I am restoring an old TRC-455, and want to align it by Sams. I have a Tek scope,
but a standard 10x probe. Do I need a probe with a certain bandwidth?

Vinnie S.

Vinnie S. wrote:
I am restoring an old TRC-455, and want to align it by Sams. I have a Tek scope,
but a standard 10x probe. Do I need a probe with a certain bandwidth?

Vinnie S.

You need to be able to see the audio waveform. If you can stretch it
out enough to see the RF waveform, you can "see" harmonics if it's
not a perfect sine wave. Every complex waveform is a lot of sine waves.

Vinnie;

The answer is "it depends".

If the alignment procedure requires you to measure voltages and adjust for
specific values then the scope and the probe must have a bandwidth beyond
the max frequency of interest. For example at 27 MHz the scope and probe
have to be rated for more than 30 MHz. Most bandwidth specifications are at
the "3 db" points meaning the response is down by 50% at the stated
bandwidth. Depending on the filter used on the scope input channel the scope
response may roll off at 3 db per octave, doubling in frequency, or faster.
Of course the response starts to roll of somewhat before that point.

Now if all you're looking for is a relative reading, peak response or
modulation checks for example, a lower bandwidth scope and probe could work
so long as the response is enough to give a good display on the screen. I
would guess a 15MHz bandwidth scope may work OK.

One other thing to watch out for is circuit loading due to the scope probe
resistance AND capacitance. The probe capacitance can be in the order of
some 10's of picofards. This can cause serious circuit detuning if you use a
probe in a circuit where the tuning capacitance is in the same range as the
probe to as much as 10 to 20 times that value.

I've seen a lot of very nice 30 to 100 MHz scopes for sale at various
hamfests for very reasonable prices. If you don't have one and you plan on
doing more electronics work investing in a good scope is a good investment.

--
Regards,
Leland C. Scott
KC8LDO


"Vinnie S." wrote in message
news
I am restoring an old TRC-455, and want to align it by Sams. I have a Tek
scope,
but a standard 10x probe. Do I need a probe with a certain bandwidth?

Vinnie S.

On Sun, 03 Jun 2007 21:29:09 -0400, Vinnie S.
wrote:

+++I am restoring an old TRC-455, and want to align it by Sams. I have a Tek scope,
+++but a standard 10x probe. Do I need a probe with a certain bandwidth?
+++
+++Vinnie S.
*************

A scope probe with 50 MHz bandwidth will be suficient. The bandwidth
of the probe is stated so that you will avoid attenuation issues at
high frequencies. Measurements above the rated bandwidth of the scope
probe will yield inaccurate measurement levels. If you are just
looking for the presence of a signal and the absolute level is not
needed then don't worry to much about the bandwidth of the scope
probe.

james

On Wed, 06 Jun 2007 15:21:49 GMT, james wrote:

On Sun, 03 Jun 2007 21:29:09 -0400, Vinnie S.
wrote:

+++I am restoring an old TRC-455, and want to align it by Sams. I have a Tek scope,
+++but a standard 10x probe. Do I need a probe with a certain bandwidth?
+++
+++Vinnie S.
*************

A scope probe with 50 MHz bandwidth will be suficient. The bandwidth
of the probe is stated so that you will avoid attenuation issues at
high frequencies. Measurements above the rated bandwidth of the scope
probe will yield inaccurate measurement levels. If you are just
looking for the presence of a signal and the absolute level is not
needed then don't worry to much about the bandwidth of the scope
probe.

james


I just wanted to measure modulation on a TRC-455 that I am restoring. I have a
10x probe with the bandwidth being 60Mhz in the 10x position.

But I have bad news. I apparently need and RF generator for alignment of the
receiver. I do not own one. I have everything else. So off to ebay I go. Any
recommendations?

Vinnie S.

