Cool if you used one coax for all three 800W radios .. did you ?
Even such triplexers can be done with careful design and then pruning
the Farads, Henrys and walls in the box.
I think there was a 100W grade one coax triplexer in QST or QEX not so long ago.
73,
Jukka OH6LI
2012/7/6 Martin Durham <w1md@cfl.rr.com>:
> We ran 3 K3's into a C31XR with approx.. 800W from each 'band'...only 800w
> because we were AC limited at the QTH. A custom highpower TRI-plexer was
> built and used on the C31XR. It worked amazingly well...ran ARRL CW this
> past spring as PJ4X...
>
> The tri-plexer is 'not' your average 'build at home' affair...and it is NOT
> cheap...but it works. :)
>
> Interesting thread.
>
> 73,
>
> Marty
> W1MD
>
>
> -----Original Message-----
> From: cq-contest-bounces@contesting.com
> [mailto:cq-contest-bounces@contesting.com] On Behalf Of Keith Dutson
> Sent: Thursday, July 05, 2012 9:21 AM
> To: 'Timothy Coker'
> Cc: 'Tom W8JI'; cq-contest@contesting.com
> Subject: Re: [CQ-Contest] Bandpass filter
>
> Did not realize you were using a C31XR. I would not have guessed a
> situation like this where two rigs were connected to the same antenna.
> Personally, I find that an unreasonable risk.
>
> 73, Keith NM5G
>
> _____
>
> From: Timothy Coker [mailto:n6win73@gmail.com]
> Sent: Wednesday, July 04, 2012 10:31 AM
> To: Keith Dutson
> Cc: Tom W8JI; cq-contest@contesting.com
> Subject: Re: [CQ-Contest] Bandpass filter
>
>
> Let the flames begin, LOL.
>
> Sorry Keith, the measured isolation between 15m TX and 20m RX on the C31XR
> with physical separation of only 18" is legitimate. Now do consider that I
> am only an average ham using a Kenwood SW-2000 that specs to +/- 10%
> accuracy. You are right though... 135w was excessive, it was 125w +/- 10%.
> Natan from the old F12 even sent me a response about this issue in 2002
> stating that the back fed power would be over 100w depending on band
> combination. I found that Ice 419As with no stubs would not burn out under
> those conditions while running SO2R as a very novice contestor (A better
> SO2R operator would probably burn them up because they would transmit on
> both rigs more often than I was able to). Now that I am wiser I have
> invested in both stubs and higher overhead band pass filters.
>
> Now that I am not writing from my vehicle I have the benefit of my test
> measurements available to me. Let me give a more accurate accounting of my
> measurements:
>
> C31XR individual feed lines 15m 1500w TX and 20m RX:
>
> No filters: 125w back fed power (-10.8dB)
> W3NQN 20m RX: 1w back fed power (-63.52dB)
> 23' open stub 20m RX: 1w back fed power (-63.52 db) This level of
> attenuation I question and a more accurate test meter should have been used.
> 23' shorted stub 15m TX and W3NQN on 20m: 1w back fed power (-63.52dB) No
> additional isolation with the 15m TX stub.
>
> *23' open stub AND W3NQN on 20m RX: 0w back fed power (>-80dB)
>
> On the other band combinations I measured (without filtering) between
> -17.9dB to -28.8dB
>
> Based off the QST article a combiner with band pass filters would help those
> of us with driven elements spaced so closely on a single boom and that had
> the ability to switch to a single feedline (like the C31XR). From my own
> testing even the Inrad combiner will not always provide greater attenuation
> as compared to the closely spaced driven elements on an antenna like a
> C31XR. However on 15m TX and 20m RX the combiner would give me an additional
> 20.6dB of isolation and is something to consider for reducing the back fed
> power on that band combination.
>
> When I TX on 20m and RX on 15M I have measured isolation at -27dB. The Inrad
> combiner was measured by the ARRL at -26.9dB. Here is a band combination
> that would make me no better off.
>
> Those of us wanting to run high power and use a single feedline with
> combiner would need to invest in high power filters for their higher bands.
> 4O3A seems to be the only person offering such a combination.
>
> On 40m 1500w TX with an 80m RX, feed points spaced at ~15' distance, I find
> 2w back fed power (-28.8dB). Used was a XM240 at 68' and an 80m inverted-v
> @53' on the same tower. Antenna spacing is obviously king here... but guys
> like myself don't always have that luxury when it comes to wanting to fit
> six contest band monobanders on a residential lot.
