New HF station - Connecting to instruments via Attenuator - Page 1
Forum section: electronics / rf-microwave

author: bingo600
author_rank: Super Contributor
timestamp: December 20, 2022, 07:06:10 am
content: DisclaimerBe gentle i'm not an EE (just a hobbyist), and have been "off the bands for many yearsI'm installing myfirstHF station/EFHW in the summerhouseI have a FT991A , and a IC-706MKIIG (for playing around)I would like to prepare for connecting the radios to some of my instruments.And bought a "High Power" Attenuator + 4 small ones.High powerA Bird Tenuline 8322 - 200W continuous -30dB Attenuator - N plugsLiḱe this one -https://www.martinrfsupply.com/bird-8322-rf-attenuator-200w-30db-used.aspxLow power4 x HuberShuner - 6610_SMA-50-1 SMA Attenuators.Setup to be:Radio (50dBm/100W) --> Tenuline (-30dB) --> (20dBm/100mW) --> 2 x HS -10dB --> (0dBm/1mW)I am planning to be able to connect the output to :Scope - Rigol + 50Ohm Through TerminatorsCounter - HPAK & PhilipsSA (HP 8594E) - I have a DC-Block on the SA Input.I think i have to use 50Ohm +AC couplingon the instruments , correct ??Would it be better to get a SMA DC-Block , and always have it on the Attenuator line ??I'm not planning on "full power all the time", when looking at stuff.I might connect the Attenuator line to either my Palstar 2K Ant-Tuner (2'nd output) or to the MFJ 6-Chan Ant switch (MFJ 4716)What would be preferable ?I only have One Antenna , so i might leave out the MFJ for starters.Do you have any advises against "beginner mistakes", besides "don't bypass the attenuator line"TIA/BingoPs:The MFJ has Gas discharge "fuses", and can be set to ground antenna when no power is applied , that's actually the reason i bought it.But i suppose the "Disconnect plugs physically, when leaving" still applies ??I do have Alpha-Delta Arrestors on both HF (1KW) + VHF/UHF (200W) on the wall outside the shack , and 16mm ground cable going to 2 x 220cm ground rods.

author: geggi1
author_rank: Frequent Contributor
timestamp: December 20, 2022, 10:42:38 am
content: What are you planning to measure?If you are going to measure offline looking at harmonics, transmitted signal you got the correct setup. You should consider a rf power splitter if you want to hook up more than one instrument. Just remember that when measuring only with the oscilloscope the attenuation is not correct because the scope is not 50 ohm.If you want to do online measurements while transmitting on your antenna you will also need a RF-tap or a directional cupler.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 20, 2022, 12:41:10 pm
content: To get a freq reading or a AM or SSB envelope reading, just wrap a wire around the outside your coax about 6 times and connect to the test gear.A CW signal will give you freq reading just fine. A directional coupler is "better" in the sense that you get a predictable magnitude response., But I don't think this is necessary.To measure VSWR, you need an RF bridge. Just a VSWR meter, usually with a power meter. Your Palstar has that. Nice unit.It is usually best to evaluate your antenna system under full power (or half power)I have lots of test gear, I do not recall a 50 ohm input that is AC, they are DC. I do not think that matters.I don't think your Rigol has a 50 ohm input?? You have the terminator, I think.Your Attenuators will work just fine for "off line" measurements.30 dB attenuator should reduce the signal by a factor of 1000.So your test equipment should see .1 Watt at 100 watt output. About 2 volts into 50 ohms.I do not think you need more attenuation.

author: bingo600
author_rank: Super Contributor
timestamp: December 20, 2022, 02:17:05 pm
content: Quote from: geggi1 on December 20, 2022, 10:42:38 amI have 50 ohm pass through BNC connectors for the scope.Quote from: geggi1 on December 20, 2022, 10:42:38 amAnd one of these too : -50dBm "tap/sampler"https://www.ebay.com/itm/153941653684

author: bingo600
author_rank: Super Contributor
timestamp: December 20, 2022, 02:24:22 pm
content: Quote from: Wallace Gasiewicz on December 20, 2022, 12:41:10 pmI was planning on adding 20dBm more attenuation, to get to 0dBmMy HP-E4418B Power meter with the 8481A Thermocouple sensor, has a max of 20dBm - And starts at 10MHz (so i guess i'll be measuring (calibrating) power on 20m)I would like a bit of headroom for that one. If sensor dies it's rather expensive.Thank you for some very usefull answers/Bingo