Vinnie;

Why don't you just try using another radio as the signal source? Run it in
to a dummy load. A loop or two around the dummy load may pick up enough
signal leakage that you can feed it in to the rig you're setting up.

--
Regards,
Leland C. Scott
KC8LDO

"Vinnie S." wrote in message
...
On Wed, 06 Jun 2007 15:21:49 GMT, james wrote:

On Sun, 03 Jun 2007 21:29:09 -0400, Vinnie S.
wrote:

+++I am restoring an old TRC-455, and want to align it by Sams. I have a
Tek scope,
+++but a standard 10x probe. Do I need a probe with a certain bandwidth?
+++
+++Vinnie S.
*************

A scope probe with 50 MHz bandwidth will be suficient. The bandwidth
of the probe is stated so that you will avoid attenuation issues at
high frequencies. Measurements above the rated bandwidth of the scope
probe will yield inaccurate measurement levels. If you are just
looking for the presence of a signal and the absolute level is not
needed then don't worry to much about the bandwidth of the scope
probe.

james


I just wanted to measure modulation on a TRC-455 that I am restoring. I
have a
10x probe with the bandwidth being 60Mhz in the 10x position.

But I have bad news. I apparently need and RF generator for alignment of
the
receiver. I do not own one. I have everything else. So off to ebay I go.
Any
recommendations?

Vinnie S.

On Wed, 06 Jun 2007 18:55:21 -0400, Vinnie S.
wrote:

+++On Wed, 06 Jun 2007 15:21:49 GMT, james wrote:
+++
+++On Sun, 03 Jun 2007 21:29:09 -0400, Vinnie S.
+++wrote:
+++
++++++I am restoring an old TRC-455, and want to align it by Sams. I have a Tek scope,
++++++but a standard 10x probe. Do I need a probe with a certain bandwidth?
++++++
++++++Vinnie S.
+++*************
+++
+++A scope probe with 50 MHz bandwidth will be suficient. The bandwidth
+++of the probe is stated so that you will avoid attenuation issues at
+++high frequencies. Measurements above the rated bandwidth of the scope
+++probe will yield inaccurate measurement levels. If you are just
+++looking for the presence of a signal and the absolute level is not
+++needed then don't worry to much about the bandwidth of the scope
+++probe.
+++
+++james
+++
+++
+++I just wanted to measure modulation on a TRC-455 that I am restoring. I have a
+++10x probe with the bandwidth being 60Mhz in the 10x position.
+++
+++But I have bad news. I apparently need and RF generator for alignment of the
+++receiver. I do not own one. I have everything else. So off to ebay I go. Any
+++recommendations?
+++
+++Vinnie S.
*****************

I have an HP 8656 generator. A bit pricy even still today. I got mine
at a fantastic price 8 yrs ago. Bought it when the factory was closing
down and moving as excess equiptment for around $400. They are still
commanding around $700 to $1000.

Really for CB work if you can find any of the older B&K CB test
equiptment in decent shape I would suggest those. Equiptment like HP,
Wavetek, and others are very pricy for home test equiptment.

james

James;

One of the problems buying used test equipment is the manufacture finds
there is some weakness in the design resulting in frequent failures, one
reason why they may quit manufacturing it.

I don't know if the HP signal generator you mentioned is one such item. I
remember in some back issues of QEX somebody came up with a modification to
replace a section in the output of a HP signal generator that was known to
be particularly failure prone, the original part used isn't available
anymore if I remember right.

