THP Technical Topics
QSK (Full Break-In) Operation of THP Amplifiers
All THP amplifiers use high-speed, high current relays
for QSK operation. It is appropriate to consider a few timing issues to
consider when operating QSK.
Typically the THP T/R amplifier relay will engage 7-8ms
after the amplifier is keyed by your transceiver, and the THP amplifier
relay will drop-out typically 5-6ms after your transceiver un-keys the
amplifier. Normally, most transceivers key the amplifier immediately upon
keying your radio (your first “dit” or “dah”). However, it takes the
transceiver some time to actually generate the RF signal – usually this is
longer than the time for the THP relays to operate (which is good). The
following are some typical measured and/or spec’d “amp key to RF output”
delays of recent popular transceivers:
Kenwood TS-480, TS-2000: 10ms
Icom IC-7000: 10ms
Elecraft K3: 8ms, but adjustable to longer delays
Yaesu FT-1000 MKV/Filed: 5ms, but adjustable to
Yaesu FTDX-9000, FT-2000: 15ms
TenTec OmniVII & Orion I/II: 15ms
For transceivers with an adjustable delay, we
recommend that you set the delay for 10ms. Remember, it takes the
transceiver at least 5ms to generate RF after being keyed, so adding a
little delay to this will not noticeably affect your keying unless you
operate at very high CW speeds. The length of a “dit” in milliseconds can
be calculated as follows:
Dit length (ms) = 1200/WPM
So for 25WPM, the length of a “dit” is 48ms.
Therefore, adding just a few milliseconds of delay to your amp-enable-to-RF
output will not normally be noticeable. Of course, you can always adjust
your CW “weighting” control if you feel this is necessary.
Finally, most transceivers also take 3-6ms for the RF
to decay when you release the key, and do not un-key the amplifier until
this has occurred. A few transceivers do un-key the amplifier slightly
before RF has decayed to zero (IC-706/7000, TenTec OmniV, and possibly other
transceivers), however the 5-6ms relay release timing of the THP amplifier
relays normally ensures that even with these transceivers the RF has decayed
to zero before the relays operate.
120VAC vs 240VAC Powering of THP Amplifiers
Note: The HL-2.5 MUST be powered from 240VAC.
The THP HL-1.1, HL-1.2 and HL-1.5 amplifiers may be
configured for operation from either 120- or 240-VAC. We recommend using
240VAC if at all possible. There are several reasons for this:
Most US residential house wiring uses 14-gauge solid copper wire, and
is therefore limited (and fused) to 15-amps. This is very close to the
current required by the HL-1.1 and HL-1.2 amplifiers at 120VAC, and is
certainly below the 20-amps maximum required by the HL-1.5 amplifier.
While you will normally NOT blow your fuse or circuit breaker during
amateur intermittent operation (even at 20-amps on a 15-amp circuit), the
voltage drop in your AC circuit can be substantial. Voltage drops of as
much as 20VAC have been measured on residential 15-amp circuits at 15-amps
when the amplifier is located on the opposite side of the house from the
This high voltage drop will result in corresponding drop in the drain
voltage on the final transistors for the HL-1.2 and HL-1.5 amplifiers,
resulting in lower output power and higher intermodulation products.
Since the HL-1.1 amplifier uses a switching power supply, there will
be no change in the regulated drain voltage, however the AC input current
will be increased above the normal 15-amp maximum when the AC input voltage
drops, which increases the AC input voltage drop! In this amplifier, the
POWER output remains constant because of the regulated switching power
supply, therefore the input current MUST increase as the input AC voltage
It is not uncommon for there to be only one branch circuit feeding
your shack. Therefore, the (typical) three-amps required by your
transceiver will also add to the overall AC current required.
Finally, at the very least you will experience flickering of lights
in your home as you key your transceiver!
You are spending several thousand dollars when you
invest in an HF amplifier. Please consider spending a few hundred dollars
more to have a dedicated 240VAC line run to your shack.
Transceiver Interface Cables
THP provides ALC & Amplifier Keying cables (RCA) for
all amplifiers, and Band Data cables for some popular transceivers (RS232
for Kenwood, Band Data for Yaesu, and CI-V for ICOM). However, additional
cabling is required for many transceivers. Examples:
Some transceivers don’t have standard RCA ALC and amplifier-keying
interfaces. These include:
Kenwood transceivers: ALC and amplifier keying is provided on an
accessory connector only. This is a 8-pin MiniDIN on the TS-480, and 7-Pin
DIN on most other Kenwood radios.
Icom IC-706/7000 transceivers. Both ALC and amplifier keying outputs
are only available on the 13-pin DIN accessory connector.
Elecraft K3 transceiver: ALC and Band Data are only available on the
15-pin HD15 Accessory connector.
Yaesu FT-857/897 transceivers do not have RCA keying outputs.
Even if a transceiver has an RCA amp-key output, this may only be
available as a relay contact. A solid-state switching output may only be
available on an accessory connector. A solid-state switching output is
recommended for QSK (full break-in) operation, or if you simply wish to turn
off that clacking internal amplifier-keying relay in your transceiver.
Yaesu Field/MKV/2000 transceivers only have a solid-state amplifier
keying output on the Band Data connector.
Icom IC-746/756 only have solid-state switching outputs on an
Kenwood radios have a solid-state output that goes to +12V for
amplifier keying. This is essentially opposite the “key to ground” of most
Please contact Array Solutions for the specific cable
you require for your THP amplifier.
