TNC. There are some very sluggish receivers kicking about and
>>>>>>>>> TXD
>>>>>>>>> needs to be long enough for that rx to unmute. My Icon  
>>>>>>>>> handheld
>>>>>>>>> scanner is pathetic in this regard, with the mute being so  
>>>>>>>>> slow
>>>>>>>>> that
>>>>>>>>> I can miss at least half of the digi beacon, even when I'm at
>>>>>>>>> the
>>>>>>>>> digi site.
>>>>>>>>>
>>>>>>>>> Get that CRO working and save your hair, lest you should  
>>>>>>>>> end up
>>>>>>>>> like
>>>>>>>>> me :-)
>>>>>>>>>
>>>>>>>>> Ray vk2tv
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> David and Justine Olsen wrote:
>>>>>>>>>
>>>>>>>>> I am presently running TxD of 60 and TXTWIST of 50. I've  
>>>>>>>>> tried a
>>>>>>>>> range of TXTWIST but none sound too different
>>>>>>>>>
>>>>>>>>> David
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 18 Feb 2010, at 00:36, Scott Evans wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> ABAUD is just the speed set for serial port 1 ... what
>>>>>>>>> TXDELAY are
>>>>>>>>> you running? because depending on how quick you radio is  
>>>>>>>>> you may
>>>>>>>>> need
>>>>>>>>> to lengthen the delay a little, also check the TXTWIST setting
>>>>>>>>> too,
>>>>>>>>> this controls the level between the 1200Hz & 2200Hz tones.
>>>>>>>>>
>>>>>>>>> On Wed, 2010-02-17 at 21:51 +1000, David and Justine Olsen
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>> ABAUD is set to 19200
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 17 Feb 2010, at 21:37, Norm, VK3XCI wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> Sort of like 9600 baud?
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> 73 de Norm, VK3XCI
>>>>>>>>>> Mildura, Australia
>>>>>>>>>> The Wintersun City
>>>>>>>>>> QF15bt.
>>>>>>>>>>
>>>>>>>>>> David and Justine Olsen wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> I've gone through all of the TT4 audio adjustments as
>>>>>>>>>>> explained in
>>>>>>>>>>> the help docs by listening on another set, but still no
>>>>>>>>>>> success
>>>>>>>>>>> being
>>>>>>>>>>> received by any digis.
>>>>>>>>>>>
>>>>>>>>>>> One thing that has me curious, is the the squak from my Tx
>>>>>>>>>>> sounds
>>>>>>>>>>> nothing like those from others. The others are a deehdaaah
>>>>>>>>>>> kind of
>>>>>>>>>>> sound with two distinctly different tones ate the beginning
>>>>>>>>>>> and
>>>>>>>>>>> end
>>>>>>>>>>> tone, whereas mine is a sqaaaark :-) of mixed tones at the
>>>>>>>>>>> same
>>>>>>>>>>> time.
>>>>>>>>>>>
>>>>>>>>>>> David
>>>>>>>>>>>
>>>>>>>>>>> VK4MDX
>>>>>>>>>>>
>>>>>>>>>>> _______________________________________________
>>>>>>>>>>> OZAPRS mailing list
>>>>>>>>>>> OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>>>>>>>>>> http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>>>>>>>>>>
>>>>>>>>>>>
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>>>>>>>>>>>
>>>>>>>>>>>
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>>>>>>>>>>
>>>>>>>>> _______________________________________________
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>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> -- 
>>>>>>>>> Scott Evans <scott at vk7hse.hobby-site.org
>>>>>>>>> <mailto:scott at vk7hse.hobby-site.org>>
>>>>>>>>>
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>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> -------------------------------------------------------------- 
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>>>>>>>>> --
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>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
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>>>>>>>>>
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