Last years 21cm interferomerter observation.

[Jan Lustrup]

Here are last year’s  21cm observations with my two dish interferometer.

With just one dish I see only 4 sources (Sun, Cassiopeia A, Cygnus A and Taurus A).

With two dishes I now see over 50 sources, with weakest just under 10 Jy. This is a BIG improvement!

 

My setup is two 1.9meter dishes with stovepipe feeds. The LNA’s are SM5DGX type (NF <0.2dB)

The antennas are spaced 17.2 meters on an east / west base line. I used two “Sawbird+H1” lna’s + a 1420MHz interdigital 5MHz band pass filter. RF Detection is done with an “AD8362” detector and by phase switching correlation with a “lock-in amplifier”. Detection fringes are displayed in two hour long, +/- 1 Volt graphs & logging is done with “RadioSkypipe” software.

 

The relative broad main antenna beam causes some problems with sources close together as fringes interact (an FFT display would help here). Other problems are sometimes caused by ground noise pick-up at low elevations and / or sun noise pick-up via side lobes.

 

Jan Lustrup  LA3EQ

Norway.

 

 

Standard setup parameters:
"SM5DGX" LNA,   sawbird H1 to filter to sawbird H1 to the AD8362 RF detector to lock-in amp
Equations = zero, AVG x25, Graph scale: Normaly  two hour, two volt peak to peak recordings													Background noise >40mV
Date dec.2025 Yellow background shows sources seen with only one dish.
source	date	Celestrial radio sources		CTA	CTB	3C	M	J	RA	DEC	ELEVATION	JANSKY @ 1420MHz	fringe period	mVolt ptp
1	16.11.2025	The  Sun	Our Star						X	X	X		X	23000
2	15.11.2025	Cassiopeia A	Remnent			3C461			23:23	58,8	90,4	2400	316	4960
3	15.11.2025	Cygnus A	Elliptical galaxy			3C405			19:59	40,7	72,3	1495	219	4820
4	16.11.2025	Taurus A	CRAB NEBULA	CTA36		3C144	M1		05:34	22	53,6	940	179	2330
5	16.11.2025	Our Moon	399800km						X	X	24,0	900		1110
6	12.06.2025	Nebula	W38		CTB52		M17		18:17	-16,1	16	380	173	870
7	20.06.2025	VIRGO A				3C274	M87	J1230+1223	12:30	12,4	44,0	198	170	710
8	18.11.2025				CTB53				18:26	-12,3	19,1	200@960MHz	170	540
9	25.11.2025		NGC6604		CTB50				18:18	-11,9	19,6	330	170	500
10	19.11.2025	Nebula	W51		CTB73	3C400			19:23	14,5	46	375?	172	470
11	20.06.2025	Orion Nebula		CTA37		3C145	M42	J0535-0523	05:35	-5,4	26,2	300	167	425
12	31.10.2024	Nebula	W28				M20		17:58	-22,1	9	360	179	420
13	02.11.2024				CTB59				18:47	-2,0	29,5	300	166	300
14	13.06.2025				CTB60	3C392			18:56	1,3	32,9	171	166	280
15	16.11.2025	Jellyfish nebula	supernova remnant			3C157		IC443	06:17	22,4	54,3	150	280	230
16	02.11.2024	Orion Horse Head	nebula			3C147.1		J0541-154	05:41	-1,9	29,7	256@2700MHz	166	200
17	18.11.2025					3C123			04:37	29,7	61,3	46	191	200
18	28.11.2025				CTB56				18:33	-8,7	22,9	135@960MHz	168	200?
19	09.06.2025	D Galaxy				3C295			14:08	52,0	83,8	23	270	150
20	23.07.2025	Hercules A				3C348		J1651+0459	16:51	4,6	36,6	47	167	150
21	01.03.2025	Quasars				3C273B		J1229+0203	12:29	2,1	33,7	46	166	140
22	01.03.2025	D Galaxy		CTA76		3C353		J1720-0058	17:20	-0,6	30,6	57	197	120
23	22.11.2025	NEXT				3C147			05:42	49,9	81,4	21	258	120
24	22.11.2025		weak	CTA91					20:46	50,3	82,2	180@960MHz	167	90
25	17.11.2025	Rosette nebula			CTB21				06:32	4,8	35,4	300	167	90
26	25.07.2025	Quasars				3C380			18:28	48,7	80,3	14	251	90
27	25.07.2025	X				3C119			04:32	41,6	73,2	8	222	90
28	22.07.2025					3C452			22:46	39,7	71,3	11	216	90
29	23.11.2025			CTA33			HB9		05:01	46,5	78,1	160@960MHz	241	90
30	22.07.2025							J2253 1608	22:54	16,1	47,7	11	173	85
31	02.11.2024	Hydra A	Low elevation	19.5deg	CTA47			J0918-1205	09:18	-12,1	19,5	50	170	80
32	17.11.2025					3C270		J1219 0549	12:19	5,8	37,5	21	167	80
34	27.11.2025					3C286			13:31	30,5	62,1	16	193	80
35	20.11.2025	Perseus A				3C84		NGC1275	03:20	41,5	73	13	222	80
36	18.11.2025					3C111			04:31	38,0	69.5	15	211	80
37	25.07.2025		few fringes seen	CTA106		3C465			23:04	27,0	58,6	8	186	80
38	28.11.2025					3c66			02:23	43,0	74,5	9	227	70
39	18.11.2025					3C33			01:09	13,3	45	12	170	70
40	21.11.2025					3C98			03:59	10,4	42	10	223	70
41	23.11.2025						HB11		08:12	47.9	79.1	40@178MHz	248	70
42	21.11.2025					3C109			04:14	11,2	42,8	10	223	70
43	21.11.2025				CTB98	3C438			21:56	38.00	69,5	7	211	70
44	16.11.2025	into noise	noisy			3C433			21:24	25,1	56,7	12	183	60
45	18.11.2025	Tree line!	Low elevation	CTA99		3C444			22:14	-17,0	13,6	10	174	60
46	18.11.2025					3C134			05:04	38,1	69,7	10	211	60
47	01.01.2025		make new one.			3C409			20:14	23,6	77	13	235	40
48	20.11.2025		weak			3C234			10:02	28,8	60,3	29@178MHz	189	40
49	make a new observation					3C227			09:48	7,4	39	7	167	40
50	make a new observation							J1007 0730	10:08	7,5	39	6	167	40
51	20.11.2025					3C192			08:05	24,2	55,7	5	182	40