Frequently Asked Questions (FAQs)
Q: I have
an Elecraft K3. Does the HL-1.5 and HL-2.5 track the band data output of
the BCD band data output of the K3 looks just like the BCD band data output
of Yaesu transceivers, and so the HL-1.5 and HL-2.5 amplifiers will decode
and track the band changes of the Elecraft K3. You will need a cable that
connects to the K3 HD15 accessory connector to bring out the band data and
ALC interfaces connections from the K3. Array Solutions makes the K3THP1
and K3THP2 cables for the HL-1.5 and HL-2.5 amplifiers, respectively. There
is also a K3THP3 cable which just brings out the K3 ALC interface for the
HL-1.1 and HL-1.2 amplifiers.
Early K3 transceivers had only open-drain band data outputs, and the K3
ALC input was not compatible with the standard -4VDC ALC standard. Beginning
with K3 serial number around 2370 (and deliveries beginning in December
2008), the band-data outputs are now TTL compatible and the ALC input
voltage range has been corrected. Elecraft has also published an official
modification for both of these issues (see K3 mods at
Incidentally, while TTL-compatible band data outputs are necessary for
the HL-1.5, the open-drain band data outputs will work with the HL-2.5.
Q: Do I really need to use ALC with the THP
A: ALC is
not absolutely necessary, but it does provide overdrive protection for the
amplifier. We recommend that ALC be connected and properly adjusted (refer
to the amplifier manual) if an ALC interface is available on your
Q: Do the
HL-1.5 and HL-2.5 amplifiers support band data interfacing to TenTec
Currently THP does not support the RS232 serial interface for TenTec. Of
all the TenTec transceivers, the Orion I/II do have a Band Data output,
however this does not follow any standard protocols.
Q: Is the HC-1.5KAT Auto-tuner fully bypassed when it
is turned off?
Internal relays bypass the tuner completely when the HC-1.5KAT is off or not
HC-1.5KAT Tuner manual specifies a maximum tuning power of 80W. Can I
damage the HC-1.5KAT if I accidentally use more power than this during
of all, the HC-1.5KAT disables the amplifier prior to tuning, so you don’t
have to worry about turning off your amplifier when tuning is necessary. In
any case, the HC-1.5KAT will not be damaged with tuning power levels up to
even 500 watts. However, high power tuning could be bad for your
transceiver, therefore we suggest you limit your tuning power to less than
the full output power capability of your transceiver.
Q: I see
that THP recommends setting specific band segments when using the HC-1.5KAT
on 160- and 80-meters. Why is this?
HC-1.5KAT uses variable capacitors driven by stepper motors as opposed to
many competitors that use fixed, relay-switched capacitors. While the
variable capacitors are higher Q, higher voltage rated, and permit smooth
tuning, they are limited in value. Therefore, THP provides for optimum
tuning when a band segment is manually selected prior to tuning.
According to the HC-1.5KAT manual, you should reduce power when the SWR is
in the 3-4:1 range. Can you elaborate on this?
HC-1.5KAT can operate safely at an SWR of 4:1. However, these conditions do
result in high RF voltages on the feedline which can lead to possible RF
burns, cable failure, and even arcing of the RF connectors. Therefore it is
prudent to reduce power under high SWR conditions.
QSK Drop-out Time of Some Radios
Most transceivers take
3-6ms for the RF to decay when you release the key, and do not un-key the
amplifier until AFTER this has occurred. A few transceivers do un-key the
amplifier BEFORE the transceiver's RF has decayed to zero, which means
that you can hot-switch the amplifier when the transceiver un-keys the
amplifier. These transceivers include the ICOM IC-706/7000 (RF persists
4.5-5.5ms after un-keying the amplifier), and TenTec Omni V/VI (RF
persists ~10ms after un-keying the amplifier) if you use the TX OUT-TX EN
output for keying instead of the relay output. There is no delay if you
use the relay output of the Omni V/VI transceivers, but this relay output
wasn’t really designed for QSK operation with amplifiers. Therefore, you
should only operate semi-break-in CW with the IC-706/7000, and Omni V and
Omni VI transceivers. The TenTec Omni VII and Orion I/II transceiver have
an “External T/R Delay” menu setting which can be adjusted for optimum
amplifier drop-out switching. If you wish to operate QSK CW with the Omni
VII and Orion I/II, you should increase the “External T/R Delay” on these
transceivers to maximum, and then back it off to the point where you can
just hear band noise or signals between your morse characters.
Q: I am trying to interface my IC-703 with the HL-45B amplifier. I built
up an interface cable based on information in the HL-45B manual, but as
soon as I turn on the IC-703, the HL-45B is forced to 20 meters and I
can’t change bands. Any ideas?
A: The IC-703 (like the IC-706 and IC-7000) has a bi-directional keying
output. As such, there is 8VDC on that output when it is not grounded for
keying. The HL-45B keying input apparently has some sort of internal
connection (probably very high impedance) between the keying input and the
band-data input on the amp. So when a positive voltage is applied to the
keying input (when the amp is not being keyed), enough voltage couples to
the band data circuitry on the HL-45B that it is forced to 20 meters. All
you need to do is to add a diode in series with the HL-45B keying input
(cathode towards the IC-703). This blocks the voltage from the IC-703 to
the HL-45B, but you will still be able to properly key the HL-45B with the
Note newer models of the 45B will include the series diode inside the
amplifier. Starting June 2009.