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 20, 2022, 05:50:53 pm
content: I am always paranoid around those sensors also!!Hook up the scope first just to be sure. Much higher power would be tolerated by the scope!

author: radiolistener
author_rank: Super Contributor
timestamp: December 22, 2022, 02:15:55 am
content: be careful with this part:Radio (50dBm/100W) --> Tenuline (-30dB)Make sure that you attach attenuator properly (use high power input on a radio side).Make sure attenuator can handle enough power.

author: bingo600
author_rank: Super Contributor
timestamp: December 22, 2022, 07:58:40 pm
content: Quote from: radiolistener on December 22, 2022, 02:15:55 amThank you for the tip/warningThe Bird Tenuline is rated for 200W continuoushttps://www.martinrfsupply.com/bird-8322-rf-attenuator-200w-30db-used.aspx

author: A.Z.
author_rank: Super Contributor
timestamp: December 26, 2022, 01:15:23 pm
content: Quote from: bingo600 on December 20, 2022, 07:06:10 amnot willing to bring this too much off topic, but given the premise, may I dare to ask why are you going for an EFHW instead of a so-called "random" ? Also, and since I'm at it, will you give your endfed antenna a "counterpoise" (aka "return path") or are you going to follow the "EFHW doesn't need it" idea ? And finally, did you consider using a remote AMU to feed your endfed ?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 26, 2022, 08:14:50 pm
content: If you want to get really fancy and monitor your antenna system in real use in real time, this brand of power/SWR meter appears to be currently the best practical meter.I do not have one but a few other people have used it and indeed it appears to be very good.http://www.telepostinc.com/lp100.html

author: bingo600
author_rank: Super Contributor
timestamp: December 27, 2022, 07:05:39 pm
content: Quote from: Wallace Gasiewicz on December 26, 2022, 08:14:50 pmI have seen that one but too much $$$The 500/700 is even "wilder"http://www.telepostinc.com/LP-500.html

author: bingo600
author_rank: Super Contributor
timestamp: December 27, 2022, 07:31:42 pm
content: Quote from: A.Z. on December 26, 2022, 01:15:23 pm1:My initial choice was a multiband-dipole like a w3dzz , but the physicals aka. shack & trees would make centerfeed impractical.2:I'm limited by wirelength (ground space) , and a EFHW with a 80m " trap addon", seemed to fit.Quote from: A.Z. on December 26, 2022, 01:15:23 pmAs mentioned here:https://hyendcompany.nl/tech_info#mainFor starters i'll be using the first piece of Coax, connecting to the antenna Coax (4.2m) as "counterpoise", and then a common mode choke like thishttps://www.wimo.com/en/11540And then again Coax to the "Arrestor" , and to the station.But i also have 25m of 2.5mm CCA (wrong loudspeaker cable buy). And have no problem adding a "4.2m genuine counterpoise" to the above solution, if someone can tell me, that it would make the setup better with both "counterpoises"Quote from: A.Z. on December 26, 2022, 01:15:23 pmI suppose by AMU, you refer to what some calls a "ATU/Ant. Tuner".I did consider it , but have chosen to start out with a manual Palstar 2K, next to the station./Bingo