Others have picked up old Tech scopes real cheap that had problems, hoping
to fix them, and finding out that the blown parts, like Tunnel Diodes, are
now almost imposable to find since almost nobody makes them anymore. And the
ones that do, if you can find the exact one you need, want such a high price
for them it isn't worth it.
--
Regards,
Leland C. Scott
KC8LDO


"james" wrote in message
...
On Wed, 06 Jun 2007 18:55:21 -0400, Vinnie S.
wrote:

+++On Wed, 06 Jun 2007 15:21:49 GMT, james wrote:
+++
+++On Sun, 03 Jun 2007 21:29:09 -0400, Vinnie S.
+++wrote:
+++
++++++I am restoring an old TRC-455, and want to align it by Sams. I
have a Tek scope,
++++++but a standard 10x probe. Do I need a probe with a certain
bandwidth?
++++++
++++++Vinnie S.
+++*************
+++
+++A scope probe with 50 MHz bandwidth will be suficient. The bandwidth
+++of the probe is stated so that you will avoid attenuation issues at
+++high frequencies. Measurements above the rated bandwidth of the scope
+++probe will yield inaccurate measurement levels. If you are just
+++looking for the presence of a signal and the absolute level is not
+++needed then don't worry to much about the bandwidth of the scope
+++probe.
+++
+++james
+++
+++
+++I just wanted to measure modulation on a TRC-455 that I am restoring. I
have a
+++10x probe with the bandwidth being 60Mhz in the 10x position.
+++
+++But I have bad news. I apparently need and RF generator for alignment
of the
+++receiver. I do not own one. I have everything else. So off to ebay I
go. Any
+++recommendations?
+++
+++Vinnie S.
*****************

I have an HP 8656 generator. A bit pricy even still today. I got mine
at a fantastic price 8 yrs ago. Bought it when the factory was closing
down and moving as excess equiptment for around $400. They are still
commanding around $700 to $1000.

Really for CB work if you can find any of the older B&K CB test
equiptment in decent shape I would suggest those. Equiptment like HP,
Wavetek, and others are very pricy for home test equiptment.

james

On Sun, 10 Jun 2007 12:03:04 -0400, "Leland C. Scott"
wrote:

+++James;
+++
+++One of the problems buying used test equipment is the manufacture finds
+++there is some weakness in the design resulting in frequent failures, one
+++reason why they may quit manufacturing it.
+++
+++I don't know if the HP signal generator you mentioned is one such item. I
+++remember in some back issues of QEX somebody came up with a modification to
+++replace a section in the output of a HP signal generator that was known to
+++be particularly failure prone, the original part used isn't available
+++anymore if I remember right.
******************

The HP generator I have is a standard that HP sold for commercial and
industrial use throughout much of the 1990's but now is discontinued.
The one I have is a HP8656A with the attenuator replaced with the
same one that was used in the HP8656B. One of the HP8656A's main
weakness was that of the attentuator at the output. The genreator has
an input for connection to a high stability time base which improves
the performance especially when using it at frequencies around 800
MHz. I also have a 10MHz. high stability TXCO that keeps the accuracy
of the generator frequency set to less than +/- 1 Hz.

Obsolescence is not necessarily due to problem plagued unit though
that can be a cause. WIth HP8656/57 series that may not have been the
problem. Lower demand and cost of manufacturing can also lead to
obsolescence. Lack of demand can be due to not having features and
options that the end user demands. Often a new model is introduced
with more bells and whistles as well as defect fixes that will all but
obsolete the previous model.

I have been very happy with the unit I have. The front keypad is still
in very excellent shape as the unit I have was on the factory floor
and control of it was via the GPIB connection from an HP workstation.

james

"james" wrote in message
...
I have been very happy with the unit I have. The front keypad is still
in very excellent shape as the unit I have was on the factory floor
and control of it was via the GPIB connection from an HP workstation.

Well that's good. I'm a bit leery of spending big bucks on used test gear
since you don't know what the last guy did to it abuse wise, something
stupid like keying up the xmit with the signal generator still attached. I
found that if the equipment looks good cosmetically there is a good chance
the guy selling it didn't abuse the equipment, much.

I would like to get a nice spectrum analyzer but anything worth having is in
the $2K range, a bit too much to take a chance on it from a total stranger.
I could spent $6K on a nice new portable LCD one. 8-))


--
Regards,
Leland C. Scott
KC8LDO