 

 

 

[Peet Denny]

Very exciting stuff, Jan.

I'd love to progress eventually to building a small interferometry array.

How hard was it to sync timing on the two dishes? I understand that at 1.4GHz, the timing needs to be pretty bang on.

Got any photos of your setup? :) 

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[wallacefj]

Wonderful! Thanks for sharing!

Sent from my Galaxy

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[Marcus Fisher]

You should do a presentation at Eastern conference on this setup and results (first week of August)

[Jan Lustrup]

Hi,

I use beam heading towards the meridian (due south) and set up the elevation as needed on both antennas and do  2 hours for each observation displayed & saved to “RadioSkypipe” software.

I use the Sun to calibrate the elevation and azimuth, and after that I use a digital angle measuring unit to set the dish to the correct declination while the azimuth always stays due south..

To find the elevation I use “RadioEyes” program by Jim Sky.

I use a DBM mixer on one antenna coax to invert the phase 100 times a second (I use a 100Hz oscillator for this) , and this same signal is the “reference timing” signal that goes the reference input of the lock-in amp (or switching rate of your synchronous detector circuit). Other than that there are no timing issues as the earth rotation does the rest.

Even the two antenna coaxial cables do not have to be exactly the same length!

 

My setup is on a wooden “breadboard” as I have not built a box for it yet.

Images below is drawing of setup, photo of both antennas detecting Cygnus A and my radio room with the “breadboard phase correlator” setup on the table.

73’s Jan LA3EQ

 

 

 

 

 

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[Andrew Thornett]

Wow! Great post and great work. Are you going to write this up for SARA J. And present at SARA conference?

Sent from Outlook for Android

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From: 'Jan Lustrup' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Tuesday, February 17, 2026 11:31:33 AM
To: sara-list@googlegroups. com <sara...@googlegroups.com>
Subject: [SARA] Last years 21cm interferomerter observation.

 

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[Marcus D. Leech]

On 2026-02-17 06:31, 'Jan Lustrup' via Society of Amateur Radio Astronomers wrote:

Here are last year’s  21cm observations with my two dish interferometer.

With just one dish I see only 4 sources (Sun, Cassiopeia A, Cygnus A and Taurus A).

With two dishes I now see over 50 sources, with weakest just under 10 Jy. This is a BIG improvement!

I have often said that interferometers just "want to work".   

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