author: A.Z.
author_rank: Super Contributor
timestamp: December 28, 2022, 08:19:40 am
content: Quote from: bingo600 on December 27, 2022, 07:31:42 pmI see, well... if you can't use a centerfed, there isn't just the endfeddid you consider an OCF dipole ?https://www.dj0ip.de/off-center-fed-dipole/such an antenna would move the feedpoint away, even if not to the end, and give you multiband coverage with pretty good performance (ok, as for all horizontal antennas, that depends from height from ground), alternatively, willing to go multiband and to use an endfed, you may consider a non resonant endfed, the so-called "random"; such an antenna would give you multiband coverage and will be as simple as an EFHW, the only important thing will be picking a good size, here's a reference (and some further infos and details)https://udel.edu/~mm/ham/randomWire/for example, the classic "84' radiator" plus "17' counterpoise" would allow you (with the help of an AMU) to cover all bands from 80 to 10 meters, to feed such an antenna with coax, you'll then need a 9:1 transformer and, by the way a good choke, the 9:1 can be built as described herehttps://vk6ysf.com/unun_9-1_v3.htmbut using an FT240-43 (or two of them stacked, depends from the power you plan to use), while the choke is described herehttps://vk6ysf.com/balun_choke_balun_hf.htmbut instead of 14 turns, wind 17 turns using RG-316 coax; the installation goes as follows, place the antenna (feedpoint and endpoint) as high as possible, from the feedpoint (9:1 UnUn) go down to (near) ground and at that position place the choke, at the "antenna side" of the choke (coax going up to the antenna) connect (to the ground of the coax connector) some radial wires (insulated wires laying down on ground), with such a setup the braid of the coax between the 9:1 and the choke will act as part of the counterpoise system and the radials will complete it; such a config is fine is the coax acting as a counterpoise is far away from the "noise cloud" since, otherwise it will pick up whatever noiseQuoteYes, AMU (Antenna Matching Unit) since it doesn't "tune" the antenna it just adapts the R/X components of the impedance to let the TRX see the 50 Ohms it expects; using a remote AMU one may avoid the 9:1 (placing the AMU unit at the antenna feedpoint) and have better match and less losses, by the way you'll still need the choke since the AMU does nothing for common mode currents, not its taskA lot of people blames both the OCFD and the "random" due to "RF in the shack" or "difficulty to tune on some bands", in my experience this is generally due to bad design or, in the case of the "random" a bad choice for the radiator length

author: bingo600
author_rank: Super Contributor
timestamp: December 28, 2022, 10:12:35 am
content: Quote from: A.Z. on December 28, 2022, 08:19:40 amThank you for your always informative answers.Re AntennaI already have bought the EFHW, and the "Common mode" "Coax piece w. ferrites on"https://www.ebay.de/itm/154783102064SWMBOBwas NOT happy, when i said i'd install a wire antenna in the garden.So a single "hangdown counterpoise" might be ok, but if i installed a "star of counterpoise wires" that would result in "severe ear damage"My antenna layout is dictated by the trees, it would be aHorizontal L, involving 3 trees.Unfortunately just 5..6 meter up ... Nothing i can do about that.I'm not in this for DX'ing or CW .. Just some "chat" , that said. I wouldn't mind getting the optimal out of my setup.Any hints to what length a possible single counterpoise should be, you mentioned 17' (5.18m)The tip at Hyendfeed mentionedlambda x 0.05(aka 4.2m for 80m), quite a bit shorter than 17'.Re multiple Ferrite coresI don't plan on sending more than 100W, since that's what the stations can do, no plans for a PA.That would be 100W (constant at times) , whatever that is is PEP.Can that be done with one Ferrite core , or is two a better choice ??I might consider the linked Common mode balun , if the Coax one does a bad job.You don't seem impressed by EFHW's ... Would you care to explain why ?/Bingo

