For Pete Gianakopolis - IC-R70 comments/question
fcat...@msn.com
Ebay. It has the 500 kHz CW narrow filter included and came with the
manual and original box. After using this radio for a couple of weeks
I'm very impressed short of the weird ergonomics and the end of band
tuning anomalies. The sensitivity and selectivity are superb and the
BP shift and IF notch are among the best I've used. The audio is a bit
on the shallow side but I replaced a few of the electrolytic coupling
caps with film caps and the difference was very noticeable. I also
removed the LW/MW input attenuator and disabled the input rf amp defeat
for MW/LW. It can now be switched on and off from the front panel
switch. What is your experience with this radio and are there any other
improvement modifications that you know of?
Comments on this receiver from others are welcome.
Frank
K3YAZ
Tucson
Radioman
Radioman
Radioman
Radioman
Radioman
Radioman
Radioman
clean my glasses first.
I had an R 70, sorry I let it go. I'll take its tuning strangeness just
to avoid
the memory battery over an R71A. I think most of the "71" mods apply.
Radioman in Michigan
Jake Brodsky
> Comments on this receiver from others are welcome.
I'm not Pete, but I have owned an R-70 for a long time (20 years?). My
take on it is pretty much what you seem to think. The AM detector
leaves something to be desired. It sounds a bit distorted.
I know that Sherwood sells an R-70 synchronous detector. I haven't got
$400 to throw at this, to tell whether it's worth the money. I will say
I've yet to hear anything negative about their products.
I have the CW filter, and the FM board. Sideband, CW, RTTY, and FM all
work quite well. The Notch and PBT are very good.
I have some microcontroller chips and I'm thinking of writing some
software to handle the four bit strobed interface in the back of the
unit. I'm not sure how complex it is, but I feel I'm about to find out.
DE AB3A
fcat...@msn.com
was able to improve the distortion issues considerably by using a 1 Meg
resistor connected from the -10V rail to the diode's cathode. The AM
clarity was noticeably improved as was the low signal S/N ratio. Terry
Fugate from the Yahoo Kenwood R-2000 group did numerous experiments
with different detector diodes and biasing them in his R-2000 and
achieved some respectable results. It was just pure luck that the R70
had a negative rail for direct biasing with just the addition of a
resistor.
Frank
K3YAZ
Tucson
Pete KE9OA
That is a nice receiver, and the mods that you have done seem to cover
everything. The only thing that I can recommend....if this receiver uses
diodes to switch the input bandpass filters, I would replace them with
1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up to
around 90mA, but that might be pushing them.
Philips also has some suitable PIN diodes, but you want to make sure that
you have a long enough minority carrier lifetime.
Congratulations on the new receiver! I haven't picked up anything new for
awhile, except that NRD-91.
Pete
<fcat...@msn.com> wrote in message
news:1153448399.6...@i42g2000cwa.googlegroups.com...
fcat...@msn.com
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?
Frank
dxAce
fcat...@msn.com wrote:
> Thanks for the info and advice Pete. I recently saw a comment that
> standard 1N4002 type (60 Hz) diodes are actually good replacements for
> the PIN diodes on the front-end band pass switching networks. Have you
> heard of this?
Whatever happened to all those Schottky Diode mods that seemed to be the rage
years ago? Would this be something similar?
dxAce
Michigan
USA
Telamon
dxAce <dx...@milestones.com> wrote:
That is a standard silicon power supply diode with something like .6 -
.7 volts forward voltage drop. The Schottky would be at least half that
and many are more like .25 volt.
If you don't bias the diodes into their linear range then it takes
signal power just to turn them on/off and that's where some of the
distortion comes from and the non-linear area contributes as well so the
smaller Schottky is an advantage.
--
Telamon
Ventura, California
Pete KE9OA
could cause poor isolation, but if you reverse bias the unused filter
diodes, they might work.
Pete
<fcat...@msn.com> wrote in message
news:1153589114.6...@i42g2000cwa.googlegroups.com...