>
> Let me remind the flamers that I never sent a flame at Tom. I made mention
> that I know he is a damned smart guy. I simply read his numbers without full
> understanding. I have since come to learn new information from him. Notice
> how right Tom was about the 15m TX stub doing nothing and how wrong I was
> going off memory while posting half correct information away from my
> findings spreadsheet. But my findings about the back fed power does indeed
> not take a rocket scientist to figure out... only an average ham with
> sub-par measuring equipment.
>
> 73,
>
> Tim / N6WIN.
>
>
> On Wed, Jul 4, 2012 at 7:52 AM, Keith Dutson <kdutson@sbcglobal.net> wrote:
>
>
> Does not take rocket science to question your measurement of 135 watts
> feedback power. About the only way this could happen is if the two antennas
> were physically attached together. And that is even questionable based on
> different bands being measured. I think there is a flaw or
> misrepresentation in your measurement.
>
> Keith NM5G
>
>
> -----Original Message-----
> From: cq-contest-bounces@contesting.com
> [mailto:cq-contest-bounces@contesting.com] On Behalf Of Timothy Coker
> Sent: Tuesday, July 03, 2012 5:07 PM
> To: Tom W8JI
> Cc: cq-contest@contesting.com
> Subject: Re: [CQ-Contest] Bandpass filter
>
>
> I recently measured the power coming back down my 20m line while
> transmitting on 15m. It's over 135 watts of power when using my K3 and Acom
> 2000 at 1500w forward output. Not milliwatts...
>
> A W3NQN BPF on the 20m coax, placed before the wattmeter and dummy load was
> able to knock the measured power down to 1w of back fed power. A TX stub
> then placed on my 15m TX line then resulted in less than 1W being back fed
> on the 20m line.
>
> I know you're a smart guy Tom, but not sure where your numbers come from.
> My station QTH has room for one tower and my 20-10m antenna is a C31XR with
> individual feedlines. I cannot go without good filters and expect my K3
> front ends to survive.
>
> 73,
>
> Tim /N6WIN
> On Jul 3, 2012 8:02 AM, "Tom W8JI" <w8ji@w8ji.com> wrote:
>
>> > My understanding is that the main function of my 40m BPF (when
>> > thinking
>> of
>> > my second radio on 20m) is to reduce the second harmonic on 20m
>> > produced by my 40m TX.
>>
>> Nearly all modern radios have excellent harmonic suppression, while
>> external power amplifiers do not.
>>
>> If we have a second harmonic issue, a critically located stub or
>> stubs, or a trap, is far more effective and less costly than a high
>> power BPF.
>>
>> The distance from the source and load, and the characteristics of the
>> suppression device, source, and load, usually greatly affect the null
>> depth of any suppression. For example optimum stub placement from a
>> pi-L network is quite different than optimum placement from a pi network
> or T network.
>> It's different for every antenna, too.
>>
>> The tradeoff is always cost and work, and immunity to system
>> characteristics. A great big expensive filter can work well no matter
>> where it is placed in the line. A cheap system, like a stub, might not.
>>
>>
>> >So if I am on 7.025 running, I will create a very strong second
>> >harmonic signal on 14.050. Depending on my TX power, antenna
>> >proximity, and antenna polarization, that signal might be enough to
>> >couple enough power on my 20m line to fry my second radio front
>> >end.
>>
>> I doubt that would happen. Most amps are -46dBc or more. With 1500
>> watts, that's about 40 milliwatts. 40 milliwatts will never fry a
>> receiver. Added to that suppression, we have coupling losses between
>> the antennas that are likely 20 dB or more.
>>
>> The only reason to add a filter or stub is if something is out of
>> spec, or someone closeby wants to operate right on top of the second
>> harmonic. For example, I can hear, and be bothered by, harmonics that
>> are only 100 microwatts from hundreds of miles away, **IF** I happen
>> to operate on that harmonic.
>>
>> Of course that level is thousands of times less than a level that
>> could be damaging to another local receiver.
>>
>> The real function of a bandpass on transmitting is mitigating problems
>> from someone, local or distant, operating near the harmonic.
>>
>> If there are issues with TX noise bothering our receivers on an
>> adjacent band except near the harmonic, it is worth looking closely at the
> gear.
>> Something is wrong, beyond lacking an extra filter.
>>
>> At even 30-40 dB of external TX antenna filtering, cabinet and line
>> cord leakage will usually dominate harmonic and spurious radiation
>> into the RX antennas.
>>
>> 73 Tom
>>
>> _______________________________________________
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