The swr bridge certainly could be part of the problem. Another often
overlooked cause of this problem is where the input and output coax
shield/center
conductor is split apart to make connections to the relay and coax connectors.
If you measure the conductor diameter and spacing here and calculate the zo
of the short line section that is created, you will find the impedance can
exceed 200 ohms. The section is short but the high impedance can add a
surprising amount of inductance to the circuit. Some or most relays will also
have the
same effect.
The effect can be compensated to a large degree by adding small capacitors,
say 5 or 10 pF across the ends of the split coax. While this works, it may
take some experimentation to find the optimum value capacitor.
The infinite 6m vswr sounds suspect unless there is some kind of low pass
filter in the circuit. The coax and relay effect mentioned above should not
cause this on 6m.
Happy hunting!
73, K5GW
In a message dated 12/7/2005 7:47:20 P.M. Central Standard Time,
w3ll@arrl.net writes:
When passing thru the Henry 4 K-2 amp, with the amp turned off, the exciter
sees an SWR of between 1.1 to 2.0 depending
on the band the exciter is set on (75M thru 10M). The SWR is higher at the
higher frequencies. The SWR is infinitely
high on 6M.
If connected directly to the antenna(s), the exciter sees 1.1 SWR on all
bands. I'm using a SteppIR antenna whose
elements can be tuned to present a flat impedance at any frequency between
40M and 6M.
With the amp turned on, the exciter sees an SWR of 1.1 on all bands (75M to
10M).
My question is why does the amp introduce a higher SWR in bypass and not
allow a 6M signal to pass thru without
introducing an infinitely high SWR?
In the off position, the signal passes thru an input bypass relay and then
to an internal SWR bridge at the output side
of the amp and then to the antenna.
With the amp turned on, the signal passes thru the input relay and to the
appropriate band input impedance matching
module. This explains the 1.1 SWR on all bands with the amp turned on.
The only components in the path, with the amp turned off, is the bypass
relay and the SWR bridge - all internal to the
amp. Can these be causing the exciter to see the higher SWR and infinite 6M
SWR? Is the internal SWR bridge the culprit?
Any ideas?
73,
Bud W3LL
w3ll@arrl.net
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