[OZAPRS] Setting up TT4 Tx on 2m
Norm, VK3XCI
vk3xci at aanet.com.au
Sat Feb 20 09:07:44 EST 2010
OK, this worked for me with my OT+, No CRO, no fancy techo bits. Your mileage
may vary.
I had exactly the same symptoms, hitting the local digi about 1 in 10 tries. I
was able to use a set-up I knew worked, on a spare frequency, the ever faithful
Tiny-2 and IC-215 set up to digi, The test was OT+ and FM828. Both ran into
dummy loads and were around 10m apart.
I dropped the audio DOWN TO MINIMUM on the OT+ and incremented slowly 'till I
got the first packet back. Noted the level. Increased through the
digi-every-packet point 'till I missed the first digi packet. The truth, as they
say, lies between. The audio adjustment is done thru the setup software so is a
bit of a pain, but still took less than 2 stubbies.
Interesting, I have to reset it when connected to my HT by dropping the level
using the hardware Hi-lo jumper.
Hope it helps
73 de Norm, VK3XCI
Mildura, Australia
The Wintersun City
QF15bt.
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
>>>>>>>>
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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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