[Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS near Boston
B. Smith
smithab11 at comcast.net
Sat Feb 23 13:30:32 EST 2019
Perhaps they used 70 ohms to match a half wavelength doublet antenna.
k4che
On 2/21/2019 11:55 AM, Francesco Ledda wrote:
>
> Of course, the transmitter has its own tunable coupler, and all the TX
> couplers I have seen tune the antenna to 50 ohm.
>
> It may be that older ships had 70 ohm transmission lines and they
> stick with 70 ohm for historical reason.
>
> In the 80s, I know that many NATO ships mostly used high temperature
> Teflon insulated RG-115, and it was 50 ohm.
>
> *From:* milsurplus-bounces at mailman.qth.net
> <milsurplus-bounces at mailman.qth.net> *On Behalf Of *Peter Gottlieb
> *Sent:* Thursday, February 21, 2019 10:04 AM
> *To:* Francesco Ledda <frledda at att.net>
> *Cc:* MilSurplus QSLNet <milsurplus at mailman.qth.net>; Jim Whartenby
> <antqradio at sbcglobal.net>
> *Subject:* Re: [Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS
> near Boston
>
> Multi couplers are for receivers, and isn’t the optimum coax impedance
> around 70 ohms for signal loss? The optimum for power transmission is
> closer to 50 ohms IIRC. These were made some time ago, perhaps before
> 50 ohms was settled on as the standard for radio gear except CATV
> systems. Just trying to think out loud why those things were 70 ohms.
>
> Peter
>
>
> On Feb 21, 2019, at 10:56 AM, Francesco Ledda <frledda at att.net
> <mailto:frledda at att.net>> wrote:
>
> I understand the mismatch and its engineering implications.
>
> My question is why would anybody design mismatch in the system.
> Most transmitters used an antenna coupler anyway.
>
> *From:* milsurplus-bounces at mailmanqth.net
> <mailto:milsurplus-bounces at mailman.qth.net>
> <milsurplus-bounces at mailman.qth.net
> <mailto:milsurplus-bounces at mailman.qth.net>> *On Behalf Of *Jim
> Whartenby
> *Sent:* Wednesday, February 20, 2019 10:53 PM
> *To:* Francesco Ledda <frledda at att.net <mailto:frledda at att.net>>
> *Cc:* MilSurplus QSLNet <milsurplus at mailman.qth.net
> <mailto:milsurplus at mailman.qth.net>>
> *Subject:* Re: [Milsurplus] [Boatanchors] CU-872A/U antenna
> coupler FS near Boston
>
> Frank asked: "Wonder why?"
>
> Most likely since at HF, the impedance mismatch is pretty much
> insignificant, especially if one considers the length of the coax
> run from antenna to RX.
> https://www.pasternack.com/images/ProductPDF/RG8A-U.pdf
>
> So about 1 dB loss at 30 mc per 100 feet or 0.2 db loss at 1 mc
> per 100 feet.
>
> From: http://wc7i.com/Vertical%20Antenna%20Conclusions.htm
>
> Z of a vertical antenna is about 36 ohms, Z of horizontal antenna
> is about 72 ohms, both give a 1.4:1 VSWR. The VSWR from mating a
> 50 to 75 ohm coax is 1.5:1 In all of the above cases, the load
> mismatch attenuation is under 0.2 dB
>
> Comparing UHF connectors to most modern connectors is also
> interesting. I myself wonder why the the UHF connector is still used?
>
> See:
> https://www.hamradio.me/connectors/uhf-connector-test-results.html for
> connector comparisons from SMA to UHF.
>
> Regards,
>
> Jim
>
> /I wonder why people argue over the 10% of their differences and
> ignore the 90% they agree on?/
>
> On Wednesday, February 20, 2019, 6:09:03 PM CST, Francesco Ledda
> <frledda at att.net <mailto:frledda at att.net>> wrote:
>
> Also, the CU-1099/FRR is 70 ohm. It was used with receivers with Z
> 50 ohm. Wonder why....
>
> Sent from my iPad
>
>
> On Feb 20, 2019, at 17:50, W2HX <w2hx at w2hx.com
> <mailto:w2hx at w2hx.com>> wrote:
>
> Probably the gain in the unit compensated for any losses due to
> impedance mismatch
>
> Sent from Nine <http://www.9folderscom/>
>
> ------------------------------------------------------------------------
>
> *From:*Nick England <navy.radio at gmail.com
> <mailto:navy.radio at gmail.com>>
> *Sent:* Wednesday, February 20, 2019 5:00 PM
> *To:* W2HX
> *Cc:* MilSurplus QSLNet; r-390 at mailman.qth.net
> <mailto:r-390 at mailman.qth.net>; John Flood
> *Subject:* Re: [Milsurplus] [Boatanchors] CU-872A/U antenna
> coupler FS near Boston
>
> The parts list says it has UG-58A/U connectors. Everything I can
> find says that is a 50 ohm connector.
>
> I think all the military type N listings are 50 ohm.
>
> Nick England K4NYW
> www.navy-radio.com <http://www.navy-radio.com>
>
> On Wed, Feb 20, 2019 at 2:56 PM W2HX <w2hx at w2hxcom
> <mailto:w2hx at w2hx.com>> wrote:
>
> John et al.,
>
> This is an interesting multicoupler. One interesting thing
> I've wondered about...It has a 70 ohm antenna matching input
> impedance. And i always wondered if the antenna connector was
> a 75 ohm N connector or the standard 50 ohm (The difference is
> that the male center pin is thicker on the 50 ohm version, and
> will damage a 75 ohm female part)
> Just something to look out for.
>
> Wikipedia has a nice photo of both impedances and genders.
>
> 73 Eugene W2HX
>
> ________________________________________
> From: boatanchors-bounces at mailman.qth.net
> <mailto:boatanchors-bounces at mailman.qth.net>
> <boatanchors-bounces at mailman.qth.net
> <mailto:boatanchors-bounces at mailman.qth.net>> on behalf of
> John Flood via Boatanchors <boatanchors at mailman.qth.net
> <mailto:boatanchors at mailman.qth.net>>
> Sent: Wednesday, February 20, 2019 1:24 PM
> To: MilSurplus QSLNet; r-390 at mailman.qth.net
> <mailto:r-390 at mailman.qth.net>; BOATANCHORS2 LIST
> Subject: [Boatanchors] CU-872A/U antenna coupler FS near Boston
>
> Greetings,
> This is working, some "test" readings are a bit on the low
> side so perhaps some of the 6922 tubes are getting tired.
> There is some glue residue below the normal data tag most
> likely from some other data tag that was mounted there.
> Looking for a local sale in the Metrowest or North Shore
> Boston (This of course means that the first reply will come
> from Alaska!). I'm not really interested in shipping this or
> dealing with Paypal any more in MA. Any interest? I could
> bring it to the Lewiston ME, Nashua, NH, or Framingham, MA
> fleas. Nearfest as well but I hope it finds a home sooner
> than May!
> John Flood N1JAF978-979-2807
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