Michael Black
> I am not sure if the capacitance of the power diodes would be too high. This
> could cause poor isolation, but if you reverse bias the unused filter
> diodes, they might work.
>
> Pete
>
like PIN diodes, I think some of the higher voltage ones. This has been
stated in various places, though I have no idea about whether it's a valid
solution for this specific receiver.
Michael
fcat...@msn.com
version of this slow diode that was recommended. It would tend to have
lower junction capacitance because of the wider depletion region due to
the heavier doping for the high voltage standoff. Once the diode is
biased on dc wise, the forward drop is not significant because it
doesn't "switch" with the signal current. I think the trend to
Schottky diodes was because of the lower intrinsic capacitance.
Frank
Jake Brodsky
> Now that I think of it Michael is correct. It was the 1N4007, the 1 kV
> version of this slow diode that was recommended. It would tend to have
> lower junction capacitance because of the wider depletion region due to
> the heavier doping for the high voltage standoff. Once the diode is
> biased on dc wise, the forward drop is not significant because it
> doesn't "switch" with the signal current. I think the trend to
> Schottky diodes was because of the lower intrinsic capacitance.
There are better switching diodes than the 1N4007, though they are more
expensive and less commonly available. It's not a bad switching diode
for RF if you don't have anything else handy. If I'm not mistaken,
Ulrich Rhode wrote an article in QST some years back about the use of
such diodes in high performance receiver designs. His opinion was that
although cheap, the 1N4007 didn't have a place in higher performance
designs.
DE AB3A
fcat...@msn.com
when it comes to speed and reverse recovery characteristics, however,
for switching in and out bandpass filters I think the reverse bias
junction capacitance is the major issue to prevent unwanted signal
coupling. I would definitely look for true PIN diodes if I were
upgrading the filter switching diodes rather than use 1N4007s. It's
just interesting that there have been articles on the fact that they
appear to work reasonably well in some cases. I know the Kenwood
R-2000 I had used the equivalent of 1N914s for these diodes in the
front end and they were horrible with all kinds of cross talk from
stronger, out of band signals.
Frank
r2000...@hotmail.com
fcat...@msn.com wrote:
> There's no question that the 1N400X series is a poor switching diode
> when it comes to speed and reverse recovery characteristics, however,
> for switching in and out bandpass filters I think the reverse bias
> junction capacitance is the major issue to prevent unwanted signal
> coupling. I would definitely look for true PIN diodes if I were
> upgrading the filter switching diodes rather than use 1N4007s. It's
> just interesting that there have been articles on the fact that they
> appear to work reasonably well in some cases. I know the Kenwood
> R-2000 I had used the equivalent of 1N914s for these diodes in the
> front end and they were horrible with all kinds of cross talk from
> stronger, out of band signals.
>
> Frank
>
The R2000 uses BA282 band filter switch diodes.
The RX Unit (X55-1340-00) in the R2000 sevice manual gives the
part number, which I just verified by looking at the stock diodes
that I saved when I upgraded both of my R2000s.
See <http://www.vishay.com/diodes/list/product-85526/>
For the 6MHz and 9MHz bands, good HP PINs give a slight but
noticable improvement. I expected a big improvement in the below
500KHz range but found nothing that I could hear.
I still lurk and will make the odd post when I have something usefull
to add. All prior Email accounts are abandoned and dead.
Terry
Pete KE9OA
Also, it could be that low Q caps are being used in the lower bands. I have
both an NRD-515 and an NRD-91. Both of these receivers exhibit rolloff below
700kHz.
These comparisions are made, using a Drake R7, Palstar R30, Yaesu FRG-100,
Icom R-75, Lowe HF150, HF-225, and HF-250. I did repair a Kenwood R-2000 a
few years ago, and wondered if it had some sort of attenuation below 1.5MHz.
I noticed this same characteristic with a Kenwood R-5000 and an AOR-3030.