author: A.Z.
author_rank: Super Contributor
timestamp: December 28, 2022, 10:57:24 am
content: Quote from: bingo600 on December 28, 2022, 10:12:35 amwell, if you already bought the antenna then go for it, as for the choke, from your description it should be a so-called "maxwell" or "W2DU" choke, that is a number of ferrite cores placed over a run of coax, if that's the case... well, it depends from how well it's built, because, see... to be as effective as a Guanella choke, the W2DU should be pretty long and use several ferrites AND different materials to be able to be effective on all bands; for some further infos and details, see herehttps://www.dj0ip.de/rf-cmc-chokes/different-kinds-of-chokes/Quote5.6m from ground isn't so good, you should reason in terms of wavelength (lambda, that is 300/MHz), a good choice would be an height around 0.60 lambda (or more) at the lower frequency, but that isn't always possible, so one must accept compromises, another decent height is 0.30 lambda; see the "problem" if we want to call it so is that at lower heights (depending from frequency btw) the antenna radiates at high angles, for lower bands (40, 80 or below) NVIS is acceptable, but going up in frequency, the high angle radiation means that quite a bunch of RF will be wasted heating cloudsQuoteIf you got that antenna, then go for the recommended setup; notice that nothing forbids you to experiment a bit with the counterpoise, if would just be a matter of connecting some piece of wire to the outside of the choke coax connector (antenna side) and laying it on ground (ok, SWMBO... but I think she'll allow some experiments), or you may use a short wire and connect it to a ground stake, again, it's a matter of experimenting; the idea is measuring the CMC on the coax (after the choke) and reducing it as much as possible, to do that you may use this simple devicehttp://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htmQuotewell, you bought the antenna and it includes the 49:1 transformer, so... go for it; willing to build your own, you may consider using a single FT240-61 (or FT240-43) or a pair of them, stacked; in general a single 240 should be more than adequate for 100W (and more)QuoteIt's not that, each and every antenna is somewhat a compromise and each one has its pros and cons, the point is that an EFHW will work fine on its harmonics but not so fine on other frequencies, so, if one can setup only one antenna, I think that a "random" may serve better, allowing to cover more bands, just that, nothing elseOh, and since we're at it, maybe your SWMBO could tolerate an antenna like this onehttps://www.dj0ip.de/vertical-antennas/simple-multi-band-vertical/just an idea, by the way

author: bingo600
author_rank: Super Contributor
timestamp: December 28, 2022, 11:34:09 am
content: QuoteLooks like a nice antenna, just two issues.1:RF voltage & small grandchildren is a no-go2:SWMBO would NEVER accept guy wires in the garden, and she'd prob trip over them.I think i just have to settle for the EFHW, for now.Btw: The "Clamp on RF current meter" looks nice ...I just have to find a "100µA" meter .....Something like thishttps://www.aliexpress.com/item/1005004691594858.html/Bingo

author: A.Z.
author_rank: Super Contributor
timestamp: December 28, 2022, 02:17:45 pm
content: Quote from: bingo600 on December 28, 2022, 11:34:09 amWell, it comes together in minutes, and for the meter you may just use a multimeter you have aroundI believe that, since you're going for an endfed, and since you're wondering about the counterpoise and choke, it would be a good idea to build such a "probe" and use it to check if you have CMC, that will tell you if the choke/counterpoise system is working or if you need to improve it, and will also tell you if you've "RF in the shack", it's a small, simple tool, but may be very useful at timesGetting back to the vertical antenna, another idea may be using the endfed for general band use and adding a single band vertical for the band you want to try some DX on, in such a case, an antenna like the one described herehttps://en.wikipedia.org/wiki/HB9XBG_Antennahttps://upload.wikimedia.org/wikipedia/commons/b/b6/HBradio_6-2020_page_41-44.pdfmay fit, it doesn't require radials, doesn't require an AMU, is fed directly using coax and offers pretty decent gain and low takeoff angle; by the way, the above are for 20m and 40m, but nothing forbids one from building an HB9XBG for whatever other bandoh... and aside from the components in the "match box" at the base of the antenna, the remainder of the material is quite easy to source, and the antenna itself is just a run of zip cord

author: A.Z.
author_rank: Super Contributor
timestamp: December 28, 2022, 02:36:07 pm
content: Quote from: A.Z. on December 28, 2022, 02:17:45 pmForgot, the small "RF probe" will also tell you where to place a choke, let me explain, let's say that by using it, you find that there's RF on the outside of the coax, that is you have a CMC issue, now, setting the TX at low power on the lower frequency (or at the frequency where the problem is worst), you key it, then, starting from the antenna side you start sliding the probe along the coax and reading the values until you'll find a spot, along the coax, where the value is lower, THAT one is the spot where a choke will be more effective at stopping the CMC