Yaesu FT-101ZD Receiver Diode Upgrade

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stevstro1
New Member
5
Apr Thu 13, 2023 5:03 pm
Sycamore, IL

Yaesu FT-101ZD Receiver Diode Upgrade

Post by stevstro1 »

Hi,

I have a '101ZD and have heard there's a diode upgrade for the rx section that improves its performance. I'm wondering if anyone has information on this that they would care to share.

Thanks & 73,

Steve/W9XF
KX5JSC
Member
1860
Dec Sat 28, 2019 3:18 pm
Corinth, TX, USA

Re: Yaesu FT-101ZD Receiver Diode Upgrade

Post by KX5JSC »

What kind of upgrade?

John
stevstro1
New Member
5
Apr Thu 13, 2023 5:03 pm
Sycamore, IL

Re: Yaesu FT-101ZD Receiver Diode Upgrade

Post by stevstro1 »

Supposedly the upgrade improves receiver sensitivity. I don't have any additional information as I saw it as a general post in a different forum. I requested details, but never received a response.
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manualman
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3625
Nov Sat 07, 2009 10:37 pm
Sayreville, NJ 08872
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Re: Yaesu FT-101ZD Receiver Diode Upgrade

Post by manualman »

Easy to find using Google!

From Yaesu FT-101ZD Survival Guide
http://www.foxtango.org/ft-library/FT-L ... 1ZDSG3.pdf" -="window.open(this.href);return false;

Modification of the diode ring mixer:
Yaesu used here 4x 1S1007 silicon diodes, in a ring-mixer
configuration. They are not bad but the performance can
easely improved, by using Schottky Barrier diodes such
as the HP 5082-2800.
If you have the possibility, select them for equal forward
current from a batch at the suppliers place, or order a
special quad.
Selecting is an easy affair:
Use your multimeter in the diode range and connect to
the diodes with a serial resistor of 4.7 K-ohm (value is
not important). You now measure the forward current.
Select 4 diodes that have the same value on the meter or
as close as possible. In a normal batch is it rather easy to
find 4 diodes with the same value.
Now, remove diodes D502 to D505 from the board and
replace them with the schottky barrier diodes, in the
same configuration, the ring end is the cathode.
After replacing, the bridge has to be aligned for maximal
carrier suppression with VR-501 and TC-502.
Alignment is done in tx mode ( Heater switch OFF)
because it is most important to have a good carrier null
for a clean output SSB signal.
Connect a oscilloscope to pin 2 of the print (SSB out),
and null the oscillator signal with VR-501 and TC-502,
repeat several times in USB and LSB mode for the lowest
output. ( I had a value of less than 5mV.)
When you have selected equal diodes, both the pot and
potmeter are near the middle of their range.
I measured the old 1S-1007 diodes, they were close but
not as equal to each other as the schottkys.
Other modifications to the FT-101ZD by Wim Penders PA0PGA
Tests on 40 and 20 meters showed a audible lower noise
level and much improved received signals, because the
schottky diodes handle bigger signals more easely.
There is also less “splatter” from other stations (exept the
ones with their overdriven kilowatts and compressors), so
it seems that not all splatter is generated on the band but
also for a part in the receivers.
Listening on 40 and 20 shows that the average signal
levels not much differ from before the mod, but the
signals are much cleaner and the noise level is lower,
ideal for DXing.
The noise level on the higher bands is lower than the
atmospheric noise from the antenna, I can even hear a
difference on 80m.
Signal comparations have been done with another trusty
FT-101ZD, on the same antenna and time.
The tx has now a much cleaner signal on the
oscilloscope, with no flat topping, even when the mike
level is fully up.
I use a standard Yaesu low-impedance handmike and
receive good modulation reports.
All in all is it a easy job, that results in a real
improvement on both rx and tx side. I have done this
mod too on my FT-901DM, with equally good results.
Pete WA2CWA "A cluttered desk is a sign of genius"
https://www.manualman.com"
stevstro1
New Member
5
Apr Thu 13, 2023 5:03 pm
Sycamore, IL

Re: Yaesu FT-101ZD Receiver Diode Upgrade

Post by stevstro1 »

Thanks for the information, Pete! I just heard from a friend who did the mod & is very happy with the results.

73,

Steve
stevstro1
New Member
5
Apr Thu 13, 2023 5:03 pm
Sycamore, IL

Re: Yaesu FT-101ZD Receiver Diode Upgrade

Post by stevstro1 »

I'm hoping someone could point me to the actual physical location of the 1S1007 diodes (D502-D505) mentioned in the FT-101ZD receiver upgrade reply to my post. My 74-year-old eyes aren't able to locate them. From the information regarding the upgrade, they appear to be on the AF board.

Thanks & 73,

Steve
W9XF
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