Pete
<r2000...@hotmail.com> wrote in message
news:1153686195....@i3g2000cwc.googlegroups.com...
willis...@earthlink.net
Pete KE9OA wrote:
> Oftentimes, it is the type of ferrite material used in the mixer baluns.
> Also, it could be that low Q caps are being used in the lower bands. I have
> both an NRD-515 and an NRD-91. Both of these receivers exhibit rolloff below
> 700kHz.
> These comparisions are made, using a Drake R7, Palstar R30, Yaesu FRG-100,
> Icom R-75, Lowe HF150, HF-225, and HF-250. I did repair a Kenwood R-2000 a
> few years ago, and wondered if it had some sort of attenuation below 1.5MHz.
> I noticed this same characteristic with a Kenwood R-5000 and an AOR-3030.
>
> Pete
Pete,
A while back you were sending out mods to improve the AR3030. If you
still have them or any more that you discovered I would really
appreciate it if you could pass them along to me.
Geoffrey S. Mendelson
> I did repair a Kenwood R-2000 a
> few years ago, and wondered if it had some sort of attenuation below 1.5MHz.
> I noticed this same characteristic with a Kenwood R-5000 and an AOR-3030.
Kenwood units often have extra anttenuation below the 160 meter ham
band to prevent strong broadcast stations from overloading the front ends.
On units sold in the U.S., they often increased it without documenting it.
As an example, my TS-430 had a 220 ohm resistor instead of the (what I
remember as) an 80 ohm one. I replaced it with a 22 ohm resistor from a
"mod" I found and it helped.
My R-5000 also benefitted from a similar "fix".
When I did live in the U.S. (Philly) I was less than five miles from several
AM broadcast transmitters and needed it. Here in Jerusalem, it's the other
way around. Without the mod, the best I could ever get from an AM
broadcast station was S9.
Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel g...@mendelson.com N3OWJ/4X1GM
IL Voice: (07)-7424-1667 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/
Mark Zenier
>
>> Thanks for the info and advice Pete. I recently saw a comment that
>> standard 1N4002 type (60 Hz) diodes are actually good replacements for
>> the PIN diodes on the front-end band pass switching networks. Have you
>> heard of this?
It's supposed to be the higher voltage parts in that series, (the 1N4007).
>Whatever happened to all those Schottky Diode mods that seemed to be the rage
>years ago? Would this be something similar?
Semiconductor-wise, they're pretty much the opposite.
A Schottky diode uses only one type of semiconductor and the junction
is silicon-metal. (The modern version of a cat's wisker detector).
Their feature is that they don't store a cloud of electrons or holes
inside their junction so that they don't have a feature called "reverse
recovery". (Executive summary, they don't look like a short circuit for
a few nanoseconds when the current switches direction). Reverse recovery
causes all sort of problems in switching power supplies, and is also
the cause of RFI from regular old transformer/rectifier power supplies.
A PIN diode uses both P and N type doping in the junction, but in
addition there is a layer of Intrinsic (neutrally doped) silicon
in the middle. This causes a bunch of stored charge to hang around
in the middle of the junction, so that for high frequencies it doesn't
look like a diode anymore. They're used for switches by forward
biasing them to turn them on, or when reverse biased the stored
charge eventually gets swept out of the junction and they look like
an open circuit (or really, a capacitor). As I understand it,
there's a tradeoff between storage time (and switching speed) and
capacitance. The designer would like as much storage time (sets the
low frequency response) and the minimum capacitance.
Mark Zenier mze...@eskimo.com
Googleproofaddress(account:mzenier provider:eskimo domain:com)
Slow Code
news:1153589114.6...@i42g2000cwa.googlegroups.com:
> Thanks for the info and advice Pete. I recently saw a comment that
> standard 1N4002 type (60 Hz) diodes are actually good replacements for
> the PIN diodes on the front-end band pass switching networks. Have you
> heard of this?
>
> Frank
If you can stick with PIN diodes.
They give better isolation when reverse biased that other types.